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Hi, Want to get some advices on HV transformer connection type. I see two different transformer connections in 2 different projects which are just nearby. One is having a YY transformer (110kV), another one has a DY transformer (66kV). I'm not sure why the design is such different given a...

Hi, Following the recent earthquake happened in Myanmar, a question comes to mind about seismic design. Thailand is not considered as a seismic region. However, the Myanmar earthquake extends to Thailand, even to Bangkok which seems to be very far away from Myanmar, causing severe damage there...

Hi Scotty, The 2 UPS are synchronized. So in that case with the said setup, there may be a chance of multiple switching where there is, say, an inverter fault, which is not desirable? Thx

Thx Che Kuan. Therefore you think the reason why the that final circuit MCB is not included in the calculation is mainly becoz it is already checked against the manufacturer's table?

That's why i'm not sure how a fault scenario analysis can be done for this kind of fault, and wonder how normal it's being done, and want some advice here from any expert.

Understood Thx. I saw a few discrimination studies that ignored the final circuit MCBs in the calculation, but just calculate up to the upstream of the final circuits. I'm not sure why is that so I guess it may be up to a certain ratio of upstream to downstream rating would imply discrimination...

Thanks. But what I mean is phase to phase short circuit of the 2 different sources at the ATS. Do I need to do this calculation as well?

Do I need to do any fault scenario analysis of two power sources short circuit at the ATS?

When I do a fault discrimination analysis, if I have a final circuit of 32A 1ph MCB with an immediate 400A 3ph upstream MCCB, do I still need to detail check the discrimination, or, from the ratings of the upstream and downstream breakers I can already told discrimination is achieved?

Noted and thanks waross and che12345. I just wonder if a setting of higher than 0.2s is possible, given a fixed installation 5s disconnection time would comply with IEE?

Thanks Che Kuan. It's an original aim not to install any RCD at the downstream 32A MCB circuits to avoid any accidental tripping to the circuits. I'm just wondering why the MCCB ground fault setting is recommended to set as low as 0.2In? I think the ground fault current at the 400A MCCB location...

Hi, I have a query regarding an installation where there is an upstream 400A MCCB supplying several 1ph 32A type D MCBs. According to the manual of the 400A MCCB, the ground fault current setting is set at 80A with 0.2s tripping time. However, at 80A, the 32A MCB downstream only trip as...