LABORATORY MANUAL
POWER SYSTEMS LAB
EE-328-F
(VIth Semester)
Prepared By:
Rajiv Kumar
B. Tech. (EEE), M. Tech. (EEE)
Department of Electrical & Electronics Engineering
BRCM College of Engineering & Technology
Bahal-127028 (Bhiwani)
Modified on 14 November 2014
1
SYLLABUS
EE-328-F
LTP
--2
Sr. No
POWER SYSTEMS LAB
Practical: 25 marks
Class work: 25 marks
Total: 50 marks
List of Experiments:-
1. To draw the operating characteristics of IDMT relay.
2. To study the performance of Earth fault relay.
3. To study the performance of an over voltage relay.
4. To study the performance of under voltage relay.
5. Testing of breakdown strength of transformer oil.
6. To study flash point test of transformer oil.
7. To find ABCD, Hybrid & Image parameters of a model of transmission line.
8. To study performance of a transmission line under no load condition & under
load at different power factors.
9. To observe the Ferranti effect in a model of transmission line.
10. To study performance characteristics of typical DC distribution system
in radial & ring main configuration.
11. To study characteristics of MCB & HRC Fuse.
12. To study radial feeder performance when a) fed at one end b) fed at both ends.
2
Page No
Index
S.No. Name of Experiment
3
1
To draw the operating characteristics of IDMT
relay
2
To study the performance of Earth fault relay
3
To study the performance of an over voltage relay
4
To measure the dielectric (Breakdown) strength
of transformer oil
5
To find ABCD, Hybrid & Image parameters of a
model of transmission line
6
To observe the Ferranti effect in a model of
transmission line
7
To study radial feeder performance when a) fed at one
end b) fed at both ends.
8
To study characteristics of MCB & HRC Fuse
9
To study the performance of adifferential over
current relay
10
To study the operation of static definite time
reverse power relay
Page No.
Date
Signature
Experiment – 1
Aim: To draw the operating characteristics of IDMT relay
Objective: The aim of the experiment to investigate the operation, inverse characteristics and to
determine the purpose of time and plug settings for over current relay in electrical supply system.
By configuring these settings correctly, and by coordinately the operations of the relays, it is possible
to isolate the smallest section of the system in the shortest time possible, thereby minimizing
unnecessary disruption to other consumers whilst preventing damage the equipment within the fault
section.
In the radial feeder configuration, supply from one end only, discrimination of faults can be achieved
by incorporating time delays at each relay point. This enables the relay closest to the fault to trip,
isolating the fault circuit without affecting the other non-faulty circuits. A disadvantage of this system
is that for faults near the source, the fault current can be much greater than at the opposite end of the
feeder due to the impedance. For a fault at point F in figure (1), the circuit breaker at point C opens
before those at point A and B, leaving most of the feeder operational. The relays have a time grading
of 0.5s (to allow for relay and circuit breaker operation plus error allowance), illustrating
discrimination by time grading only.
The disadvantage can be overcome by employing relays with an inverse current / time characteristic –
i.e. the time delays are reduced for higher currents. These relays are known as IDMT relays (Inverse
Definite Minimum Time). A minimum time of operation is incorporated to ensure co-ordination
between the relays when the fault level does not vary along the feeder.
Apparatus Required:
1) Timer
2) IDMT relay (MODEL NO.ICM-21NP))
3) Auxiliary D.C. supplies = 110V
4) 1 phase Dimmer stat = 230V, 10A
5) Ammeter AC (0-15A)
6) Rheostat (38 ohm, 8.5 Amp)
7) Experiment Kit
8) Connecting wires
Circuit Diagram:
4
Procedure:
1. Make the connection as shown in the circuit diagram.
2. Select current setting (set phase trip) less than 100%, keeping phase TMS at maximum position.
3. Select any time setting.
4. Switch on variac and check power ON indication provided on relay front panel.
5. Vary dimmer stat and observe current value till Pick-Up will show ‘Red’ indication when current
value exceeds set phase trip position.
6. Switch OFF dimmer stat without disturbing its position with the help of DPT switch. Also reset
time.
7. Measure the relay time from timer by switching on DPT switch.
8. Now increase the fault current and note down timer time after switching ‘OFF’ and ‘DPT’ switch
every time with same time setting.
