Recent content by HienN

I am the one who still confuse what is you really want. 1. For the switchgear: Normally, the control power is VDC or 110VAC fed from the external source. For example, the UPS, which is energized from another transformer, let's say, even your factory use medium voltage for big motor. It also...

I think this case will depend on the type of Breaker you intend to use (Motorized or mechanical). As a matter of fact that the 02 cases will use a typical "Tripping circuit", where the trip coil is energized via external signals (via reset, emergency, or via protection relays contacts...). The...

LionelHuzt: It could be understood. However, I think, just base on the safety aspect. The main coil as well as protection relays shall be energized from the external sources (like batteries or UPS). So, there will be time to cut off the main contacts during the short circuit problem. For...

Rafiq Bulsara, Many thanks to you for the valuable supports. I will do it myself. Regards,

Thank you for all of your useful posts. I confirmed that the base capacity of 110/22kV Transformer is 40MVA. Z% is at 13 percent. The next step is how to calculated the short capacity at the source? Is that SC capacity at the source is ~300MVA? When sizing the transforme capacity, why we...

Could you post the diagram up here. We should see the diagram.

Ters: Some more words, for big motors (hundreds of kW up), "starting regime" is required by manufacturer. (Like 01 hot, 02 cold…) For example, it can only be restarted after several minutes for cooling down (cooling the motors down only). At the same time, power fuses could also have time to...

I think the most important thing is us. Regards

Not only overcurrent protection. it should better be added with Short circuit (instantaneous) current protection. In this case, we can eliminate the power fuses. For most of contactor switching, equipped with fuses may be standardized. The manufacturer offers you fused compartment as an option...

Thank you, If I dont ask, it may lead me to many misunderstading in actual application. By the way, what is the difference between the base and forced cooling capacity? If this 63MVA is forced cooling capacity then I would ask for the base? Moreover, at the same time with this, for 110/22kV...

I like Oldnotbold post. Gave him a star.

But I was wrong, the impedance is not that small. It should be around 12 to 14% for 63MVA transformer. With this impedance, the short circuit current will reduce dramatically.

Rafiq Bulsara, Utility company transformer is 63MVA capacity with 8% PU. Overhead line distance is about 1.5km.

Electricpete: I agree with you for this case. I did mean by saying that all large motors need fuses. But would like add up by saying a little bit more that: For big motors (Medium voltage motors) that use contactor as switching equipment. Fused vacuum contactor is the cheapest one in...

Marmite:I did some calculation for transformer 110/22kV and found that the short-circuit current at the 22kV size would have been around 23.6kA. Then, consulted some other Vendor like Schneider (local), and knew that it was not that high (just around 10~16kA). Not satisfied yet, I switched back...