Power Utility Issue

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
Ok those were the original readings. I had them come out because it was over 5% and also for them to further diagnose what was wrong. They wound up re-taping the transformer to get the voltages within 5%. These are the values after they retapped


Secondary

Tap changed

Went From D to C
VFD % 89.6

VAB 487

VBC 475

VCA 488


IA - 433

IB - 385

IC - 272

For all of the people thinking that this could be an issue with the “ VFD “, again we have 3 other newer smaller vfds running and working, able to run and they also have this this unbalanced amperage but our large drive is not able to handle it.

This is a Utility Issue!!!!
What is the correct terminology that I need to use to go to the Utility with, in order for them to further investigate and repair this problem with their feed for the Pump station ? They have come back and claimed they are within ANSI standards. The standards are for 3% nominal voltage. Are there no standards for amperage ? I need to reply back to the Utility with further info regarding this situation and that’s why I came here in the engineering section to get some advice.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
When they did their testing I had them test amperage on the primary and secondary side of the transformer while the VFd was running and they told me that on 1 leg the amperage was low on both sides of the transformer. That to me is saying that their is an issue with the substation on that line feeding the transformer but since the voltage is with 3% they are saying they are meeting their requirements.
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
So, I don't know what you've got in between the point of measurement and the input terminals to the VFDs, but both your loads are showing a current imbalance of about 50%. The level of tolerance to imbalance depends on model and load level. Some are even capable of operating with a single phase input.

If those readings are average, VAB is excessive as it exceeds 5% utilization voltage limit.
Yes. I'll try this again. The generator and VFD are obviously working fine. Clearly the utility side is not. That's where the issue lies.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Are you using a line reactor on the input of the 600HP VFD?
A line reactor will reduce the voltage ripple on the DC bus of the VFD. Excess ripple may be causing the drive to trip.
Generators typically will have a higher source impedance than the POCO service, and so this acts like a line reactor to help smooth and equalize the currents thru the VFD rectifiers (therefore reducing the DC bus voltage ripple).
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
Yes. I'll try this again. The generator and VFD are obviously working fine. Clearly the utility side is not. That's where the issue lies.
100% agreed ! My other 50hp Schneider vfds working good on trending and at the vfds they are showing the same the same amperage issues but are able to handle
Are you using a line reactor on the input of the 600HP VFD?
A line reactor will reduce the voltage ripple on the DC bus of the VFD. Excess ripple may be causing the drive to trip.
Generators typically will have a higher source impedance than the POCO service, and so this acts like a line reactor to help smooth and equalize the currents thru the VFD rectifiers (therefore reducing the DC bus voltage ripple).
yes we are and again the VFD is purring like a kitten now about 90 hours straight on a backup generator that’s also purring. The drive doesn’t fault. Only when connected to Bad Utility power ! And only the large ABB drive. The newer Schneider drives work with the bad unbalanced current. You can see the unbalance on the 3 phase air conditioning. So it has nothing to do with the drives
 

kwired

Electron manager
Location
NE Nebraska
Ok those were the original readings. I had them come out because it was over 5% and also for them to further diagnose what was wrong. They wound up re-taping the transformer to get the voltages within 5%. These are the values after they retapped


Secondary

Tap changed

Went From D to C
VFD % 89.6

VAB 487

VBC 475

VCA 488


IA - 433

IB - 385

IC - 272

For all of the people thinking that this could be an issue with the “ VFD “, again we have 3 other newer smaller vfds running and working, able to run and they also have this this unbalanced amperage but our large drive is not able to handle it.

This is a Utility Issue!!!!
What is the correct terminology that I need to use to go to the Utility with, in order for them to further investigate and repair this problem with their feed for the Pump station ? They have come back and claimed they are within ANSI standards. The standards are for 3% nominal voltage. Are there no standards for amperage ? I need to reply back to the Utility with further info regarding this situation and that’s why I came here in the engineering section to get some advice.
Voltages of 487, 475, and 488 might be within tolerance level, but are definitely not balanced very well.

You can run these drives off single phase input, but they need to be oversized to compensate. Even here it is drawing more from two lines to compensate for what it is short of on the other. If it works on your standby source then it about has to be a problem in the utility system, unless there was coincidental failure of something still in use about the time they switched how you are supplied
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
Voltages of 487, 475, and 488 might be within tolerance level, but are definitely not balanced very well.

You can run these drives off single phase input, but they need to be oversized to compensate. Even here it is drawing more from two lines to compensate for what it is short of on the other. If it works on your standby source then it about has to be a problem in the utility system, unless there was coincidental failure of something still in use about the time they switched how you are supplied
Ok we are 100% that it is a Utility power issue.
We are being fed from a backup substation since the substation we are normally on they are upgrading. Whenever they have switched us to this station in the past 10-20 years this same scenario has happened. The Utility has suggested for us to purchase $40,000 Voltage Regulators. We don’t have a problem with voltage. This is the utility trying to get away from the fact that it is their issue IMO. I also feel that in order for them to correct the problem at the substation we are at now they would have to schedule an outage since there is no other back up and that may be another reason why they are trying to put it off. Either way I need to get back to them in regards to there ongoing issue with some good terminology and recommendations for their Troubleshooting at their substation in order to correct their issues. We are towards the end of the line off this sub station that we are connected to now and there is no other industrial facilities with heavy amperage draw besides us, pulling from their station.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
Also, can anyone tell me the requirements that the Utility has to abide by in this scenario. Can they tell me, the customer that they are giving us voltage within range and that’s all they are required to do even if what they are giving us is unusable power because of this issue ?
Need an engineer, or someone with a background in power utilities to state what the requirements are in regards to this issue we are having with our utility.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
Sounds like the sub station is undersized, and their voltage regulator is kicking the voltage back up, but the transformers just don’t have enough juice. If it was summer, probably would see some smoke! LOL!
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Have waveform and phasor measurements been made of the voltage provided by the utility? For example, by using a power quality analyzer like a Fluke 434 or 435. The waveform may be distorted and causing more current to be drawn from phases with more peak voltage across them, even when their RMS values are relatively close. And so the RMS line voltages alone may not be telling the whole story.