9. Repeat same procedure for different time setting keeping current setting same.
Observation Table:
Sr. No.
Fault Current
(A)
PSM
Timer time for
TSM=
Timer time for
TSM=
Timer time for
TSM=
Result:For lower values of current the “time current ” characteristics are inverse and for higher value for
current observed times are constant
5
Experiment No. 2
Aim: To study the performance of Earth fault relay
Objective: To study the protection of equipment and system by relays in conjunction with switchgear.
Theory: The function of a relay is to detect abnormal conditions in the system and to initiate through
appropriate circuit breakers the disconnection of faulty circuits so that Interference with the general
supply is minimized.
Earth fault protection can be provided with normal over current relays, if the minimum earth fault
current is sufficient in magnitude. The design of a comprehensive protection scheme in a power system
requires the detailed study of time-current characteristics of the various relays used in the scheme.
Thus it is necessary to obtain the timecurrentcharacteristics of these relays. The over current relay
works on the induction principle. The moving system consistsof an aluminum disc fixed on a vertical
shaft and rotating on two jeweled bearings between the poles of an electromagnet and a damping
magnet. The winding of the electromagnet is provided with seven taps (generally0, which are brought
on thefront panel, and the required tap is selected by a push-in -type plug. The pick-up current setting
can thus be varied by the use of such plug multiplier setting. The pick-up current values of earth fault
relays are normally quite low.
Equipment Required:
1) Timer
2) IDMT relay (Model APR-11 P)
3) Auxiliary D.C. supplies = 110V
4) 1 phase Dimmer stat = 230V, 10A
6) Ammeter AC (0-15A)
7) Rheostat (38 ohm, 8.5 Amp)
8) Experiment Kit
9) Connecting wires
Circuit Diagram:
Procedure:
1. Make the connection as shown in fig.
2. Set current and time setting of relays as per requirement
3. Set phase trip to 50% and set phase time at X1 with phase TMS at maximum position.
4. Switch on variac and check power ON indication provided on relay front panel.
5. Very dimmer state with fault current of 1A, relay will trip after certain time delay.
6
6. Switch OFF dimmer state without disrobing its position and change the position of DPT switch.
Also reset time.
7. Switch ON dimmer state changes the position of switch and measure the relay time from timer.
8. Reap eat same procedure for varying a different fault current.
9. Repeat this procedure consider different set phase time (TMS)
Operation:
With supply on load are continuously monitored Electronic comparator checks this value with set
value (N) of phase & earth fault trip, which can be adjusted on front plate. Pick up response is (1.1 N)
IDMT timing is applicable to over current above 2N as per chosen curve. Time setting multiplier for
actual tripping time delay. TMS is adjusted by 11-position switch & with variable preset pot. These
pots adjusted time for intermediate values indicated on TMS switch. Tripping cause is indicated by
LED lamp (OC/EF). When over current trips the circuit relay ‘ NO’ contact changes to ‘NC’ when
relay trips indicating LED to ‘NC’ when relay trip indicating LED to ‘NC’ when relay trips indicating
LED to ‘NC’ when relay trip indicating LED flag will remain ON till manually reset.
Observations:
Current setting =……, Phase TMS
Sr. No. Fault Current
PSM
Timer time for Timer time for Timer time for
(A)
TSM=
TSM=
TSM=
Result:For lower values of current the “time current “characteristics are inverse and for higher value of
current, time observed is constant.
Viva Question
1 Application of IDMT relay.
2 Drawback of IDMT relay
3 Importance of DC supply
4 Detail of other Inverse type of relays
5 Importance of static relays
6 Why IDMT relay suitable for protection of long length of LV/MV TL.
7
Experiment – 3
Aim: To study the performance of an over voltage relay.
Apparatus Required:1) Static over voltage relay (Model No.: -ASOV)
2) Auxiliary D.C. supplies 110V
3) Time interval meter
4) Single pole variac 230V, 4A
5) Voltmeter (0-300V) AC
6) Rheostat (400 ohm, 1.7 Amp)
7) Connecting wires
8) Experiment Kit
Circuit Diagram:
Procedure:
1. Connect the ckt as shown in fig procedure is done & time is noted.
2. Set current and time setting of relays as per requirement.
3. Connect Auxiliary D.C. Supply (110) to pin 11 & 12 of relay and pin no. 3&4 to the time
interval meter.
