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Sympathetic Tripping
Are solidly grounded MV (11KV) feeders susceptible to sympathetic tripping?

I am aware that sympathetic tripping occurs in resistance grounded systems where a feeder trips due to an earth fault occurring on another feeder.

Does the phenomenon apply to solidly grounded MV feeders also?

I have read an old post: "earth fault protection settings for an 11kV feeder," https://control.com/thread/1242974574. This is a very old post but quite relevant to me at this point.

Would anyone please come to the rescue?

By PC Load Letter on 2 October, 2019 - 2:18 pm

Hi,

There is not much info to answer your question correctly. I will keep it brief - yes if the OC settings are not properly cordinated then yes, let it be solidly earthed or high impedance earthed system it will cause unwanted tripping.

Couple of examples

1. Improperly cordinated OC/EF relays can cause tripping of upstream relays while the downstream needs to trip first and clear the fault.

2. Improper time settings with OC/EF setting can cause severe voltage dips in the bus. If the bus or feeder has a voltage element which will act before the fault is cleared then the adjacent feeders will trip as well on UV (not on OC unless there is a generator in that particular feeder).

It’s a lot easier if you can provide a SLD of your system and give a idea of the protections in place so that we can give a better answer.

Alright bye bye for now.

Many thanks for your response.

I am aware that lack of co-ordination between upstream and downstream feeders but that wasn't what I was referring to in my question.

The circuit on page 9 of this link https://www.littelfuse.com/~/media/protection-relays/presentations/littelfuse_protectionrelays_ground_fault_protection_for_vfds.pdf is was I was referring to.

I would have posted the diagram here instead of the link but I don't know how to.

Thanks once again.