Practical Simulation of Power System Protection

MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (14-18)
ISSN 2230-7656 (c) MIT Publications
14
Practical Simulation of Power System Protection
Laboratory Experiments Using Construction-wise
Classified Relays
Kalpesh J. Chudasama
Electrical Engineering Department
A.D. Patel Institute of Technology
New V.V. Nagar, Gujart, India
e-mail: kjc_jalpan@Yahoo.co.in
Hardik Shah
Electrical Engineering Department
A.D. Patel Institute of Technology
New V.V. Nagar, Gujart, India
Brijesh Patel
Electrical Engineering Department
A.D. Patel Institute of Technology
New V.V. Nagar, Gujart, India
ABSTRACT
Power system protection is a key part of the power system. The course is offered in undergraduate disciplines worldwide.
Howsoever the conventional protection philosophy rapidly changing from electromechanical and static to numerical relay
technology it will take a long time for complete substitution in developing countries. It is very important for graduating
students and faculties with respect to relaying education and research to have theoretical and practical knowledge of both
conventional and numerical protection. This paper discusses the practical simulation of laboratory experiments of power
system protection regular course offers in Degree engineering and polytechniques institutes using one example for each
construction wise classified relays like electromagnetic, static and digital relays. This paper explains and provides help to
understand such kind of experiment development in educational engineering institute for relaying education and future
research work to the electrical engineering faculties and students and to understand the operational behavior of relays to
the field engineers. This paper discusses the detail understanding of the some practical simulation of real power system
protection.
Keywords: TMS (Time Multiplier Setting), TOC (Time Operating Characterstic), Overcurrent (O/C), Overload (O/L),
Potential Transformer (P.T.), Current Transformer (C.T.)
INTRODUCTION
As we all know the power system is cater huge energy
demands and it is spread over in big area containing many
major and costlier components like Generator, Transformers,
Transmission lines, Induction motors, Bus bars etc. Modern
power system is going to be more and more complex. The
effective, fast, accurate and reliable protection of such power
is system not only necessary but must; otherwise it can cause
large revenues losses. Previously Electromagnetic and static
relays was the major part of protective system. Static relays
have many advantages over elecromagnetic like low burden,
no moving parts, fast response, precise characteristic, and
sensitivity, miniaturization, less maintenance, low resetting
time, low overshoot and transient overreach. Static relays have
some limitations like sensitive to voltage spikes, variation of
characteristic with temperature and age, overload capacity and
reliability as in [01]. With the developments in VLSI
technology, microprocessors that appeared in seventies have
evolved and have made remarkable progress in recent years.
Numerical relays are finds its major important because of many
advantages over electromagnetic and static relays. The
inherent advantage of microprocessor-based protective
schemes, over the existing static relay is their flexibility due
to its programmable approach, fast, more accurate and reliable
relaying. It can provide protection with low cost and compete
with conventional relays. A number of characteristics can be
realized using the same interface [2],[6] discussed Laboratory
used for teaching, design and conducting research in area of
microprocessor based relays.[3] To model large variety of
power system behavior utilized offline digital transient
simulation programme and find relay response.[4] discussed
a Power System Protection Laboratory at the Energy Research
Centre utilized computer simulation and relay testing station
for enhancing teaching and research in relay education.[5]
designed wired and commissioned Laboratory projects of
Power System and Power System Protection through senior
design projects.
The present paper gives real field exposure and calculations,
by simulating the protective scheme, taking example of each
construction wise classified relays. The motive of the paper is
to provide practical exposure and practical aspects of power
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (14-18)
ISSN 2230-7656 (c) MIT Publications
15
system protection through understanding the protection using
construction wise specified relays which are utilizing in
developing countries to the students and some extent to field
engineers also. Industry also in need of well practical trained
students so their in-house training period and cost can be
reduced. We have simulated here reverse power protection
scheme with electromagnetic reverse power relay, transformer
differential protection scheme with static relay and overcurrent,
with numerical relay. All relay used for the practical simulation
are of ALSTHOM make. Now it is known as AREVA. This
paper intended to present idea about how to develop the
practical simulation using any company make relays. The
practical simulation tables for the above experiments are
prepared in power system laboratory of the institute.
