UPS sizing for motor load

• Aug 16, 2004

• #2

RonShap

Electrical

Aug 15, 2002

230

US

Depends on the type of UPS and type of motor/application. If the starting power factor will be very low, and considering the inrush, you will need to share that with the UPS Vendor to determine how much it needs to be derated. The UPS is generally rated at .8PF

 

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• Aug 17, 2004

• #3

rbulsara

Electrical

Aug 19, 2003

4,242

US

You need to check with UPS mfr.

UPSs have limited capacity to deliver short circuit current or starting current for loads such as motors.

Most UPS will transfer to it's static bypass source in 10 seconds if the load is more than 125% its rating.

Make sure this is acceptable for your application. Check against your motor's starting current and its duration (acceleration time) vs. UPS overload characteristics.

Using solid-state starters or VFD's should help.

 

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• Aug 17, 2004

• #4

controlnovice

Electrical

Jul 28, 2004

976

US

Is your UPS battery driven or does it use a fly-wheel?

 

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• Aug 18, 2004

• #5

jraef

Electrical

May 29, 2002

11,368

US

You may be able to help the UPS by using a soft starter on the motor as well. I recently did some A/C compressor motors that needed to be run on a UPS and adding soft starters allowed us to use a 25kVA instead of the next size up, a 50kVA. The soft starters kept the motor starting current below the peak rating of the UPS.

"Venditori de oleum-vipera non vigere excordis populi"

 

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