8
4. Switch on the D.C. supply & make sure that relay is on Glowing of LED on the front panel of
the relay.
5. Switch on power supply from dimmer as well as to time interval meter.
6. Adjust the voltage setting of the relay.
7. Adjust the time setting of relay.
8. Now by making DPDT switch on, increase the value of voltage by dimmer stat up to the point
at which the relay trip. Trip can be observed by glowing of trip LED on front panel of relay.
9. Switch is made off and relay is reset.
10. Now Switch is made on & time interval meter reading is noted.
11. For the same voltage setting , time setting is changed & same procedure is repeated until all the
time setting are covered.
12. Again voltage setting is changed & same procedure is repeated.
Result: The static over-voltage relay is studied
9
Experiment –4
Aim: To measure the dielectric (Breakdown) strength of transformer oil.
Equipment Required:
1. Portable oil testing set-220/250 V
2. HV transformer-50 kV/250 V
3. Gap setting gauges -0.15711 width
Theory
The two unit portable testing set is designed for the periodical testing of samples of insulating oils
drawn from plant on site and for checking the dielectric strength of new samples of oil. The equipment
is designed to operate from 200/250V, 50Hz, Single phase AC supply. Test gap voltage up to 50kV, it
consists of two units, one is containing the testing transformer and other is control and metering
equipments. These equipments are kept in a metal box to provide full protection to the apparatus
during transport and storage. The gap is adjusted between electrodes in accordance with British
Standard Specification (BSS) no. 148
Connection Diagram:
Observation Table:
S. No.
1
2
3
4
5
10
Break down Voltage (Volts)
Procedure:
1. Place the High Voltage transformer unit about 7 away from the control unit.
2. The control unit is connected to supply voltage taking care that the earth connections are
effective.
3. The multiple point control switch is set at its lowest tapping.
4. The push button on control unit is pressed firmly for at least 5 seconds. Note that no
Breakdown to occurs, in which case button should be released at once without delay. Break
down is indicated by a continuous discharge across the gap, bubbling of oil in the cell and
meter indicating a sudden voltage drop.
11
Experiment – 5
Aim: To find ABCD, Hybrid & Image parameters of a model of transmission line
Apparatus Required: - Transmission Line model is consisting of four sections of transmission Kit
Voltmeter-1, Ammeter-1, Power Supply-220V, Connected Wire (As per Requirement)
Theory: - ABCD Parameter are widely used in analysis of power transmission engineering where they
will be turned as “Generalized circuit parameter” ABCD parameters are also called as Transmission
parameter. It is conventional to designate the input port as sending end and the output port as receiving
end while representing ABCD parameter
Vs = AVr + B Ir
Is = CVr + Dir
[Vs/Is] = [A B/C D] [Vr / Ir]
Assuming the receiving end open Circuit i.e.
A =Vs / Vr Where Ir = 0
B = Vs / Ir Where Vr = 0
C = Is / Vr Where Ir = 0
D = Is / Ir Where Vr = 0
Circuit Diagram:-
In transmission line if impedance at the sending end with Z12 at receiving ends be Z11 and simulations
the impedance looking back from receiving end with Z11 at input part is Z12 then Z11 and Z12 termed as
the image impendence of the network
√AB
√BD
Z11 = CD and Z12 = AC
√BD
α = tanh-1 = AC
Calculation & Observation:Open Circuit:S. No
12
Vs
Is
Vr
A= V1 / V2
C = I1 / V2
Short Circuit:S. No
Vs
Is
Ir
B= Vs / Ir
D = Is / Ir
Procedure:1. To find out A and C parameters connect voltage supply of 220V to sending end and open circuit
receiving end.
2. Observe the voltage of Vs, Is and Vr with the help of voltmeter and ammeters in the
experimental kit.
3. To find out B and D receiving end is short circuited and supply of 220V is given to sending
end.
4. Observe the voltage of Vs , Is and Ir
Result: - The Calculated A, B, C, D Parameters are
A=
B=
C=
D=
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Experiment – 6
Aim: To observe the Ferranti effect in a model of transmission line.
