Why Might High Speed Trip Relays Malfunction in Bus Bar Protection Schemes?

[m.s.j]

In a bus bar protection scheme applied for a double bus high voltage substation, protection systems design group have chosen high speed trip relay with operation time equal to 4 ms and a 2.5W DC bobbin; because they want to decrease the thermal stresses on output contacts of protection relays. As you know in high impedance bus bar protection scheme they must start several trip relays in bus bar faulty conditions simultantinusly.Therfore, dc circuit currents specially the circuits that involve to protective relays, must be considered carefully in detail design step.
But in practice they met some mal-operation of trip relay in pre-commissioning stage. According to pre-commissioning reports,
mal-operation had been accompanied with a DC battery system alarm for Earth leakage.
Can you explain the reason of that mal-operation?

BEST REGARDS
MSJ


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[anorlunda]

There is not enough information provided to explain that malfunction. There could be damaged insulation in the wires. We just can't tell.

The malfunction is not necessarily related to the double bus high voltage substation protection application.