Submersible tripping out on current unbalance.

11bgrunt

Senior Member
Location
TEXAS
I posted about this a few years back. The POCO made adjustments to their regulators and the situation did get better.

I will be looking at another location with the same type of customer equipment.
The POCO serves these accounts overhead Wye-Wye 480/277 with three transformers. This location is just a few miles of mainline from the substation PWT. The POCO primary tap this well is on is not well balanced and cannot be made any better unless the 3 phase primary line is redesigned and rebuilt.
Will a transformer change to Delta primary improve the voltage balance on the POCO secondary to the well and then improve the current unbalance issue?
This would be the first time for them to have a Delta primary bank on a four wire Wye line and will probably be a hard sell. The big POCO nearby serves all pump loads with delta primary transformer banks, because they always have.
Thanks,

https://xenforo.mikeholt.com/threads/submersible-tripping-out-on-current-unbalance.139721/

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paulengr

Senior Member
YY is cheaper and makes sense when most customers are single phase anyway. But it passes zero sequence currents, and it can have circulating currents that you cannot block or detect which causes overheating. Delta-wye blocks those, blocks all triplen harmonics (3, 9, 15...), and phase shifts everythjng 60 degrees so an unbalance is split between two phases which tends to even everything out more. But since you are dealing with line to line voltages instead of line to neutral the transformer needs a little more insulation so it is more expensive. I’m an industrial guy so delta wye is almost automatic where utilities almost always choose wye wye. But once you’ve dealt with their ugly side you will be much happier avoiding them.
 

11bgrunt

Senior Member
Location
TEXAS
YY is cheaper and makes sense when most customers are single phase anyway. But it passes zero sequence currents, and it can have circulating currents that you cannot block or detect which causes overheating. Delta-wye blocks those, blocks all triplen harmonics (3, 9, 15...), and phase shifts everythjng 60 degrees so an unbalance is split between two phases which tends to even everything out more. But since you are dealing with line to line voltages instead of line to neutral the transformer needs a little more insulation so it is more expensive. I’m an industrial guy so delta wye is almost automatic where utilities almost always choose wye wye. But once you’ve dealt with their ugly side you will be much happier avoiding them.
Years ago motor loads would have been served by this POCO with a Delta secondary. Grounded corner 480 was the norm, Today Y-Y is all they will offer a new customer. I saw a few lids blow off back in those Delta days if we didn't operate them correctly. Everything is a tradeoff. The Y-Y is probably easier to teach and for folks to understand. I think using Delta primary would blend the high and low legs and result in a secondary voltage that would be closer to balanced than it is today. From your post, it appears you agree.
 

kwired

Electron manager
Location
NE Nebraska
Years ago motor loads would have been served by this POCO with a Delta secondary. Grounded corner 480 was the norm, Today Y-Y is all they will offer a new customer. I saw a few lids blow off back in those Delta days if we didn't operate them correctly. Everything is a tradeoff. The Y-Y is probably easier to teach and for folks to understand. I think using Delta primary would blend the high and low legs and result in a secondary voltage that would be closer to balanced than it is today. From your post, it appears you agree.
Pad mount units may possibly be delta primary, but they also want to have less pole pigs to have to stock to build those services with the source at the top of the pole.

Some don't want to have 480 volts to ground either, especially for farms and other places where unqualified have a better chance of ending up working on those systems so this leaves wye systems of 277 volts to ground more favorable over corner ground 480 to ground delta systems.
 

ElectricMatt

Senior Member
Location
Waco, tx
I have several wells with the sub monitors on them and have dealt with the same issue every time the temperature changes. The best solution I found was doing a phase roll. I have done this on about half a dozen wells and rolled it till I found the best balance. Franklin likes the monitor to be set at 5%, but will still warranty up to 10% out of balance.

2 of those wells are on delta primaries with a corner ground delta secondary. The issue with them is the horrendous planning of the lines in a rural area. However since I did a phase roll on both of them I have not received a current unbalanced in probably a year and a half.


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Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Are you sure it’s the bank causing the problems?

the reason I say that is it could be the pump.
I had a customer complaining about the open delta we were serving his well pump with. It worked for 20+ years. Now all the sudden the monitor was tripping out on imbalance.
i took my Dranetz there and monitored. It tripped out often, but but not every time.
once I looked at our report I could zoom in on the graph and see the voltages were very consistent until the unit tripped.

looking even closer at the graph I could see the current increase led the voltage dip just enough to make a determination the pump was dragging.
No, he wasn’t happy with my finding, but he changed his pump motor out.

the bank is still there, and I haven’t heard back from him.
that was two years ago...

roll the phases as suggested, see if the phase trip is consistent.
 

paulengr

Senior Member
Years ago motor loads would have been served by this POCO with a Delta secondary. Grounded corner 480 was the norm, Today Y-Y is all they will offer a new customer. I saw a few lids blow off back in those Delta days if we didn't operate them correctly. Everything is a tradeoff. The Y-Y is probably easier to teach and for folks to understand. I think using Delta primary would blend the high and low legs and result in a secondary voltage that would be closer to balanced than it is today. From your post, it appears you agree.
Delta delta works same as YY except it avoids circulating currents and has the high delta primary cost. I’m talking about Y delta a true isolation transformer.