Equipment Required:
1. Three phase alternator rating: 400V, 5kVA, 1500 rpm.
2. Ammeter
3. Voltmeter
4. Rheostat
Theory:Ferranti Effect
A long transmission line/cables draws a substantial quantity of charging current. If such a
line/cable is open circuited or very lightly loaded at the receiving end, the voltage at receiving end may
become greater than voltage at sending end due to capacitive reactance. This is known as Ferranti
Effect. Both capacitance and inductance is responsible to produce this effect. The capacitance (which
is responsible for charging current) is negligible in short line but significant in medium line and
appreciable in long line. Hence, this phenomenon occurs in medium and long lines. The figure shown
below is representing a transmission line by an equivalent pi (π)-model. The voltage rise is
proportional to the square of the line length.
The Line capacitance is assumed to be concentrated at the receiving end.
In the phasor diagram shown above OM = receiving end voltage Vr
OC = Charging current drawn by capacitance = Ic
MN = Resistive drop
NP = Inductive reactance drop
Therefore; OP = Sending end voltage at no load and is less than receiving end voltage (Vr)
Since, resistance is small compared to reactance; resistance can be neglected in calculating Fer
ranti effect. From π-model, Vs=Vr-Impedance drop under open circuit condition Ir=0 and hence,
Vs=Vr-IcR-jwL*Ic i.e. receiving end voltage is greater than sending end voltage and this effect is
called Ferranti Effect. It is valid for open circuit condition of long line.
When load current is increased of R-L loads the resultant current is not remains leading, because of the
inductive drop. Hence, receiving end voltage (Vr) is lesser than sending end voltage (Vs) under full
load conditions
Observation Table:
Length of
Sending end
Receiving end
Sending end
Receiving end
S. No.
the line(km) voltage Vi(volts) voltage Vo(volts)
current Ii(amp)
current Io(amp)
1
2
3
4
5
Procedure:
14
1.
2.
3.
4.
5.
6.
15
Select initial length of line(say 30kms).
Start the motor-generator set.
Note down the sending end voltage Vi, sending end current Ii and receiving end voltage Vo.
Disconnect the supply of motor-generator set.
Increase the length of line.
Repeat the steps 2-5.
Experiment – 7
Aim: To study radial feeder performance when a) fed at one end b) fed at both ends.
Theoretical Background:
Whole of the power system can be subdivided in to number of radial feeders fed from one end.
Generally such radial feeders are protected by over current and earth fault relays used as primary relays
for 11 kV and 66 kV lines. For lines of voltage rating beyond 66 kV, distance protection is applied as a
primary protection whereas over current and earth fault relays are used as back up relays.
A simplified radial feeder network without transformers (in actual practice transformers do exist at
substations) is shown in single line diagram of fig. 1.1 below.
If the fault occurs in distribution network, fuse should isolate the faulty section. Should the fuse fail,
relay R3 shall give back-up protection. Relays R1, R2, and R3 act as primary relays for faults in section
I, section I, and section III respectively. If fault in section III is not cleared by relaying scheme at
relaying point R3, relay R2 will act as a back-up. Similarly back-up protection is provided by relay R1
for faults in section II. A,B, C and D are substations in fig. 1.1.
Generally Inverse time over current relays with Definite Minimum Time feature (IDMT relays) are
used in practice. There are many types of such relays available in relay market, viz. normal inverse
relays, very inverse relays and extremely inverse relays. The characteristics of these relays are shown
in fig. 1.2. The other types of o/c relays are 3 second relay and 1.3 second relay. This means the time
of operation of the relay is either 3 or 1.3 second at Plug Setting Multiplier (PSM) equal to 10. Long
time inverse relays are used for o/c cum overload application. Voltage restrains o/c relays have their
own application.
Very inverse relays are less prone to the ratio ZS/ZL. Extremely inverse relays are yet better. Very
inverse relays are faster in operation for close-in faults yet maintaining the discrimination with fuse
and other relays. Extremely inverse relays are more meritorious in this aspect too. Instantaneous o/c
relays are not immune to ZS/ZL ratio. Definite time o/c relays are 100 % immune to this ratio. Very
inverse relays can be used with an additional advantage while protecting a machine or a transformer as
they match with the heating characteristic of equipment better than their normal inverse equivalent.
