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Numerical relay protection coordination using simulation software
Conference Paper · January 2013
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Numerical Relay Protection Coordination using
Simulation Software
S. Nikolovski*, M. Havranek , P. Marić*
*
Faculty of Electrical Engineering Osijek, Croatia
srete.nikolovski@etfos.hr
mario.havranek@gmail.com
predrag.maric@etfos.hr
Abstract - The paper presents protection coordination of
renewable energy source connected to bilaterally supplied
distribution network. Multifunctional numerical relays with
the switching equipment, renewable energy source facility
and the distribution network have been detail modeled in
DIgSILENT Power Factory software. Overcurrent,
overvoltage,
undervoltage,
directional
overcurrent,
underfrequency and overfrequenecy functions have been
used for protection coordination. Different relay
characteristics have been presented in one time-overcurrent
plot. The damage curve and characteristic currents of
electrical equipment in the network have been shown to set
the relay tripping times and current settings and for a good
and thorough protection of the equipment. Protection
coordination settings have been checked and verified
simulating faults with the real system values.
I.
INTRODUCTION
Power system protection is a task of challenge for
power engineers. For better understanding such a task,
power system simulation tools are used. The paper
presents numerical protection adjustment in simulation
tool - DIgSILENT Powerfactory with own database of
numerical relays that contains time-curent curves of all
protective devices. The time-current curves (TCC) can be
coordinated with each other and with the short circuit
analysis results. Multiple easy-to-use graphical tool for
resolving protection devices coordination problems has
also included in this simulation tool. The sample case of
the numerical protection adjustment is presented on the
small power plant (renewable source) connection to the
bilaterally supplied distribution network Fig 1. ABB
numerical relays and Končar RFX numeric field terminal
have been used in simulations.
The DigSILENT Power Factory protection modelling
features have been implemented with the following
philosophy: the protection should be as realistic as
possible; the user has to be able to create a new complex
protection devices or alter existing ones. Although the
protection models may show high complexity, their use
must be kept easy. All protection models will act on
circuit-breakers [1]. Protection devices are normally
stored in the object which they act upon, but they may be
stored elsewhere when needed. Recommended, and by
default is that protection devices which act upon a single
circuit-breaker are store in the cubicle which contains that
circuit-breaker (highly recommended). Protection devices
which act upon a two or more circuit-breakers connected
MIPRO 2013/CTS
to the same busbar are stored in that busbar [2]. As a rule,
the relay is best stored in the same folder as the e and/or
current transformers which it uses.
Figure 1. Small power plant (renewable source) connection to
distribution network
II.
RELAY MODEL CREATION
The simplest way to create the relay model is
normally done by right clicking a circuit-breaker and
selecting New Protection device-Relay model, an empty
relay model (ElmRelay) will appears. The relay model
has a reference to the relay type, the location, the device
number and the list of slots. The location is normally set
automatically when the relay is defined in the single line
diagram by right clicking the cubical [1]. The whole
process of creating a specific relay model thus only asks
for selecting a relay type from the database, in this case
ABB numerical relays. Otherwise, a specific unknown
relay type (according to the database) can be created
using advanced DIgSILENT Powerfactory functions such
as DSL, or using the database relay type with the same
functions and adaptable function settings. The Končar
RFX numerical field terminal model has been created
using multifunctional ABB REF 54x relay model
template from the database applying the overcurrent
function settings only. Fig. 1 describes the protection
coordination scheme for the modelled system. The ABB
REM 543 relay has been installed on J2 field for
1107
generator and block-transformer primary protection (acts
on circuit-breaker on J2), the ABB REF 542 has been
installed on the J1 field for protection of cable between
small power plant and 20 kV switchyard (acts on circuitbreaker on J1), the Končar RFX field terminal has been
installed on 20 kV switchyard. Relays installed on
External Grids (ABB REF 542 ) acts on corresponding
circuit-breakers of external grid facilities.
A. Overcurrent protection adjustment
The function of this protection is single-phase, twophase or three- phase overcurrent detection [2]. After the
relay model has been defined and all slot elements have
been created, the editing of the relay settings may be
started. The overcurrent protection includes: the timeovercurrent protection and the instantaneous overcurrent
protection. The time-overcurrent protection (relay) allows
settings: the time-overcurrent characteristic, the pick up
current and the time dial. The time-overcurrent
characteristic use the time delay which can be an
independent (definite) time or inverse time delay. In this
case, the time-overcurrent characteristic is the definite
time characteristic with an option to time dial set and to
choose the time-overcurrent characteristic. Fig. 2 presents
the time-overcurrent protection adjustment, while Fig. 3.
presents instantaneous overcurrent protection.
Figure 3. Adjusting the instantaneous overcurrent protection
The relay trips if the remaining angle is smaller than 90°
and if both the polarization and the operating
voltage/current are large enough [2]. The directional
overcurrent protection adjustment has been presented on
Fig.4.
