Power Utility Issue

klillemo

Member
Location
Twin Cities, MN
  • Conflicting data between Voltage and current measurements
    • Voltages are balanced, currents are not
  • Phase information is missing
    • Capacitance on individual line conductors for temporary service may not match original service conductor line capacitance
  • Need to measure Voltage, Current and Phase to know the whole story
    • Simple RMS measurements are not identifying the difference between services
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
  • Conflicting data between Voltage and current measurements
    • Voltages are balanced, currents are not
  • Phase information is missing
    • Capacitance on individual line conductors for temporary service may not match original service conductor line capacitance
  • Need to measure Voltage, Current and Phase to know the whole story
    • Simple RMS measurements are not identifying the difference between services
I agree, a phasor or scope picture would tell much more.
As usual though, we may never know how this turned out..
 

rockyBSEE

New User
Location
United States
I have a 480v 1600 amp service feeding a 600 hp VFD controlled potable water pump. The Power utility has recently shut down our substation and picked us up from another substation while they are performing work. When we tried to run out 600 hp pump after this swap over our VFD would trip out on “Fault Supply Phase” The Voltage coming from our Utility is within 3% but the Current on the Primary and Secondary side of the Utility transformer is off by more then 40% between 2 phases. This is what trips out our VFD. Luckily we have 3 other 50hp VFDs that our of a newer type and are able to handle this massive current imbalance.

When we questioned the Utility about this they told us that they are within the ANSI standards with what they are providing us :

Per ANSI Standard C84.1-1995, “Electric supply systems should be designed and operated to limit the maximum voltage unbalance to 3% when measured at the electric utility revenue meter under no-load conditions”. The supply voltage at the meter revenue point are well within the requirements even under full load conditions.

Question:
Are the Utilities only required to supply voltage balance to a certain amount but not current balance ? For the last 3 weeks we have been running a diesel pump and now it needs service and we had to bring in a 500kw generator to run our 600hp electric pump sucking 600 gallons of diesel a day. This is mind boggling to me. Yes when they switch back to their other substation which could be another month from now we will be back to normal but right now just seems like the Utility should be repairing the issue they are having that isn’t giving us the required current that we need. We are towards the end of the line downstream of their substation.
Thanks for the help
JDrais
Utilities are only required to provide voltage within specific voltage limits. These are defined by the State Utility commission and/or service requirement tariff in your State. They may be different for residential v. commercial & industrial. The IEEE published document C84.1 which is a great document in this regard and should be easy for any utility to comply with. However, the utilities legal obligation typically comes from the local utility regulator in the state and the utility should be willing to put in writing so the specific requirement and basis. That being said, it is only a voltage requirement (no current - this is primarily a customer controlled thing) and it will include long term (5 minute typical duration) RMS high and low limits and voltage % balance which can be a function of the load current on the utility circuits - they may need to balance single phase load on a three phase circuit to meet the voltage obligation - but you typically will need good long term recording data to get them to do something with regard to load balance so you can prove the conditions(s) at your service point.

That being said you should not be having the issue you describe.

You mention, "When we tried to run our 600 hp pump after this swap over our VFD would trip out on “Fault Supply Phase”.

What does "Fault Supply Phase" mean?
It seems to me this could mean more than one thing.
So you need to run down all the possible conditions that will cause this parameter to post and initiate trip.
Parameters usually have a magnitude and time delay associated with them so you might need to make an adjustment to the parameter when fed from the alternate source.
But you really need to be sure of what is the cause.
Is this parameter "voltage imbalance", "low voltage", "loss of phase" etc, etc - the term "fault" is not specific enough to fully troubleshoot.
I would make sure you fully explore this parameter with the manufacturer and a Power Quality / VFD programming specialist (like me or others in my firm.).

You mention, "The Voltage coming from our Utility is within 3% but the Current on the Primary and Secondary side of the Utility transformer is off by more then 40% between 2 phases."

You are talking about two things here
First you say the utility voltage is within 3%.
Are you measuring this and how are you calculating this?
Make sure that you are calculating it based on C84.1 and confirm that your drive uses the same calculation for the parameter if it is causing the trip for voltage imbalance.
Is this parameter ("Supply Phase Fault") defined as voltage imbalance? If so, is there a time delay associated with it?
You need to check and verify this.

