What's new
What's new
By:
Advanced search…

Phase imbalance from power company

S

Strostkovy

Titanium
Joined
Oct 29, 2017
We had another power outage for a few hours this morning. After it came back on the compressor was tripping out with phase imbalance errors. Error logs show 50% less current on leg A, but only while the motor is unloaded. While loaded the phase imbalance is less than 50%.

I measured the power and it is fluctuating wildly by several volts, but one phase is always 4-6V lower.

The 40hp compressor pump sup the 400 gallon tank no problem, and then trips out within one minute of running unloaded. Is this 6V phase difference enough to cause that much current imbalance?

I have not yet checked the currents while it is running loaded. I did use a thermal camera on everything between the service entry and the motor and saw no hot connections, even though at a minimum 500 watts would have to be dissipated.
 
Strostkovy said:
We had another power outage for a few hours this morning. After it came back on the compressor was tripping out with phase imbalance errors.
Click to expand...

The problem is upline. Get Powerco on it. You can only PARTIALLY even look at symptoms. And could not fix them even if you wanted to do.

They can do. They should even KNOW which "disease".

And without even putting their (far more appropriate) measuring goods to work.

"Not new news", IOW.
 
I was gonna tell you there's no way you have imbalanced power, then I saw where you are located so now I'm gonna say be glad you have any power!
 
If you have 240V service, 6 volts is 2.5%, which is just on the edge of being overly imbalanced. 4 volts would not be an issue. Normally, the powerco will have things balanced to 2%, some may say 3%, which you are still below.

If you have large current imbalances, and automatic trip-outs on phase imbalance, the meter may not be telling the complete truth.

Yes, talking to the powerco is in order, if you can get through past all the other 3 phase users who will be calling up and howling about it also.
 
I would say they changed something upstream. as they might have moved a couple of wires around and have more load on the one phase now due to some sort of issue or maintainence. Call them asap.
 
Where I used to work, we had a power outage one day. So we cleaned for about
45 minutes until the power came back, but it wasn't quite right? Machines
were throwing all kinds of error codes, only some of the computers would re-boot.

Multimeter, and the voltages were all over the map. 77 is pretty close to 110 right?

It was 50-50 as to weather they would fix the problem shortly, so just sit it out, or
call. Its a good thing I called. It wasn't the power on the lines, our transformers
on the pole got fried.

Call the power company.
 
We called the emergency line for PG&E and they sent someone out. They said yeah there is an imbalance but it's not that bad and we really should have phase imbalance monitors on our building. We checked the specifications and they allow "as close to 2.5% as practicable" and measure from the average, not phase to phase. So with one line sitting pretty at 208 it pretty much lets them get away with whatever they want.

I did at least find out that the power outage was due to a shorted underground cable (due to old age) and that it is currently open circuit and they are feeding our chunk of the grid from both ends, and apparently it's a known issue that one side drives a lot harder than the other when they do this. They were not willing to give us any contact to people who knew more, or even give our contact information to someone who could let us know when the power would be more stable once the cable is fixed.

There are currently over 50 outages in PG&E's service area, as usual, so they don't put much priority to getting things working correctly once power is on, so it could be weeks.

PG&E does not care about their customers. We pay $0.42 per kilowatt hour and average an outage per month, not including brownouts, which occur often.
 
Strostkovy said:
We called the emergency line for PG&E and they sent someone out. They said yeah there is an imbalance but it's not that bad and we really should have phase imbalance monitors on our building. We checked the specifications and they allow "as close to 2.5% as practicable" ....
Click to expand...

AAargh.

1) you do have phase imbalance monitors. They're called your machines.

2) are you allowed to tell them you will pay as close to 100 percent of their bill, as is practicable??

This month it's only practicable to pay 75 percent of your charges.....
 
jim rozen said:
AAargh.

1) you do have phase imbalance monitors. They're called your machines.

2) are you allowed to tell them you will pay as close to 100 percent of their bill, as is practicable??

This month it's only practicable to pay 75 percent of your charges.....
Click to expand...

They seem to have no problems cutting power to paying customers. I'd hate to see what they do to nonpaying customers.
 
Strostkovy said:
...the power outage was due to a shorted underground cable (due to old age) and that it is currently open circuit and they are feeding our chunk of the grid from both ends, and apparently it's a known issue that one side drives a lot harder than the other when they do this.
Click to expand...

Yeah, that'll do it.

Always good to know that they know they're faced with a problem... and that they're really impressed upon correcting it...

Winter frost cycles loosen things up underground a bit now'n then. There's a nice puddle in a ditch southeast of me a mile that's been bubbling since thaw started back in February... a gas main got put in there a half-dozen years back... it's probably cracked. I imagine that if there was a nearby lightning strike, mebbie the ditch grass catches fire, there'd be a new monument to the Unknown Soldier there... The gas co knows about it...
 
