EXPERIMENT 8

AIM: 1) To plot characteristics of % biased differential relay

PROCEDURE:

1) Make the wiring sequence as per the wiring schedule. Keep both the dimmers at

minimum position (CCW)

2) Ensure that ‘Bypass Switch’ on EMT-39 panel is at ‘OFF’ position i.e RHS side.

3) Differential relay we are using is a three phase relay indicating three phases as R, Y and

B. while performing experiment we are using only one phase say ‘R’ phase.

4) Relay setting: now switch on auxiliary supply for Differential relay by making ON 4A

MCB ar EMT 16A. press Menu key you will observe two options i.e View and Edit.

Press 2 key for edit, it will ask for password. Press ‘1234’ and press enter, it will show

accepted. The options in the edit modes are Group1, Group2, Active group, clock, LCD

and reset. Select Group1 by pressing 1. Now setting corresponding to Group1 are

displayed. Now enter the following setting in for group1 by using numeric keys and enter

key.

Pickup(ik) = 0.2 pu, slope1 = 20%, slope2 =50%, Breakpoint(kp)=1pu, Diff. Hiset =00

pu, CTR(W1)=1pu, CTR(W2)=1pu, Inrush(2f)=00%, over excitation(5f)=00%, Vector

group=Dd0. after entering above parameters press reset on relay

5) Now switch on AC supply by making both the MCB ON at EMT16A.

6) Now press start push buttons PB1 on both EMT39/1 and 2 simultaneoulsy to switch ON

the protection circuit and contactor.

7) Now slowly increase the dimmer on both the panels EMT23/1 and EMT23/2

simultaneously observing on EMT39/1 and EMT39/2, adjust both to 1A.

8) Now keeping secondary current I2 constant(on EMT39/2), i.e 1A , increase primary

current I1 (on EMT39/1) until the relay trips. Note down this I1, reading in the

observation table.

9) To take other set of readings press reset button, change slope1 =40% , press start push

buttons, increase primary current until relay trips.

10) Now take various readings of I1 for different relay settings of slope1 (DF1) as given in

the observation table.

11) Calculate the differential current Id=I1-I2 and restraining current Ir=(I1+I2)/2 as given in

the table.

12) Now calculate slope1 (df1) from formula: DF1 =(Id-ik)/(Ir-ik/2) *100 where ik=0.2pu =

1A.

13) The same experiment may be repeated for the other two phases.

Table 5.1 Observation Table for differential relay %bias characteristics

Sr.no % Bias

Slope1

(DF1)

setting

I2 on

EMT39/2

(A)

I1 on

EMT39/1

(A)

Differential

current

Id=|I1-I2|

Restraining

Current

Ir=(I1+I2)/2

Calculated

% bias

using

formula

1 20 1A

2 40 1A

3 60 1A

4 80 1A

5 100 1A

Note: The PSM being a ratio of fault(secondary) current to relay coil current setting, it is

difficult to adjust fault current such that it is an integer as before you can set current to

any 15A by rotating knob of variac, the relay would have tripped. Hence, before pressing

start push button, rotate knob clockwise approximately. Note down the fault current

quickly. Correct the knob position again, repeat the step so as to achieve match.

Obviously PSM will be a real number and not integer.

CONCLUSION:

AIM: 2) Pick up test for differential relay

Block diagram for differential relay pick up test

Circuit diagram for Differential Relay pick up test

Writing sequence

No. From To No. From To

1 EM16A(9) EMT23/1(1) 2 EMT16A(10) EMT23A/1(3)

3 EMT23A/1(6) EMT23A/1(9) 4 EMT23A/1(8) EMT23A/1(11)

5 EMT23A/1(14) EMT39/1(1) 6 EMT23A/1(16) EMT39/1(2)

7 EMT 39/1(3) EMT47(1) 8 EMT39/1(4) EMT47(2)

9 EMT 39/1(5) EMT47(21) 10 EMT39/1(6) EMT47(22)

PROCEDURE:

1) Make the writing sequence as per wiring schedule. Keep dimmer on EMT23A/1 at

minimum position(CCW).

2) Ensure that ‘Bypass switch’ on EMT39 panel is at ‘OFF’

Position i.e. RHS side.

3)Differential relay we are using is a three phase relay indicating three phase phases as

R,Y and B.While performing experiment we are using only one phase say ‘R’ phase.

4) Relay Settings: now switch on auxiliary supply for Differential relay by making ON

4A MCB as EMT16A.

Press Menu key you will observe two options i.e. View & Edit. Press 2 key for edit, it

will ask for password. Press ‘1234’ & press enter, it will show accepted. The options in

edit modes are Group1, Group2, Active group, clock, LCD & reset. Select Group1 by

pressing 1. Now setting corresponding to group1 are displayed. Now enter the following

setting in for group1 by using numeric keys & enter key.

Pickup(ik)=0.2pu, slope1=40%, slope2=80%,Breakpoint(kp)=1pu,

Diff. Hiset=0pu, CTR(W2)=1pu, Inrush(2f)= 0pu,

Over excitation(5f)=0 %,vector group= Dd0.

5)Now switch on AC supply by making both MCB ON at EMT16A.

6)Now press start push button PB1 on EMT39/1 to switch ON the protection circuit &

contactor.