Fault currents are a function of %Z. YY is generally worse. If you truly want to reduce fault currents then use a high resistance grounded wye. This is cheaper than solidly grounded Y. The ground fault currents are so low that you can take a direct hit (touch) at 4160 and walk away. I have a friend that has “tested” 7200. On a solidly grounded wye or delta we would have used garbage bags to pick up the pieces. It’s the phase shifting that makes the magic happen.
 

11bgrunt

Senior Member
Location
TEXAS
On site this morning.
75HP 480V. Above ground motor with shaft drive to pump. Not a sub pump motor or the SubMonitor control I have seen before.. Motor was 8' of sealtite away from control.
Franklin control is labeled a soft start. All looked good this morning. IDed POCO phasing through the panels to the pump. I had a recorder at the control.
Volts and currents were acceptable, no load and loaded. Pf .81.
Able to visit with the pump tech. It had been default 5% and tripping. He talked to Franklin and cranked the voltage unbalance to 7% and three days ago he moved up to the 10% limit. No phase unbalance trips since. Now we are in a holding pattern. If we have to go back, rolling the phases will be explored.
Thanks to all that offered advice.
 

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kwired

Electron manager
Location
NE Nebraska
On site this morning.
75HP 480V. Above ground motor with shaft drive to pump. Not a sub pump motor or the SubMonitor control I have seen before.. Motor was 8' of sealtite away from control.
Franklin control is labeled a soft start. All looked good this morning. IDed POCO phasing through the panels to the pump. I had a recorder at the control.
Volts and currents were acceptable, no load and loaded. Pf .81.
Able to visit with the pump tech. It had been default 5% and tripping. He talked to Franklin and cranked the voltage unbalance to 7% and three days ago he moved up to the 10% limit. No phase unbalance trips since. Now we are in a holding pattern. If we have to go back, rolling the phases will be explored.
Thanks to all that offered advice.
What is running current in relation to motor full load rating? What, if any, is input volts imbalance?
 

11bgrunt

Senior Member
Location
TEXAS
What is running current in relation to motor full load rating? What, if any, is input volts imbalance?
Power supply is 480/277Y.
Motor data plate Volts -460
Amps-88
Recorder max-
A 283.1 -76.3A
B 282.3 - 72.3A
C 282.8 - 73.0A
At this reading, voltage imbalance % is fractional. There is no trip for voltage unbalance.
Franklin describes current unbalance as difference between any two legs.
This reading has a current unbalance of 5.5%.
1589834558786.png
 

paulengr

Senior Member
That’s not excessive. Typical settings for protective relays are 10-15%. Every 1% voltage imbalance is a 6-8% current imbalance. Current imbalances come from either a big resistance in the “power supply” or a problem in the motor itself...turn to turn faults which slowly lead to failure.

But when I say power supply voltage imbalance means look upstream. Current unbalance only means look downstream.

Case in point. I was dealing with a 350 HP air compressor with a six lead motor that was on Star delta starting. It wiped out motors twice in 48 hours. No incoming voltage unbalance but 10% current unbalance. When loaded it was at 106% FLA on a 1.15 service factor but derating for the 10% meant it was overloaded but the overload relay wouldn’t recognize it, Checking at the compressor (starter was remote) there was both voltage unbalance (2%) AND current unbalance, No connection or wiring issues based on low ohm bridge. Popped the lids on the contactors and found badly worn contact tips on the delta contactor. After swapping tips, no more issues.
 

ElectricMatt

Senior Member
Location
Waco, tx
That’s not excessive. Typical settings for protective relays are 10-15%. Every 1% voltage imbalance is a 6-8% current imbalance. Current imbalances come from either a big resistance in the “power supply” or a problem in the motor itself...turn to turn faults which slowly lead to failure.

.
Franklin will not warranty the motor if you have it over 10% unbalanced current. I have several of these that run at 8-10 on franklin systems. I wish I could get them to run at 5% unbalances.


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11bgrunt

Senior Member
Location
TEXAS
Franklin will not warranty the motor if you have it over 10% unbalanced current. I have several of these that run at 8-10 on franklin systems. I wish I could get them to run at 5% unbalances.


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5% is tough to do with their control. I always thought the Franklin method for calculating the unbalance was part of the problem.
 
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