Plant power issues - Need advice

[JC565]

Im not an electrical engineer or electrician so please take it easy on me! lol I got some good electronics training in the airforce so I know enough to be dangerous.

I work in an injection molding facility and we have been having alot of problems with different things. Motor overloads, modern heat controllers failing to maintain temps, burned breakers, robots cutting off for no apparent reason, computer UPS's switching on and off alot... etc. We have no caps and no filters and our average power factor is .83.

Ive been trying to do some investigating, and I bought a 190-504 Scopemeter so I can check out some waveforms but I wont have it until Friday. Not sure what I can check with it, but Ill learn or sell it if I cant. In the course of trying to figure out what might be going on, I took a look at our supply. We have a 750Kva Transformer (12470GY/7200 : 480Y/277) .... By my calculations (meaning typing it into a calculator I found in google) I'm getting 902 Amps of 480 available. We have Square D switch gear rated at 3000 amps (I assume that means 3000 total and not 1000 per phase???) We have a 230 transformer coming off that 480 main that supplies a pretty good amount of our equipment but I dont know the exact number.

That switch gear has a Micrologic 6.0A and the built in ammeter is currently showing 640 amp, peaking over 720 at some points. I checked it this morning and when I checked we are probably only running at 40-50% production. Some simple napkin math makes me think that when we switch on another 30% of the plant we are going to be bumping the limits of that 900 amp transformer... and maybe that is and has been the problem all along.

I know I need to do a single line, and I need to get all my name plate data together... and that should happen in the next week or two...

Do you guys think Im on the right track? What I really need from you guys is a "heres your smoking gun to get the owner to hire someone to fix it" .... I just have to justify the expense by showing there IS a problem.

thanks everyone

 

[petersonra]

Motors tripping on overloads and UPS's turning on and off sounds a lot like you have some undervoltage issue.

Best bet is probably to get a recording power quality meter and see if you are getting voltage sags. If so, then you need to figure out why. If the switchgear ammeter is showing a max of 720 Amps, that should not cause the transformer any issues.

Could be the utility voltage is low to start with. Might be taps on the transformer to fix that.

It is hard to tell why the robots might stop, or why the heaters can't keep up.

It is possible you have more than one problem too. For instance, maybe the heaters are just undersized to begin with.

I don't know if you are on the right track or not. I don't think the scope meter is going to do it for you. Might want to consider renting a recording power quality monitor instead. The scopemeter will not do you much good except while you are actually watching it.

it seems odd to me that someone would have paid for 3000 A switchgear that is being fed by a 900 Amp transformer.

ETA: It is possible the Micrologic 6.0A has a Modbus output you might be able to use to send data to some kind of data logger. probably not something you could setup yourself though.

You might want to start by seeing if the power company will install a power quality monitor. Often if you ask the right person there, they will do it for free and give you a report on what they find.

You probably should start a log of when these problems occur. If they happen at the same time every day, that is a big clue.

 

[__dan]

Two things and both are not things the scopemeter will tell you.

Three phase loads will tolerate +- 10% on the Voltage, if balanced, pretty well but they will not tolerate phase to phase Voltage imbalance greater than ~ 1%. Rather than Voltage drop when all phases are balanced, I would look for the phase to phase Voltage imbalance > 1%.

Next would be the main or system bonding jumper. Make sure your neutral to ground Voltage is not over ~ 500 milliVolts indicating a solidly grounded system with the system bonding jumper is in place correctly, working.

If it's plantwide with motor overloads tripping, line to line Voltage imbalance is indicated. One phase is lower or higher Voltage than the others. Inverter and drives will tolerate line to line imbalance much better but tolerate a missing system bonding jumper much less so. Drives, inverters, and UPS tripping, read the error codes and consult the drive manufacturer for their insight on their error codes, but again, make sure the neutral to ground Voltage is not elevated. Noise and higher voltage on the neutral, they will not like that.

Also a good look at everything with a thermal scanner would probably show a lot more than the scopemeter.

 

[petersonra]

If he decides to measure the N-G voltage to make sure the main bonding jumper is in place, it would need to be done across the MBJ with the power on.