7)Now slowly increase the dimmer on panel ENT23/1 observing on EMT39/1 increase

until relay trips. Note down this pick up current reading in observation table.

8)To take other set of readings press reset button on relay.

9)Now change the pickup value as per the table given blow and note down readings of

pickup current.

10) The same experiment may be repeated for other two phases also.

Observation Table for Pick up test

Sr. No. Pickup setting(ik) (pu) Observed Pick up

current(A) Pu setting % of 5A(relay Rating)

1 0.2 20% 1A

2 0.4 40% 2A

3 0.6 60% 3A

4 0.8 80% 4A

5 1.0 100% 5A

Conclusion:

Aim: 3) Transformer protection using differential relay for in

zone trip faults.

Fig. Block diagram for transformer protection using differential relay:

Fig. Circuit diagram for transformer protection using differential relay:

PROCEDURE:

1) Make the wiring sequence as per wiring schedule. Observe the table of wiring

for Xmer & CTs.

Sr no Resource Primary side Secondary side Specs.

1 Transform

er

Star with neutral

NC Delta

1KVA

415V/230V AC

Star/Delta

2 CT 6nos.

In series with each

transformer

winding primary

and secondary

Each star

connected for relay

interface. 3

primary side CTs

& 3 Secondary

side CTs

5/5 Amps each

transformer 6nos.

Note: Trip contact from % differential relay is NO type must be converted to NC

type by using EMT39 panel before it can be used to trip EMT1 which is acting like zone

circuit breaker.

2) Differential relay we are using is a three phase numerical relay indicating three

phases as R, Y and B.

3) Relay setting: Now switch on auxiliary supply for Differential relay by making

ON 4A MCB at EMT16A. Press Menu key you will observe two options i.e. View &

Edit. Press 2 key for edit, it will ask for password. Press '1234' & press enter, it will show

accepted. The options in edit modes are Group1, Group2, Active group, clock, LCD &

reset. Select Group1 by pressing 1. Now setting corresponding to group1 are displayed.

Now enter following setting in for group1 by using numeric keys & enter key.

Pickup (ik) = 0.2pu, slope l (DF1) = 40%, slope2 (DF2) = 80%, Brkpt (kp) = 1pu,

Diff. Hiset = 00pu, CTR (W1) = 2pu, CTR (W2) = 1.12pu, Inrush (2f) = 00%, over

excitation (5f) = 00%, Vector group = Yd 1.

After entering all above parameters come out of edit mode and press reset key on

relay.

4) Keep load selection switch on EMT-42A at 1259 position & on EMT14B at

OFF 7 position.

5) Keep ‘Bypass switch’ on EMT-39 Panel at ‘ON’ position Le. LHS Side.

6) Now switch on AC supply by making 4A MCB ON at EMT16A.

7) Now press starts push buttons PB1 on EMT39 first & then on EMT1 to sw1tch

ON the protection circuit, contactor & 3O supply.

8) Observe the LED’s on Relay. If ‘l>Dif. TRIP’ LED is ON then press res& push

button on keypad. If all the LED’s except AUX. Supply on LED are OFF no need to

press res& push button.

9) Now keep ‘Bypass switch’ on EMT-39 Panel at ‘OFF’ position i.e. RHS side.

10) Now to create a fault of LL on primary side connect resistor on EMT14B to

transformer primary (EMT49) 'side between R & Y phases keeping resistance selection

switch on EMT14B at OFF position.

11) Now put the resistor selector switch on EMT14B at 7509 position & then on

6009 position and note that the relay will trip. Note down the resistance value from

EMT14B and % of primary (lp) & secondary (Is) current from relay display in

observation table.

12) Press rest button on relay panel.

13) Now to create LN fault on primary side remove previous connection of

EMT14B‘& connect resistor from EMT14B between R & N of primary of transformer

EMT49 keeping selector switch on EMT14B at OFF position.

14) Now press start push buttons PB1 on EMT39 first & then on EMT1 to switch

ON the protection circuit, contactor & 3% supply.

15) Now put the resistor selector switch on EMT14B at 7509 position, then on

6009, then on 3009, & 212$) position and note that the relay will trip. Note down the

resistance value from EMT14B and % of primary (1p) & secondary (Is) current from

relay display in observation table.

16) Press res& button on relay front keypads.

17) Similarly to create fault of LL on secondary side, remove previous connection

of EMT14B & connect resistor from EMT14B to secondary side of transformer (EMT49)

between R-Y phases keeping selector switch at OFF position.

18) Now press starts push buttons PB1 on EMT39 first & then on EMT1 to switch

ON the protection circuit, contactor & 3O supply.

19) Now put the resistor selector switch on EMT14B at 750Ω position, then on

600Ω, then on 300Ω, 212Ω and 162Ω position and note that the relay will trip. Note

down the resistance value from EMT14B and % of primary (Ip) a secondary (Is) current

from relay display in observation table.

Faults

Name

Fault side (EMT

49)

Shorting

resistance value

(EMT14B)

Primary current

(Ip) %

Secondary

current (Is) %

LL (R-Y) Primary side

LN (R-N) Primary side

LL (R-Y) Secondary side

CONCLUSION: