3 Phase 4 wire Voltage issues

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rfunk1929

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N.Y.
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Facility Maint
Hello all
I run the maintenance shop at a senior living facility. Our feed from the road to our building is supplied by NYSEG. For the past few weeks I had several electrical motors/VFD'S/ Contactors and Ballasts go bad. Not new by any means but then my elevator stopped running due to low voltage too drive. So I started going around the building checking legs on panels and all 3 legs are low. I went to our main connect that is 20ft from Transformer on pad . I got on leg 1 262v to N Leg 2 264v to N and leg 3 263v to N. This is while under load on a 480/277 service. My question is what is the allowable voltage drop from the supplier to our connection. In any other building I have been in each Leg was very close to 277 as it should be and 480 leg to leg at over 100ft from transformer. I had the power company out and they agreed voltage was low and that they are going to bump sub station but this morning still lower then I would like to see. It is better then yesterday I was getting like 256v on the legs. I cannot find anyplace what the acceptable power should be from the supply with this type of service. should it be 480/277 + or - a volt or two or does it fall under the 5% / 3% rule. Any info would be greatly appreciated.
 
What is capacity of transformer and how much load was on it at time you measured those voltages?

Start overloading it and you will start to see voltage dropping as a general rule.

POCO's are good at sizing their service transformers smaller than most would size a customer owned transformer.

Also possible load has been added over time and existing transformer now has more load than when it's size was selected, or you going through a spell where load is temporarily higher than you normally see for some reason. Not sure what your weather been like but a heat wave could be the cause for such thing.
 
I'm sure the summer time a/c usage has not helped but the power here even in the winter has been lower then I like to see. My plan is to kick on our generator so our building load is on that and see what our numbers are for incoming power with no load and see what I get. I worked at a saw mill and with all the saws and Equipment going we still had 478v at the main leg to leg.
 
rfunk1929 said:
I'm sure the summer time a/c usage has not helped but the power here even in the winter has been lower then I like to see. My plan is to kick on our generator so our building load is on that and see what our numbers are for incoming power with no load and see what I get. I worked at a saw mill and with all the saws and Equipment going we still had 478v at the main leg to leg.
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could be the POCO has had enough load added over time that they need to make some changes and at very least maybe put in a tap changer closer to your location on their system? Boosting at point they currently have for a tap changer maybe puts some far enough upstream a little on the high side but you are far enough downstream that you still lagging on the voltage. Just a possibility. And if summertime loads are generally higher than other times that don't help either.
 
I agree. This is the first place I have ever seen voltage this low on. I just got off the phone with my friend who is a linemen and he said acceptable operating range for voltage at the point of entrance of service on a 480/277 is 432v-504v. He did say that the equipment would function better and be more efficient at 477v-501v. while 432v seems very low to me I guess while under load it should be ok. I just wonder what that does to your amperage at that point. He said NYSEG should be able to adjust the taps on the transformer to get my voltage to a more efficient voltage but he also said it is NYSEG and if it is within their limits most wont mess with unless the linemen is a good guy and don't mind doing some extra work. My next gen test is next Tuesday so I will check the lines with no load on then to see what I have. Or just keep bugging NYSEG until they bump it up a little more.
 
rfunk1929 said:
Hello all
I run the maintenance shop at a senior living facility. Our feed from the road to our building is supplied by NYSEG. For the past few weeks I had several electrical motors/VFD'S/ Contactors and Ballasts go bad. Not new by any means but then my elevator stopped running due to low voltage too drive. So I started going around the building checking legs on panels and all 3 legs are low. I went to our main connect that is 20ft from Transformer on pad . I got on leg 1 262v to N Leg 2 264v to N and leg 3 263v to N. This is while under load on a 480/277 service. My question is what is the allowable voltage drop from the supplier to our connection. In any other building I have been in each Leg was very close to 277 as it should be and 480 leg to leg at over 100ft from transformer. I had the power company out and they agreed voltage was low and that they are going to bump sub station but this morning still lower then I would like to see. It is better then yesterday I was getting like 256v on the legs. I cannot find anyplace what the acceptable power should be from the supply with this type of service. should it be 480/277 + or - a volt or two or does it fall under the 5% / 3% rule. Any info would be greatly appreciated.
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263V is lowest that should be supplied by POCO.
has the transformer been changed or worked on? Could be if someone changed the XF a tap could be off one step
regulators close between you and the substation? Could be the regulators are messing up or set wrong.
find out what maintenance or changes they have made in the last 10 weeks that could have made a difference.
Ask for a datalogger to be installed at the service point, and that your burning motors with the low voltages
 
rfunk1929 said:
Hello all
I run the maintenance shop at a senior living facility. Our feed from the road to our building is supplied by NYSEG. For the past few weeks I had several electrical motors/VFD'S/ Contactors and Ballasts go bad. Not new by any means but then my elevator stopped running due to low voltage too drive. So I started going around the building checking legs on panels and all 3 legs are low. I went to our main connect that is 20ft from Transformer on pad . I got on leg 1 262v to N Leg 2 264v to N and leg 3 263v to N. This is while under load on a 480/277 service. My question is what is the allowable voltage drop from the supplier to our connection. In any other building I have been in each Leg was very close to 277 as it should be and 480 leg to leg at over 100ft from transformer. I had the power company out and they agreed voltage was low and that they are going to bump sub station but this morning still lower then I would like to see. It is better then yesterday I was getting like 256v on the legs. I cannot find anyplace what the acceptable power should be from the supply with this type of service. should it be 480/277 + or - a volt or two or does it fall under the 5% / 3% rule. Any info would be greatly appreciated.
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The supply voltages are typically set by the agency of your state government that has authority over electric utilities. In my state that would be the Illinois Commerce Commission, but other states use different names.
 