Probably going to need a moon suit for that to do it safely. Probably not something that an amatuer should be attempting.

 

[__dan]

If he decides to measure the N-G voltage to make sure the main bonding jumper is in place, it would need to be done across the MBJ with the power on.

Probably going to need a moon suit for that to do it safely.

Disagree. The system bonding jumper can be visually inspected from a safe visual range. Do have to open the necessary cover for that through which does indicate dressing for it.

The voltage difference from neutral to ground can be measured at any point on the system and that's where I usually see the problem first, at a remote location away from the source. Have never tried to measure drop across the MJB or SBJ. Visual yes, you have to see it to see what they did or tried to do.

 

[petersonra]

Disagree. The system bonding jumper can be visually inspected from a safe visual range. Do have to open the necessary cover for that through which does indicate dressing for it.

The voltage difference from neutral to ground can be measured at any point on the system and that's where I usually see the problem first, at a remote location away from the source. Have never tried to measure drop across the MJB or SBJ. Visual yes, you have to see it to see what they did or tried to do.

if you measure it at a remote location you will be including whatever voltage drop there is on the N conductor in the measurement, making it meaningless.

 

[ptonsparky]

You may not have PFC capacitors but the utility may. We have had issues with those switching and VFDs problems. My experience is limited so take that into consideration.

 

[JC565]

Motors tripping on overloads and UPS's turning on and off sounds a lot like you have some undervoltage issue.

Best bet is probably to get a recording power quality meter and see if you are getting voltage sags. If so, then you need to figure out why. If the switchgear ammeter is showing a max of 720 Amps, that should not cause the transformer any issues.

I looked at the max recorded values in the ammeter and they were as follows. 1 - 1544 2 - 1256 3 1272 G 344 We do have some things that run on single phase so maybe thats why that one leg is higher? Bust still 1544 looks pretty excessive to me.

Could be the utility voltage is low to start with. Might be taps on the transformer to fix that.

It is hard to tell why the robots might stop, or why the heaters can't keep up.

It is possible you have more than one problem too. For instance, maybe the heaters are just undersized to begin with.

I don't know if you are on the right track or not. I don't think the scope meter is going to do it for you. Might want to consider renting a recording power quality monitor instead. The scopemeter will not do you much good except while you are actually watching it.

it seems odd to me that someone would have paid for 3000 A switchgear that is being fed by a 900 Amp transformer.

ETA: It is possible the Micrologic 6.0A has a Modbus output you might be able to use to send data to some kind of data logger. probably not something you could setup yourself though.

You might want to start by seeing if the power company will install a power quality monitor. Often if you ask the right person there, they will do it for free and give you a report on what they find.

You probably should start a log of when these problems occur. If they happen at the same time every day, that is a big clue.

Ill get with the power company and see if they can do it for me. Our voltage is low, ive never seen an actual 480 or 230 volts on anything in the building. Not out more than 10% though. Unless is sagging more when the load is way up.

 

[JC565]

Two things and both are not things the scopemeter will tell you.

Three phase loads will tolerate +- 10% on the Voltage, if balanced, pretty well but they will not tolerate phase to phase Voltage imbalance greater than ~ 1%. Rather than Voltage drop when all phases are balanced, I would look for the phase to phase Voltage imbalance > 1%.

Noted. Thanks

Next would be the main or system bonding jumper. Make sure your neutral to ground Voltage is not over ~ 500 milliVolts indicating a solidly grounded system with the system bonding jumper is in place correctly, working.

Sounds like something I need to get into the panel for and let an electrician do.

If it's plantwide with motor overloads tripping, line to line Voltage imbalance is indicated. One phase is lower or higher Voltage than the others. Inverter and drives will tolerate line to line imbalance much better but tolerate a missing system bonding jumper much less so. Drives, inverters, and UPS tripping, read the error codes and consult the drive manufacturer for their insight on their error codes, but again, make sure the neutral to ground Voltage is not elevated. Noise and higher voltage on the neutral, they will not like that.