16
Extremely inverse relays can best co-ordinate with the fuse characteristic. The aim of this experiment
is to reveal these facts experimentally.
Fig. 1.2 Normal, Very and Extremely Inverse Characteristics
Laboratory Simulations:
Referring to a.c.circuit of fig. 1.3. A live model of a radial feeder fed from one end can be selfunderstood.
This is only a single phase version of a radial feeder. Faults in different sections can be created by
switches S1, S2 and S3. Fault limiting resistance of 18 ohms is used for practical purposes only. Here
C.T. secondary rating is 5 Amp and relay rating is 1 Amp. This is contradicting the practice for for
practical purpose.
Observation Table:
17
Table:1.1 Measured fault currents for extreme
faults in each section
Fault Location Fault current (A)
Table:1.2 Calculated relay settings
Relay P.S.
TMS
R1
R2
R3
Table:1.3 Normal Inverse Relays
Fault
Location
Relay R1
PSM Obs time
of
op
(sec)
Measured
time of op
(sec)
%
Error
Relay R2
PSM Obs time
of
op
(sec)
Measured
time of op
(sec)
%
Error
Relay R3
PSM Obs
time of
op (sec)
Measured
time of
op (sec)
F1
F1’
F2
F2’
F3
F3’
Relays
R1
R2
R3
Table 1.4
Difference in time of operation of relay for extreme faults
Section
Observed
Calculated
I
II
III
Procedure:
1. Measure the fault currents for corresponding rheostat in minimum (zero resistance) and
maximum (full resistance) positions and using the corresponding fault-switch S1, S2, or S3 (refer
fig. 1.3). Maximum fault currents in sections I, II and III are denoted by F1, F2, F3 respectively
and the minimum fault currents by F1’, F2’, F3’ respectively. Deactivate the relays for this
purpose. Record the readings in table 1
2. Calculate the plug –settings (or Tap Value) of relays R1, R2 and R3. (Plug settings will be same
irrespective of type of relays). For this purpose, assume the number of distributors each of 0.5
Amp rating from the following possibilities (The experiment is a simulation and hence the
distributor current is 0.5 Amp. In actual practice it may be 500 Amp or more or less):
Number of distributors: 1, 2, 3 or 4.
(Calculations of the plug setting shall be done w.r.t. following considerations)
(I) The plug setting shall be more than or equal to the maximum full-load current passing
through the relay.
(II) The pickup of the relay varies from 1.05 to 1.3 times the plug setting of the relay
(III) For back up, relay R1 shall reach for the fault F’2 and R2 for the fault F’3.
3. Time Settings. (Normal Inverse Relays)
For deciding time-settings, co-ordinate the characteristics of relay R3 with that of an MCB.Use
discriminating time-interval of 1.0 sec. b/w two characteristics. This will decide TMS of R3.
Why discrimination time of 1.0 second? (Try answer to this question.)
For coordinating R2 & R3 use the worst possible current to decide TMS of R2 (F3 in table:1.1).
Similarly decide TMS of R1 by using F2 and setting of R2. Use discriminating time interval
between two successive relays as 0.4 seconds (why 0.4 seconds?) for these calculations.
Tabulate the results as in table (2).
18
%
Erro
r
4. Time-settings (Very Inverse Relays) can be carried out for very inverse relays also. The results
are to be tabulated as in the case of normal inverse relays as per calculated settings.
5. Set the normal inverse relays as per the settings in table 1.2
6. Calculate the time of operation of the main and back-up relay for extreme fault in each section
using the relay settings in table:1.2 and the fault current readingsrecorded in table:1.1. Enter
these in table:1.3 as “Calculated Time of Operation”
7. Vary the 550 ohms load resistance such that the current in the radial feeder varies from 0.5
Amp to about 4 Amp. See that MCB trips and relay R3 does not trip.
8. Now create extreme faults (one by one) in each section starting from section III. For each fault,
measure the time of operation of the main and the back-up relay (to measure time of operation
of back-up relay, the main relay has to be deactivated using switches T2 or T3 (as the case may
be) in fig. 1.4). Record these in table 1.3 as “Measured Time of Operation”. Calculate the error
between the calculated and the measured time of operation for each fault and record it in table:
1.3.
