Recent content by nkn5

thanks David. transformer has its own differential protection and over current as backup at the unit substation. As you rightly mentioned, there are two more similar cables from the Primary station feeding to receiving unit station with transformers. Attached a oneline diagram. Each of the...

thank you. I got this now. Since there are no generally acceptable standards, there are no UL listing for certain products.

Hello all, I have a case where a long underground cable to be protected by step distance protection. This cable feeds a unit substation with a power transformer which effectively falls in zone-2 of the cable to be protected by distance protection. I would like to understand if zone-2 and...

thanks for your responses. I could see UL requirements defined in their white book for some voltages above 34.5KV. Also for example, see this link...

Hello, I have a requirement from my client to have all equipment in a 69KV outdoor Switch-yard be UL listed. However, I coudln't find any outdoor products in the market with an UL or Recognized UL mark. Some of the vendors I contacted, said they cant supply. I'm bit confused if really UL...

Thankyou Skogsgurra and Waross!! You just taught me phase sequence detection using open delta PT. I will study more about it to get my own understanding. We are now testing the motor uncoupled from the pump for bump testing. So I wouldn't worry much even if the motor run reverse for a few...

Hello, The phase shift by transformers shouldn't be a problem as the generators would be synchronizing to the voltage on your 400V bus. Is is just than the generators will be running 300 lagging from that of utility which is corrected by the transformers (assuming dYN11). If you're still...

Hello, I have case to troubleshoot. We have two identical motors following attached schematic. The controller has an indication of 'phase reversal' probably comparing with what is defined in factory as correct. This indication makes the motor / pump unavailable for a remote start. We are...

Hello, Could you please share your experiences on primary injection tests for circuit breaker of high current ratings (say 1600 to 5000 Amps) with integral trip units. I can't see many commercially available test equipment capable of supplying the level of currents. Needless to say, true...

Hello all, Thanks for your inputs. Those are helpful. Sorry for coming back lately. Anyway, below is the reply we received from Manufacturer. "By making the proposed modification, the direction of rotation should remain the same, if line 1 supply is connected to U2 instead of U1 and so forth...

Thanks for inputs. @ ScottyUK: Well, I'm also concerned about the warranty issue. We are trying to contact the manufacturer. Also there are no CTs on the motor end, they are only on the switch-gear end. @ Skogsgurra: In this case, the motors are to be started on full voltage. No VFDs. If the...

Hello, We have case from construction site, where the cable is glanded incorrectly on the star point terminal box instead of main terminal box on the other side of a medium voltage star connected motor. It is difficult now to get the extra length of the cable required to re-route, we started to...

waross, Yes, It can be borrowed. I am considering that option vs a proposal to buy one for ourselves. But leaving the existing grounding set on line is not possible, the gas-turbine generator breaker would be 'open'ed when it is not in operation. So the impedance grounding at the star point is...

Yes it exists. Two reasons I know, 1. To reduce the fault current on the other side transformers. Say if you are wiring to distribution boards for light fixtures etc. 2. Your question. To correct the voltage if required.

davidbeach, I'm concerned if a unlikely ground fault on 11kV side will damage the transformer core if solidly grounded. The LV generator-transformer unit is anyway grounded at the generator (solid grounding). My question is about the 11kV part of the network. While I could ground the on HV...