MCAG14 Restricted Earth Fault Tripping
MCAG14 Restricted Earth Fault Tripping
(OP)
Hi Guys,
Please could you help with any suggestions.
I got a 1000kVA 11KV dry cast resin transformer with two LV panels connected to it. It has a MCAG14 on the interconnecting LV panel but also seems to have a set of CT's connect to the other LV panel, The REF tripped around a year ago which in return activated the shunt trip on the transformer. The transformer was reset and the REF was fine for a few month and then tripped again, this tripping became more frequent. The only way to prevent the REF from tripping now is to set the REF relay from 0.025-0.1A TO 0.1-0.4A, CT ratio is 400/5. Could this tripping be down to the adjustable stabilizing resistor, There is a large data lab being fed off of the system. Could it be seeing an external earth fault due to the stabilizing resistor or due to a problem with the neutral CT.? Ps It has a test block allowing access to CT'S and Relay.
Im new to REF so your help will be much appreciated. Thanks
Please could you help with any suggestions.
I got a 1000kVA 11KV dry cast resin transformer with two LV panels connected to it. It has a MCAG14 on the interconnecting LV panel but also seems to have a set of CT's connect to the other LV panel, The REF tripped around a year ago which in return activated the shunt trip on the transformer. The transformer was reset and the REF was fine for a few month and then tripped again, this tripping became more frequent. The only way to prevent the REF from tripping now is to set the REF relay from 0.025-0.1A TO 0.1-0.4A, CT ratio is 400/5. Could this tripping be down to the adjustable stabilizing resistor, There is a large data lab being fed off of the system. Could it be seeing an external earth fault due to the stabilizing resistor or due to a problem with the neutral CT.? Ps It has a test block allowing access to CT'S and Relay.
Im new to REF so your help will be much appreciated. Thanks






RE: MCAG14 Restricted Earth Fault Tripping
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If we learn from our mistakes I'm getting a great education!
RE: MCAG14 Restricted Earth Fault Tripping
I am not overly familiar with this type of relay, but did the trips occur during a storm or other simular occurance? Perhaps a neutral to ground connection? Also, when was the last time this relay was tested? If this is an older building, a degraded grounding network can also cause issues.
RE: MCAG14 Restricted Earth Fault Tripping
RE: MCAG14 Restricted Earth Fault Tripping
Anecdote: I set one of these schemes that had the same problem. The three-line diagram and single-line diagrams for the project corroborated and showed the correct CT neutral polarity (towards ground) but in the field it was the opposite and the commissioning guys missed it. It finally mis-operated on feeder single-phase switching, which looked like an in-zone ground fault to the relay. Very embarrassing, especially considering that our commissioning department was responsible.
RE: MCAG14 Restricted Earth Fault Tripping
RE: MCAG14 Restricted Earth Fault Tripping
At my current position our commissioning guys are very good, and they use Primary Injection and probably a couple other methods I'm not familiar with.
RE: MCAG14 Restricted Earth Fault Tripping
Forcing current through the neutral CT can be done using judicious opening of the HV earthing switches. If you're in a power plant and can get access to the pilot exciter or the firing control circuit of a static exciter then the generator itself makes a great injection source.
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If we learn from our mistakes I'm getting a great education!