Phases out of balance when 3-phase motors are running

[Tank11]

I'm working with a local hockey rink and the electrical system is experiencing phase imbalances when large 3-phase motors are running. The chiller and main cooling tower units are both 3-phase and when in operation, B phase becomes 10% out of balance with A, and C becomes 10% out of balance with B.

Any ideas on what could be causing this? There is a large capacitor at 150 KVAR. There is also a VFD feeding a cooling tower.

 

[TwoBlocked]

Perhaps the chiller and/or cooling tower also have single phase loads.

 

[zbang]

"Out of balance" kind of implies that two of three phases are the same, are you saying that if A=100, then B=90 and C=80? What about each piece of equipment is operating separately? Actual current and voltage readings, as well as where you're measuring, are usually helpful.

Has the PFC been checked? If some or all the caps on one phase are out, that could mess with what you're measuring.

 

[ptonsparky]

I agree, check the PFC unit. Better, at least more expensive, ones have fusing.

 

[Jraef]

What’s unbalanced, voltage or current?

 

[ptonsparky]

Do you have all the current and voltage results?

 

[ptonsparky]

What is C in reference to A?

		System voltage			total	FLA of Motor
% VOLTAGE IMBALANCE		480.00​	6.67%​		% CURRENT IMBALANCE	200.00​
PHASE	VOLT w/Load				Amp No PFC Cap
A-B	480.00​			16.00​	100.00​
B-C	432.00​			32.00​	90.00​
A-C	480.00​	MAX	MAX-AVG	16.00​	100.00​	MAX
AVG	464.00​	480.00​	16.00​	32.00​	96.67​	100.00​
STAND DEVIATION	22.63​				4.71​
TOTAL IMBALANCE	6.90%​	Investigate			6.90%​	OK, if not SFA