REVERSE POWER PROTECTION
Figure 1: Power circuit for reverse power protection
Reverse power protection is required against reversal of power
in a power system. Power normally flows from the alternators
to the bus. If the input to the prime-mover of any of alternators
stops, the bus bar starts feeding the alternator and it runs as
synchronous motor. The prime mover will act as a load on
the motor. This means the flow of power is reversed. This
does not pose any harm for the alternator but the reversal of
power is very harmful to the prime mover. For small steam
turbines relays are set to operate when forward power reduces
below 3% of rated power and for large turbines sensitive
setting of 0.5% of rated power is used. These relays are known
Figure 2: Control circuit for reverse power protection
as Low Forward Power Relay. Hydro-turbine relays are set
to operate at 3% of reversal of power Gas turbine relays are and one off position. 1 no. position represents the normal
set to operate for 10% reversal of rated power.
condition means power flows in forward direction from
generator to infinite bus bars. While 2 no. positions of switch
Protective Relay
presents the turbine (prime mover) faulty condition. The
Reversal of power is sensed by a reverse power relay. It is a toggle switch used as steam valve interlock. Initially the Rotary
directional relay with leading maximum torque angel. Switch is put up on 1no. Position and MCB put up on with
“Ref.[7]” is the manual of ALSTHOM make CCUM-21 toggle switch in off position. Pressing on push button the
Definite Time Reverse Power relay used for the practical circuit work healthy and no relay operation was observed.
simulation. CCUM high speed induction cup unit initiates a Once the contactor energized the steam valve interlock toggle
static timing unit which provides output contacts for alarm switch is change to on position to represents that steam supply
and trip contacts. Power flow direction can be checked by is given to turbine. The steam valve interlock is used to prevent
sensing the magnitude and sign of power. The construction is the mal operation of relay under manual starting and stopping
induction cup type. Under healthy condition or under fault of the generator. If contactor is put up on with toggle switch
condition where the current flow is in normal direction the on position then alarm will sound but reverse power relay
relay does not operate. As the reversal of current occurs, the will not operate as per the control circuit designed for the
torque in the reverse direction causes moving system to rotate simulation. The reverse power relay is only trips when rotary
and close the trip contacts, and actuate the circuit breaker.
switch is on position 2 and the same procedure mention above
followed up. If one want to stop generator then first the toggle
Simulated Protective Scheme and Circuits
switch should put off (means steam cutoff) otherwise alarm
As shown in Figure 1 Power circuit mainly contains MCB, sound without relay flag dropout. The toggle switch
Rotary switch, Single phase variable rheostatatic load of arrangement is used in practical simulation to understand the
maximum capacity of 10A, P.T., C.T., Toggle switch to concept of steam valve interlock used in the field in this kind
represent steam valve interlock. Figure 2 Control circuit of conventional protection. Reverse power relay and alarm
contains mainly same MCB, on- off and reset push buttons, sound simultaneously in the simulation only when reverse
contacts and coil of contactor and reverse power relay power occurs. During manual start and stop without taking
CCUM21. Connections were done as per circuit diagram. The care of steam valve interlock Relay will not operate but the
rotary switch shown in Figure 1 has two on (1 & 2) alarm sounds.
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (14-18)
ISSN 2230-7656 (c) MIT Publications
16
TRANSFORMER DIFFERENTIAL
PROTECTION USING STATIC RELAY
wave shape monitoring facility relay not operate for no of
times no load starting check. For normal load and the external
fault relay not operate. Relay operates only for internal faults.
Differential protection of transformer is used to protect the Figure 4 represents the control circuit of the simulation.
power transformers from internal faults. As we know that there
many problems in transformer differential protection like
different voltage ratings and current ratings of primary and
secondary side, Current transformers ratio and phase angel
errors, internal phase shift, tap changing, Magnetizing inrush
current, saturation of transformer core. There are also remedies
for each problem very well discussed in [1] Main is to use
bias differential relay for the differential protection.
Protective Relay
The simulation of the practical consist protection of single
phase transformer of only 1 KVA using ALSTHOM make Static
bias differential single phase relay MBCH12. This relay is
high speed bias differential relay suitable for the protection Figure 4: Control circuit for power transformer protection
of two or three winding power transformers. The relay is
extremely stable during through faults even under condition
Practical Calculations
of CT saturation and during condition of ratio unbalance
resulting from tap changing and CT errors and provides high In filed application of differential protection for 3 phase power
speed operation for internal faults. Relay has features of transformer many steps are to be followed like current
calculations at HT and LT side, ICT calculations, Tap setting,
magnetizing inrush restraint and over-excitation restraint.
Ratio error of CT and ICT etc;. For this laboratory simulation
Simulated Protective Scheme and Circuits
setup for checking relay operation against magnetizing inrush,
The main equipments used in Figure 3 are single phase 230/ internal short circuit and external short circuit the following
110 V transformer; current transformers, Bias differential relay calculations done as per the equipment utilized.
(MBCH-12) as in [7] and rheostats to simulate the scheme.S3
and S2 are the toggle switch for creating short circuit in primary
and secondary winding respectively. S3 switch used for
creating external (through) fault. To limit the fault current
rheostat are used in series with the toggle switches used for
creating internal and external faults. We can test the relay
behavior for the different conditions like magnetizing inrush
current normal load, external fault internal fault.
