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Implementation of
Synchrophasor Technology for
Better System Utilization &
Reliability
WAMS-WIDE AREA MEASUREMENT SYSTEM
PMU-PHASOR MEASUREMENT UNIT
Need for Synchrophasor
Technology
1.
2.
3.
4.
Visualisation of dynamic behaviour
Stability aspects
Operate the system at its limits
Protections backup & adaptive +
adaptive islanding
5. State determination
6. Empower system operators
Phasor Representation
A phasor is the complex form of the AC waveform
√2Acos(2 πf t +ө) or Aejө or A< ө
PHASOR REPRESENTATION
Standards
• The original standard for PMUs, C37.1344, was
released in 1995 and was reaffirmed in 2001.
• The new standard IEEE PC37.118 “Standard
for Synchrophasors for Power Systems” has
now replaced the earlier one.
• There are no IEC standards at the moment and
it is most likely that the IEEE will become IEC
standard as was in the case of the COMTRADE
standard.
MACRODYNE 1690 PMU
Phasor Measurement Units
A PMU by our convention measures bus voltage (phase or sequence)
and all 3-phase line currents on all branches (transmission lines and
transformers) emanating from the substation alongwith the phasor
angles
FEATURES OF A PMU
• TIME TAGGED AC PHASORS
• +VE SEQUENCE VOLTAGES AND CURRENTS AS REAL &
IMAGINERY QUANTITIES OR OUPUT AS MAGNITUDE & PHASE
ANGLE FOR LOCAL & REMOTE APPLICATIONS
• FREQUENCY & RATE OF CHANGE OF FREQUENCY
• VARIABLE DATA TRANSFER RATES– 1 PER CYCLE, 1 PER
2CYCLES OR 1 PER 4CYCLES
• SYNCHRONISED SAMPLING BY USE OF GPS- TIME TAGGING
ACCURACY UPTO 50 µSECOND(GPS ACCURACY OF 1
µSECOND)
• ACCURATE PHASE ANGLE CALCULATION WITH ACCURACY OF
UPTO 1 DEGREE OR LESS
FEATURES OF A PMU-CONTINUED
• CAN HANDLE 6 ANALOG CUURENT INPUTS WITH 3 ANALOG
VOLTAGE INPUTS WITH OPTIONAL EXTENSION BY 100%
•
2 SETTABLE LEVELS FOR FREQUENCY AND RATE OF CHANGE
OF FREQUENCY
•
SETTABLE LEVELS FOR UNDER VOLTAGE & OVERCURRENT
PICKUP
• ONE ‘NO’ CONTACT FOR ABNORMAL FREQUENCY, RATE OF
CHANGE OF FREQUENCY, UNDERVOLTAGE & OVERCURRENT
PICKUP
• LOSS OF DC AND OTHER INTERNAL SELF MONITORING
FEATURES OF A PMU-CONTINUED
• REMOTE COMMUNICATION PORT FOR TCP/IP
AND STREAMING DATA IN IEEE1344 OR PC
37.118 SYNCHROPHASOR FORMAT
• OPTIONALLY ADDITIONAL OPTICAL
COMMUNICATION PORT FOR TCP/IP AND
STREAMING DATA IN IEEE1344 OR PC 37.118
SYNCHROPHASOR FORMAT
• FRONT MOUNTED MENU DRIVEN DISPLAY
FOR DISPLAYING +VE SEQUENCE VOLTAGE
AND CURRENT AS AMPLITUDE AND PHASE
ANGLE
Compute MW & MVAR
Power P = V I cos(θ−φ)
Reactive Power Q = V I sin(θ−φ)
Synchronized Measurements
Location 2
Location 1
Phase angular difference between the
two can be determined if the two local
clocks are synchronized.
Synchronizing pulses obtained from
GPS satellites.
