G. H. RAISONI COLLEGE OF ENGINEERING DEPARTMENT …ghrce.raisoni.net/download/sgp_expts.pdf · G....

DEPARTMENT OF ELECTRICAL ENGINEERING VIIIth SEM B.E.

G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 1

G. H. RAISONI COLLEGE OF ENGINEERING

DEPARTMENT OF ELECTRICAL ENGG.

VIII SEMESTER B.E.

SWITCHGEAR AND PROTECTION LAB

INDEX

Sr.

No.

Name of Experiment Page

No.

1 TO STUDY THE OPERATION OF DEFINITE TIME

OVERCURRENT RELAY.

2

2 TO PLOT THE CHARACTERISTICS OF SINGLE POLE OVER

CURRENT OR EARTH FAULT USING STATIC I.D.M.T.

RELAYS

5

3 TO STUDY THE OPERATION OF STATIC OVER VOLTAGE

RELAY

8

4 TO PLOT THE CHRACTERISTICS OF ELECTROMAGNETIC

IDMT RELAY (MODEL NO.ICM-21NP)

10

5 TO STUDY THE OPERATION OF STATIC DEFINITE TIME

REVERSE POWER RELAY (MODEL APDR-21)

13

6 A) TO STUDY THE MAGNETISATION CHARACTERISTICS

OF C.T.

B) TO STUDY THE PROBLEM ASSOCIATED WITH C.T.

MAGNETISATION.

16

7 TO PLOT THE CHARACTERISTICS OF FUSE WIRE 18

8

TO STUDY DIRECTIONAL OVER CURRENT RELAY ( ACDR

11 HPD)

20

9 TO STUDY AND PLOT THE CHARACTERISTICS OF

IMPEDANCE RELAY ( ABB-RAKZB

23

10 TO STUDY TRANSFORMER DIFFERENTIAL PROTECTION 26

11 TO STUDY UNRESTRICTED EARTH FAULT RELAYS. 28



EXPERIMENT NO.1

AIM: - TO STUDY THE OPERATION OF DEFINITE TIME

OVERCURRENT RELAY.

APPARATUS: -

1) Timer

2) Static definite O/C relay (Model ACTU 32 P)

3) Auxiliary D.C. supply = 110V

4) 1 phase variac =230V, 4A

5) Ammeter AC (0-5A) and (0-1/2 A)

6) Rheostat (100 ohm, 5Amp)

7) Experiment Kit

8) Connecting wires

CIRCUIT DIAGRANM:

A

(0-5A)

1PH

230V

50 HZSUPPLY

ON

OFF

46

35

110V

DC+ -1211

36 OHM, 8.5A

230V1-PH

SUPPLY

START

STOPTIMER

THEORY:

1. Principle and operation of static definite time over current relay, time –

current charact. equation.

2. Block diagram of static over current relay.



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.

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 current setting of the relay.

7) Adjust the time setting of relay.

8) Now by making DPDT switch on, increase the value of current 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 current setting , time setting is changed & same procedure

is repeated until all the time setting are covered.

12) Again current setting is changed & same PROCEDURE IS REPEATED.

OBSERVATION TABLE: -

Sr.

No.

Relay set time

in sec

Set phase trip

=100%

Ammeter

reading

Timer

time

Set phase tri[p

=180 %

Ammeter

reading

Timer

time

1.

2.

3.

4.

CHARACTERISTICS TABLE: -

Current setting = ……………, Pick up current = ……

Sr. No. Fault current (A) PSM Timer

time, for

TMS =

Timer

time, for

TMS =

Timer

time, for

TMS =

1



2

.

.

.

10

RESULT & CONCLUSION: -

The operation of definite time O/C relay is studied in this experiment. The

reading is obtained for various time settings as well as current setting. It was

found that for various time delay observed for peak up values of current is

same.

