Criteria For Selection of resistors in Trip Circuit Supervision Relays: In Trip Circuit Supervision Relays, the Selection of Resistors should should met the Following Criteria, Requirement:
1) During PreClose , two coils should be picked up . while Post Close , only one coil should be Picked. 2) According to TCS Relay (Areva) ,Maximum Trip circuit Supervision current should not Exceed 20mA. 3) Minimum Pickup Voltage For TCS Relay coils(RL2 , RL3) = 16.80 V (From SAT Values) Suppose,. i)
if we Select very less Resistance it will exceed the maximum Trip Circuit supervision Current
ii)
if we select very High resistance, During preclose Condition, Relay coil will not pick up and thus Supervision is not possible.
Results:
Resistors
500 ohms
4000 ohms
8000 ohms
Maximum Trip circuit supervision Current (mA) Minimum Voltage Across TCS coil (V)
24
13.62
9.1
45.15
24.85
16.5
Conclusion: Selection of the Resistor Values should be in such a way that it should balance the above two criterias. Thus 4000 ohms resistor is a better value.
Example: Default condition:
We are selecting 4000 ohms resistor across each coil of TCS relay, The resistance of the coil (RL2) = 3570 ohms. The resistance of the coil (RL3) = 3550 ohms. The Ext. resistance of the coil (RL2) = 4000 ohms. The Ext. resistance of the coil (RL3) = 4000 ohms. Breaker Trip coil Resistance = 525 ohms 1) During Preclose condition , Coil RL2 , RL3 gets Picked up . thus the total current flowing through the Circuit = 110/(3570+4000+3550+4000+525) =110/15645 = 7mA In this Condition, i) voltage developed across RL2 coil = 7mA * 3570 oh ms = 25 Volts ii) voltage developed across EXt . Resist for RL2 coil = 7mA * 4000 ohms = 28 Volts iii) voltage developed across RL3 coil = 7mA * 3550 oh ms = 24.85 Volts iv) voltage developed across EXt . Resist for RL3 coil = 7mA * 4000 ohms = 28 Volts V) voltage developed across the Breaker Trip Coil is = 7mA * 525 ohms = 3.675 Volts
2) During Post close condition , Only Coil RL3 gets Picked thus the total current flowing through the Circuit = 110/(3550+4000+525) =110/8075 = 13.62mA In this situation, i)
voltage developed across RL2 coil = 13.62mA * 3570 ohms = 48.62 Volts
ii) voltage developed across EXt . Resist for RL2 coil = 13. 62 mA * 4000 ohms = 54.48 Volts iii) voltage developed across the Breaker Trip Coil is = 13.62mA * 525 ohms = 7.15 Volts
Condition 1: Suppose, instead of 4000 ohms , if We select 8000 ohms resistor across each coil of TCS rel ay: The resistance of the coil (RL2) = 3570 ohms. The resistance of the coil (RL3) = 3550 ohms. The Ext. resistance of the coil (RL2) = 8000 ohms. The Ext. resistance of the coil (RL3) = 8000 ohms. Breaker Trip coil Resistance = 525 ohms 1) During Preclose condition , Coil RL2 , RL3 gets Picked up Thus the total current flowing through the Circuit = 110/(3570+8000+3550+8000+525) =110/23645 = 4.65 mA In this Condition, i) voltage developed across RL2 coil = 4.65mA * 3570 ohms = 16.60 Volts
ii) voltage developed across EXt . Resist for RL2 coil = 4.65mA * 8000 ohms = 37.2 Volts iii) voltage developed across RL3 coil = 4.65mA * 3550 ohms = 16.5 Volts iv) voltage developed across EXt . Resist for RL3 coil = 4.65mA * 8000 ohms = 37.2 Volts V) voltage developed across the Breaker Trip Coil is = 4.65 mA * 525 ohms = 2.4 Volts
2) During Postclose condition ,
Only Coil RL3 gets Picked up Thus the total current flowing through the Circuit = 110/(3550+8000+525) =110/12075 = 9.1mA In this Condition, i) voltage developed across RL2 coil = 9.1mA * 3570 o hms = 32.52 Volts ii) voltage developed across EXt . Resist for RL2 coil = 9. 1 mA * 8000 ohms = 72.8 Volts V) voltage developed across the Breaker Trip Coil is = 9.1mA * 525 ohms = 4.7 Volts In this situation During Preclose Condition the developed voltage across the Relay coil is not sufficient to pick up the relay. since the Minimum required volage to pick up the relay is 16.8 Volts Whereas, Developed voltage across the coil during preclose condition is only 16.5V
Condition 2: Suppose , if We select 500 ohms resistor across each coil of TCS relay: The resistance of the coil (RL2) = 3570 ohms. The resistance of the coil (RL3) = 3550 ohms. The Ext. resistance of the coil (RL2) = 500 ohms. The Ext. resistance of the coil (RL3) = 500 ohms. Breaker Trip coil Resistance = 525 ohms 1) During Preclose condition , Coil RL2 , RL3 gets Picked up .
Thus the total current flowing through the Circuit = 110/(3570+500+3550+500+525) =110/8645 = 12.72 mA In this Condition, i) voltage developed across RL2 coil = 12.72 mA * 357 0 ohms = 45.41 Volts ii) voltage developed across EXt . Resist for RL2 coil = 12.72mA * 500 ohms = 6.36Volts iii) voltage developed across RL3 coil = 12.72 mA * 3550 ohms = 45.15 Volts iv) voltage developed across EXt . Resist for RL3 coil = 12.72mA * 500 ohms = 6.36 Volts V) voltage developed across the Breaker Trip Coil is = 12.72 mA * 525 ohms = 6.678 Volts
2) During Postclose condition ,
Only Coil RL3 gets Picked up. Thus the total current flowing through the Circuit = 110/(3550+500+525) =110/4575 = 24 mA In this situation, i) voltage developed across RL2 coil = 24mA * 3570 oh ms = 85.68 Volts ii) voltage developed across EXt . Resist for RL2 coil = 24 mA * 500 ohms = 12 Volts iii) voltage developed across the Breaker Trip Coil is = 24mA * 525 ohms = 12.6 Volts According to TCS Relay (Areva), Maximum Trip circuit Supervision current should be less than 20mA. Whereas, During Post Close Condition we are exceeding the Maximum Limit.
