Islanding condition, its causes,
mode of origination and detection
Millend Roy
Bachelor of Technology in Electrical Engineering, IIT ISM Dhanbad, Dhanbad 826004,
Jharkhand
Professor Swades De
Electrical
Engineering, Indian Institute of Technology, New Delhi 110016
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Abstract
With the escalation of energy demands all over and terror of draining conventional
fossil fuels, the assimilation of distributed generation networks to centralized
traditional networks was introduced. Distributed generation (DG) refers to the
production of electricity near the consumption place through renewable energy
resources especially wind, solar, tides, biomass, geothermal heat and so on. The
heightened perforation of DG, renewable energy application, and the installation of
micro-grid concept have changed the architecture of conventional electric power
networks. Channelizing the field of study, the different problems and issues faced
in the trending DG networks has been an interesting topic for researchers where
several faults need to be worked upon. Islanding detection in DG systems is a
challenging issue that causes several protection and safety problems. A micro-grid
operates in grid connected mode or standalone mode. In the grid connected mode,
the main utility network is authoritative for effortless operation in masterminding
with the protection and control units, while in standalone mode, the micro-grid
operates as a self-reliant and self sufficient power island that is electrically
disconnected from the main utility network. Additionally, without stern frequency
control, the equity and harmony between load and generation in the islanded circuit
will be disrupted, leading to anomalous frequencies and voltages. Hence different
anti-islanding detection methods are studied which reports to the control system
how to perform in case of any islanding. Here basically an attempt is made to build
a real time power system with several trending distributed generation systems
being installed at the load end and then to monitor the behaviour of all the
electrical parameters in case of any faults or disturbance. Even cases of islanding
are considered and next protection of the power system is also considered by
inculcating within different relays and circuit breakers wherever required.
Keywords: distributed generation (DG), grid connected mode, islanded mode,
fault analysis based on real time, phasor measurement units (PMU)
Abbreviations
Table 1List of Abbreviations
DER
DG
Distributed Energy Resources
Distributed Generation
EMS
Enegy Management System
GPS
Global Positioning System
IdMs
Islanding Detection Methods
IPDN
Integrated Power Distribution Network
NYISO
New York Independent System Operator
PCC
Point of Common Coupling
PDC
Phasor Data Concentrator
PMU
RTDS
Phasor Measurement Unit
Real Time Digital Power System Simulator
SCADA
Supervisory Control and Data Acquisition System
SE
State Estimator
SVC
Static Variable Compensator
UDP
User Datagram Protocol
INTRODUCTION
Background
Power grid architectonics have emerged remarkably since previous decades, from
an unidirectional centralized management approach to a rational and decentralised
doctrine which allocate autonomous solutions in administering today's amplifying
demand complications. The notion of decarbonizing while boosting electrifications
have bricked way for DG technologies to knock the existing power grids, affording
a substitute power generation that is more handy to consumers. Hence DG is a term
that refers to the production of electricity near the consumption place. Solar power
generators, wind generators, gas turbines and micro-generators such as fuel cells,
micro turbines and so on are all examples of distributed generators. Hence it can be
addressed that conventional power distribution systems are passive networks,
where electrical energy at the distribution level is invariably outfitted to the
customers from power resources which are associated to the bulk transmission
scheme.
a) Conventional centralized power distribution system
b) Microgrid network consisting of DG sources at load end
Fig 1 Shifting of Technology from Centralized to Decentralized; (Source:- “A Review of
Islanding Detection Techniques for Renewable Distributed Generation Systems.”Renewable
and Sustainable Energy Reviews, Pergamon, 2 Sept. 2013,
www.sciencedirect.com/science/article/pii/S1364032113005650.)
Advantages of integration of DG resources include substantial environmental
profits, enlarged adaptability, restraint of transmission and distribution (T&D)
capacity promotion, abbreviated T&D line losses, remodeling power quality,
providing better voltage support and so on. However diverse problems need to be
tackled before the DG units are applied to the networks. These problems include
voltage stabilization, frequency ballast, intermittency of the renewable resources
and power quality controversies. Such technical challenges are being resolved by
professional engineers and researchers using advanced technologies and power
economics.[1]
Islanding as defined by IEEE standards :- A condition in which a portion of an
area of ELECTRIC POWER SYSTEMS (EPS) is energized solely by one or more
local EPS through the associated point of common coupling (PCC) while that
portion of the area EPS is electrically isolated from the rest of the area EPS.


1
2
Fig a Islanded mode operation; (Source:- 2018, IIT Roorkee July. “Mod04lec16.” YouTube,
YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=F0ZTgrgMZAk&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=35.)
An analogy is a conglomerate of island banded together by a bridge type link like
below. The bridges speak for power lines intertwining sections of the grid. If the
bridges are fragmented, then each island would become secluded, both tangibly
and electrically. In order for the grid to still operate on the island, it must generate
enough power to accommodate load requirements. Each island will possess a
contrasting frequency. And when the acquaintances are rebuilt, the two connecting
islands must synchronize their frequencies before connecting or both islands will
fail.
Fig b Interlinking of ideas between original island and electrical island; (Source:- Harvepino.
“Aerial Footage of Scenic Road Stock Footage Video (100% Royalty-Free)
22185361.” Shutterstock, www.shutterstock.com/video/clip-22185361-aerial-footage-scenicroad-on-tiny-islands.)
An islanding condition can be intentional or unintentional. Intentional islanding is
performed due to the obligatory maintenance needed for the main utility, whereas
unintentional islanding may occur at any time due to regular faults or other
uncertainties in the power system. Therefore, islanding detection is considered as
an important task for IPDNs. IEEE 1547 and UL 1741 standards describe DG
interconnection, planned and unplanned power islanding, and other important
operating considerations. [2] More about intentional and unintentional islanding
can be studied from the following journals.[3][4]
Unintentional islanding is a threat to power system security. All the problems
discussed below adds to it.

SAFETY CONCERN: - As the grid may still be powered in the event of a power
outage, due to electricity supplied by distributed generators. Therefore it may
expose utility workers to life critical dangers of shocks and burns who may think
that there is no power once the utility power is shut down.

DAMAGE TO CUSTOMER’S APPLIANCES: - Due to islanding and
distributed generation there may be a bi directional flow of electricity. This may
cause severe damage to electrical equipments and devices. Some devices which are
more sensitive to the voltage fluctuations should be equipped with surge
protectors. Now question is what are surge protectors??- Device designed to
protect devices from voltage spikes i.e. a transient event, typically lasting 1 to 30
microseconds, which may reach over 1,000 volts. A transient surge protector tries
to control the voltage supplied to an electric device by either blocking or shorting
current to decrease the voltage under a safe threshold. Blocking is done by utilizing
inductors which brings about a sudden change in current. Shorting is achievable by
using spark gaps, discharge tubes, zener-type semiconductors, and MOVs (Metal
Oxide Varistors), all of which begin to conduct current once a certain voltage
threshold is gained, or by capacitors which do not cause a sudden change in
voltage. Some surge protectors use multiple elements.

INVERTER CONTROL MODE SWITCHING: - Several inverters are installed
with the distributed generators like solar and wind. The inverters have some
control strategy and if the micro grid is islanded from the main grid then the PCC
voltage, frequency are going to be changed. The control strategy running inside the
inverters of different types of renewable resources takes the voltage and frequency
feedback from the point of common coupling (PCC). Now if the frequency and
voltage of the PCC change, so input to the controller of the inverter change.
Therefore the controller may go to some other mode of operation. Islanding cause
problems in proper functioning of the inverters.

GRID PROTECTION INTERFERENCE: - Different types of relay, reclosures,
fuses used in grid for protection may mal-operate during islanded mode of
operation.
Hence islanding in power networks is a big challenge for protection engineers. As
DG integration increases, the need for unintentional islanding detection will be
more significant and challenging. Therefore, many new islanding detection
methods (IdMs) have been developed to deal with these problems. Furthermore,
the standards for intentional and unintentional islanding provide safe operational
strategies and overcome the consequences of DG islanding, if properly
implemented. For years, many IdMs have been presented, which reveal the fact
that islanding is an open research problem.[5]
Statement of the Problems

The simulation is carried on a software named RSCAD which is a production of
REAL TIME DIGITAL based POWER SYSTEM SIMULATOR (RTDS). Real
time simulation is a more often than not used tool for studying power system habits
in feedback to situations and circumstances. These sort of pragmatic test can
unearth potential problems in advance. Remidial measures could then be captured
before enforcing the logic in the original system. Hence RTDS is a tool for the
design, development and testing of power system protection and control schemes.
Since RSCAD is a newly built software, it's working is also under research, hence
to access any tool or proper building of the model, proper research requires to be
done else it may end up with error prone results.

Now to study and monitor the real time data obtained from the simulation, PMUs
are required. The existency of PMU block in RSCAD helps to collect data and feed
to PMU CONNECTION TESTER, where it is checked whether all the PMUs used
in the simulation are exporting data or not. Next the data collected is put to the
OpenPDC Manager, where all these are converted to an excel file from where they
can be assessed.

Since the modelling is to create a basic power system with all possible faults it may
have and even the protection schemes installed within it, thorough study of fault
analysis, bus classification, behaviour and working of PMUs, relay connections
and linkage to circuit breakers are required as the pre-requisites.

Studying PMUs and their CYBER SECURITY, how the data can be privatised and
kept safe from the malicious programmers are also equally important since use of
corrupted and attacked data may cause a huge loss to power economy.
Objectives of the Work

An encyclopedic analysis of diversified IdMs regarding their doctrine of
operations, advantages and disadvantages, performance assessment, and real time
utilizations is bestowed.