Normal condition
Current in transformer secondary winding I2’ = 110V ÷
185ohm = 0.59A, Current in CT(25/5A) at transformer
secondary i2’ = 0.59 ÷ 5 = 0.118A, Current in transformer
primary I1 = (0.59×110) ÷ 230 = 0.28A, Current in CT (10/5)
at transformer primary I1’= 0.28 ÷ 2= 0.14.
Under internal fault
R = (18 × 185) ÷ (185 + 18) = 16.4 ohm,
Current through short circuit = 6.7A, I2 = 0.59 A, I2’ =
0.1189 A, I1= 3.2A, I1’=1.6A, (i1’-i2’) =1.48A > basic setting,
(i1’ – i2’) ÷ ((i1’+ i2’) ÷2) = 1.72
Under external fault condition
I2 = 6.7A, I2’ = 1.34 A, I1= 3.2A, I1’=1.6A, (i1’-i2’) =
0.26A
(i1’-i2’) ÷ ((i1’+i2’) ÷2) = 0.17.
The Bias setting of the relay is set up for 20%. The will
relay not operate for external fault and will operate for internal
primary or secondary short circuit fault.
Figure 3: Power circuit for power transformer protection
OVER CURRENT PROTECTION WITH
DIGITAL RELAY
For magnetizing inrush at no load position (S4 open), Overcurrent protection characteristics are plotted for RITXAutotransformer supply increased to 230V and on pushbutton 210 digital relay using CFB test kit [9] is the manual for the
pressed relay not operate. As MBCH-12 has harmonic restraint test kit.
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (14-18)
ISSN 2230-7656 (c) MIT Publications
Protective Relay
17
and extremely inverse characteristics by giving input to only
1 and 2 terminal from CFB test kit and output relay of P3
“Ref. [8] RITX-210” is the manual for ALSTHOM make
connected to CFB test kit relay contact input.
digital relay which have also optional communication version
availability. It can protect one, two or three phase applications
Overcurrent Protection (Standard Inverse
against overcurrent, short circuit, overload, non-directional
earth fault and over temperature. It can control contactor or Current –Time Characteristic, I) Settings
circuit breaker. These relay has many facilities to use. In Operating Characteristic: toc 1 (Toc 1: Standard inverse),
laboratory we have tested the flush mounted version of RITX- Current setting: 3.00 (relay rated current: 1A), TMS: 0.1,
210 with ALSTHOM relay testing kit for overcurrent, overload Configuration of Protection: On 1 (1: Enable to trip).
condition. The relay has also facility to exchange information
with a supervisory system. The relay front panel view LED
display, LED indicators, Key pad and rear end output relay
terminals, control i/p terminals RS 485 terminals etc;. LED
display displays the phase current values. Six LED indicators
for different protection like overload (Ip), over current (I>),
short-circuit (I>>), earth fault (Io), over temperature (in
cooperation with PTC sensors), Remote protection input (ZZ).
Simulated Protective Scheme and Circuits
Figure 6: Stanadard inverse definete Minimum
characterstic (I>), TOC = 1
Figure 5: Connection diagram for RITX-210 relay
As shown in Figure 5 for flush mounted arrangement of
RITX 210 relay current input is given to 1 and 2 from relay
testing Kit. Auxiliary supply is connected at A1-A2 of Vx.
Four output available in C version. Output contacts can assign
to the following terminal connection of the relay: 13-14
(p1 relay), 23-24 (p2 relay), 33-34(p3 relay), and 41-42-44
(p4 relay). It is possible to change the relay setting only in
OFF-LINE mode. All output relay configuration procedure
and other facilities detail are very good given as in [8]. We
have configured output relay P3 relay to P3-1 using navigating
Keypad. P3-1 means P3 relay contacts are energized if tripping
of any protection which is set to trip take place. There is also
configuring mode of operation available that can be set p3c-0
or p3c-1. 0 means no latching after energizing means relay is
self-reset if a cause for its energizing ceases and for 1 latching
of the energized relay until it is reset from the device key pad
or adequately communication link or input S1-S2. It is
configured p3c-0 for laboratory purpose. The relay is tested
for overcurrent protection for standard inverse, very inverse,
Figure 7: Very inverse Inverse Definete Minimum
characterstic (I>), TOC = 2
Figure 8: Extremely Inverse Definete Minimum
characterstic (I>), TOC = 3
MIT International Journal of Electrical and Instrumentation Engineering, Vol. 2, No. 1, Jan. 2012, pp. (14-18)
ISSN 2230-7656 (c) MIT Publications
Time taken for the relay to trip for current ranging from 3A to
6.4 A was noted as shown in Table 1. P3 was enabled 1 and
p3c enabled 0. Graph for current/time for different
characteristic is plotted in Figure 6 The same procedure
repeated for tms = 0.2 and tms = 0.3. Similar settings and
procedure repeated for toc 2 (Very inverse I-t charactsestic)
and toc 3 (extremely inverse I-t characteristic) and plotted in
Figure 7 and Figure 8 respectively with readings in Table 2
and Table 3 respectively.