Also a good look at everything with a thermal scanner would probably show a lot more than the scopemeter.

I was really only interested in seeing the wave forms. Lesson learned I guess. My lady is in school for EE so I'm going to hang onto it for her.

 

[__dan]

if you measure it at a remote location you will be including whatever voltage drop there is on the N conductor in the measurement, making it meaningless.

Yes and no. The ~ 500 miliVolts accounts for the Voltage drop. Usually I am wiring something and at the final checkout I measure the N to G Voltage, so it's always at the remote location.

Under 500 milliVolts is Ok imo. Over 500 milliVolts I will usually always track it back upstream. Usually that's always the missing or improper MJB or SJB. Only on a long run temp service would I see excessive VD N to G, on an otherwise properly grounded system. Regular commercial grade stuff over 500 mV N to G has usually always been the missing MJB or SJB, which I would say is about the most common error to find.

 

[__dan]

Noted. Thanks

Sounds like something I need to get into the panel for and let an electrician do.

I was really only interested in seeing the wave forms. Lesson learned I guess. My lady is in school for EE so I'm going to hang onto it for her.

It's kind of assumed the wave form could be bad, flat topped, and the meter will give scary numbers for THD, Voltage distortion, current distortion.

Current distortion is caused by the load and may be something you can live with. Voltage distortion, Voltage is supposed to be stiff. So excessive Voltage distortion could be something that you need to find the cause of or that may need fixing. It is assumed the meter will read some kind of distortion.

Instead of the meter, distortion will cause the transformers to run too hot too touch. If you go near the transformer and notice they really run hot. That's the information you could be looking for.

Thermal scanning could give some numbers to see if they really are out of spec.

 

[__dan]

And yes, if your plant is routinely tripping a lot of stuff, you need to call an electrician.

 

[jim dungar]

Who owns the transformer?
It is common for a utility t.o put in a much smaller transformer than you think you need for your service. The problem with this is the poor voltage regulation you get when you pull the load you designed for. The poor regulation causes the symptoms you describe in the OP.

Get your utility engineer to your site, have them bring a power recorder. Call your account rep. Do not accept a simple 'lineman with a meter'.

I am 90% sure this is a power source issue.

 

[JC565]

It's kind of assumed the wave form could be bad, flat topped, and the meter will give scary numbers for THD, Voltage distortion, current distortion.

Current distortion is caused by the load and may be something you can live with. Voltage distortion, Voltage is supposed to be stiff. So excessive Voltage distortion could be something that you need to find the cause of or that may need fixing. It is assumed the meter will read some kind of distortion.

Instead of the meter, distortion will cause the transformers to run too hot too touch. If you go near the transformer and notice they really run hot. That's the information you could be looking for.

Thermal scanning could give some numbers to see if they really are out of spec.

Ive got a flir... Ill get some images and post them shortly. We do have some transformers and they do feel hot, but the main 480 to 230 doesnt feel terrible.

I appreciate all of everyones input tremendously.

 

[JC565]

Who owns the transformer?
It is common for a utility t.o put in a much smaller transformer than you think you need for your service. The problem with this is the poor voltage regulation you get when you pull the load you designed for. The poor regulation causes the symptoms you describe in the OP.

Get your utility engineer to your site, have them bring a power recorder. Call your account rep. Do not accept a simple 'lineman with a meter'.

I am 90% sure this is a power source issue.

The Co-op owns it. And the owner just recalled the conversation with them telling us they would upsize it when we were ready. (we probably had 400-600 less hp in the building back then)

With my limited knowledge and the measurments i have seen over the years I do also believe voltage is the issue. As I stated above, Ill get more data and post it. Will call the Co-op to get this all done right but I appreciate the help and maybe someone might have this issue in the future to compare their numbers too.

Thanks again for the help!

 

[jim dungar]

Ive got a flir... Ill get some images and post them shortly. We do have some transformers and they do feel hot, but the main 480 to 230 doesnt feel terrible.

I appreciate all of everyones input tremendously.

Transformers run hot by design.
It is not uncommon to find core temperatures in excess of 150C.