A contrast of varied IdMs in terms of accuracy, computational burden, speed and
cost is executed based on the critical reports.

Manipulating the behaviours of relays and to study the operation so that it can
perfectly understand the situation and send proper signals to the circuit breakers.
Scope of Research

Since simulation is done in RSCAD, the basics of it are discussed here in this
paper as it's a new real time handling software where research is still under
progress.

Now, as the basic skeleton model used is a 9 bus system, ideas regarding buses are
compulsory. The basics of bus classification and the different types of buses used
in the 9bus system are also studied.

Fault analysis and studying of different faults that may happen in a power system
are taken into account as they serve as the basis of simulation for unintentional
islanding.

Now for analysing the simulation data collected, PMU serves the purpose. Hence
why PMU is preferred over SCADA, demerits of SCADA and all other
comparisons are studied.

Next comes the protection of the power system model created, as any unnecessary
transients would damage the overpriced instruments used in the model. Hence
concepts of relay working logics and circuit breakers whenever faults occur are
equally considerable in the field of study.

Installation of DG resources at the load end of the model would create a realistic
view of the modern-day decentralised power system. Therefore logics required for
the synchronous working of the DGs with the utility grid have also been studied.

For synchronous working of both the microgrid and the utility grid, frequency
component and peak and rms values of voltage and current should be same. Now
due to the varying loads in the load end the frequency changes every second.
Hence to have such a situation in our model, import of real load data is made from
NYISO where varying load of every 5 mins is uploaded. Now RSCAD has no such
provision to accept data from files, it can accept data only through port. Hence
UDP is used to send data to the port from where data can be accessed. Hence how
frequency varies and code snippet for the UDP connection are also explained to
have a clear view.

Lastly the observations encountered are studied and tried to match the obvious if
its possible.
LITERATURE REVIEW
Power Mismatch Conditions
During islanded mode of operation, main grid is disconnected from the micro grid.
Now this does not mean that POWER OUTPUT from the load = POWER
GENERATED from the DG sources. This condition is known as power mismatch
condition. It totally depend on the mode of operation of the micro grid system i.e.
how many loads are switched on or off, how many DGs are in working condition
or how many of them are off. [6]

∆P (active power mismatch) = P (active load power) – P (DG active power
generation) = P (active power taken or given to grid).

∆Q (reactive power mismatch)= Q (reactive load power) – Q (DG reactive power
generation) = Q (reactive power taken or given to grid).

0% ∆P indicates P(load) =P(DG)

+10% ∆P indicates P (load) > P (DG); the system is loaded and the voltage is
going to reduce. Hence under voltage relay is going to experience some tripsing.
And if ∆Q is +ve Q (load) > Q (DG), then under frequency relay is going to be
actuated.

-10% ∆P indicates P (load) < P (DG), then over voltage relay is going to be
actuated. Similarly if ∆Q is -ve Q (load) < Q (DG), then over frequency relay is
going to be actuated.







1
2
3
4
5
6
7
Fig c Non Detection zone; (Source:- Local and Remote Techniques for Islanding Detection in
Distributed Generators - Scientific Figure on ResearchGate. Available from:
https://www.researchgate.net/figure/Non-detection-zone-of-OUV-and-OUFtechniques_fig1_221907530 [accessed 11 Jul, 2019])
NON DETECTION ZONE (NDZ) defines for what particular percentage of
power mismatch the islanding relay does not detect the islanding condition. All the
DERs are to be equipped with under voltage and over voltage relays and under
frequency and over frequency relays to detect whether the changed voltage and
frequency are within the limits or not. According to IEEE standards OVR=1.11 per
unit and UVR= 0.88 per unit; OFR=60.5per unit, UFR=59.3 per unit and the
islanding detection should be within 1-2 seconds. [7]
The relation between the thresholds of power mismatch and voltage/frequency
limits can be derived using the following equations.[1]


{(VVmax)2−1}≤△PP≤{(VVmin)2−1}{(VmaxV)2−1}≤P△P≤{(VminV)2−1}
[Qf{1−(fminf)2}]≤P△Q≤[Qf{1−(fmaxf)2}]
Where Vmax, Vmin, fmax, and fmin are the maximum and minimum voltage/frequency
threshold limits of the relays in the DG system; ∆P and ∆Q represent the power
mismatches prior to the main grid disconnection; Qf is the load quality factor
usually considered to define parallel RLC load.
Anti-Islanding or Islanding Protection and Detection
The act of preventing islanding from happening is actually what is anti-islanding. It
is recommended that all distributed generators shall be equipped with devices that
prevent islanding.
Before prevention of islanding, first pre-requisite is how to detect when islanding
is happening. There are many ways to detect and resolve islanding:Table 2Different techniques for detection of islanding
IdMs (Islanding Detection Methods)
techniques
Remote detection Techniques
Hybrid
ent
Voltage unbalance and frequency set point
Power Line Carrier Communication
ift
Voltage dependency and reactive power shift
Signal Produced by Disconnect
Voltage Fluctuation Injection
Supervisory Control and Data Acquisition Technique
Shift
ift
Synchrophasor/PMU based Technique
t
Signal Pr
W
Ti
Auto
Local Detection Techniques
It is based on the measurement of system parameters especially voltage, frequency
etc at the DG site .[8]It is classified into:-
Passive islanding detection
Here the system parameters (including voltage, current, impedance, power and
frequency) are monitored at the PCC or DG terminals. These framework reveal
symbolic disparity when the main grid is disconnected from the microgrid. The
protection relays thus sense these variations and operate to trip the main breaker
switch. They have large NDZ where they fail to detect islanding condition and
have lesser detection speed [5] [1] .

POWER QUALITY MONITORING/HARMONIC DISTORTION:Applicable for the inverter based DERs basically solar and wind systems; Inverters
work on pulse width modulation techniques to generate low frequency output
signals from high frequency pulses and generate higher order harmonics. Therefore
in this method the harmonics and ripples in the voltage are measured at the PCC.
To understand much more effectively, this journal would help a lot.[9]
Fig 2 Process to follow in harmonic distortion based detection; (Source:- 2018, IIT Roorkee
July. “Mod04lec16.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=F0ZTgrgMZAk&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=35.)
Now if ‘d’ is >= certain threshold, then islanding condition is present else not
present. One of the major drawbacks is the threshold selection.

RATE OF CHANGE OF OUTPUT POWER: - The rate of change of output
power, dtdp at the DG side once it is islanded will be higher than that of rate of
change of output power before the DG is islanded for the similar percentage of
load variation. [10] This method is much more compelling when the DG has
unbalanced load inspite of having balanced load. [11] [12]

OVER/UNDER VOLTAGE PROTECTION and OVER/UNDER
FREQUENCY PROTECTION: - Here the accustomed traditional protection
relays are established on a distribution feeder to regulate the bizzare circumstances
during diversified modes of micro-grid operation.[13] The relays kickoff when the
voltage and frequency values overpass a fixed threshold deadline, thus
disconnecting the DGs from the main network. Customarily, the utility grid
operations will be contingent upon the variations in the active and reactive powers
(∆P and ∆Q) antecedent to a detachment from DG sources may crop up.
At the non-zero ∆P, an alteration in the amplitude comes into sight at PCC, which
the O/UVP relay identifies and disconnects the DG. Contrarily, at non-zero ∆Q, a
load voltage phase shift appears that deflects the inverter current frequency. The
O/UFP relay notices this change and disrupts the DG.

RATE OF CHANGE OF FREQUENCY:- The rate of change of frequency,
df/dt, will be very high when the DG is islanded. [15] The rate of change of
frequency (ROCOF) can be given by:-
dfdt=△P×f2×H×GWhere,&ThickSpace;△P&ThickSpace;=power&
ThickSpace;mismatch&ThickSpace;at&ThickSpace;the&ThickSpa
ce;DG&ThickSpace;side&ThickSpace;&ThickSpace;&ThickSpace;
&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSp
ace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&Thic
kSpace;&ThickSpace;&ThickSpace;&ThickSpace;H&ThickSpace;i
s&ThickSpace;the&ThickSpace;moment&ThickSpace;of&ThickSp
ace;inertia&ThickSpace;for&ThickSpace;DG&ThickSpace;system
&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSp
ace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&Thic
kSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;G
&ThickSpace;is&ThickSpace;the&ThickSpace;rated&ThickSpace;
generation&ThickSpace;capacity&ThickSpace;of&ThickSpace;the
&ThickSpace;DG&ThickSpace;systemdtdf=2×H×G△P×f
Where,△P=powermismatchattheDGsideHisthemomentofinertiaforD
GsystemGistheratedgenerationcapacityoftheDGsystem
Large systems have large H and G whereas small systems have small H and G
giving larger value for df/dt( ROCOF). [16] Relay audits the voltage waveform and
will function if ROCOF is greater than the threshold setting for a convinced span
of time. The setting has to be selected in such a manner that the relay will prompt
for island condition but not for load variations. This design is highly
recommendable when there is enormous mismatch in power but it flops to operate
if DG’s capacity matches with its local loads.[1]
DRAWBACKS:
Requires a minimum power mismatch of 15%

Performance can be affected by the type of loads and generator inertia constant

IMPEDANCE MONITORING:-
Fig 3 Grid connected mode of operation for a parallel RLC load; (Source:- 2018, IIT Roorkee
July. “Mod04lec16.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=F0ZTgrgMZAk&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=35.)
Now at the point of common coupling for grid connected mode of operation; the
voltage, current and then impedance= voltage /current are measured. The
impedance turns out to be :-
∣Znormal(jω)∣=(Rg2+ω2Lg2Rg+R1)2+(ωC−ωL1−Rg2+ω2Lg2ωLg)21
Fig 4 Islanded mode of operation; (Source:- 2018, IIT Roorkee July.
“Mod04lec16.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=F0ZTgrgMZAk&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=35)
Here the grid is disconnected; hence it is working in islanded mode. Again the
voltage, current and then impedance= voltage /current are measured at PCC. The
impedance turns out to be :-
∣Zisland(jω)∣=R21+(ωC−ωL1)21
Therefore due to change in impedance values, it can be declared whether the
microgrid is in islanded mode or grid connected mode. [17]

