Transformer Protection on a 1+ Substation
Transformer Protection on a 1+ Substation
(OP)
We designed a 1½ substation in a 230 MW Power Plant. It has three line outputs and three transformer inputs from the power plant. Due to budget restrictions each of the transformer inputs have two transformers instead of one and they are not in paralel. Each transformer have three generating units connected and they are joined in a HV busbar before being connected to the 1½ connection.
Each transformer has diferential and overcurrent protection connected from the CT's on the transformer and the LV circuit breaker.
What do you recommend that I connect as protection in order to protect the HV side between the transformer and the HV circuit breaker? Please be aware that two of the lines coming to the substation have impedance protection and the second zones are set to operate at 0.4 seconds, which make an overcurrent directional relay a problem due to coordination time between the 67 relay, the second zone distant relays and the transformer diferential and overcurrent relays...
Each transformer has diferential and overcurrent protection connected from the CT's on the transformer and the LV circuit breaker.
What do you recommend that I connect as protection in order to protect the HV side between the transformer and the HV circuit breaker? Please be aware that two of the lines coming to the substation have impedance protection and the second zones are set to operate at 0.4 seconds, which make an overcurrent directional relay a problem due to coordination time between the 67 relay, the second zone distant relays and the transformer diferential and overcurrent relays...






RE: Transformer Protection on a 1+ Substation
Please, clarify "...which make an overcurrent directional relay a problem due to coordination time between the 67 relay,..." while keeping in mind that ANSI Device No. 67 is AC Directional Overcurrent Relay.
RE: Transformer Protection on a 1+ Substation
As I first thought, I´m planing on a 67 directional overcurrent relay with a time dfinite curve. So, the 21 relays (2nd zone relay)on the far terminals should be set at 0.6 sec., the 67 relay at 0.3 sec. and of course the transformer differential relay instantaneous.
What I wanted was another kind of protecction instead of the 67 relay in order to lower the time of the 21 relays.
RE: Transformer Protection on a 1+ Substation
RE: Transformer Protection on a 1+ Substation