Viva Question

1 Application of DTOC relay.

2 Draw back of DTOC relay

3 Importance of DC supply

4 Detail of other O/C relays

5 Use of timer



EXPERIMENT NO.2

AIM: -

TO PLOT THE CHARACTERISTICS OF SINGLE POLE OVER

CURRENT OR EARTH FAULT USING STATIC I.D.M.T. RELAYS

APPARATUS: -

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

A

(0-15A)

1PH

230V50 HZ

SUPPLY

ON

OFF

46

35

110VDC+ -

1211

36 OHM, 8.5A

230V

1-PH

SUPPLY

START

TIMER

STOP

THEORY: -

1. Define PSM, TSM.

2. Equation of time –current characteristics.

3. Principle & Operation of static IDMT Relay with block diagram



PROCEDURE: -

1) Make the connection as shown in fig.


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,relayb will trip after

certain time delay.

6) Switch OFF dimmer state without disrobing its position and

change the position of DPT switch. Also reset time.

7) Switch ON dimmer state change 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.

OBSERVATION

1 CHARACTERISTICS TABLE: - current setting =……, Phase TMS

Sr.

No.

Fault current

(A)

PSM Timer time for

TSM =

Timer time for

TSM=

Timer time for

TSM=

1

2

.

.

10



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 Draw back of IDMT relay


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.



EXPERIMENT NO.3

AIM: - TO STUDY THE OPERATION OF STATIC OVER VOLTAGE

RELAY

APPARATUS: -

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


7) Connecting wires

8) Experiment Kit

CIRCUIT DIAGRAM:-

v

OFF

ON

START

STOP

T

I

M

E

R

110V

DC11

+

12

-

(0-300V)

9

10

3

4

1-PH

230V,

50HZ,

SUPPLY

300 OHM,1.7A

STATIC OVER VOLTAGE RELAY

THEORY: -

1. Principle and operation of static over voltage relay.

2. Application of static over voltage relay.

PROCEDURE:-



1) Connect the ckt as shown in fig procedure is done & time is

noted.


3) Connect Auxiliary D.C. Supply (110) to pin 11 & 12 of relay and

pin no. 3&4 to the time interval meter.

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.

OBSERVATION TABLE: -

Sr.

No.

Time Knob

Position in

seconds.

Set

Voltage

105%=

Timer

time

Set

Voltage

130%=

Timer

time

Set

Voltage

155%=

Timer

time

1

2

.

.

10

RESULT: The static over-voltage relay is studied.

Viva Question

1 Application of over and under voltage relay.

2 Draw back of electromagnetic as compare to static relays relay


4 Range of under voltage relay



EXPERIMENT NO.4

AIM: - TO PLOT THE CHRACTERISTICS OF ELECTROMAGNETIC

IDMT RELAY (MODEL NO.ICM-21NP)

APPARATUS: -

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)


7) Experiment Kit

8) Connecting wires

CIRCUIT DIAGRAM :

A

(38 ohm,8.5A)

OFF

ON

110V

DC

230V

1-PH

50HZ

SUPPLY

(0-10A)

230V50HZ,

1-PH

SUPPLY

1

2

5

6

+3 - 4

S

T

O

P

START

T

I

M

E

R



THEORY: -

1) Construction and operation of Induction disc/ watt-metric type

electromagnetic Relays.

2) Time current characteristics equation

3) Derivation of torque produced.

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 OR CHARACTERISTICS TABLE: -

Sr.

No.

Fault current (A) PSM Timer time For

TSM =

Timer time

For TSM=

Timer time

For TSM=

1

2

.

.

.

10

RESULT:



For lower values of current the “time current ” characteristics are inverse and for

higher value for current observed times are constant.