Figure 4. Adjusting the directional overcurrent protection
Figure 2. Adjusting the time-overcurrent protection
The pick up current is set to 1.00 p.u secondary which
equals 150 A primary and the definite time is set to value
of 2.00 seconds (Fig. 2) .On the Fig. 3. the pick up current
is set to 1.80 p.u secondary which equals 270 A primary.
The time setting on Fig. 3 is set by default to 0.00 seconds
which corresponds to instantaneous operation.
In the network supplied by two power sources is necessary
to use Directional relay – a part of the relay model [1].
The directional relay calculates the angle between the
polarization voltage or current and the operating current.
The polarization current or voltage is rotated for the
amount of the expected angle first.
1108
The tripping direction is an important fact for this type
protection adjustment because of the current income
during the short circuit.
B. Undervoltage and overvoltage protection adjustment
The voltage drops can occur due to the network
overload, the faulty operation of a transformer tap
changer and during the short circuit. In this case
undervoltage and overvoltage protection monitors any
phase to phase voltage and will act on 20 kV circuitbreaker if the voltage drops or rise under/over certain
limit that will lead to separate the connection between the
power plant and the rest of the system. The adjustment of
the undervoltage protection is presented on the Fig. 5 and
Fig. 6.
MIPRO 2013/CTS
C. Underfrequency and overfrequency protection
adjustment
Variations in the power supply frequency can occur
due to overloads when the network is fed by a limited
power source (power plant islanding operation), generator
frequency regulator faulty operation, power plant
disconnection from the interconnected network [2].
Adjustment of the underfrequency and overfrequency
protection is shown on Fig. 9 and Fig. 10.
Figure 5. Adjusting the undervoltage protection
Figure 6. Adjusting the undervoltage protection (fast)
Figure 9. Adjusting the underfrequency protection
On the other hand, the protection is necessary during the
voltage increase over the allowed limit. Adjustment of the
overvoltage protection is shown on Fig. 7 and Fig.8.
Figure 7. Adjusting the overvoltage protection
Figure 10. Adjusting the overfrequency protection
III.
TIME-OVERCURRENT PLOT CREATING
The plot VisOcplot is showing different relay and fuse
characteristic in one time-overcurrent plot. Additionally
the damage curve and characteristic currents of electrical
equipment in the network can easily be shown. This will
help to set the relay tripping times and current settings and
the selecting of fuses for a good and thorough protection
of the equipment.
Figure 8. Adjusting the overvoltage protection (fast)
MIPRO 2013/CTS
There are several ways to create a time-overcurrent
plot (VisOcplot). The easiest way to create and show a
VisOcplot is to select one circuit-breaker, where
overcurrent relays are installed than right-click the circuitbreaker to open the context sensitive menu. This will
show the option Create Time-Overcurrent Plot and Add to
Time-Overcurrent Plot. PowerFactory will then create a
1109
rest of the distribution network and the small power plant
are both isolated from the short circuit by tripping of those
two relays. Such an action indicates good protection
coordination.
The time- overcurrent plots may also be used to
change the relay characteristic graphically because a relay
characteristic is normally the minimum of two or more
sub-characteristic [1].
The three- phase short circuit is simulated on the cable
between small power plant and 20 kV switchyard (the first
simulation case - location J1 on Fig.1) The vertical redcoloured curve on the Fig. 11 represents the short circuit
current value on the short circuit location. The first relay
that will trip is the relay situated in the cubicle of the J1field -ABB REF 542 and also the nearest to the shortcircuit location. The tripping time for this relay shown on
the Fig.11 (red -coloured curve) equals 0.02 s. The second
tripping time according to this time-overcurrent plot
belongs to the relay situated on the 20 kV switchyard, the
RFX numerical terminal filed, shown as dark-bluecoloured curve with the tripping time of 0,04 s. Tripping
times of those two relays indicate good protection
coordination because the short-circuit location is hereby
isolated from the rest of the power system.
I =535,068 pri.A I =1301,183
I =2140,272
pri.A
pri.A
I =534,935 pri.A
I =1302,703
I =2139,741
pri.A
pri.A
[s]
10
5.000 s
1
0.600 s
0.194 s
DIgSILENT
100
100
DIgSILENT
new diagram showing the time-overcurrent plot for all
relays selected. It is also possible to create an a user
defined “x-value” by right-clicking the graph and
selecting the Set Constant and x-value option. The vertical
line will show the values at the intersections of all
characteristics. The line movement can be realised by
mouse dragging. The intersection of the calculated current
with the time-overcurrent characteristic is labelled with
tripping time.