VOLTAGE UNBALANCE:- During islanding, DG has to operate so as to
continue power supply to the loads in the island. If the variation in loading is huge,
then islanding conditions are perfectly identified by surveying several parameters:
voltage magnitude, phase displacement, and frequency alteration. Nonetheless,
these techniques may not be competent if the variations are less. As the distribution
networks mostly include single-phase loads, it is widely possible that the islanding
will alter the load equity of DG. Moreover, even though the change in DG loads is
small, voltage unbalance will occur due to the change in network condition.[18]

PHASE JUMP DETECTION METHOD: - In the PJD method, [19] a phase
discrepancy between the voltage and current at DG terminals is monitored for a
sudden phase jump. During the islanding condition, an alteration occurs in the
phase angle, which is corelated with the pre-set threshold value. The method fails
to detect the islanding condition when the DG power and local load are closely
matched. Therefore, the PJD method suffers from large NDZ. The NDZ of the PJD
method is derived using the following expression as:-
tan−1⎝⎜⎛1+P△PP△Q⎠⎟⎞≤μthreshold
Where µ threshold denotes the phase-jump threshold. The circuit reactive elements
may affect the accuracy of the PJD method; therefore, it is not suitable for
industrial applications.[1]
Active islanding detection
Active methods directly collaborate with power system transaction by
recommending perturbation signals. The extraneous signal injection brings
momentous variations in the scheme parameters under the islanding condition and
triggers the relays to operate. Here the large NDZ problem is overcome.
Drawback: -Injection of high frequency signals produce voltage or current
harmonics which affect the performance of such methods.(Total Harmonic
Distortion)[8]

SIGNAL INJECTION BASED TECHNIQUES: -They inject disturbance
signals like low frequency or high frequency signals, pulse signals and negative
sequence based signals through inverter controllers. Islanding is detected based on
electrical quantities and parameters behaviour at PCC which are measured and
estimated due to injected disturbance signals.
Fig 5 Grid connected mode; (Source:- 2018, IIT Roorkee July. “Mod04lec18.” YouTube,
YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=YKcFu4_ONEs&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=37)
During the grid connected mode, I (disturbance) is injected with frequency 30 Hz
if the fundamental frequency is 60 Hz. Harmonic currents appear due to non-linear
loads, or electronic components of the renewable energy sources. The impedance
of the load path is higher than the source path; as a result the 60 Hz current
component is going to flow through the load and the rest through the source.
Fig 6 Islanded Mode; (Source:- 2018, IIT Roorkee July. “Mod04lec18.” YouTube, YouTube,
24 Aug. 2018, www.youtube.com/watch?v=YKcFu4_ONEs&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=37)
The circuit breaker is open showing islanded mode of operation. As a result the
grid current = 0 i.e. all the current flows through the load.

IMPEDANCE MEASUREMENT: - This technique is dependent on the change
in the high frequency impedance of the calculated data accumulated from voltage
and current measurements. High frequency impedance turns more significant at the
time of islanding condition. Generally used in power systems constituting
synchronous DGs, they possess a small NDZ for the systems comprising single
inverter based DGs. [20]

ACTIVE FREQUENCY DRIFT (AFD): - The AFD is based on the injection of
a current waveform distortion to the original reference current of the inverter to
force a frequency drift in case of islanding operation.
Fig 7 (a) Original reference current and AFD reference current waveforms (b) Original reference
current and injected current waveforms; (Source:- Yafaoui, A., Wu, B., & Kouro, S. (2011).
Improved active frequency drift anti-islanding detection method for grid connected
photovoltaic systems. IEEE Transactions on Power Electronics, 27(5), 2367-2375.)
By introducing a zero conduction time tz at the end of each half cycle, the phase
angle of the fundamental component of current is shifted.
During normal grid connected operation the inverter generally operates with unity
power factor and is synchronized to the grid voltage and will conduct at grid
frequency. In islanding operation, the perturbation added to the current will
generate a permanent drift in the operating frequency towards the local load
resonance frequency so as to keep unity power factor. This drift will finally arrive
at the frequency boundary limits set for islanding detection. [21]
The dead time tz and the original time period T can be related to define the
chopping factor Cf used to perturb the waveform.
Cf=T2tz
The AFD reference current waveform can be given by: -
iafd(t)={Isin⁡(2πvt)&ThickSpace;⇒0≤ωt&lt;π−tz0&ThickSpace;
&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSp
ace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&Thic
kSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&
ThickSpace;⇒π−tz≤ωt&lt;πIsin⁡(2πvt)&ThickSpace;⇒π≤ωt&lt;2
π−tz0&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&Th
ickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;
&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSp
ace;&ThickSpace;&ThickSpace;⇒2π−tz≤ωt&lt;2πwhere&ThickSp
ace;v=f(11−Cf)iafd(t)=⎩⎪⎪⎨⎪⎪⎧Isin(2πvt)⇒0≤ωt<π−tz0⇒π−tz
≤ωt<πIsin(2πvt)⇒π≤ωt<2π−tz0⇒2π−tz≤ωt<2πwherev=f(1−Cf1)
When this modified waveform is applied to an isolated DG system with RLC load,
the frequency of the load will change according to the equation given by:
arg[R−1+(jωL)−1+(jωC)]−1=0.5πCf

POSITIVE FEEDBACK BASED TECHNIQUES: - Electrical quantities like
frequency, phase angle and voltage deviation etc. are given as feedback to
inverters. Feedback is designed in such a way that DER operates in unstable
region.
1. SLIDING MODE FREQUENCY SHIFT: - The SMFS method uses the phase
angle of the inverter output current, which is monitored as a function of terminal
voltage frequency. The SMFS method uses positive feedback to change the phase
voltage at DG terminals by regulating the frequency deviations, thus identifying
the islanding condition. The change in the phase angle of the inverter output
current is always relative to the grid output voltage; thus, the frequency of the grid
voltage deviates from its nominal value upon the main grid disconnection.[1]
(http://energyprofessionalsymposium.com/?p=35452)
2. SANDIA FREQUENCY SHIFT:- The SFS method is basically an extension of
the AFD method. The process of applying SFS can be summarized as follows: -

Inject a current harmonic signal with a limited duration into the Point of Common
Coupling (PCC) so as to comply with the maximum THD allowed by
interconnection standards.

The injected current signal distorts the inverter current by presenting a 0A
segment.

The desirable effect of the 0A segment, is that the fundamental component of the
inverter current leads the voltage by a small angle ӨAFD, which is frequency
dependent and it creates a positive feedback.

When the grid is disconnected, the frequency of the voltage of the PCC tends to
drift, reaching values higher until the frequency is out of the OFP/UFP trip window
(Range) and the inverter is disconnected.

A positive feedback is utilized to prevent islanding.
The NDZ of the SFS highly depends on its design parameters. The design
parameters include both chopping factor Cf and feedback gain factor K. If these
handlers are not correctly adapted, it may show a failure as outcome or
deterioration of the system power quality through injection of large amounts of
harmonics. However, SFS may decline to detect islanding considering a fact that
the deviations of voltage and frequency are less due to the power balance between
DG sources and local loads.[22] The chopping factor is a function of the error in
the line frequency and may be computed as follows:
Cf=Cf0+K(fa−fline)where&ThickSpace;Cf0:−is&ThickSpace;the&
ThickSpace;chopping&ThickSpace;factor&ThickSpace;when&Thi
ckSpace;there&ThickSpace;is&ThickSpace;no&ThickSpace;freque
ncy&ThickSpace;error&ThickSpace;&ThickSpace;&ThickSpace;&
ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpa
ce;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;K:−&T
hickSpace;an&ThickSpace;accelerating&ThickSpace;gain&ThickS
pace;that&ThickSpace;does&ThickSpace;not&ThickSpace;change
&ThickSpace;direction&ThickSpace;&ThickSpace;&ThickSpace;
&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSp
ace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;fa:−is
&ThickSpace;the&ThickSpace;line&ThickSpace;frequency&Thick
Space;measured&ThickSpace;at&ThickSpace;PCC&ThickSpace;&
ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpa
ce;&ThickSpace;&ThickSpace;&ThickSpace;&ThickSpace;&Thic
kSpace;&ThickSpace;fline:−&ThickSpace;is&ThickSpace;the&Thi
ckSpace;nominal&ThickSpace;line&ThickSpace;frequencyCf=Cf0
+K(fa−fline)whereCf0
:−isthechoppingfactorwhenthereisnofrequencyerrorK:−anaccelerati
nggainthatdoesnotchangedirectionfa
:−isthelinefrequencymeasuredatPCCfline
:−isthenominallinefrequency
3. SANDIA VOLTAGE SHIFT:- Sandia Voltage Shift (SVS) applies positive
feedback to the amplitude of Va. If there is a decrease in the amplitude of Va
(usually it is the RMS value that is measured in practice), the inverter reduces its
current output and thus its power output.[23]
If the utility is connected, there is little or no effect when the power is reduced.
When the utility is absent and there is a reduction in Va, there will be a further
decrement in the amplitude of Va as governed by the Ohm’s Law response of the
(RLC) load impedance to the decreased current. This additional decrement in the
amplitude of Va leads to a further reduction in inverter output current, finally
leading to reduction in voltage that can be identified by the UVP. It is possible to
either have an increment or decrement of the power output of the inverter, leading
to an analogous OVP or UVP trip.[1] It is however preferable to respond with a
power reduction and a UVP trip as this is less likely to damage load equipment.
Hybrid islanding detection
System is monitored using passive islanding detection technique, when an island is
detected it is further checked by active islanding detection technique. Hence here
NDZ problem removed and even the percentage of DGs in the unstable mode is
minimized.

