We are operating 3 phases radial system with part of load is 2 phases transformer and some percent of load also use 3 phase load especially for motor /AC or other 3 phases load.

The fact that system loading cause the voltage to be unbalance about 2-3 % of the average voltage value. We know that it may increase the motor temperture excessively, due to presence of negative seq current.

Would please help me or direct me to find the reference what is the acceptable unbalance voltage provided by the utility for customer?

Thanks for your help

My curve shows a 5-10% derating.
This is my referrence: https://img.photobucket.com/albums/v706/templdl/Accessories/Image029.jpg
As shown it is not recommended that more than 5% be allowed.

http://www.ecmweb.com/mag/electric_basics_voltage_imbalance/ http://www.bacharach-training.com/norm/protecting.htm