Viva Question

1 Pickup, PSM and TSM

2 Draw back of IDMT relay

3 Derivation of Torque equation in detail

4 Detail of other Inverse type of relays

5 Why IDMT relay suitable for protection of long length of LV/MV TL.

6 Reset time and trip time

7 Why characteristics is plotted between PSM and operating time?



EXPERIMENT NO.5

AIM: - TO STUDY THE OPERATION OF STATIC DEFINITE TIME

REVERSE POWER RELAY (MODEL APDR-21)

APPARATUS: -

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 :

A

V

P

H

A

S

E

S

H

I

F

T

I

N

G

T

R

A

N

F

O

R

M

E

R

R R

Y

B

N N

(0-300V)

1 PHVARIAC

270V,

4A

R

E

L

A

Y

CT

7 8

11 3

12 4

PT

START

ST

O

P

1 PH

230V,

50HZ, AC

SUPPLY

R

Y

B

N

3 PH440V

AC

SUPPLY

(0-2A)

T

I

M

E

R



THEORY:

1. Describe the operating principle, constructional feature and area

of application of reverse power relay.

2. Draw simplified block diagram of static reverse power O/C relay.

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 circuits 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.


3) Switch on supply to 3phase dimmerstate and also D.C. supply to

relay.

4) By vaaarying 3 phase dimmerstate adjust the value of current .

5) Now keeping current at this val;ue constant change the angle of

phase shifting tranfofmer gradually.

6) Observe the tripping zone of reverse power relay.

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: -

Sr. No. Phase angle Φ Trip response

1 0°

2 30°

3 60°

- -

- -

- -

- Till 360°



Sr.No. Time setting in sec Trip time in sec

1 0

2 1

3 -

4 -

Till 10

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



EXPERIMENT NO: - 06

A) TO STUDY THE MAGNETISATION CHARACTERISTICS OF

C.T.

B) TO STUDY THE PROBLEM ASSOCIATED WITH C.T.

MAGNETISATION.

APPARATUS:-

1) Current transformer ( CT ) – 5/1 Amp

2) Ammeter :- ( 0-10 A)

3) Multimeter

4) Rheostat ( 38 ohm , 1.7 amp )

5) 1 phase Dimmerstate.

THEORY:-

Plot the excitation curve and explain

(i) From origin to ankle point

(ii) From ankle pt. to knee

(iii) Knee region

(iv) Saturation region

CIRCUIT DIAGRAM :

A

(O-1A)

V

1:5 A

CURRENTTRANSFORMER

(0-75V)

ORMULTIMETER

230V50HZ,

1PH,SUPPLY

300ohm,1.7A

O.

C.

PROCEDURE:-

(1) Make connections as shown

(2) Current is increased by 1 phase shown

(3) A certain value of current , measure voltage from

multimeter



(4) Again increase the value of current and note down voltage.

(5) Similar procedure is done and current is increased till the

saturation of C.T.

(6) Draw graph of current Vs voltage.

CONCLUSION :-

Magnetization curve of C.T. is studied. Ankle point, knee

point and saturation is observed.

Viva Question

1 Difference between protective CTs and measuring CTS

2 Why CT get saturate in differential protective scheme during external fault

3 Use of CTs in protection of any equipment

4 No. of CTs require for protection of transformer and generator and their

connection.



EXPERIMENT NO :- 07

AIM :- To plot the characteristics of Fuse wire

APPARATUS- 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:-

L

O

A

D

FUSE

DIMMERSTATE1PH

230V,8A

1PH

230V

50HZ,

SUPPLY

A

(0-15A)38 ohm,8.5A

THEORY: - 1) Detail theory and operation of fuses

2) Characteristics of Fuse

3) Types of Fuses

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 .

OBSERVATION:

Sr.No Current ( Amp) Time (Sec)

1

.

.

5

RESULT AND CONCLUSION :-

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



EXPERIEMNT NO:- 08

AIM :- TO STUDY DIRECTIONAL OVER CURRENT RELAY ( ACDR 11

HPD)

APPARATUS :-

1) ASHIDA make single pole directional O/C relay ACDR 11 HPD

2) Phase shifting transformer

3) Dimmerstat ( 3 phase , 440 volt, 50 Hz )

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:

A

(0-2A)

3-PH

SHIFTING

TRANSFO

RMER

R R

Y

B

NN 3 4

128

7

1615

110VDC+ -

TO TRIP

CIRCUIT

B

Y

R

3-PH

440V

50 HZ

AC

SUPPLY

PTCT

TIMER

1000ohm,1.2A

11



THEORY : -

1. Directional O/C relay

2. Directional relay connection

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.

