High Voltage

They are recording the crest (or peak) voltage of the 240 volt rms nominal phase to ground voltage (240 x square root of 2).

Maybe I didn't ask the wright question. If we have a system rated for 277 and we are getting peaks of 300 to over a 1000. What kind of problems if any could this cause?

There are many problems which could cause the symptoms you describe. It could be a malfunctioning switch on power factor correction capacitors (yours or the power company's), a bad connection on one of the hot phases causing excess neutral current, harmonics from a nearby plant, or other faults. Are the transformers yours (part of a unit substation) or the power company's? It doesn't make a difference electrically, but it will affect what steps you can take ion troubleshooting the problem. Also, is the transformer neutral directly grounded, or connected through a resistor?

• I suggest checking the neutral-to-ground voltage, particularly during the spikes. If you see more than about 5 volts on a direct-grounded unit, you likely have a problem with the neutral connection from the transformer to ground.
• Look for a pattern in the voltage activity. Does it happen at a certain time of day, or when certain equipment is operating, starting or stopping?
• Also, find a time when you can disconnect all of the load on that service for several hours, then run the recorder on the transformers. If the high voltage and spikes still occur, the problem is at or above the transformer. If not, it's either in your plant or is load-dependent (such as the bad connection on a hot phase).

1. We do not use capacitors on our side.

2. Transformers belong to the power company.

Electricians have refered to our system as an ungrounded sytem. Only three phases coming to our gear. No neutral or ground.

After our fire we had techs come and check all equipment and wires with megar. Replaced all bad equipment. The old switch gear is what was damaged by the fire. Replaced with new Eaton. Came with a monitor. New monitor failed so we sent it back to the factory. They claimed the internal memory showed failed due to an excess of 1000 volts. When this spike occurred we had several motors turn off just like someone hit the off button.

Well, that's a new one on me. I've never heard of a 277V delta system. 277 is the nominal phase-to-neutral voltage of a 480V wye connected system. I don't know of any reason it shouldn't be used, it's just not very common.

I'd still check the voltage with the plant off-line. If the spikes remain, it's definitely the power company. If the spikes disappear, connect one load or panel at a time & check the voltage.

Although no expert on land based distribution systems, my gut feeling here is that there is a large inductive load being switched nearby on the HV line (not the 480v but the 3.3Kv or higher line). This could be a large pump, or even a generator with poor regulation. You don't say what part of the world you are in, but I know here in the UK, there are strict limits to the size of motor you can start DOL. You are going to need more help from the power company, in finding the source, as they will have to monitor further up the distribution system. You could ask around to see if any local company has installed new plant, and if the problems occurred shortly after the new equipment was commissioned? One of your points was that "all the motors stopped", and this would indicate to me a big voltage dip, causing the motor contactors to drop out - again I think symptomatic of a large load being started. I hope you will keep us all informed as to what you find out in the end??

Ok... for what it is worth, here is what I think you have and should do.

You have 3 phase 4 wire "Wye" system where the phase to phase voltage is 480 volts, this means the phase to neutral voltage is 277 volts. It appears that you have no 277 volt loads in your facility so the "neutral" was not brought in to your plant.

This is permitted, at least it is under the Canadian code - I do not know about the US code.

Your neutral may or may not be grounded, if it is not grounded, you should have a "ground fault detector" installed on your three phase distribution system somewhere. As well, if the system is not grounded, there should still be an incoming "bonding" conductor from the switchgear.

If the neutral is grounded, a volt meter placed across a hot phase conductor and ground will show 277 volts. If you see anything less then 277 volts, say 80 volts (or some other random number) your system is not grounded and you have a ground fault somewhere on that particular phase, check all three phases.

The first thing you need to do is understand what type of system you have as ungrounded system can generate some pretty strange voltages due to load imbalances, which should be minimal in your case as you appear to have no phase to neutral loads.

Once you understand exactly what type of system you have, a proper course of action can be planned. If voltage issues from an ungrounded system are ruled out you will need to get a recording voltage analyzer on the system to watch and see what is going on.

It is never, in their opinion, the power companies fault or problem to regulate, you will need to document what is happening then go to them with the data.

Rick...

What about the open-delta, this can have very floating voltage on the open leg, and if the motor control (or anything else) is hooked across this leg the voltage can drop and controls drop-out causing motor stops. This may have happened when the fire caused things to get re-wired and some phases may have been mis-labeled.

Dan

I agree... another reason as to why they need to "know" what it is they have as far as a system is concerned.

I don't understand how the "delta & wye" thing works. Maybe if I did it might be easy to understand. I think the hight voltage problem is what caused the fire and thats why the power company is on defense.

jasons, you sound American. If the local Power Company has an over voltage that high, they will correct it. I can't believe they will try and dodge it. They are responsible for the power they provide to your plant, what happens inside the plant is your problem.

James