How do you know the current on the primary of the utility transformer "is off" by 40%?
Not sure what you mean by "off".
The primary current in the utility transformer will be a function of (proportional to) the secondary current.
If this transformer is dedicated to you, then that primary current is your secondary current reflected back to the primary and it would be your current that is off.

Now, we can get into some more detail and find out what kind of transformer pad mount or aerial and the windings wye-wye, or, delta-wye, or, delta-delta, or, wye-delta. Then we can maybe theorize that there may be some other issue like a blown line fuse on the utility primary feeding the primary transformer winding or a blown fuse on a utility capacitor bank.

Before we go there the current should not cause an issue as you are already saying that the voltage imbalance is within 3%.
What is it actually? and, at what value will your parameter trip and for what duration?
Sometimes adjusting the time delay will make the tripping go away if it is set too short.
The current imbalance on the utility side is of no consequence to you as long as your voltage remains balanced, but, its possible your parameter needs to be set to work with the characteristics of both utility sources as the sources may be slightly or significantly different, and, your parameter may be set too tight.

If this transformer is dedicated to you, then it is your current that is imbalanced and you may need to look within.

One thing that you need to check is, the stiffness of the two utility feeds.
Ask the utility to give you the short circuit at your service for each source feed.
If these are different than you may need to make adjustment for each condition.

Does the 600 HP VFD have harmonic filters on the front end?
Do you have capacitors in your facility or does a neighbor or the utility have these and are you having fuses blow that may be causing imbalance?
Have you taken voltage harmonic readings and current harmonic readings at your point of service?
You need to do this while connected to each service and compare those readings and this may provide additional insight along with the source stiffness (utility short circuit).

You mention, "this is what trips out our VFD. Luckily we have 3 other 50hp VFDs that are of a newer type and are able to handle this massive current imbalance."

A current imbalance should be of little consequence to your drives.
Again if this is a dedicated transformer this is "your current imbalance" and you might want to fix it by balancing your load.
If there are multiple customers off this transformer, then others may need to balance the load.

Maybe I'm misinterpreting what you are saying.
Are you saying they measured the primary current in the transformer windings or coming to the transformer windings?
Or did they measure current in the primary line where there is a tap to your transformer?
The first one would be your load imbalance issue and the second one would be their line imbalance issue.
If this is their line problem, they need to balance load or may have a blown capacitor fuse on one phase.
So, it is very important for troubleshooting and to communicate effectively with the utility to get them to fix their problem that we are clear on where the current imbalance is measured.
Regardless, if your voltage is within tolerance your drive should not trip!!
So either your parameter (Voltage Imbalance) is set too tight since the alternate line is different with respect to voltage imbalance, or, this is not an imbalance issue.
Current imbalance, unless it causes out of tolerance voltage imbalance (and you are saying it is not), is of no consequence.
Also - you are not seeing a "Current Imbalance" fault!
There may be other issues you need to consider.

Get the short circuit values and measure the harmonics and compare the lines.
Find out where the primary current was measured.
Find out if there are capacitors on your line and if they may have a blown fuse - a trained eye can ride the circuit and easily detect this.

Why does the 600 HP drive trip and not the 50 hp drives?
Compare the parameter settings.
But, the 600 Hp drive most likely will create much higher levels of harmonics than the (3) 50 HPs and you may have a resonance condition, especially if the alternat utiluty source feeder is less stiff than your normal source feeder.
They 600 HP drive is also a different impedance than the (3) 50 HPs and this is likely why the system responds differently on the alternate source - the alternate source is probably less stiff!

I'm also assuming your power system is grounded, and it is not ungrounded.
If ungrounded, there might be other considerations.

I don't think current imbalance is your root cause.
No "Current Imbalance" trip parameter is posting.
Have you optimized the parameter programming and had per reviews on this?
Reviewing all the drive parameters would
be recommended.
 

