Problem With Periodic Overvoltage Surges

If you have, "two incomers coupled through a bus coupler", how can they operate independently?

Since you are an electrical engineer, do you have any thoughts on the subject?

The bus coupler would be in OFF condition under normal conditions. In case I want to do some maintenance work on one of the two transformers, I can switch off the incomer which is being powered by that transformer and charge the bus through the other incomer and the bus coupler.

OK, let's go another route.

Have you done anything to try to solve the problem, other than come here and ask for help?

If you have done anything to try to solve the problem, other than come here and ask for help, what was it?

Can you add any more information the meager trickling offered so far?

1) We have checked the transformer neutral (to find out if its floating or if its effectively earthed)

2) We have cleaned all possible insulating supports (in case theres some tracking because of dust and in case if the neutrals floating then there is a chance of overvoltahe in the system)

3) We have tightened all the nutbolts of the power cables (to avoid sparking)

4) We have meggered the cable which connects the incomer and transformer. (again faulty cable and a floating neutral may lead to an overvoltage)

Dear MSCS,

You have mentioned that normally bus-coupler is kept in OFF condition i.e.,one 2Mva trasformer catering the particular drive loads thro' one incomer. Please mention the distance of MCC panel to motor i.e., the length of the cable connected betn.MCC panel to motor .For higher length of cables, inductors are used to mitigate generation of higher voltage due to Ring effect(for PWM Drives). Please take care of the above and hope ,your problem may be solved.

Thanks,

Manindra

Have you checked what is the actual voltage at the two transformers that feed the two ends of your distribution panel? Maybe the source for one of them actually has an overvoltage. Until you rule that out, there may be a good reason your VFDs are tripping.

Hate to spoil the surprise but VFDs don't overvoltage trip from power side only, sometimes OV comes from load side (what they see as load anyway). First make sure on what is the OV source. And are any PFC caps on line at switching time? S.M.

Your stated observation that all three VSDs trip (and I assume they are tripping at the same time) suggests to me that the problem is "real" and is from the supply side. If it was a load problem, then you would expect only one to trip.

I would expect that the operational power station would have appropriate monitoring devices that could be connected to monitor the infeed and confirm the waveform/voltage/phase match for the suspect feeder.

Is there a tap changing transformer in the feeder? Maybe the transients are causing the trip.

Is there one large load that "dumps" and the transformer reaction spikes the other VSDs?

What else is on that "network" that could cause transients?

Have you run the system for prolonged time of the single "good" feed?

Are the trips happening at shift changeover or some other significant time in the operation of the facility?

do the VSDs have proper protection to stop them affecting the incoming supply waveform (and thus tripping the others)?

There are many investigiations that you still need to do and please be assured you will find the answer by following good Engineering practice.

Define the problem (in time and space. What, When, Where, How often, etc)

Look at what has changed, or whether the problem existed since the plant was commissioned. (like service of the transformer or exchanged for maintenance.)

Determine hypothesis for possible failure modes.

Test (desktop review) whether those failure modes match the What, when where etc conditions.

Verify this by removing that stimulus or altering it in a controlled manner.

CHECK the results again and test any other viable causes. (Rarely there are two together.)

Verify again.

Take steps to correct the identified disturbance.

Take steps to make sure that the same thing doesn't happen in other processes (Like your other transformer feed.)

Good luck. Enjoy the journey.

:)

need your more information :

1. are these 2 transformer get from one source ?, if not you must check carefully on both voltage and frequency

2. If these come from one source, are these transformer has the same spec ie. brand, vector group, step voltage ?, must have same output.

3. Please check with coupler open with no load, both output voltage-Must has the same output of voltage. And try to load on each transformer with isolated from other of course and compare with load on the other, their must have the same point of value, if not - could be one of this transformer drive the fault.

May be tripped VFD in load side . you cheak load side and breaking resister.

If you monitor every vital component in the system bu trips/alarms you can avoid disasters like fire/explosion. It is advisable to include duplicate components to avoid power failure.

Do you have a surge protection device installed ? Several clients have reported solving the tripping problem after having installed a set of SPD's. Their VF Drives have been often tripping for inexplicable reasons. If interested, can send you a paper on SPD usage with VFD's from Phoenix Contact.

MADHAV