Power System Testing and Commissioning EET 414/3
Laboratory Module
EXPERIMENT 3
RELAY TESTING AND CALIBRATION
1. Objective
1. To familiarized with over-current and earth fault relay testing
2. To find the inverse time/ current characteristic curves for IDMT Relay.
2. Introductions
The induction relay is used in the great majority of time-graded over-current
protection schemes. It construction may vary but its characteristic and method of setting
are common to all types.
The basic requirement is that firstly, it has to have an inverse time/current
characteristic ; that is it has a long operating time at low multiples of setting current and a
shorter operating time at high multiples of setting current. Secondly, it must have the
means of adjusting the current setting and the time of operation at a given multiple of
setting.
A protective relay which operates when the load current exceed a preset value, is
called an over current relay. The value of the preset current above which the relay
operates is known as its pick-up value. An Over Current Relay (OCR) is used in
substation for the power equipment protection against short circuit of phase to phase and
ground fault.
Time current characteristics
A wide variety of time current characteristics is available for over current relays.
The name is assigned to an over current relay indicates its time-current characteristic as
described below.
i). Definite-time Over current Relay
A definite-time OCR operates after a predetermined time when the current exceeds its
pick-up value. Curve (a) of Figure 5.1. shows the time-current characteristics for this
type of relay. The operating time is constant, irrespective of the magnitude of the
current above pick-up value.
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ii). Instantaneous Over current Relay
An instantaneous relay operates in a definite time when the current exceeds its pick
up value. The operating time is constant, irrespective of the magnitude of the currents
and there is no intentional time delay. It operates in 0.1s or less. Sometimes the term
like high set or high speed is used for very fast relays having operating times les than
0.1s.
iii). Inverse-time Over current Relay
An inverse-time OCR operates when the current exceeds its pick up value. The
operating time depends on the magnitude of operating current. The operating time
decrease as the current increases. Curve (b) of Figure 5.1. shows the inverse time
current characteristic of this type relay.
iv). Inverse Definite Minimum Time Over current (IDMT) Relay.
This type of relay gives an inverse-time current characteristic at lower values of the
fault current and definite-time characteristic at higher values of the fault current.
Generally, an inverse time characteristic is obtained if the value of the plug setting
multiplier between 10 and 20, the characteristic tend to become a straight line, i.e.
toward the definite time characteristic such as Figure 5.2. These relays are widely
used for the protection of lines.
v). Very Inverse-time Over current Relay
A very inverse-time over current relay gives more inverse characteristic than previous
ones.
The very inverse characteristic gives better selectivity than the IDMT
characteristic. Hence, it can be used where an IDMT
extremely inverse relays are employed.
I
3.5
relay fails in selectivity,
Its time-current characteristic according to
t = K. This relay is very suitable for the protection against overheating for
machines, power transformers, grounding transformers, and expensive cables.
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Operating time
INVERSE TIME CHARACTERISTIC
DEFINITE TIME CHARACTERISTIC
Pick Up Value
Actuating Quantity
Figure 5.1. Characteristic of Definite and Inverse time OCR
Figure 5.2. Moderately, Very and Extremely inverse-time
characteristics
The time-current characteristic for relay that respective of the magnitude of the
current in generally is given by t = K / (I n –1). The approximate expression is t = K / I n.
For definite time characteristic, the value of n is equal to 0.
According to the British
Standard, the following are the important characteristic of over-current relays,
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i). I.D.M.T
t=
0.14
I
1
ii). Very inverse
t =
13.5
I 1
iii). Extremely inverse
t =
80
I 1
Laboratory Module
0.02
2
The time-current curves for induction relays can be approximated by the following
equation
 A

t = TD  P
 B
 M 1

where,
t
: trip time (sec)
M : multiple of pickup current (M>1)
TD : time dial setting
A,B,p : curve shaping constant such as in Table 5.