Jdrais

Member
Location
Florida
Occupation
Electrical Contractor
Utilities are only required to provide voltage within specific voltage limits. These are defined by the State Utility commission and/or service requirement tariff in your State. They may be different for residential v. commercial & industrial. The IEEE published document C84.1 which is a great document in this regard and should be easy for any utility to comply with. However, the utilities legal obligation typically comes from the local utility regulator in the state and the utility should be willing to put in writing so the specific requirement and basis. That being said, it is only a voltage requirement (no current - this is primarily a customer controlled thing) and it will include long term (5 minute typical duration) RMS high and low limits and voltage % balance which can be a function of the load current on the utility circuits - they may need to balance single phase load on a three phase circuit to meet the voltage obligation - but you typically will need good long term recording data to get them to do something with regard to load balance so you can prove the conditions(s) at your service point.

That being said you should not be having the issue you describe.

You mention, "When we tried to run our 600 hp pump after this swap over our VFD would trip out on “Fault Supply Phase”.

What does "Fault Supply Phase" mean?
It seems to me this could mean more than one thing.
So you need to run down all the possible conditions that will cause this parameter to post and initiate trip.
Parameters usually have a magnitude and time delay associated with them so you might need to make an adjustment to the parameter when fed from the alternate source.
But you really need to be sure of what is the cause.
Is this parameter "voltage imbalance", "low voltage", "loss of phase" etc, etc - the term "fault" is not specific enough to fully troubleshoot.
I would make sure you fully explore this parameter with the manufacturer and a Power Quality / VFD programming specialist (like me or others in my firm.).

You mention, "The Voltage coming from our Utility is within 3% but the Current on the Primary and Secondary side of the Utility transformer is off by more then 40% between 2 phases."

You are talking about two things here
First you say the utility voltage is within 3%.
Are you measuring this and how are you calculating this?
Make sure that you are calculating it based on C84.1 and confirm that your drive uses the same calculation for the parameter if it is causing the trip for voltage imbalance.
Is this parameter ("Supply Phase Fault") defined as voltage imbalance? If so, is there a time delay associated with it?
You need to check and verify this.

How do you know the current on the primary of the utility transformer "is off" by 40%?
Not sure what you mean by "off".
The primary current in the utility transformer will be a function of (proportional to) the secondary current.
If this transformer is dedicated to you, then that primary current is your secondary current reflected back to the primary and it would be your current that is off.

Now, we can get into some more detail and find out what kind of transformer pad mount or aerial and the windings wye-wye, or, delta-wye, or, delta-delta, or, wye-delta. Then we can maybe theorize that there may be some other issue like a blown line fuse on the utility primary feeding the primary transformer winding or a blown fuse on a utility capacitor bank.

Before we go there the current should not cause an issue as you are already saying that the voltage imbalance is within 3%.
What is it actually? and, at what value will your parameter trip and for what duration?
Sometimes adjusting the time delay will make the tripping go away if it is set too short.
The current imbalance on the utility side is of no consequence to you as long as your voltage remains balanced, but, its possible your parameter needs to be set to work with the characteristics of both utility sources as the sources may be slightly or significantly different, and, your parameter may be set too tight.

If this transformer is dedicated to you, then it is your current that is imbalanced and you may need to look within.

One thing that you need to check is, the stiffness of the two utility feeds.
Ask the utility to give you the short circuit at your service for each source feed.
If these are different than you may need to make adjustment for each condition.

Does the 600 HP VFD have harmonic filters on the front end?
Do you have capacitors in your facility or does a neighbor or the utility have these and are you having fuses blow that may be causing imbalance?
Have you taken voltage harmonic readings and current harmonic readings at your point of service?
You need to do this while connected to each service and compare those readings and this may provide additional insight along with the source stiffness (utility short circuit).

You mention, "this is what trips out our VFD. Luckily we have 3 other 50hp VFDs that are of a newer type and are able to handle this massive current imbalance."

A current imbalance should be of little consequence to your drives.
Again if this is a dedicated transformer this is "your current imbalance" and you might want to fix it by balancing your load.
If there are multiple customers off this transformer, then others may need to balance the load.

