380KV HYUNDAI 380KV CB TRIPPING CIRCUIT PROBLEM
During trip the breaker from trip relay (LOR) Pole Discrepancy Stage-1 was operated.
After investigation the following point were observed.
1.The overall trip circuit length more than 300 mts.
2.The resistance of the circuit loop 14 ohms. ( Resistance measurement refer drawing)
3. Resistance of trip coil unit ( Coil + Stabilizing resistance + Capacitor ) 40 ohms.
4. Trip circuit cable size 2.5 Sqmm.
5. Trip circuit voltage used 127 dc.
As per stranded minimum operating voltage of trip coil is 70 v dc.
Due to more loop resistance and coil resistance voltage drop was more in the trip circuit. So during tripping operation ( by operating last lockout of the circuit) trip coil not getting enough voltage to trip the breaker and PD operated immediately ( Pole Discrepancy Stage-1 lock out relay very near to the trip coil).
We are decided to reduce the loop resistance of the trip circuit by increasing the cable size upto 12 Sq.mm. ( ( 2 x 6Sq.mm).
The loop resistance was reduced upto 8 to 9 ohms from 14 ohms and circuit was worked properly.
But this is the temporary solution and permanent solution is reduce the trip coil unit resistance from 40 ohms to below 20 ohms.
During trip the breaker from trip relay (LOR) Pole Discrepancy Stage-1 was operated.
After investigation the following point were observed.
1.The overall trip circuit length more than 300 mts.
2.The resistance of the circuit loop 14 ohms. ( Resistance measurement refer drawing)
3. Resistance of trip coil unit ( Coil + Stabilizing resistance + Capacitor ) 40 ohms.
4. Trip circuit cable size 2.5 Sqmm.
5. Trip circuit voltage used 127 dc.
As per stranded minimum operating voltage of trip coil is 70 v dc.
Due to more loop resistance and coil resistance voltage drop was more in the trip circuit. So during tripping operation ( by operating last lockout of the circuit) trip coil not getting enough voltage to trip the breaker and PD operated immediately ( Pole Discrepancy Stage-1 lock out relay very near to the trip coil).
We are decided to reduce the loop resistance of the trip circuit by increasing the cable size upto 12 Sq.mm. ( ( 2 x 6Sq.mm).
The loop resistance was reduced upto 8 to 9 ohms from 14 ohms and circuit was worked properly.
But this is the temporary solution and permanent solution is reduce the trip coil unit resistance from 40 ohms to below 20 ohms.
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