VOLTAGE UNBALANCE AND FREQUENCY SET POINT:- Voltage
unbalance =V₂/V₁ where V₂ is negative sequence voltage and V₁ is the positive
sequence voltage. Voltage unbalance is the passive technique. Fundamentally here
the ratios are taken of certain frameworks (namely voltage) at the terminal of PCC.
[8] If the proportion is surpassing certain threshold, then there is islanding. This act
as the first indication whether there is islanding or not. Now if it is islanding, then
a disturbance signal is injected to the controller of the inverter i.e. the active
technique is taken care of; else not required.[24]
Fig 8 Flowchart showing voltage unbalance and frequency set point; (Source:- 2018, IIT
Roorkee July. “Mod04lec18.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=YKcFu4_ONEs&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=37)

TECHNIQUE BASED ON VOLTAGE AND REACTIVE POWER SHIFT :Here the rate of change of voltage is the passive technique. Yet the real power shift
(active) is enforced to the system if the passive technique cannot admirably
discover the islanding condition. [25]
DG generates a level of reactive power flow at the point of common coupling
(PCC). This power flow can only be maintained when the grid is linked. Islanding
can be detected if the level of reactive power flow is not preserved at the set value.
For the synchronous generator based DG, islanding can be disclosed by increasing
the internal induced voltage of DG from time to time and observing the change in
voltage and reactive power at the terminal where DG is fixed to the distribution
system. A large change in the terminal voltage, with the reactive power remaining
almost unchanged, indicates islanding.

VOLTAGE FLUCTUATION INJECTION: - This technique is based on the
voltage fluctuation injection, which can be obtained using a high impedance load.
The islanding detection correlation factor (CF) is recommended for small-scale
DGs, generally less than 1 kW. The two-stage method, which is the passive
technique (rate of change of frequency (ROCOF)/rate of change of voltage
(ROCOV)) for the protection scheme, and the active technique (CF) as a backup is
used to achieve higher effectiveness. This technique utilizes digital signal
processing to forecast the ROCOF, ROCOV, and CF of the distribution
synchronous generator and to accurately detect islanding and non-islanding
disturbances. The NDZ is decreased when the ROCOF is applied with a change in
the active technique for islanding detection.
Remote Detection Techniques
These are based on communication between utilities and DGs. Although these
techniques may have better reliability than local techniques, they are expensive to
implement and hence uneconomical .Some of the remote islanding detection
techniques are as follows:-
Power line carrier communication
Fig 9 Power line carrier communication; (Source:- 2018, IIT Roorkee July.
“Mod04lec18.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=YKcFu4_ONEs&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=37)
Here a transmitter (T) is placed near the grid protection switch, and a receiver(R) is
installed at the PCC. The transmitter continually broadcasts low energy
communication signal (due to low pass filter nature of the power system) through
the power line to the receiver to transmit islanded or non-islanded information.
When the grid is disconnected, the transmitted signal is cut off because of the
substation breaker opening and the signal cannot be received by the DG; which
invokes the controller of the inverter to shut down the particular system. No
current is going to be supplied from the system to the load. In radial system, only
one transmitting generator needed that can continuously relay a message to many
DGs in the network.[26]
The main drawbacks are
i. To connect the transmitter and receiver device to a substation; a high voltage to
low voltage coupling transformer is required which costs high.
ii. If the method is applied in the non-radial system, it results in the use of multiple
signal generators whose implementation will require three times the cost.
Signal produced by disconnect
This method is similar to the PLCC, with only difference is the mode of
transmission used here specifically microwave link or telephone link. Its strengths
are additional supervision and full control of both the grid and DG. The main
drawbacks are:i. Relative expensiveness
ii. Significant licensing
iii. Design complications
Supervisory control and data acquisition technique
SCADA (central control system) supervises the status of circuit breakers which are
present inside the micro grid or smart grid system. Therefore monitors the auxiliary
contacts those are liable to check the conditions of islanded operation. Upon
islanding, a series of alarms is activated and the corresponding circuit breaker is
tripped. [27] Major drawbacks:-
i. Cost of implementation is very expensive since each inverter requires separate
instrumentation equipments and sensors.
These communicate with all DGs and offer synchronized operation between micro
grid utility grid to avoid any phase difference.
Synchrophasor measurement unit based technique/ PMU based
islanding detection technique
Fig 10 PMU based islanding detection; (Source:- 2018, IIT Roorkee July.
“Mod04lec18.” YouTube, YouTube, 24 Aug. 2018,
www.youtube.com/watch?v=YKcFu4_ONEs&list=PLLy_2iUCG87D59Bc8Jqfqt43LvPC0KgC&index=37)
Two PMUs are installed one at the grid side and the other at the DG side. Now the
data collected about the voltage and currents signals from the PMUs are transferred
to the relay which detects any sort of islanding. A circuit breaker is connected
which triggers the decision to be taken by the relay.
Now suppose the major substation is disconnected and the breaker on the left hand
side is open. The grid connected voltage phasor consisting of the magnitude as
well as the angle is detected by the PMU 1. Similarly the DG connected voltage
phasor is detected by the PMU 2. These data are sent to the relay where
comparison is done either based on the magnitude or based on the phasor angle or
frequency. Disconnection indicates unstabilized changed voltage and frequency
which triggers the circuit breaker to open.
Signal Processing Based Methods
These help to improve the detection performance, decrease detection time and
reduce NDZ. These tools help to analyse and extract important features of a
measured signal in order to perform efficient power system operations. [28]
Fourier transform
FT is a frequency domain analysis gizmo used to concentrate the aspects of a
signal at the specified frequencies. FT is not capable of considering time domain
analysis. DISCRETE FOURIER TRANSFORM(DFT) and FAST FOURIER
TRANSFORM(FFT) transform the finite length of the discrete time sequence into
discrete frequency sequence. Such tools help to develop efficient and fast IdMs. [29]
DISADVANTAGE:- Reduced spectral estimation and low frequency resolution.
Wavelet transform
Wavelet transformation is a strong candidate for extracting important features from
a distorted voltage, current, or frequency signal. Methods based on WT are
associated with STFT (short time fourier transform) and the multi-resolution
techniques. [30]
In WT-based IdMs, the wavelet coefficients of the measured signal are compared
with the pre-defined threshold value. If these coefficients attain a larger value than
the pre-defined threshold value, the islanding condition will be detected. [30] The
impacts of mother wavelet selection, threshold settings, and different sampling
frequencies are the limitations of such methods. Moreover, WT can only detect the
low-frequency band, and therefore, the wavelet packet transform (WPT) is applied
to analyse the high-frequency components using the d-q axis of three-phase
apparent power.[31] The WPT method is mostly related to the discrete wavelet
transform (DWT), except for the fact that WPT gives equal resolution to low- and
high-frequency signals. WPT can extract significant features from a measured
voltage or current signal using approximation and detail decomposition. [32]
[33]
S-Transform
ST is an extension of the WT concept. It converts a time-domain function into a
two-dimensional frequency-domain function.[31] Like other time-domain methods,
the ST method is also utilized to extract important features from a measured signal
at PCC, thereby detecting the islanding condition. Initially, ST processes the
measured voltage or current signals at DG terminals and generates the S-matrix
and the equivalent time-frequency contours. Then, the spectral energy content of
these contours is calculated as containing the information of frequency and
magnitude deviations for islanding detection. To process a signal, the ST method
requires more computational memory than the other similar techniques. Moreover,
the processing time of such methods is large.
Time-time transform
The TTT method analyses and transforms one dimensional time domain signal to
two dimensional time domain signal by giving time-time distribution on a
particular window.
In the TTT method, the low frequency components are concentrated at different
places while the high frequency components are concentrated around the
localisation point having more energy concentration [34] .
TTT based techniques show good performance in noisy environment.
Kalman Filter is a well-known time frequency based harmonic analysis tool used
in power systems to extract and filter harmonic features from the measured voltage
and current signals.
Auto co-relation factor
ACF is a mathematical model used to excerpt the secluded information from a
computed power or energy signal. While considering the finite duration sequences,
ACF is expressed using the finite summation limits. [28]
This method uses calculated envelopes to extract transient features, for which the
variance of samples provides the criteria for islanding detection.
Intelligent Based Methods
They are analogous to communication or signal processing based approach, except
that they do not desire any threshold selection. These artistry are able to sort out
the multi-objective problems which the conventional approaches cannot handle.[1]
First, the input signal in the form of voltage or current measured at the PCC is fed
to the system for data training and feature extractions using a training algorithm.
This process is performed offline in order to save time and avoid computational
burden. The online process is performed using an intelligent classifier model for
making the final decision. In general, the intelligent IdMs suffer from the large
computational burden.
Fig 11 Algorithm for Intelligent Based Methods; (Source:- Kim, M. S., Haider, R., Cho, G. J.,
Kim, C. H., Won, C. Y., & Chai, J. S. (2019). Comprehensive Review of Islanding Detection
Methods for Distributed Generation Systems. Energies, 12(5), 837)
Artificial neural network
The ANN based approaches extract important features from the measuring data,
which are used for identifying variations in power system parameters. [35]
The dendrites basically gather the information about the parameters from the PCC.
It is actually a computational model of a biological procedure which tries to learn
and instruct itself from the past experiences like the biological brain of the neural
network.
ANN-based IdMs detect the islanding condition by providing a high-accuracy and
suitable operation for the systems using multi-inverters. ANN-based schemes
perform the islanding detection efficiently but a large processing time and feature
selection with multiple DG configurations still need to be addressed.
Fig 12 Comparison of Biological and logical neural networks; (Source:- Richárd, N. (2018,
September 4). The differences between Artificial and Biological Neural Networks. Retrieved
May 29, 2019, from Towards Data Science: https://towardsdatascience.com/the-differencesbetween-artificial-and-biological-neural-networks-a8b46db828b7?gi=d9b833c22055)
Decision tree
Another classification technique utilized for islanding detection. The DT classifiers
are used with wavelet transforms. [36]
Usually the voltage or current signals measured at the DG terminals are fed to WT
for feature extraction. The extracted features are then processed using a DT
classifier to detect islanding condition. ACCURACY achieved = 98%.
Probabilistic neural network
PNN is applied in traditional pattern recognition schemes using the artificial neural
hardware. PNN contains the following four layers: the input layer, pattern layer,
summation layer, and output layer. These layers perform their functions for feature
classifications and do not need any learning technique. [37]
Support vector machine
SVM is a powerful classification tool used for signal and system analysis by
constructing a decision boundary (hyper plane) to split the data needed for training
by looking at the extremes of the data sets. The SVM classifier, in association with
autoregressive modelling, is used to extract the signature features from the
measured PCC voltage or current signals. The SVM-based IdMs provide high
accuracy and fast detection speed. However, due to the large computational burden
regarding the data training and algorithm complexity, SVM-based IdMs are
considered impractical for real system implementations. [38]
Fig 13 Support Vectors; (Source:- Fuangkhon, Piyabute & Tanprasert, Thitipong. (2009). An
Incremental Learning Algorithm for Supervised Neural Network with Contour Preserving
Classification. 740 - 743. 10.1109/ECTICON.2009.5137153.)
Fuzzy logic
It is actually a superset of Boolean logic (representation of 0 or 1 i.e. either
completely true or false; hence discrete). But if we have to represent in continuous
manner, Boolean logic stops working. Hence FUZZY LOGIC comes into view
which represents the uncertainty (we do not know up to what extent it can go). [39]
To represent the intensity , level or degree FUZZY LOGIC is used.
FL was first introduced using DT transformation, where the combination of fuzzy
membership functions and the rule based formulations were used to improve the
fuzzy systems. Such methods show an efficient performance when applied in
islanding detection algorithms.
Limitations:- Highly abstract due to several min and max class operations.
Sensitive to noisy data due to repeated generation of rules of membership functions
and classifications.
METHODOLOGY
Concepts
Before going to the simulation process, certain concepts need to be understood that
would fill the gap between practical and theoretical concepts.
Knowing about RTDS
RTDS is a real time power system simulator, which employs an advanced, and
easy to use graphical user interface. The RTDS allows users to accurately develop
their models and simulate them efficiently. The software used to architect the
power system model in RTDS is RSCAD, which involves a library of power and
control system components. RSCAD permits the developer to choose a pictorial
portrayal of the power system or control system components from the library in
order to design the needed circuit. Once the system has been drawn with the entry
of required parameters, the compiler in RTDS generates the low level code that is
needed to perform simulation on the RTDS simulator. RTDS is capable of
generating the real time signals, which enable the user to simulate the situations,
which generally occurs in the power system. [40]
RSCAD software handling
RSCAD is software which permits the user to develop a test case by using the
numerous different components present in the RSCAD library. The following steps
are required to prepare and run a new simulation case. [40]
Fig 14 Options available on opening RSCAD; (Source:- Kankanala, Padmavathy & Saran,
Ankush & N. Schulz, Noel & Srivastava, Anurag. (2008). Designing and Testing Protective
Overcurrent Relay using Real Time Digital Simulation.)

