Odd question - unbalanced load

[Jack Linville]

Imbalance Compensation

Imbalance Compensation

I was going to say in order to balance current in the load I would start with adjusting voltage/s. Theoretically it should be possible.

So far as in practice, an imbalance of loads is an imbalance. If loads can be shifted to balance the current, that is the obvious method to use.

By changing the relationships of voltage and current via impedance adjustment, the Power Factor and phase angles would necessarily be influenced. I'm glad someone already posted the relevant formulas.

 

[SAC]

Guys, I did this scenario.Please check if my calcs are correct.
Load:
Phase "A" to neutral = 5,000 watts
Phase "B" to neutral = 5,000 watts
Phase "C" to neutral = 4,000 watts

Supply voltages:
Vab = 128.27 /30 deg. volts
Vbc = 128.27 /-90 deg. volts
Vca = 102.62 /150 deg. volts

The resulting line amps = 67.51 amps (balanced)

I plotted the current curve over time, and I don't see that the sum of these is balanced - peak current of about 1A. But this is the type of thing I was getting at in my earlier post.

 

[IamJonscranium]

Great. Thank you. Between the 2 of you, my guestion(s) have been answered. Sorry for the confusion along the lines of grounding (pun intended).

Now, let me twist a little. If there *wer* a ground rod at the load in addition to the one at the source, wouldn't there be a gound current (albeit it very small because of the large ground impedance compared to that of the neutral conductor between source and load)?

I ask becasue in my reading of the IEEE 142 I seem to recall seeing a non-separately derived system for a UPS that was fed from a 3p4w source and both source transformer and UPS were grounded to earth ground.

I reference page 56 from the 2007 revision. Figure 1-39

Can you post a scan of this?

Charlie B hit the nail on the head. We only create one system ground. You're sure that the UPS isn't through a control transformer in the panel?

When you have a fault, the fault current needs to be able to make it's way back to the source. If you have multiple grounds, who's to say that current will get to the source? You won't know where the current will go.