Maybe I'm misinterpreting what you are saying.
Are you saying they measured the primary current in the transformer windings or coming to the transformer windings?
Or did they measure current in the primary line where there is a tap to your transformer?
The first one would be your load imbalance issue and the second one would be their line imbalance issue.
If this is their line problem, they need to balance load or may have a blown capacitor fuse on one phase.
So, it is very important for troubleshooting and to communicate effectively with the utility to get them to fix their problem that we are clear on where the current imbalance is measured.
Regardless, if your voltage is within tolerance your drive should not trip!!
So either your parameter (Voltage Imbalance) is set too tight since the alternate line is different with respect to voltage imbalance, or, this is not an imbalance issue.
Current imbalance, unless it causes out of tolerance voltage imbalance (and you are saying it is not), is of no consequence.
Also - you are not seeing a "Current Imbalance" fault!
There may be other issues you need to consider.

Get the short circuit values and measure the harmonics and compare the lines.
Find out where the primary current was measured.
Find out if there are capacitors on your line and if they may have a blown fuse - a trained eye can ride the circuit and easily detect this.

Why does the 600 HP drive trip and not the 50 hp drives?
Compare the parameter settings.
But, the 600 Hp drive most likely will create much higher levels of harmonics than the (3) 50 HPs and you may have a resonance condition, especially if the alternat utiluty source feeder is less stiff than your normal source feeder.
They 600 HP drive is also a different impedance than the (3) 50 HPs and this is likely why the system responds differently on the alternate source - the alternate source is probably less stiff!

I'm also assuming your power system is grounded, and it is not ungrounded.
If ungrounded, there might be other considerations.

I don't think current imbalance is your root cause.
No "Current Imbalance" trip parameter is posting.
Have you optimized the parameter programming and had per reviews on this?
Reviewing all the drive parameters would


be recommended.
Our ABB drive could not take the imbalance. We ran it perfectly for 3 weeks with a 500kw generator until the Utility put us back to the original substation and now it’s running perfect again. The problem was with the unbalanced primaries coming from the other Substation that caused a voltage imbalance (within ANSI standards ) but causing a large amperage imbalance tripping the drive.
 

Attachments

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
3% voltage imbalance can easily cause 20-30% current imbalance.
 

retirede

Senior Member
Location
Illinois
Utilities are only required to provide voltage within specific voltage limits. These are defined by the State Utility commission and/or service requirement tariff in your State. They may be different for residential v. commercial & industrial. The IEEE published document C84.1 which is a great document in this regard and should be easy for any utility to comply with. However, the utilities legal obligation typically comes from the local utility regulator in the state and the utility should be willing to put in writing so the specific requirement and basis. That being said, it is only a voltage requirement (no current - this is primarily a customer controlled thing) and it will include long term (5 minute typical duration) RMS high and low limits and voltage % balance which can be a function of the load current on the utility circuits - they may need to balance single phase load on a three phase circuit to meet the voltage obligation - but you typically will need good long term recording data to get them to do something with regard to load balance so you can prove the conditions(s) at your service point.

That being said you should not be having the issue you describe.

You mention, "When we tried to run our 600 hp pump after this swap over our VFD would trip out on “Fault Supply Phase”.

What does "Fault Supply Phase" mean?
It seems to me this could mean more than one thing.
So you need to run down all the possible conditions that will cause this parameter to post and initiate trip.
Parameters usually have a magnitude and time delay associated with them so you might need to make an adjustment to the parameter when fed from the alternate source.
But you really need to be sure of what is the cause.
Is this parameter "voltage imbalance", "low voltage", "loss of phase" etc, etc - the term "fault" is not specific enough to fully troubleshoot.
I would make sure you fully explore this parameter with the manufacturer and a Power Quality / VFD programming specialist (like me or others in my firm.).

You mention, "The Voltage coming from our Utility is within 3% but the Current on the Primary and Secondary side of the Utility transformer is off by more then 40% between 2 phases."

You are talking about two things here
First you say the utility voltage is within 3%.
Are you measuring this and how are you calculating this?
Make sure that you are calculating it based on C84.1 and confirm that your drive uses the same calculation for the parameter if it is causing the trip for voltage imbalance.
Is this parameter ("Supply Phase Fault") defined as voltage imbalance? If so, is there a time delay associated with it?
You need to check and verify this.