The RSCAD/Draft software module is started.

A new ‘Project’ and ‘Case’ directory is created in the ‘File Manager’ module.

Next the new circuit diagram is created for simulation and the circuit is compiled.

Lastly the simulation case is opened from RSCAD/RunTime.
The RSCAD/Draft software module is used to built the circuit that will be
simulated employing the RTDS simulator.












1
2
3
4
5
6
7
8
9
10
11
12
Fig 15 In Draft window; (Source:- Kankanala, Padmavathy & Saran, Ankush & N. Schulz,
Noel & Srivastava, Anurag. (2008). Designing and Testing Protective Overcurrent Relay
using Real Time Digital Simulation.)
After the successful compilation of the system, the user simulates the system by
using the RSCAD/ RunTime software module.
Fig 16 In Runtime window; (Source:- Kankanala, Padmavathy & Saran, Ankush & N.
Schulz, Noel & Srivastava, Anurag. (2008). Designing and Testing Protective Overcurrent
Relay using Real Time Digital Simulation.)
In RunTime mode, the user is able to add switches, buttons, meters and sliders for
fault application, can plot graphs for voltage, current, power, fault, and frequency
etc, can increase or decrease different physical quantities. After completion of the
selection of plots in the RunTime, the user is able to simulate the system by
pressing a button “Start Simulation” which is available in the RSCAD/RunTime
module.
Bus classification and concept of load flow
A bus is a node at which one or many loads and generators are connected. In a
power system, each node is co-related with 4 quantities namely magnitude of
voltage, phase angle of voltage, active or true power and reactive power in load
flow problem two out of these four quantities are specified and remaining two are
require dto be determined through the solution of equations. Depending on the
quantities that have been specified, the buses are classified into 3 categories. Buses
are classified according to which two out of the four variables are specified.

Slack /Swing/Reference bus:- For the slack bus, it is assumed that the voltage
magnitude∣V∣ and voltage phase ∂ are known, whereas real and reactive powers Pg
and Qg are obtained from load flow equations. So one bus has to be made reference
i.e. it has to be taken as 1∠0∘Another way to define it is :- slack bus is a generator
bus i.e. connected to generator which is taken as reference.Pslack+Pgenerator
=Pdemand+Ploss

Generator/ Voltage controlled/PV bus:- Here the voltage magnitude
corresponding to the generator voltage and real power Pg corresponds to its rating
are specified. It is required to find out the reactive power generation Qg and phase
angle of the bus voltage. It is also called voltage controlled bus where we use
compensator compensation techniques like static VAR compensator (SVC).

Load/PQ bus:- No generator is connected to the bus. At this bus the real and
reactive power are specified. It is desired to find out the voltage magnitude and
phase angle through load flow solutions. It is required to specify only Pd and Qd at
such bus as at a load bus voltage can be allowed to vary within the permissible
values.



1
2
3
Fig 17 9 Bus System Line Diagram; (Source:- Use of ANFIS Control Approach for SSSC
based Damping Controllers Applied in a Two-area Power System - Scientific Figure on
ResearchGate. Available from: https://www.researchgate.net/figure/Single-line-diagram-ofa-3-machine-9-bus-system-All-impedances-are-in-per-unit-on-100MVA_fig3_276427706
[accessed 11 Jul, 2019])
The 9 bus system is shown above along with all the buses and their classification to
have a clearer view of the classes.
The active and reactive power flow equations of a power system are non-linear
with unknown bus voltages and phase angles. The load flow feature of RSCAD
DRAFT shown in fig 14, uses the Fast-Decoupled Newton-Raphson method for
the power flow calculations which provides a solution to this set of non-linear
equations. Prior to running the power flow, a bus label component (where bus type
must be specified whether slack bus, PV bus or PQ bus) is required at every bus in
the power system.
Fig 18 Bus nodes; (Source:- Taken from our simulation at IIT Delhi)
From the power flow solution, the voltages and angles at all the buses can be
determined. Once the power flow is completed, the RSCAD simulation should be
compiled. The compile uses the power flow results to initialize the sources,
generators, dynamic loads, exciters and governors which therefore creates a quasisteady state starting point for the simulation. If the power flow does not converge it
means that either the set of nonlinear equations itself does not have a solution or
the equations could be ill conditioned and the numerical method used to solve the
nonlinear equations is inappropriate. When the algorithm takes a large number of
iterations it may indicate that the steady state solution is close to voltage
instability.
Fault analysis
Electrical systems ocassionally experience several types of faults. These faults are
hazardous to the safety of both equipment and people. Faults in a 3 phase system
can be unsymmetrical:-single line to ground, double line to ground, line to line or
three phase symmetrical. Power system operation during any of these faults can be
analysed using sequence components discovered by Charles L. Fortescue.

Symmetrical Faults :- Before the fault, voltage and current were 120º phase
displaced and balanced i.e. magnitudes of all the phases were same. Even after the
fault, voltage and current magnitudes and phases remain balanced. Therefore this
type of faults are known as symmetrical faults. Now faults can be either short
circuit (L-L-L) or ground (L-L-L-G) faults.

Unsymmetrical Faults :- Before the fault, the system is in balanced condition, but
after sudden faults, they become unbalanced. Specifically line to ground (L-G) ,
line to line (L-L) and double line to ground (L-L-G) faults are common.
Fortescue Theorem states that if there are n unsymmetrical phasors, then this
phasors can be resolved into n-1 symmetrical phasors and 1 co-phasal quantity.
Since here dicussions are related to current and voltage vectors, therefore there are
only 3 unsymmetrical vectors which can be divided into 2 symmetrical vectors and
1 co-vector.
Now since faults can be permanent or temporary i.e. transient for a short period,
hence for the simulation purpose both the faults have been considered.