9. Derive the table 1.4 from table 1.3.
10. Replace the normal inverse relays by very inverse relays.
11. Repeat steps at Sr. No. 5 to 9 for very inverse relays.
12. Draw your own conclusion.
19
Experiment – 8
Aim: To study characteristics of MCB & HRC Fuse
Apparatus Required:
1) Fuse wire
2) Ammeter AC (0-10 A)
3) Stop watch
4) 1 ph Dimmerstat – 230V, 10 A
5) Loading Rheostat
6) Rheostat (38 Ohm, 8.5 A)
7) Experimental Kit
8) Connecting Wires
Circuit Diagram:
Observation Table
S.No.
20
Current (Amp.)
Time (Sec.)
Procedure:
1. Make the connections as shown in Fig.
2. Switch on the supply and keep the full load in the on position. Adjust the current to certain value
with the help of dimmerstat.
3. Stop watch is stopped when the fuse element is blown which is indicated by decreasing of current
in ammeter to zero. Note down the time of stop watch.
4. Again after changing the fuse element increase the current to certain value and repeat above
procedure.
Result: The characteristics of fuse wire is studied in this experiment and is found to be inverse type ,and is
plotted on graph paper .
Viva Question
1 Application of fuse wire
2 comparisons of fuse and circuit breaker
3 Types of fuses and their application
4 types of fuse require for protection of transformer, generator and induction motor
21
Experiment – 9
Aim: To study the performance of adifferential over current relay
Theory:Relays are of many types. SomeDepend on the operation of an armature by some form of
electromagnet. A verylarge numbers of relays operate on the induction principle. When a relay
operates itcloses contacts in the trip circuit which is normally connected across 110 V D.C.supplyfrom
a battery. The passage of current in the coil of the trip circuit actuatesthe plunger, which causes
operation of the circuit breaker, disconnecting the faultysystem. In the laboratory, a 3-phase contactor
simulates the operation of the circuit breaker.The closure of the relay contacts short-circuits the 'novolt ' coil of the contactor,which, in turn, disconnects the faulty system.The protective relaying which
responds to a rise in current flowing through theprotected element over a pre-determined value is
called 'overcurrent protection' andthe relays used for this purpose are known as over current relays.
The operating time of all overcurrent relays tends to become asymptotic to a definiteminimum value
with increase in the value of current. This is an inherent property of the electromagnetic relays due to
saturation of the magnetic circuit. By varying thepoint of saturation, different characteristics can be
obtained and these are
1. Definite time
2. Inverse Definite Minimum Time (IDMT)
3. Very Inverse
4. Extremely Inverse
The torque of these relays is proportional to  Sin, where  and  are thetwo fluxes and is the
angle between them. Where both the fluxes are produced bythe same quantity (single quantity relays)
as in the case of current or voltageoperated, the torque T is proportional to I2, or T = K I2, for coil
current belowsaturation. If the core is made to saturate at very early stages such that with increaseof I2,
K decreases so that the time of operation remains the same over the workingrange. The time -current
characteristic obtained is known as definite –timecharacteristic.If the core is made to saturate at a later
stage, the characteristic obtained is known asIDMT. The time-current characteristic is inverseover
some range and then aftersaturation assumes the definite time form. In order to ensure selectivity, it
isessential that the time of operation of the relays should be dependent on the severityof the fault in
such a way that more severe the fault, the less is the time to operate,this being called the inverse-time
characteristic. This will also ensure that a relayshall not operate under normal overload conditions of
short duration.It is essential also that there shall be a definite minimum time of operation, whichcan be
adjusted to suit the requirements of the particular installation. At low valuesof operating current the
shape of the curve is determined by the effect of therestraining force of the control spring, while at
high values the effect of saturationpredominates. Different time settings can be obtained by moving a
knurledclamping screw along a calibrated scale graduated from 0.1 to 1.0 in steps of 0.05.This
arrangement is called Time Multiplier Setting and will vary the travel of thedisc required to close the
contacts. This will shift the time-current characteristic ofthe relay parallel to itself.By delaying the
saturation to a further point, the Very Inverse and Extremely VeryInverse time current characteristics
can be obtained.