don_resqcapt19 said:
The supply voltages are typically set by the agency of your state government that has authority over electric utilities. In my state that would be the Illinois Commerce Commission, but other states use different names.
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But isn't ±10% of nominal sort of the common value for most places?
 
kwired said:
But isn't ±10% of nominal sort of the common value for most places?
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I think so. The rules in Illinois say:
Section 410.300 Voltage Regulation
a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.
b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.
c) Variations of voltage in excess of those specified above shall not be considered a violation of this Section if caused:
1) by operations of a retail customer in violation of an agreement with or the rules of the entity;
2) by the operation of apparatus on a retail customer's premises that results in large inrush currents;
3) by infrequent and unavoidable fluctuations of short duration due to system operation; or
4) by acts of nature or other situations beyond the entity's control.
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rfunk1929 said:
Hello all
I run the maintenance shop at a senior living facility. Our feed from the road to our building is supplied by NYSEG. For the past few weeks I had several electrical motors/VFD'S/ Contactors and Ballasts go bad. Not new by any means but then my elevator stopped running due to low voltage too drive. So I started going around the building checking legs on panels and all 3 legs are low. I went to our main connect that is 20ft from Transformer on pad . I got on leg 1 262v to N Leg 2 264v to N and leg 3 263v to N. This is while under load on a 480/277 service. My question is what is the allowable voltage drop from the supplier to our connection. In any other building I have been in each Leg was very close to 277 as it should be and 480 leg to leg at over 100ft from transformer. I had the power company out and they agreed voltage was low and that they are going to bump sub station but this morning still lower then I would like to see. It is better then yesterday I was getting like 256v on the legs. I cannot find anyplace what the acceptable power should be from the supply with this type of service. should it be 480/277 + or - a volt or two or does it fall under the 5% / 3% rule. Any info would be greatly appreciated.
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Motors require +/-10% long term per ANSI. The contactor must hold to 85% without tripping. Drives use similar values. So 90% of 277 Zv is 249 V…you are getting close to that. If you have 3.% voltage drop to the loads you are out of tolerance. CBEzMA standards give the utility a +/-5% window. After allowing for a 3% voltage drop from line losses and 2% sag on the utility that gives you 10%. With motors it’s a delta load so I don’t really care what voltage to neutral is anyways except to verify grounding. Measure line to line. The transformer will be 2.5% taps so even tapping up only gets you to around 266 V, exactly what you have. During summers utilities often reduce their AVRs 5% to conserve power but it causes other problems. They need to stop doing this or tap something other than the last transformer up. Be careful that you don’t get into trouble when they reduce it in the fall. I’m guessing that a 1-2% dip is low enough that the VFD declared it not good enough. That’s a common tight lower limit. I usually set them to 80-120% since industrials often have large motors and soft busses.

Motor torque is proportional to the square of voltage. So if voltage drops 10%, torque drops 21% so as a consequence the motor works harder. It might be within name plate but it stresses motors more so the insulation breaks down sooner and you may see a rash of older motors fail on insulation cracking early. Older drives had terrible short circuit ratings (5-10 kA, UL minimums). The manufacturers either “warn” you with some crazy fuse requirements or just hide it in the manuals. So if it isn’t protected especially small VFDs will be destroyed if the motor shorts to ground. So often loss of the motor destroys the VFD. On the other hand it will maintain output voltage so you can ignore los voltage on the motors.

You may want to consider paying fir a power monitor or a power analysis (monitor for 2 weeks). You may have severe harmonics causing momentary sags or you might be getting transients eating things up. This would certainly cause a lot of damage regardless of the voltage and is usually more suspect with a rash of failures.
 
Effects with motors on VFD's gets more complex. Might not even have problems in this situation if motor doesn't run very close to full rated capacity, same if drive is rated more than the motor it drives. If running the output at less than 60 Hz, you also are not running at full rating, even if you are running at max rating for whatever speed you are running.

The thing with a VFD is whether DC bus voltage drops too low. When running at lesser speeds or lower overall output rating this won't happen so easily. Could even lose an incoming line conductor and if not loaded enough never know about it, until motor demand goes up enough that DC bus drops too low. That usually will trigger drive protection with an undervoltage error code and usually needs manual reset or total power shutdown before it will allow motor to run again. It probably won't harm the motor in such cases where on a drive as output will still be within established parameters as long as DC bus remains high enough to deliver the needs.
 
USERC, which is mostly western power utilities, requires +-5% at the service entrance. So 262V L-N would be out of compliance. I have no idea what governing authority supports NY though.
 
Ok so I now have the building running on our cat generator and the voltage is 480 on all three legs and 277 to ground on all three. have roughly 117v on my longest run for outlets. switch back to utility company and have 458 461 461 on the legs and voltage at that outlet is around 108v. On the generator everything runs great even the drive for the elevator we have been having issues with but when I switch over i start having issues again.
 
rfunk1929 said:
Ok so I now have the building running on our cat generator and the voltage is 480 on all three legs and 277 to ground on all three. have roughly 117v on my longest run for outlets. switch back to utility company and have 458 461 461 on the legs and voltage at that outlet is around 108v. On the generator everything runs great even the drive for the elevator we have been having issues with but when I switch over i start having issues again.
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I would begin suspecting a bad neutral connection on your utility feed then.
 
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