Standby Generator - Allowable Frequency Dip - Motor Starting

[nhcf]

The general spec/default for max frequency dip on motor starting in gen sizing programs is 10%. I have application where software is telling me approx. 13% freq. dip when starting a large VFD driven motor.

What are the potential impacts of the higher frequency dip in a standby application?

 

[waross]

The quick answer is that voltage dip is generally not an issue when starting a VFD supplied motor.
I understand that there may be special conditions where voltage dip when starting a VFD supplied motor on a generator will exceed 10%.
We need the complete details of your application before we can give a good answer.

The specific question: "What are the potential impacts of frequency dip on a gen set?"
It depends on the reaction of the other loads on the set to under frequency.
The first impact will be the action of the "Under Frequency Roll Off" feature of the "Automatic Voltage Regulator".
UFRO will allow a 3 Hz drop in frequency and for greater frequency dips will reduce the voltage in proportion.
With a 13% frequency dip you can expect the UFRO to reduce the voltage setting by 10%.
A small UPS will often flash its light and beep. It will often pick up the load until the frequency dip recovers.

Bill
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