Apparatus Required:
1) Single pole directional O/C relay ACDR 11 HPD
2) Phase shifting transformer
3) Dimmerstat ( 3 phase , 440 volt, 50 Hz )
22
4) Ammeter (0-1 Amp)
5) Rheostate ( 300 ohm , 1.7 Amp)
6) Dimmerstat ( 1 phase , 230 volt, 4 Amp)
7) DC Power Supply ( 110 Volt )
Circuit Diagram:
Operation: Load current is continuously monitored and compared to set value and polarized with
voltage for direction sensing. As soon as the current exceeds the set value and it is operating direction
then N value (Time set value) is calculated and then the delay time count is started , two types of
curves 10 times ( N=10 ) current 3.0 sec . Delay and 1.3 sec delay can be provided. At the end of the
time count if the current still exceeds the set value TRIP is exceeded. All the monitored current value
is available at the front D is skeet’s for external recording.
If the direction is reverse then the TRIP execution is (represented) restrained high fault setting is also
provided (2N. 20 N) IF the current value exceeds the HF set value instant trip (i.e. 100 msec.) is
executed, by passing the directional restraint.
Observation Table:
S. No.
Phase Angle
MTS = MAX torque setting
45 degree
60 degree
9th Line
0 degree
30 degree
60 degree
90 degree
120 degree
150 degree
180 degree
-150 degree
23
Procedure:
1) Make the connections as shown in the fig.
2) Apply the voltage across the P.T of relay
3) The pick –up current through the relay coil.
4) Set current and time setting of relays as per requirement
5) Switch on the supply.
6) Find out the operating region and non-operating region of relay by changing angle using the phase
shifting transformer.
7) Adjust the current to such a value, which is more than plug setting.
8) Change the shifter angle such that relay operates in that region.
Result: The static directional relay is studied and graph for different maximum________ torque
setting is drawn.
24
Experiment – 10
Aim: To study the operation of static definite time reverse power relay.
Apparatus Required:
1) Timer
2) Static definite time reverse power relay (Model APDR 21)
3) Auxiliary D.C. supply = 110V
4) 3 phase variac =440V, 50 Hz, 8A
5) 1 phase variac =230V, 4A
6) Ammeter AC (0-1A) AC
7) Rheostat (300 ohm, 1.7Amp)
8) Phase shifting transformer
9) Voltmeter (0-300V) AC
10) Experiment Kit
11) Connecting wires
Circuit Diagram:
Operation: Solid static state voltage and current sensing circuits measure the instantaneous voltage
and current value in scales down format .The algorithmic circuit does the multiplication of the derived
data. The output of this circuit remains positive as the moment when power reversal occurs, output of
the circuit’s changes again. It is noted as pick up point and thus indicated by pick up LED. This also
triggers the internal timer cit. This timer is adjustable by 11 positive switches. It has very high repeat
accuracy. (Better than class 17) After the end of set timing and if power conduction are still reverse.
Procedure:
1) Make the connection as shown in fig.
2) Set current and time setting of relays as per requirement
3) Switch on supply to 3phase dimmerstate and also D.C. supply to relay.
4) By varying 3 phase dimmerstate adjust the value of current.
5) Now keeping current at this value constant change the angle of phase shifting transformer gradually.
6) Observe the tripping zone of reverse power relay.
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7) The relay will trip at certain angle of phase shifting transformer note down the angle and reset the
relay.
8) Again increase the angle and observe tripping of relay.
9) Plot the tripping region of reverse power relay on the graph paper.
Observation Table:
S. No
S. No.
Time setting (in Sec.)
1
2
3
4
5
6
7
8
9
10
Table – 1
Phase angle ф (in Degree)
0
30
60
90
120
150
180
210
240
270
300
330
360
Trip response
Table – 2
Trip Time (in Sec.)
Result: The operation of definite time reverse power relay is studied and triggering zone is plotted in
the graph paper.
Viva Question
1 Application of Reverse power relay
2 Types of relays used and its setting for protection of ring main feeders
3 Comparison of other directional relays and reverse power relays
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