Role of GPS
• Constellation of 24 satellites orbiting at 20,200 km
• Developed by US dept of defense
• Available for free for civilian use
• Beyond navigation use, it provides time reference:
– Protection systems derive usage of GPS from the timing signal
•
4 satellites are needed for knowing timing and location position
• Satellites have atomic clocks
• Provides coordinated universal time (UTC) which is international atomic time
compensated for leap seconds for slowing of earths rotations
• can obtain accurate timing pulse every second with an accuracy of 1
microsecond
PMU Facts
• PMU uses discrete Fourier transform
(DFT) to obtain the fundamental
frequency components of voltage /
current(Half cycle or Full cycle)
• Data samples are taken over one cycle /
multiple cycles.
• Currently, sampling is done at 12
samples/cycle (IEEE C37.111 Std.).
• Resolution of the A / D converter is 16
bits.
Communication Options
• Telephone lines
• Fiber-optic cables
• Satellites
• Power lines
• Microwave links
Delay Calculations……
• Fixed delay
– Delay due to processing, DFT, multiplexing and data
concentration
– Independent of communication medium used
– Estimated to be around 75 ms
• Propagation delay
– Function of the communication link and physical
separation
– Ranges from 25 ms in case of fiber-optic cables to
200 ms in case of low earth orbiting (LEO) satellites
Delay Calculation Table
Communication Associated delay – one
link
way (milliseconds)
Fiber-optic cables
~ 100-150
Microwave links
~ 100-150
Power line (PLC)
~ 150-350
Telephone lines
~ 200-300
Satellite link
~ 500-700
Standards: Key Items
• Time reference = UTC (Universal Time
Coordinated)
• Reporting rates = (10,25 phasors/sec for 50Hz
system; 10,12,15,20,30 phasors/second for 60Hz
system starting at the top of a second)
• Optional reporting rates 50/100 phasors/sec for
50Hz and 60/120 phasors/sec for 60Hz.
• Angle reference = cosine (0 deg at positive
waveform peak)
• Communication model (standard frames and data
types, interoperability)
Integration of PMU data
Hardware Requirements
• Phasor Measurement Units (PMU) placed
at strategic substations
• Communication Links, including
networking equipment at substations as
well as at control centers
• Phasor Data Concentrator (PDC)
• Computer systems located at the central
control centers, consisting of servers,
storage, workstations and printing
facilities.
Software Requirements
• Phasor data collector software, for
preprocessing of PMU data
• Basic monitoring applications
• Ergonomic graphical user interface, with
results visualization facilities
• Core power system application software;
Analytics
Communications
• Though many communication media is
possible, fiber optic provides, by and
large, the most secure and fast
communication medium.
PMU placement
It is not at all necessary to place PMUs at all
busses in the power system to make it
observable.
When a PMU is placed at a bus, then it's
neighbouring busses also become observable.
In general, a system can be made observable
by placement of PMUs on approximately 25%
to 33% of the busses in the system
Optimal
PMU
placement
problem
i.e.,
minimum PMU placement problem for system
observability, can be formulated as an Integer
Linear Programming (ILP) problem.
57 bus system
PMU placement
PMU Applications
• SCADA Displays
• State estimation
• Control (WAMS)/SPS
Measurement based controls for:
Voltage Stability
Angle Stability
Frequency Stability
• Event and system analysis
• Improved operational observability
• Dynamic System Stability Probe & Control
- Power system damping-PSS
• PMU data trends can detect CB/switch status
changes in the network, which will improve the
topology estimation
WAMS
WAM Design Constraint
Computation time
+
Communication time
<
Response time of the
system dynamics
Opportunities Provided by WAMS
• On-line or real time monitoring and state
estimation
– We can realize 1 state estimator run per cycle
– provides us an opportunity to peep into electromechanical
system dynamics in real time
» upgrade from local control to wide area controller e.g., for
PSS & damping controllers etc
» improve performance of the apparatus protection schemes
» improve performance of the system protection schemes
• Accurate measurement of transmission system
data in real time
WAM applications
• Protection
Power Swing blocking
Improved back up protection
Current Differential protection
• Continuous Closed Loop Control ???
e.g., PSS using global signals
Unfortunately: Require to accurately determine
the communication latencies for continuous
control
WAM applications
Emergency Control (System Protection Schemes)
•
Controlled System Separation
•
Triggering of load shedding based on
NON-LOCAL signals. Better df/dt relaying.