Table 1: Current-time readings for standard inverse I-t
characteristic at different TMS
I(A)
3.5 4
4.5 5
5.5
6
TMS=0.1 4.6
2.5 1.6
1.4 1.1
0.9
0.8 0.7
(sec) TMS=0.2 8.9
4.6 3.1
2.4 2.2
2
1.7 1.5
4
2.7
2.4 2
top
3
TMS=0.3 14.4 6.6 4.8
2.9
6.4
Table 2: Current-time readings for very inverse I-t
characteristic at different TMS
I(A)
3.5
4
3.5
2.3 2.1 1.5
(sec) TMS=0.2 15.4 6.5
4.3 3.4 2.7
top
3
TMS=0.1 7.8
4.5 5
TMS=0.3 24.4 10.5 6.5 5
3.9
5.5
6
6.4
1.2
1.1 0.9
2.3
1.9 1.7
3.3
2.9 2.4
Table 3: Current-time readings for extremely inverse I-t
characteristic at different TMS
I(A)
3.5
4
4.5
5
5.5
6
6.4
top
TMS=0.1
8.5
5.3
3.8
2.7
2
1.6
1.7
(s)
TMS=0.2
17
10.2 6.7
5.1
4.2
3.4
2.8
TMS=0.3
26
14.9 10.3 8
6.2
5.1
4.6
RESULTS
The laboratory experiments simulated and tested using all kind
of relays means Electromagnetic, Static and Numerical relay
Which is important to especially developing countries like
india where these relays are widely utilized and not discussed
with detail understanding in other these kind of work. Reverse
power protection experiment simulated to show that relay
operates only while reverse power occurs and also steam valve
interlock facility incorporated. Transformer protection
simulated using static relay which operate only for primary
and secondary short circuit while not operate for external or
starting with no load (Magnetizing inrush) or load conditions.
Numerical relay tested for standard inverse, very inverse and
extremely inverse characteristics using a Relay testing kit which
18
can also be tested by making piratical arrangement using
contactors and rheostats.
CONCLUSION
All protection set up are Laboratory set up and mainly to
provide the idea about the operation of real field protection
application. Such kind of laboratory simulation is very helpful
for relaying education and research work. For the reverse
power protection without using real turbine, generator set up
simulation is made to give understanding the reverse power
protection operation also considering steam valve interlock.
Transformer differential protection employed in field for large
power transformer and here it is simulated using only 1 KVA
transformer. For power transformer differential protection there
are no of things included in relay settings like CT errors, ICT
errors, tap changing effects etc; here these things are not
considered. By practical simulation using MBCH-12 static bias
differential relay single phase transformer tested for
magnetizing inrush, internal fault and external fault. RITX210 digital relay is used for testing overcurrent protection and
protection for different characteristic using relay testing kit.
This paper also provides the idea about how to develop the
practical simulation using any company make relay.
REFERENCES
[1]
Dr. M.A. Date, Prof. B.A. Oza, Dr. N.C. Nair, “Power System
Protection”, Bharti Prakshan, Second Reprint 2004, Gujarat,
India, pp. 61-62 & pp.196-206.
[2]
M.S. Sachdev, T.S. Siddu, “A Laboratory for Research and
Teaching of Microprocessor based Power System Protection”,
IEEE Transactions on Power Systms, Vol. 11, No. 2, May 1996.
[3]
M.A. Redfern, R.K. Agrawal, “A Personal Computer Based
System for the Lab Evaluation of High Performance Power
System Protection Relays”, IEEE Transactions On Power
Delivery, Vol. 6, No. 4, Oct. 1991.
[4]
Wei-JenLee, Jyh-cherng, Ren-Junli and Ponpranod
Didsayaburta, “A Physical Laboratory for Protective Relay
Education, IEEE Transactions on Education, Vol. 45, No. 2.
[5]
Bhuvanesh Oza and Sukmar M. Brahma, “Development of
Power System Protection Laboratory through Senior Design
Projects”, IEEE Transactions on Power Systems, Vol. 20,
No. 2, May 2005.
[6]
Ahmed H. Eltom and Ruspat Hamchotipum, “Microprocessor
Based Relay Laboratory with Industry Support, IEEE”, 2002.
[7]
ALSTHOM LTD., “Catalogues of CCUM21 and MBCH-12
Relays”.
[8]
ALSTHOM LTD., “RITX- 210 user manual”.
[9]
ALSTHOM LTD., “Instruction and Maintenance ManualType CFB”.
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