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.


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.

OBSERRVATION TABLE :

Sr.

No.

Phase angle MTS = MAX torque setting

45 degree 60 Degree 9th

Line

1 0°

2 30°

3 60°

4 90°

5 120°

6 150°

7 180°

8 -150 degree till

9 0 degree



RESULT:- The static directional relay is studied and graph for different

maximum torque setting is drawn.

Viva Question

1 Application of Directional over current relay

2 Derivation of max. torque angle in directional O/C relay

3 Protection of ring main feeders

4 300, 60

0and 90

0 connection in directional relays



EXPERIMENT NO : 09 AIM :- TO STUDY AND PLOT THE CHARACTERISTICS OF

IMPEDANCE RELAY ( ABB-RAKZB)

APPARATUS :-

1) 3 Phase AC Autotransformer

2) Voltmeter (0-150 V)

3) Ammeter(0- 2 Amp)

4) Rheostat – ( 300 ohm , 1.7 Amp)

5) 3 Phase Impedance Relay

6) Phase shifting Transformer

7) 1 Phase Variac / DIMMERSTAT

8) Auxiliary DC Supply

CIRCUIT DIAGRAM :

3PH

DIMMERSTAT

IMPEDANCE

RELAYV (0-75V)

Ru

Su

Tu

O/P

+

1

-

18

A

(0-2A)

R

N

O/P

PHASE

SHIFTINGTRANSFORMER

R

Y

B

3 PH440V

50 HZ,AC

SUPPLY

3 PH

440V50 HZ,

ACSUPPLY

S1 S1

1000 ohm,1.7A

N



THEORY :

1) Explain Unit and non –unit protection with examples

2) Explain characteristics of different distances relay on R-X diagram

3) Explain static impedance relay with amplitude and phase comparator.

4) Advantages of static relay over electromechanical relay.

PROCEDURE :

1) Make the connections as shown in the circuit diagram.

2) Keep the rheostat in the middle position.

3) Switch on the supply to the phase shifter and also the DC supply.

4) Now reduce the voltage of the autotransformer, note the voltages at

which the relay operates.

5) Change the position of phase shifter & repeat the steps 4,5,6.

6) After taking no of readings change the value of current and repeat

the above steps.

7) Note down the pickup impedance value of the relay.

8) Plot the operating and non-operating region of relay on R-X plane.

NOTE :- The output voltage of phase shifter is set at 110V and the voltage

output from the auto transformer is also 100 V maximum

permissible value .

OBSERVATION TABLE:

For A=20, B=6, Ia= 01 Amp

Sr No. Phase Angle( θ) Voltage ( V)

1) 0 degree

2) 30 degree

3) 60 degree

4) 90 degree

5) 120 degree

6) 150 degree

7) :

8) :

9) 360 degree

10) 0 degree



Same table for A =40, B= 8, Ia =0.5 Amp

Sr.

/ No.

I (Amp) Voltage (V) volts

1 0.1

2 0.2

3 0.3

4 0.4

5 0.5

6 0.6

7 0.7

8 0.8

9 0.9

10 1.0

RESULT :-

The relay operates for any value of the radius less than the radius of

the circle, hence the operating region of the relay inside the

circle.

Viva Questions:

1 Torque equation of Reactance and mho relay with their characteristics.

2 Effect of arc resistance in distance relay

3 Selection of distance relay.

4 Effect of power swing in distance relay



EXPERIMENT NO : 10

AIM :- TO STUDY TRANSFORMER DIFFERENTIAL PROTECTION

APPARATUS :-

1) Static Differential Relay (Model No. ACDF 31 HA)

2) 1 Ph Dimmerstat 230V, 10 A

3) 2 CT (10/ 5A and 20/5A)

4) Ammeter AC (0- 15 A) …3 No.

5) Ammeter AC (0- 5 A) …2 No.