1
2
3
4
Fig 19 Logic for Fault control both temporary and permanent used in the simulation; (Source:Taken from our simulation at IIT Delhi)
Phasor measurement units (PMUs)
In a power system operational paradigm, focussing on the transmission levels; data
are gathered through the sensors like the remote terminal units which get data from
CTs and PTs. Traditionally these analog values or signals are given to the SCADA
technology; which communicates data and sends it to the control centers. In the
control centers, Energy Management System (EMS) is present; and all the data that
come in; get into different algorithm that run as engines in EMS. Next EMS tells
the user that whether the power system is operating as they wanted to operate, or
whether any problem has occured and what are the control actions to solve the
problem.

Next important factor is how fast the data is being transferred from SCADA to the
EMS. Typically the output data rate of SCADA has been once in 4-6 seconds i.e.
data fed to the algo get the data every 4-6 seconds.
If some disturbance takes place, and if one has to study those disturbances or has to
study how the system behaves after the disturbance (post disturbance analysis)then
if the output rate is just once in every 4-6 seconds then probably that is not enough.
Because the power system tend to change very quickly; it's a dynamic system, so if
we are not able to capture the values of power system in a good percentage, then
we loose our data. Therefore we are not able to view the exact behaviour of the
power systemand if the exact behaviour is not extracted, then there might be a
chance of ending up with wrong control actions.
As a result, data is required at a much faster rate that helps to stagnate and apply all
the numerical values of data. From here to eliminate this diadvantage emerges a
newr technology named synchrophasor.

In SCADA, we are trying to gather data from different parts in power system and
even though the data might have some timing, but the problem is sending data to a
control center and some other substation located quite far away and is getting to
send the data as well to the same control center, because of the geographical
distance the substation which is closer will get to send the data much quicker than
the other substation. Hence local clocks are used to stand the data coming from the
local substations; so that we get to know what time those data belong to. So time
synchronized wide area system data is required to have an accurate view of the
entire power system.

SCADA tech. gives magnitudes of different electrical quantities like voltages,
currents, frequency and so on. Networks one has to analyse are AC which has both
magnitude as well as angle phasors. Therefore looking into just magnitude leads to
loosing of information and ending up monitoring the system wrongly.
Fig 20 PMU block in RSCAD; (Source:- Taken from our simulation at IIT Delhi)
So to solve all the above mentioned problems PMUs act as life saviours. PMUs are
devices that produce synchro-phasors, frequency and rate of frequency estimates
from voltage or current signals received from PTs and CTs and a time
synchronized signal which we can get from GPS satellites through GPS clock.
Power system protection
Two main equipments serves the purpose:- relays and circuit breakers. The main
operation of the protection system is to isolate the healthy section from the faulty
section of the power system in shortest time possible causing the minimum
disturbance. If the main protection fails to operate, there should be a backup
protection for which proper relay co-ordination is necessary.
Fig 21 Relay Operation; (Source:- Sona Electronics Team. (2015, May 18). Retrieved June
28, 2019, from http://electronicsteam.blogspot.com/2015/05/4protective-relays.htmlB)
Working Of Relays:-When fault occurs in X, information regarding the abnormal
magnitudes of currents and voltages are sent to the relay through CT and PT.
Therefore fault sensed and the trip circuit is actuated by the relay. Hence current
flows in the trip circuit and as the trip coil of circuit breaker (CB) is energized; CB
gets actuated and it operates for the opening of the system. Therefore the main
functions are to sound an alarm, close the trip circuit of a circuit breaker and
disconnect the abnormally operating part from the healthy part of the circuit.
Certain Terminologies play defining role in the working of a relay.[28]

Pick-up level of actuating signal - After crossing the threshold value (actuating
quantity may be current or voltage), relay initiates to operate. As the value
increases the electromagnetic effect of the relay coil is heightened and after
exceeding a certain level (pick-up), the moving mechanism of the relay just begins
to move.

Reset Level - Value of current or voltage less than which a relay will open its
contacts and come in normal position.

Operating time of relay - Time which elapses between the instant when actuating
quantity exceeds the pickup value to the instant when the relay contacts close.
Requirement of auto-reclosers in circuit breakers:-Now depending on the fault
type whether permanent or temporary, relay logic needs to be built. Since in
temporary, the logic should be such that it uses auto reclosing technique after the
fault removal but for permanent, the logic should have facility for manual reclosing
since here the fault has to be removed manually by the utility workers. [41]
Since around 80% faults are transient, a lot of unnecessary downtime will result if
the protection scheme simply isolates the section of a network where a fault occurs
and then halts for someone to go out into the field, check the status of the fault and
reset the circuit breaker. A much more effective strategy is to isolate the affected
part of the network and then, after a short delay, re-energise it to determine
whether the fault has cleared. If it has, the network can operate normally but if it
hasn’t, the affected area can once again be isolated. This isolation followed by reenergisation process is exactly what an automatic circuit recloser (ACR) does. In
principle, it’s a simple device. It comprises of a circuit breaker with protection
relays, a mechanism that will oblige it to be closed after a trip automatically, a
controller that provides the auto-reclose service.[42]
Protection Schemes used in relays for the simulation:-In this article main focus
was to protect the transmission and distribution lines from faults, hence certain
type of relays comes into picture which helps us to attain so. Distance relay with
directional features specifically MHO relay are mainly used in the transmission
lines with overcurrent directional relays and differential relays in the distribution
lines. RSCAD provides the facility to use their inbuilt models of distance
protection components.
1. Distance Protection:- It depends upon the distance of feeding point to the fault.
The time of operation of such a protection is a function of the ratio of current and
voltage i.e. admittance or voltage and current i.e. impedance. Since MHO relay
used; is an admittance relay, therefore discussions related to it are more specific in
this report. MHO relay is a high speed relay and is also known as angle impedance
relay. In this relay administering torque is purchased by the volt ampere element
and the restraining torque is refined due to the voltage element. Therefore a MHO
relay is a voltage restrained directional relay. The equation of the torque can be
given as :T = K1VI cos(θ-τ) - K2V2 - K3
where K3 is the control spring effect and θ and τ are defined as positive when I
lags behind V. At balance point:0 = K1VI cos(θ-τ) - K2V2 (considering spring effect as 0)
K1VI cos(θ-τ) = K2V2
Therefore, Z = K1/K2cos(θ-τ) which reflects an equation of a circle passing
through origin whose diameter is K1/K2 =ZR (ohmic setting).
a) RSCAD view of MHO relay component or Distance function block; (Source:- Dean.
(2013). 8relay)
b) Operating characteristic of MHO relay; (Source:- Shanaya. (n.d.). Engineering Notes.
Retrieved July 3, 2019, from http://www.engineeringenotes.com/electricalengineering/distance-relays/distance-relays-and-its-classification-devices-electricalengineering/32872)
Fig 22 MHO relay
In Fig 23 (a) the inputs to the component would be the voltages and currents of
different phases detected by the secondary of CTs and PTs connected in the main
transmission lines. Whereas the output will be in the form of WORD that needs to
be converted to BITs to be accessed by other logics.
Table 3Output Signals for the Distance Function Block; (Source:- Dean.(2013). 8relay)
Signal
Description
Format
Distance Element Bits:
1: Zone1 start signal
2: Zone2 start signal
21-start
3: Zone3 start signal
Integer (word)
4: Zone2 time delay operate signal
5: Zone3 time delay operate signal
Tripping Element Bits:
1: Trip A phase
1P/3PT
2: Trip B phase
Integer (word)
3: Trip C phase
4: Trip 3 phase
Reclosing Element Bits:
1: Reclose Signal
RECL
2: Reset Signal
Integer (word)
3: Cycling Signal
4: Lockout Signal
68-B or 68-T
Out of Step Element
Integer
Therefore the logic used here is such that it compares the admittance or even
impedance with the threshold zone impedance already set inside the relay. If the
impedance comes out to be less than the set impedance then it can be concluded
that fault has occured in that zone due to increase in current flow. [43]
Table 4Summary of impedance formula according to type of faults
EVENT TYPE
IMPEDANCE FORMULA
AG
VA/(IA + 3K0I0)
BG
VB/(IB + 3K0I0)
CG
VC/(IC + 3K0I0)
AB and ABG
VAB/IAB = (VA-VB)/(IA-IB)
BC and BCG
VBC/IBC = (VB-VC)/(IB-IC)
CA and CAG
ABC and ABCG
VCA/ICA = (VC-VA)/(IC-IA)
VA/IA or VB/IB or VC/IC
2. Zonal and Directional Protection with Backup relay:- In the figure shown
below, the circles represented by black lines show the zones of relay A attached to
bus, B1. Simimlarly the circles with blues lines are zones of relay B on bus B2.
Now zone 1 covers 80% of the transmission line on which the relay is fixed. Zone
2 covers around 120% line in the forward direction and zone 3 covers around 100% of the transmission line. Now building up of 3 zones is basically because of
the action as a backup relay. Suppose a relay fails to work due to mechanical
defect of moving parts of the main relay, failure of DC power supply to the relay,
failure of tripping pulse to the breaker from relay, or because of failure of current
or voltage to the relay from CT or PT circuits etc, then the relay acting as backup
comes into view to protect the zone that the faulty relay should have done. Hence
the operating times of zone 1 is instantaneous while the starting time of zone 2 is
after 20 cycles of start of the fault, whereas zone 3 starts after 60 cycles of start of
the fault.



1
2
3
Fig 23 Illustration on Zonal And directional protection

If F1 occurs:- then the primary relays should work. But suppose if they fail, then
relay A may detect as it falls in zone 3 after 60 cycles of fault operation. It would
stop the flow of current from right side. The left side flow current will be stopped
by backup relays present on the other side.