0,1
0.050 s
0.020 s
[s]
0,01
20,00100
kV
10
5.000 s
1000
[pri.A]
10000
Trafo 20 kV\Cub_2\REF 541 - J1
Rasklopiste Hrast 20 kV (HEP)\Cub_6\RIX elektra
Trafo 20 kV\Cub_1\REM 543 blok trafo
VP J2
20 kV Strizivojna\Cub_6\REF 543 Djakovo 3 re
I-t 1 Date: 9/22/2012
Annex:
1
Figure 12. Time-overcurrent plot with tripping times (short circuiton 20 kV switchyard)
0.194 s
The voltage protection coordination can be actuated
disabling the current, the distance and the frequency
functions on observed relays. The undervoltage protection
acts on generator circuit-breaker in case when the voltage
0.020 s
drops under the limited lower voltage value. Typically, the
0,01
lower voltage value on the generator relay is set to 85% of
20,00 kV
100
1000
[pri.A]
10000
Trafo 20 kV\Cub_2\REF 541 - J1
Rasklopiste Hrast 20 kV (HEP)\Cub_6\RIX elektrana
nominal value. The generator block-transformer relay
Trafo 20 kV\Cub_1\REM 543 blok trafo J2 VP 20 kV Strizivojna\Cub_6\REF 543 Djakovo 3 relej
allows the fast undervoltage tripping function with the
time delay of 0,15 s for adjusted 70% of nominal voltage
value and the slow undervoltage tripping function with the
Figure 11. Time-overcurrent plot with tripping times (short circuit
time delay of 1,00 s for adjusted 85% of nominal voltage
on the J1- field)
value. The overvoltage protection acts on generator
circuit-breaker in case when the voltage rises over the
The time-overcurrent plot on Fig.12 shows the three
limited upper voltage value. The fast tripping function acts
phase short-circuit simulation results on the power plant
with the time delay of 0,18 s when the measured voltage
place of coupling to distribution network - 20 kV
increase above the 120% of nominal value, while the
switchyard (the second simulation case – Fig.1). In this
slow tripping function acts with the time delay of 1,98 s
case, the network contribution to short circuit is 1302.703
when the measured voltage increase above the 115% of
A primary while the contribution of the small power plant
nominal value. Islanding operation of small power plants
(renewable source) is 534.935 A. The relay situated on
is prohibited according to grid code. The voltage drop on
location – J1 REF 542 will trip instantaneously with the
the generator block transformer LV and HV busbars
time of the 0.020 s (red -coloured vertical line on Fig. 12),
during the three phase short-circuit on the J1 field is
while the remote relay REF 542 situated on the external
shown on Figure 13.
network busbars will trip instantaneously with time of the
0.050 s (light -blue -coloured vertical line on Fig. 12). The
0,1
0.050 s
0.040 s
I-t 1 Date: 9/22/2012
Annex:
1110
MIPRO 2013/CTS
DIgSILENT
1,20
IV.
0,90
0,60
0,30
0,00
-0,30
-0,1000
0,0097
0,1194
0,2291
Rasklopiste Hrast 20 kV (HEP): Voltage, Magnitude in p.u.
0,3388
[s]
0,4485
1,20
0.052 s
0.228 p.u.
0,90
0,60
The main purpose of this paper is to present the usage
of the simulation tool for numerical protection functions
adjustment. DIgSILENT PowerFactory simulation
software enables detailed modelling and assistance for
coordination settings of real digital numerical relays
according to calculations of short circuit using method of
symmetrical components and the real data for all network
components. The numerical protection functions have
been tested during the short-circuit simulations on the two
network locations that are significantly sensitive to power
system protection settings. Protection functions
adjustments shown good protection coordination in both
analysed cases.
0.418 s
0.949 p.u.
0,30
REFERENCES
0,00
-0,30
-0,1000
CONLUSION
0,0097
0,1194
Gen 6.3 kV: Voltage, Magnitude in p.u.
0,2291
0,3388
[s]
0,4485
[1]
[2]
Blok trafo napon
Date: 9/28/2012
[3]
[4]
[5]
Annex: /9
Figure 13. Voltage drop on HV (upper diagram) and LV (lower
diagram) generator block-transformer busbar
DIgSILENT
During the voltage drop on the generator busbars, the
undervoltage protection trip and the small power plant is
isolated from the rest of the system.
80,00
-0.008 s
54.308 deg
[6]
[7]
DIgSILENT Power Factory, User Manual, Gomoringen, 2008.
S. H. Horowitz, A. G. Phadke, Power system relaying, 3rd ed.,
John Wiley and Son Ltd, England, 2008.
Technical Reference Manual, REF 54_, ABB, 2005.
Pilot Protective Relaying, ABB, Marcel Dekker ,Inc.; USA, 2000.
A.T. Johns and S. K. Salman, Digital Protection for Power
Systems IEEE Power Series 15, London ,1995.
M. Sachdev, M. Nagpal, A recursive least error squares
alghortihm for power system relaying and measurements
applications, IEEE Transanctions on Power Delivery , Vol. 6, No.
3. 1991, pp. 1008-1015
ANSI/IEEE C37.110 Standard : IEEE Guide for the application of
current transformers used for protective relaying purposes
60,00
40,00
0.234 s
0.000 deg
20,00
0,00
-20,00
-0,1000
0,0087
0,1174
0,2261
0,3348
generator: Rotor angle with reference to reference machine angle in deg
[s]
0,4435
generatorDate: 9/28/2012
Annex: /6
Figure 14. Small power plant generator isolation
MIPRO 2013/CTS
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