•
Triggering other schemes (generator shedding,
dynamic brake, governor)
etc.
Some may require accurate loss of synchronism prediction
SPS: How can WAMS help ?
• Angular instability :
– Predict of out of step in real time -> trigger control
actions like gen/load tripping or dynamic brake to
prevent loss of synchronism.
OR
– Allow graceful system separation and do intelligent
load/gen tripping to stabilize frequency and voltage in
island
Former is preferable - no resynchronization of systems
required BUT how does one
a) Predict out of step in real time
b) Determine quantum of control actions
For controlled system separation :
Adaptive choice of separation points conceivable
NON-LOCAL measurements may help
SPS: How can WAMS help ?
• Frequency stability :
Present day problems:
– Local frequency contaminated due to swings
(1 -2 Hz). df/dt should not trigger on swings
but on “common” motion of generator speeds.
Solution: filter, but filtering will involve delay.
– Setting of df/dt relay should reflect actual
power deficiency. Need to know total inertia
(will need to know whether islanded or not,
which generators in island)
Conclusion : NON LOCAL signals will help!!
WAMS for Transmission Protection
Systems
• Current Differential Protection can be implemented
with ease:
• Most accurate
• Provides crisp zone of protection
• Free of non-idealities like tripping on power
swings, non-tripping on voltage or current
inversion, etc.
• Can be applied to series compensated lines
• Current Differential Scheme can be used to suitably
block Zone-3 trips
WAM based Z3 Blocking
•
•
•
•
As Line BC is quite long in comparison to AB, Zone-3 on AB at A can trip on power
swing
If Current Differential Protection was implemented on line BC, it could be used to
block Zone-3 of relay AB if no fault is detected by it on BC
Since Z2 and Z3 timer setting are of the order of 15-30 cycles and 90 cycles
respectively, communication delays will not be very critical
Blocking scheme will not impair but only improve the performance of the system
A
B
A Transmission System with a short line terminating into a
long line
C
WAM Applications
• Islanding Detection
• Loss of Synchronism detection
• Average line temperature can be
estimated from true line impedance:
picture of thermal overloading if it exists
• Power System Restoration
Better picture – better confidence level –
better decisions.
More remote actions
Roadmap on improving existing
transmission system utilization
• Provide better analytics to ISO/TSO to
estimate line and system loadability
• Use WAMS to improve performance of system
protection schemes
• WAMS based Out of step protection schemes
• WAMS based islanding schemes (smart islanding)
• Use WAMS to improve security of the existing
transmission system protection schemes
(smart protection)
Initiative in WR
• Project under New Millennium India
Technology Leadership Initiative
• Along with POWERGRID, other members
of the consortium are –
– TCS
– IIT Bombay
– Tata Power
Implementation of WR Project
• Part-I : Installation of PMUs and PDCs
– Data collection at PDC level and visualisation
• Part-II : Optimal placment of PMUs
– State Estimator based on PMU data
– System wide protection schemes
– Supervised Zone-3 blocking schemes
– Emergency control schemes
– Parameter validation
Implementation of WR Project
(contd)
• Project duration: 3 years
– 2 years for implementation and 1 year for
testing
– Expert guidance from Prof. A.G. Phadke of
Virginia Tech
– Total cost : 16.75 Cr + 2.21 Cr for making data
available at SLDCs
Project Initiatives for NR
• Number of PMUs – 4 ; with PDC at NRLDC
• PMUs to be installed at Vindhyachal,
Kanpur, Dadri and Moga
• Total project cost : 3 Cr.
• Implementation period : 3 months
• Order placed on SEL
THANK YOU
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