Voltage unbalance

[JdoubleU]

What causes voltage unbalance? What Problems can it cause? What is acceptable? I believe in a 3 phase circuit that voltage drop in one phase is an example of voltage unballance. I guess a certain level could cause overheating on the neutral conductor.

 

[cadpoint]

You question is a very good one, but not a very simple one to answer. IMO

I took the liberty of searching this forum using the wordage “unbalanced voltage”, a search here will give your about the same results, these are the one that I chose to present.

Most deal with the various aspects of your original OP question but get into various different levels of power starting @ 120/208V, and higher and Delta to Delta, and Delta to Wye circuits.

If you understand the basic principles of transposing power these threads will help you down the Road there are some great presentations of math and diagrams and make it easy to follow along.

The title is of the thread link to the original thread name. Most all of these threads are LOCKED…

You have to understand that the conversation my be all math but the presentation is still there.

Hope this helps !


Balanced Neutral

What is a Balanced Voltage System?

Delta to Delta transformers

Primary current calc question for unbalanced Delta / Y

Transformer Problem

single vs. 3 phase

 

[bob]

Good information http://www.pge.com/includes/docs/pd...tatus/powerquality/voltage_unbalance_rev2.pdf

 

[JdoubleU]

Thank you very much for the resources. That really helped.

 

[robbietan]

What causes voltage unbalance? What Problems can it cause? What is acceptable? I believe in a 3 phase circuit that voltage drop in one phase is an example of voltage unballance. I guess a certain level could cause overheating on the neutral conductor.

most of the time it is caused by unbalanced single phase loads on a three phase system. sometimes it can be caused by loose terminals in the wiring.

our poco limits voltage unbalance to 2.5%, as NEMA MG-1 would state that having more than this level of unbalance would seriously decrease a motor's efficiency. motor ratings are derated 10% if the unbalance is more than 3%.

the problem here is "how" you compute for it. there are several formulas out there that can be considered "correct" but I believe NEMA's formula is "the maximum deviation between a phase voltage and the average of the 3 phase voltages divided by the average of the three voltages".