If F2 occurs:- Besides the primary relays, it can be detected by relay A as well as
relay B as it falls under zone 3 and zone 2 respectively. Although the operation of
relay B will be faster since it will operate only after 20 cycles of fault starting,
relay A will detect if even relay B has certain failures that too after 60 cycles of
operation. But both the relays stop the current flow from right by opening the
corresponding breaker. The left side flow current will be stopped by backup relays
present on the other side.

If F3 occurs:- Relay A would detect instantaneously since its in zone 1, while relay
B will detect after 20 cycles of Fault operation. Therefore relay A stops the current
flow from left side and the relay B stops the current flow from the right end.

If F4 occurs:- Relay A and B would detect almost at the same time instantaneously
since its in the zone 1 of both the relays. Hence both the currents from left and
right ends are terminated.

If F5 occurs:- Relay B would detect instantaneously since its in zone 1, while relay
A will detect after 20 cycles of Fault operation. Therefore relay A stops the current
flow from left side and the relay B stops the current flow from the right end.

If F6 occurs:- Besides the primary relays, it can be detected by relay A as well as
relay B as it falls under zone 2 and zone 3 respectively. Although the operation of
relay A will be faster since it will operate only after 20 cycles of fault starting,
relay B will detect if even relay A has certain failures that too after 60 cycles of
operation. But both the relays stop the current flow from left by opening the
corresponding breaker. The right end flow of current will be stopped by backup
relays present on the other side.

If F7 occurs:-the primary relays should work. But suppose if they fail, then relay B
may detect as it falls in zone 3 after 60 cycles of fault operation. It would stop the
flow of current from left side. The right side flow current will be stopped by
backup relays present on the other side.
The directional features of power flow can be justified by whether the relay has
voltage and current in the leading or lagging phase. Suppose if originally current is
leading voltage by suppose δ phase angle then after fault current reverses and
becomes out of phase, hence ultimately lagging voltage. The power flow equations
thus changes sign showing the directional characteristics.
3. Over-current Protection:- Similar to distance protection, here too a
comparison is made between the rms current flowing through the transmission
lines and the setting threshold values. If the values move on to a higher pitch than
the threshold then over protectional relays help to trip the corresponding circuit
breakers by sending the trip signal. The logic used has been shown below.


1
2
Fig 24 Logic for overcurrent protection; (Source:- Taken from our simulation at IIT Delhi)
Implementation of DG resources
DG resources used in the simulation are PV models, Li-ion batteries for storage of
excess power and diesel generators. Hence studies regarding all these sources are
elaborated here.

PV model :- The PV controls are based on the decoupled dq current control
startegy with internal startups and protection logic blocks. To know more about dq
current control of grid tied voltage, studying the following resource would be
plentiful. The PV sources are interfaced to the AC grid using dynamic average
model of their DC/AC voltage source converter.



1
2
3
Fig 25 PV logic used in the simulation; (Source:- Taken from our simulation at IIT Delhi)
The Photovoltaic module can be constructed in 2 ways : as a 4 parameters model or
as a 5 parameters model. The difference between them is in a shunt resistance (Rsh).
[44]
a) 4 parameters scheme
b) 5 parameters scheme
Fig 26 PV Schemes; (Source:- Metelev, I. S., Isakov, R. G., Ferenetz, A. V., Gilmanshin, I.
R., Gilmanshina, S. I., & Galeeva, A. I. (2018, September). Using of functional capability of
RTDS hardware and software complex in the educational process of electrotechnical
cpeciality master’s training in ecomony global digitalization conditions. In IOP Conference
Series: Materials Science and Engineering (Vol. 412, No. 1, p. 012053). IOP Publishing.)
The circuit with shunt resistance is more precise, but it requires more complex
calculations. Therefore the 4 parameters scheme is considered and the equation for
current- voltage dependence will be as follows:1) I = Iph - I0(exp(V + RsI NcαVT)-1)
2) Iph=GGref(Iphref + ki(T - Tref))
3) I0=I0ref(TTref)3exp(EgαVT(1 - TrefT))
4) α=αref(TrefT)
5) VT=kTq
where, Iph = photocurrent generated by a single solar cell, A
I0 = Diode inverse saturation current, A
Nc = No. of solar cells connected in series in a solar module
α = Diode ideality factor
VT = diode thermal voltage, V
G = solar insolation, W/m2
ki = temperature coefficient at short-circuit current
T = temperature, К
Eg = photovoltaic element energy gap, eV
αref, Iphref = calculated value
Gref and Tref = insulation and temperature parameters at which solar module
parameters were measured (typically Tref = 250ºC, Gref = 1000 W/m3)
q = electron charge, 1.602∙10-19 C
k = Boltzmann’s constant, 1.38∙10-23 J/K
The passport parameters of solar panels are:
Voc− open-circuit voltage, V;
Vm- voltage at maximum power, V;
Isc– short-circuit current, A;
Im - current at maximum power, А;
ki– temperature coefficient at short-circuit current;
kv– temperature coefficient at open-circuit voltage
Fig 27 PV cell to array; (Source:- University of Central Florida. (n.d.). The Florida Solar
Energy Center (FSEC). Retrieved June 21, 2019, from
http://www.fsec.ucf.edu/en/consumer/solar_electricity/basics/cells_modules_arrays.htm)
a) Overlapped bypass diodes; (Source:-Ekpenyong, E. E., & Anyasi, F. (2013). Effect of
shading on photovoltaic cell. IEEE, 01-06)
b) No-overlapped bypass diodes; (Source:- Ekpenyong, E. E., & Anyasi, F. (2013). Effect of
shading on photovoltaic cell. IEEE, 01-06.)
Fig 28 Bypass Diodes

Li-ion Batteries:- The working principle of a grid-tied PV system is synchronizing
the installation with the electric utility voltage, frequency, and phase, which
basically turns the PV system into a part of the grid. If at any given moment the
system output exceeds the owner’s demand by such an amount that the surplus
production is automatically exported to the electric utility grid and metered even
after redirecting to a battery bank by a charge controller.
Fig 29 Li-ion logic; (Source taken from our simulation at IIT Delhi)
Here Li-ion batteries act as chargeable batteries i.e. when in discharging mode it
generates power that feeds the load but when in charging mode it takes in power
from the surplus generation. The rate of charging and discharging are controllable
by users and hence act as a great source in times of requirement. Similar to PV
arrays they also produce DC power which is converted to AC through DC/AC
converter.

Diesel Generator:-Diesel Generator produces electricity but runs on diesel fuel. It
can also be used as and when required. Logic behind the building of Diesel
Generator is shown below.
Fig 30 Logic behind usage of Diesel Generator; (Source:- Taken from
our simulation at IIT Delhi)
Load variation
Since all the simulation is done on real time, hence it would be better if the load is
varied and how synchronization is done by the power generators are observed.
Synchronization involves voltage and current magnitudes and phasors as well as
frequency.
Generator takes mechanical energy as input and gives electrical energy as output
which is equal to load requirement. Now if suddenly load is increased by 10%, at
this instant electrical energy required is more than the mechanical energy provided.
So, stored rotational kinetic energy in rotor of generator is converted to supply
excess electrical energy.
Ns=120*f/P where Ns is the speed of the rotor, f is the frequency and P is the no. of
poles of the Machine.
Now suppose electrical generation exceeds load requirement which indicates that
Ns is more and so frequency generated is more which is to be brought down by
slowing down the rotor speed and maintained at reference. Similarly the opposite
happens when electrical generation is less than the load requirements. In this way
frequency synchronization is done.
Now Load data is taken from an official NYISO which has an excel sheet that
contains varied load after every 5 mins in 11 different
regions.(https://www.nyiso.com/load-data) This excel data has to be fed in the
RSCAD model where simulation is to be done. Now data can only be fed through
port. So using UDP protocol and writting code in Python data are sent to the
required ports from where they are accessed. Here is the following code snippet.
1.
2.
3.
4.
5.
6.
7.
import socket
import time
import openpyxl
str2=""
str1=""
wb=openpyxl.load_workbook("9BUS_RAW LOAD DATA FEED from NYISO.xlsx")
8. ws=wb["Mysheet"]
9. maxrow=ws.max_row
10.
11.
12.
13.
maxcol=ws.max_column
14.
s= socket.socket(socket.AF_INET,socket.SOCK_DGRAM)#means we are
host="10.194.11.44"
port=5454
using IPv4 and UDP protocol)
15.
16.
initial = time.time()
for i in range (2,maxrow+1):
17.
18.
19.
20.
for j in range(2,maxcol+1):
21.
22.
23.
24.
25.
26.
s.sendto(data, (host, port))
cell_obj = ws.cell(row=i, column=j)
str2=str2 +" "+str(cell_obj.value)
data = bytes(str2,'utf-8')
print("sent:",data)
print( time.time())
time.sleep(300)
str2=str1
wb.save("9BUS_RAW LOAD DATA FEED from NYISO.xlsx")
Code 1 Server side or sending side code snippet
1. import socket
2. host="10.194.11.44"
3. port=5454
4. s= socket.socket(socket.AF_INET,socket.SOCK_DGRAM)#means we are using IPv4
and UDP protocol)
5. s.bind((host,port))
6. while 1:
7.
print(s.recv(40))
Code 2 Client side or receiving side code snippet
Method

First of all the model is built i.e. connecting utility grid as well as microgrid from
the draft window in RSCAD and the transmission lines data are fed from
theT_Line window by specifying the length and positive and zero sequence
impedances as required.

Next the faults are made to occur in the transmission lines depending on what type
of fault user needs to watch in the runtime window of the simulation. It may be a
permanent fault provided by a switch or a temporary fault provided by a push
button.

