locked rotor current limit for 6.6 KV motor

[wilans]

would anyone please let me be informed what is the locked rotor current or DOL starting current limit according to standard for 6.6KV motor ??? motor power 500KW. I mean the maximum permissible according to Electrical standard ( e.g 6 times or 7 times, or 8 times ...)

 

[jdsmith]

would anyone please let me be informed what is the locked rotor current or DOL starting current limit according to standard for 6.6KV motor ??? motor power 500KW. I mean the maximum permissible according to Electrical standard ( e.g 6 times or 7 times, or 8 times ...)

According to what standard? NEMA requires that the motor nameplate be labeled with a KVA code letter to indicate the inrush current. API 541 and 547 specify that LRC is less than or equal to 650% of FLA. API 546 for synchronous machines specifies LRC no more than 500% of FLA.

As a purchaser you can specify whatever you want to when you issue a motor datasheet for quotation. I have specified machines with 400-450% inrush as well as 650% inrush.

The caveat with all of this is that these rating apply at nameplate voltage. Most power systems don't run exactly at their nominal voltage, and motor nameplate voltages are usually lower than the power system nominal voltage they are connected to.

If you're asking this question and you're concerned about 6x vs. 7x vs. 8x inrush you also need to think about the "stiffness" of the power system you are connected to and the voltage on the system before the motor is connected.

 

[wilans]

thanks for the response

 

[kingpb]

Being that your from Asia-Pacific, are you using US or international standards?

If my memory serves me correct, IEC allows pretty much anything, I've seen motors with 12X starting current on LV motors.

I assume this 6.6kV motor is on a 6.9kV nominal rated bus. 4-4.5X is plausible if you purchased it that way, but it costs more, otherwise it is probably going to be in the 6X'ish range.

 

[wilans]

appreciate for the response. exactly the power supply is 6.9KV. Just found that NEMA 2001 ( 600% to 800% for some design e.g design A, B, C