6) Rheostat (38 ohm, 8.5 A)

7) Loading Rheostat

8) Multimeter

9) 1 ph Transformer 230/115 V, 50 Hz, 1 KVA

10) Connecting wires

CIRCUIT DIAGRAM :

A A

AA

A

LOAD

110V DC

7

27

8

28

1PH230

50 HZA.C.

SUPPLY

(0-15A)

(0-15A)

(0-5A)

(0-20A)

(0-5A)

ML

L

M

38ohm, 8.5A

- 16+15

THEORY: -

1. Differential protection theory



2. 1ph and 3 ph Transformer differential protection scheme

3. Difference between Transformer and generator Differential

protection.

PROCEDURE: -

1) Make circuit connection as shown in ckt. Diagram.

2) Open the parallel path of secondary transformer containg rheostat with

ammeter. Transformer is connected now at full load condition.

3) With the help of dimmerstat, give some supply voltage to primary side

of transformer and observe its current. Make sure secondary current is

varying in proportion to turn ratio. And current through secondary side

of two CTs are zero.

4) Now connect the parallel path of secondary transformer by touching

wire to the secondary terminal of transformer and observe the current

through secondary side of two CTs. There is a difference of two CTs

currents and at this condition differential relay will trip.

5) Note down values of these currents through secondary side of two CTs

6) Plot the characteristics between summation and difference of these two

currents.

OBSERVATION

Sr.

No.

Secondary

current of CT=

i1(A)

Secondary

current of CT=

i2(A)

Restraining

Torque=

(i1(A) + i2(A))/2

Operating

Torque=

i1(A) - i2(A)

1

2

.

5

RESULT- Transformer differential relay is studied. The characteristics between

restraining and operating torque are straight line.

Viva question:

1 Why ratio of two Cts is different?

2 Circuit connection of 3 phase Y ∆ transformer

3 Explain biased differential relay

4 Types of fault occur in transformer

5 No. of CTs require and their connection for protection of 3 phase

transformer



EXPERIMENT NO : 11

AIM- To study unrestricted earth fault relays.

APPARATUS- 1) Static IDMT earth fault relays ( Model No. APR 41 )

2) Rheostat ( 100 ohm, 5 A)…….3 Nos.

3) Ammeter AC ( 0- 5A)…….3 Nos.

4) Ammeter AC ( 0- 1A)

5) Experimental kit

6) Aux. DC supply- 110 V DC

7) Timer

8) 3 ph Dimmerstat

9) Connecting wires

CIRCUIT DIAGRAM

+ -

110V DC

TIM

ER

ON OFF

3P

H

D

IM

ME

RST

AT

A

A

AR

Y

B

3 - PH

AC

SUPPLY

440V,50 HZ

(0-5A)

(0-5A)

(0-5A)

N

I/P O/P

100ohm,5A

100ohm,5A100ohm,5A

3

4

11 12

STARTSTOP

1 phsupply



THEORY- 1) Unrestricted and restricted earth fault relays with ckt

connection

2) Their application.

PROCEDURE- 1) Connect the circuit as shown in figure.


2) Give 3 ph. Supply to stat connected rheostat (load)

3) balance the load by making all three phase currents equal

in magnitude.

4) Create a fault by short circuiting some of the winding of a

single phase load.

5) Note down fault current and take corresponding time for

tripping relay by resetting relay and timer by switching

off without disturbing dimmerstat position.

6) Repeat same procedure with different fault current and

plot characteristics between PSM and operating

time

OBSERVATION TABLE: Relay current Setting -

TMS -

Sr. No. Fault Current (A) Timer time( Sec)

RESULT: The unrestricted earth fault relay is studied

Viva question:

1 Application of earth fault relay.

2 Importance of high impedance connected between neutral to ground

3 Difference between setting of earth fault and phase fault relays

G. H. RAISONI COLLEGE OF ENGINEERING DEPARTMENT …ghrce.raisoni.net/download/sgp_expts.pdf · G....

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