Next signals from CTs and PTs are sent for sampling the voltage and current
signals and then put into DFTs to extract samples of 60 Hz component.

PMUs detect these data wherefrom the extracted data are sent to relays where
decisions are made what step next to be taken and send them accordingly to the
circuit breakers.

When the Circuit breakers open from the utility grid, the microgrid becomes
islanded as during fault ;frequency , current and voltage magnitudes and phasors
are not syncronized. Due to lack of synchronization circuit breakers receive the trip
signal from relays and get disconnected.

The time period for disconnection may be a short period if temporary fault occurs.
If permanent faults occur then first the circuit breakers trip then again reconnect
after certain time interval hoping that the fault has cleared. When they find that the
fault has not cleared they open once again and it continues for a total of 4 times
until they quite surely understand that the fault occured is permanent and locks the
breaker in the open position for the rest period of time. Workers from maintenance
have to come and clear the fault and close the breakers to ensure continuity of
power flow.

Now during islanding a small checking is done which turns out to be quite helpful
at the end. The load requirement and the power generated from the DG resources
are compared. If load requirement is less than the power generated quickly a
communicaton signal is sent to the inverter to shut the DG since this may burn the
other home electrical appliances and even may trace back to the faulty
transmission line location where the maintenance workers are working and may
threaten their lives. If the load requirement is more than the DG, then do the
necessity so as to synchronize and turn other DGs on if available else continue the
DG to operate in low voltage operation until power from grid returns.
The 9 bus model used in the simulation is shown below:-









1
2
3
4
5
6
7
8
9
Fig 31 Final 9 bus power system model with DG sources installed; (Source:- Taken from
our simulation at IIT Delhi)
RESULTS AND DISCUSSION
Fig 32 Runtime Model; (Source:-Taken from our simulation at IIT Delhi) .
Besides creating the model in the Draft window, the above given figure provides a
better outlook of a part of the model (preferably the load end side) in the Runtime
window. The grid bus shown represents the model before the distribution lines
including the transmission lines and the synchronous generators. The grid switch is
kept for manually tripping the circuit breaker or more technically performing
intentional islanding. Unintentional islanding occurs when the fault button is
pressed and the spark sign turns red. Automatically after some time the circuit
breaker opens (turn red) hence causing unintentional islanding. The auto opening
of the circuit breaker is possible because of addition of relay working to the model.
If the fault is temporary, then auto recloser of the circuit breaker also takes place. If
the fault is permanent, then one has to manually turn on the circuit breaker for
continual flow of power from generator end to the load end. Even provisions are
made for the battery to charge and discharge as and when required. The switches
infront of the DERs provide the ability to use DERs according to our requirements.
Through the sliders one can adjust the active and reactive power flow into the load.
a) Normal Condition when both Microgrid and utility grid are working; (Source:- Taken
from our simulation at IIT Delhi)






1
2
3
4
5
6
b) Signals during Islanded mode of operation; (Source:- Taken from
our simulation at IIT Delhi)
c) After fault clearing, signals trying to synchronize with the main utility grid; (Source:Taken from our simulation at IIT Delhi)
Fig 33 Runtime results window
a) First of all the runtime model is made to run. Initially the DERs are connected
and the load is supplied by both the micro grid and the utility grid. In Fig34a) the
battery is set to discharge (Pref = +0.5) and the excess power is sent to the grid.
Receiving power by any source is provided with a minus sign, while sending
power is administered with a positive sign. Next the state of charge (SOC) of the
battery is observed. If it falls below 50%, then PREF value is set to -0.5 for
pushing it to charging mode. But overall there would be no such disturbance
shown in the signals as long as synchronized operation takes place.
b) Next cause a fault to happen by pressing the push button switch. (The change in
colour of the spark sign denotes it) It will come into observation that the Square
representing CB will also turn red representing the diconnection of the main utility
grid. This can be noticed from Fig34b) which shows the current in the main circuit
breaker as well as the grid turning to zero. At the same time the diesel generator
present tries to compensate and feed the load with the sufficient power that the
main grid was providing. Hence an increase in the overall current signal of the
circuit breaker is shown.
c) Now as a temporary fault was forced to happen, it gets cleared after sometime;
and the reclose signal from the relay is sent to the circuit breaker. The circuit
breaker recloses and checks whether the fault persists or not. As it happens to see
the fault to be recleared; it tries to synchronize the signals with the other generators
operating and helps in continual flow power to the load. In Fig34c), how the
signals try to resynchronize is shown, after which it returns to the state shown by
Fig 34a).
CONCLUSION AND RECOMMENDATIONS
Based on the review shown above, clearly each IdM has certain advantages and
disadvantages. Passive methods are simple and can detect the islanding condition
using conventional protection methodologies. However these methods fail to detect
the islanding condition when the DG and the load power are balanced, therefore
suffering from large NDZ. The active methods provide a fast detection speed and
small NDZ, but their impact on power quality may deteriorate the performance of
the power system. Remote methods have fast detection speed, high reliability and
the ability to perform well with multiple system configurations. However the
computational efficiency, implementation cost and malfunctioning due to the
failure of communication links rae the main limitations associated with remote
IdMs.
The signal processing IdMs are becoming more reliable and efficient due to the
application of signal processing, pattern recognition and artificial intelligence
tools. The intelligent methods, due to the presence of various training and testing
procedures, suffer from a large computational burden which makes them less
favourable in comparison with other signal processing IdMs.
Therefore based on the above discussions, it can be observed that the signal
processing methods are preferred on the basis of simplicity, cost, low
computational burden, accuracy and real-time industrial applications.
Coming to the future scope of the research, which the main aim is; behind studying
all such results and observations, have a much broader aspect. There are two ways
in which a relay can get disturbed signals. One being the situation when really fault
has occured and the other when cyber criminals feed in wrong data to the CTs and
PTs thus manipulating the original data and providing an erroneous data to the
relay. Now anticipating the relay operation, if it acts just according to the CT and
PT adjoint to the relay and send a trip signal to the circuit breaker then the outcome
obtained may not be a completely gratifying one, hence implementing a wrong
decision which may thwart the smooth run of a particular EPS. Hence the main
reason behind studying the PMU data received is to form a trend that could be fed
to the relay depending on which it would make decisions. This is because if an
invader is able to manipulate a single PMU data, then hopefully the other PMUs
acting when a fault has occured would provide with correct result. Now getting out
the trend that the PMUs follow when a fault occurs is the main area of research
since cyber protection comes along with the need to make the grid smarter through
different communication channels.
ACKNOWLEDGEMENTS
I would like to express my gratitude to my honourable esteemed guide, Prof.
Swades De, Professor of Department of Electrical Engineering in IIT, New
Delhi for his guidance and constant support. His perspective of how to approach in
my work has inspired me to carry on through out the internship. I am glad to work
with him.
I am very thankful to my mentor Mr. Akash Kumar Mandal, PhD student at
IIT Delhi, for his endless help that he has provided during my internship. His vast
experience in power system and linking the subject with communication touch has
been an inexhaustible source of information. I am most grateful to him for making
me understand all the brand new things that I overcome in such simple process by
giving eternal practical examples. I would like to thank him for all the mindful and
thought stimulating discussions we had, which prompted us to build logics much
easier and cooler than before without dislodging any of the main characteristics.
His thoughtfulness is a gift which I will always like to treasure. This dissertation
stands as a testament to his unconditional encouragement.
I cannot end without thanking Indian Academy of Sciences, Indian National
Science Academy and The National Academy of Sciences, India for selecting
me after completion of second year in B-tech to this summer research internship
and providing me with such wonderful and great experiences and oppurtunities.
Notes
1.
Only around 7% of faults are permanent. The vast majority of faults – around 80% – are
transient, caused by events like lightning strikes and arcing, will disappear in less than a second.
The remaining 13% of faults are semi-permanent and are typically caused by animals or branches
bridging the power lines. Even these faults usually burn away and clear in a relatively short
time.
2.
Now in transmission
lines there should be 3 pole tripping while in distribution lines single pole tripping will be mor
e helpful as single pole tripping helps in continuation of power supply to the other phases whil
e 3 pole tripping helps in better synchronization once the cicuit breakers are reconnected.
3.
A typical silicon solar cell generates a volatge about 0.7V. To achieve the necessary
current and voltage levels, solar cells are usually connected in parallel or in series and creates a
solar module, which generates higher voltage of about 16-36V. This modules when connected in
series create a PV panel. Now PV panels when grouped together make a PV array.
4.
[45]
Shading provides a massive crunch on the administration of solar photovoltaic panels.
It is clear that the creamy solution is to dodge shading altogether, though practically this is
impossible due to circumstances like cloud, rain etc.. Even if a minute sector of the solar panel is
in shade, the conduct of the total photovoltaic panel will consequently curtail since solar panels
actually subsist a number of photovoltaic cells which are wired in sync into a series circuit. This
channelizes to the fact that when the power harvest of a single cell is irresistibly reduced, the
power output for the total model in series is scaled down to the current level crossing the weakest
cell. Therefore, a little amount of shading can drastically decrease the performance of an entire
solar photovoltaic panels system. These PV modules are composed of photovoltaic cells (PV
cells) serially or parallely composed with diodes indulged in different configurations.
Furthermore, the modules have diodes that permit the current flows through a different path,
when enough cells are shaded or damaged. There are two typical configurations of bypass diodes:
overlapped and no-overlapped. It should be noted that the analysis in modules with overlapped
diodes is a more complex one, because there may be different paths for current flow.
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2.
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3.
Krishnan, G., & Gaonkar, D. N. (2012, December). Intentional islanding operations of
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