Strostkovy said:
They seem to have no problems cutting power to paying customers. I'd hate to see what they do to nonpaying customers.
Click to expand...

Elect them to Pubic Orifice and put them in charge of the power grid Kommisariat. Of course. That lot of congenital parasites never paid for a damned thing in their greedy lives to begin with. "Other People's Money" pays for their extravagant "French Laundry" lifestyle, and will always.

They'll not recall Newsom.

Same as Pelosi. Too many of his subordinate parasites are PROUD of how expert he is at political kinkey-f**ckery. Entertainment-value thing, side-show to the national circus.

You are posting from the Kalifornickyah-ALL-equally SSR?

At least in China, proper, the Char Siu is better and cheaper.

The only power-outage I recall in Hong Kong was when a rack-monkey tried to run the monthly emergency UPS exercising routine for the FM site we had racks in and sequenced it bass-ackwards .. did the cutover BEFORE bringing up the Diesels.

:(

Pissed me off.

I had three *BSD servers being dynamically updated as had gone well past the 900 day "uptime" mark!

'Nuther year or three, we'd have been in sight of the global top fifty.

Suck yer own rotten heart up yer infected patootie, find-me-f**k-me Microsnot.
 
Strostkovy said:
We called the emergency line for PG&E and they sent someone out. They said yeah there is an imbalance but it's not that bad and we really should have phase imbalance monitors on our building. We checked the specifications and they allow "as close to 2.5% as practicable" and measure from the average, not phase to phase. So with one line sitting pretty at 208 it pretty much lets them get away with whatever they want.
Click to expand...

That's actually not so unusual as a way to figure it, although it does allow a 5% imbalance highest to lowest, if pushed to the limit. 5% can require you to derate motors.
 
A few things to double-check/try:
  • Check that the voltage imbalance is present both at your service entry and the machine/motor.
  • Rebalance your load so that most of the single-phase load is on the higher-voltage phases, dragging it/them down a bit.

Given that it's only tripping when unloaded, and presumably the line currents are below the overload setpoint, I'm guessing it's the differential protection in the overload that's tripping. I believe EU overloads tend to have this while US ones usually don't. It's likely that the extra torque when under load means that the motor starts drawing current in all the windings, and volt drop in the cable evens things out a bit.

One option could be to stick a bit more impedance in the supply, potentially just in the non-faulty legs.
 
Strostkovy said:
We pay $0.42 per kilowatt hour and average an outage per month, not including brownouts, which occur often.
Click to expand...

JEEZ! That's 380% above what it costs here! Haven't had a single outage or disturbance in 7 years.

California... :nutter:

Put a clamp meter on it unloaded and see what gives. The fact that you have an error history and it's a 40hp pump tells me this is a screw compressor with a brain box. If anything, it's probably something in the brain box being hypersensitive and picky. See if you can adjust the single-phasing protection settings on it if applicable. A 6 volt imbalance is not ideal but certainly not enough to be a deal-breaker as long as the motor's thermal protection is set up correctly. Service factor of 1.15 or 1.25? Bump the overloads to 125% of FLA temporarily for giggles if that's not where they're already set at. It's entirely possible for a motor to pull *more than* FLA in an unloaded state. I've seen a few instances of it firsthand. Some motors just have especially awful power factor without any load on them.
 
You must log in or register to reply here.

Similar threads

C
DIY RPC - voltage on case & large imbalance between legs
2
Replies
28
Views
1K
rons
rons
L
Best option to power 3 phase 20hp 460v lathe motor from 220v single phase input?
Replies
7
Views
305
metalmagpie
M
scsmith42
Compressor on VFD - has anybody actually done it?
Replies
6
Views
322
scsmith42
scsmith42
M
15 hp RPC struggles to start 7.5 hp 3 phase air compressor - add cap?
2 3
Replies
44
Views
2K
JST
JST
M
Will this transformer work for stepping up current from a rotary phase converter ?
Replies
4
Views
742
SAF
SAF








 

ABOUT PRACTICAL MACHINIST

With more than 10.6 million unique visitors over the last year, Practical Machinist is the most visited site for metalworking professionals. Practical Machinist is the easiest way to learn new techniques, get answers quickly and discuss common challenges with your peers. Register for the world’s largest manufacturing technology forum for free today to stay in the know.

Learn more about us.

STAY CONNECTED

Facebook Instagram YouTube LinkedIn Pinterest Twitter Tiktok

Register Become a forum member. Register today.

Sign Up Sign up for our e-newsletter.

© 2024 Copyright Practicalmachinist.com. All Rights reserved.

Back
Top