Table 5. IEEE Standardized Relay Curve Equation Constant
_____________________________________________________
A
B
C
_______________ ______________________________________
Moderately inverse
0.0515
0.114
0.02
Very inverse
19.61
0.491
2.0
Extremely inverse
28.2
0.122
2.0
_____________________________________________________
3. Equipment and Part
1. IDMT Relay 203 (Overcurrent) – 1 unit
2. IDMT Relay 202 (Earthfault) – 1 unit
3. SVERKER 760 Relay Test Unit – 1 unit
4. Digital Multimeter 10/20A – 1 unit
5. High Resistance Cable
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IDMT 203 Overcurrent Relay :
4. Procedure
A) Overcurrent Relay characteristic test
1. Calculate the PSM at 80% of full load current. Take it as the 100% PSM setting
of the relay. Record the value in your test certificate.
2. Connect the instrument as shown in Fig. 5.1(a) with the SVERKER 760 Relay
Test Unit in the OFF position. (Always turn SVERKER 760 OFF before connecting)
4. For the connection to Overcurrent Relay (IDMT 203), make sure the connection
follow the diagram as at the side of the Overcurrent Relay. (Refer the connection
diagram). Ensure to connect the current injection set to correct terminal phase at
the relay
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5. Manually increase the current by turning the knob at 130% of PMS setting of the
relay. You will observed the relay trips if the current injected is over 100% setting.
6. Press HOLD button to stop any current injection. Reset the secondary injection
set and the relay being tested.
7. Now, activate the timer release. The current will now be injected automatically at
130% of PSM and will cause the relay to trip according to its characteristics.
8. Record the time displayed at the secondary injection set. Repeat the procedures at
200% and 300% of PSM setting.
9. Repeat the procedures for all other phases.
10. Record your reading in the Test certificate provided to you.
11. Plot a graph of time vs magnitude of current.
B) Overcurrent Relay Stability Test
1. The connection and diagram for this testing are the same as procedure A
2. Set the PSM of the relay to 2.
3. Slowly, increase the current until the relay is trip.
4. Record the value of injected current displayed at the secondary injection set.
5. Repeat the procedures for every PSM setting.
C) Earth Fault Relay characteristic Test.
1. For this experiment, use IDMT202 type of relay.
2. For earth fault setting, calculate 10% of from 5A. This will be 100% of PSM of
the relay.
3. Connect the relay to the secondary injection test set as shown in Figure 2. Ensure
Test set is OFF before making the connection.
4. Increase the current injected to the relay at 130%, 200% and 300% from the PSM.
5. Record the time for relay to trip as procedure of overcurrent relay.
6. Plot a graph of time vs current.
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D) Earth Fault Stability Test
1) Without disconnecting the wiring connection, conduct an experiment as per
procedure B of over-current relay stability test.
2) Record your data in the test certificate.
QUESTIONS
1) What can be concluded from the results obtained?
2) What is the time for the relay to trip if the fault current is 1500 Ampere?
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ADDITIONAL QUESTION
1. Explain how would you use an overcurrent characteristic to determine its time of
operation, given the following information. (Draw the curves)
Relay Specification : 1A, 3sec
Plug Setting : 125%
Time Multiplier Setting : 6
Current Transformer Ratio : 400/1 A
Fault Current : 4000A
DISCUSSION/CONCLUSION
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KOLEJ UNIVERSITI KEJURUTERAAN UTARA MALAYSIA
RELAY TEST CERTIFICATE
Job Ref NO .
Type of installation
Client
Cert no.
Circuit
Consultant/Contractor
CB Detail
Make
Volt
Rating
Serial No.
O/C Relay Detail
Make/Type
Serial No.
CT Detail
Ratio
Class
Burden
Make
Relay Setting
P.M.S [O/C]
T.M.S
P.M.S [E/F]
T.M.S
E/F Relay Detail
Make/Type
Serial No.
Tripping Time Test
Test Setting
Creep Amps.
Is Injected (A)
O/C
O/C =
T.M =
O/C [R]
Time (s)
E/F
O/C [Y]
Time (s)
E/F =
T.M =
O/C [B}
Time (s)
E/F
Time (s)
Reset Time
Pickup Current Test
Test Setting
O/C =
Test Setting (Amps)
O/C
E/F
Trip Voltage
220
T.M =
O/C [R]
Shunt Trip Tested
O/C [Y]
E/F =
Operating Value (Amps)
O/C [ B]
T.M =
E/F
Seal
Remarks:
@shukur modular_kukum
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