How do you know the current on the primary of the utility transformer "is off" by 40%?
Not sure what you mean by "off".
The primary current in the utility transformer will be a function of (proportional to) the secondary current.
If this transformer is dedicated to you, then that primary current is your secondary current reflected back to the primary and it would be your current that is off.

Now, we can get into some more detail and find out what kind of transformer pad mount or aerial and the windings wye-wye, or, delta-wye, or, delta-delta, or, wye-delta. Then we can maybe theorize that there may be some other issue like a blown line fuse on the utility primary feeding the primary transformer winding or a blown fuse on a utility capacitor bank.

Before we go there the current should not cause an issue as you are already saying that the voltage imbalance is within 3%.
What is it actually? and, at what value will your parameter trip and for what duration?
Sometimes adjusting the time delay will make the tripping go away if it is set too short.
The current imbalance on the utility side is of no consequence to you as long as your voltage remains balanced, but, its possible your parameter needs to be set to work with the characteristics of both utility sources as the sources may be slightly or significantly different, and, your parameter may be set too tight.

If this transformer is dedicated to you, then it is your current that is imbalanced and you may need to look within.

One thing that you need to check is, the stiffness of the two utility feeds.
Ask the utility to give you the short circuit at your service for each source feed.
If these are different than you may need to make adjustment for each condition.

Does the 600 HP VFD have harmonic filters on the front end?
Do you have capacitors in your facility or does a neighbor or the utility have these and are you having fuses blow that may be causing imbalance?
Have you taken voltage harmonic readings and current harmonic readings at your point of service?
You need to do this while connected to each service and compare those readings and this may provide additional insight along with the source stiffness (utility short circuit).

You mention, "this is what trips out our VFD. Luckily we have 3 other 50hp VFDs that are of a newer type and are able to handle this massive current imbalance."

A current imbalance should be of little consequence to your drives.
Again if this is a dedicated transformer this is "your current imbalance" and you might want to fix it by balancing your load.
If there are multiple customers off this transformer, then others may need to balance the load.

Maybe I'm misinterpreting what you are saying.
Are you saying they measured the primary current in the transformer windings or coming to the transformer windings?
Or did they measure current in the primary line where there is a tap to your transformer?
The first one would be your load imbalance issue and the second one would be their line imbalance issue.
If this is their line problem, they need to balance load or may have a blown capacitor fuse on one phase.
So, it is very important for troubleshooting and to communicate effectively with the utility to get them to fix their problem that we are clear on where the current imbalance is measured.
Regardless, if your voltage is within tolerance your drive should not trip!!
So either your parameter (Voltage Imbalance) is set too tight since the alternate line is different with respect to voltage imbalance, or, this is not an imbalance issue.
Current imbalance, unless it causes out of tolerance voltage imbalance (and you are saying it is not), is of no consequence.
Also - you are not seeing a "Current Imbalance" fault!
There may be other issues you need to consider.

Get the short circuit values and measure the harmonics and compare the lines.
Find out where the primary current was measured.
Find out if there are capacitors on your line and if they may have a blown fuse - a trained eye can ride the circuit and easily detect this.

Why does the 600 HP drive trip and not the 50 hp drives?
Compare the parameter settings.
But, the 600 Hp drive most likely will create much higher levels of harmonics than the (3) 50 HPs and you may have a resonance condition, especially if the alternat utiluty source feeder is less stiff than your normal source feeder.
They 600 HP drive is also a different impedance than the (3) 50 HPs and this is likely why the system responds differently on the alternate source - the alternate source is probably less stiff!

I'm also assuming your power system is grounded, and it is not ungrounded.
If ungrounded, there might be other considerations.

I don't think current imbalance is your root cause.
No "Current Imbalance" trip parameter is posting.
Have you optimized the parameter programming and had per reviews on this?
Reviewing all the drive parameters would


be recommended.
Welcome to the forum.

I think you just set the record for longest first post!
 
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