 

kwired

Electron manager
Location
NE Nebraska
Ok we are 100% that it is a Utility power issue.
We are being fed from a backup substation since the substation we are normally on they are upgrading. Whenever they have switched us to this station in the past 10-20 years this same scenario has happened. The Utility has suggested for us to purchase $40,000 Voltage Regulators. We don’t have a problem with voltage. This is the utility trying to get away from the fact that it is their issue IMO. I also feel that in order for them to correct the problem at the substation we are at now they would have to schedule an outage since there is no other back up and that may be another reason why they are trying to put it off. Either way I need to get back to them in regards to there ongoing issue with some good terminology and recommendations for their Troubleshooting at their substation in order to correct their issues. We are towards the end of the line off this sub station that we are connected to now and there is no other industrial facilities with heavy amperage draw besides us, pulling from their station.
You say voltage is fine, yet it is not balanced. I don't know what they legally are supposed to provide for balancing but I would guess it should be better than it is. Such imbalance isn't that great for three phase motors running directly from the line either, especially if running at/near full load rating. They will ride though it for some time and you may never know about it. Good phase loss protection type overloads will still trip with this kind of condition.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
The Voltage is within 3%. I posted the voltage reading after the secondary was retapped it’s in this thread.
 

kwired

Electron manager
Location
NE Nebraska
The Voltage is within 3%. I posted the voltage reading after the secondary was retapped it’s in this thread.
I've always understood it doesn't take much voltage imbalance to cause excessive motor heating, especially when operating at/near rated load. I don't know what standards there may be for POCO's related to balancing. For one thing balancing can be dependent on your loads but raw POCO volts should be pretty balanced at no load/minimal loading/balanced loading.

This page has some information on motors. I do realize you are having problems with a drive, but what I do know about drives the input needs balanced as well or else drive needs derated. Like I mentioned earlier you can run a drive from single phase input, but that means derating it by around 50% as you now only have two inputs instead of three and no more 1.73 factor on the current applies to input current to determine input power.

Forgot to add: I see our member jraef from this site apparently posts in the forum in my link above. He would be a good person to help answer some these questions I would think.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
I've always understood it doesn't take much voltage imbalance to cause excessive motor heating, especially when operating at/near rated load. I don't know what standards there may be for POCO's related to balancing. For one thing balancing can be dependent on your loads but raw POCO volts should be pretty balanced at no load/minimal loading/balanced loading.

This page has some information on motors. I do realize you are having problems with a drive, but what I do know about drives the input needs balanced as well or else drive needs derated. Like I mentioned earlier you can run a drive from single phase input, but that means derating it by around 50% as you now only have two inputs instead of three and no more 1.73 factor on the current applies to input current to determine input power.

Forgot to add: I see our member jraef from this site apparently posts in the forum in my link above. He would be a good person to help answer some these questions I would think.
Understood. The power company since they are within 3% nominal voltage will not further balance the voltage. That small imbalance of voltage is not going to make a 40+% imbalance of current. That’s not the issue although I do understand it could be partially causing some of it. Their voltage even from the normal substation that we use was always unbalance to that degree but with no issues from the other substation tripping on unbalanced
 

Attachments

kwired

Electron manager
Location
NE Nebraska
3, even 5% within nominal voltage is fine that gives you anywhere from 456 to 504 for an acceptable voltage. But I never seen 480 nominal have as much of an imbalance as you posted that was not having problems with motor overloads tripping. I still think the balance tolerance they need to adhere to is likely less than 3%, probably at least no more than 2% from a few search hits I seen and motor manufacturers seem to prefer it be 1 percent or less.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
3, even 5% within nominal voltage is fine that gives you anywhere from 456 to 504 for an acceptable voltage. But I never seen 480 nominal have as much of an imbalance as you posted that was not having problems with motor overloads tripping. I still think the balance tolerance they need to adhere to is likely less than 3%, probably at least no more than 2% from a few search hits I seen and motor manufacturers seem to prefer it be 1 percent or less.
This is the voltage

VAB 487
VBC 475
VCA 488

They will not work to balance under there ANSI standards which is 3%
 

kwired

Electron manager
Location
NE Nebraska
This is the voltage

VAB 487
VBC 475
VCA 488

They will not work to balance under there ANSI standards which is 3%
is that loaded or unloaded voltages?

Thing is they possibly have blown fuse on a capacitor or maybe just need to connect certain single phase services to a different phase and it possibly clears up the balancing issue. POCO's around here would be willing to try to solve this problem.
 

kwired

Electron manager
Location
NE Nebraska
That’s isn’t within 3%??
:unsure:
What is it supposed to be within 3% of? Nominal volts of 480, or 3% or the differentials can not be more than 3% of one another?

Differentials here is huge, we have 1, 12 and 13.

Percent within nominal of 480 is low. Have two that are ~1.5% high and one that is ~1% low
 
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