Earth Fault Problem in 260 KVA VFD

Is there an earth loop, i.e. something is earthed at more than one place?

If the system works for 10 to 12 hours and fails, and the problem is repeatable, then most likely the problem is overheating.

Has the system worked for a long period of time with no problem?

Has the air temperature been hotter than usual?

Are any of the air vents obstructed?

What was changed just before the problem started?

Is the slurry thicker or thinner than usual?

Is more slurry being processed than usual?

Do any parts show indications of overheating?

If none of the preceding correct the problem, you may have to try either increasing or decreasing the amount of cooling to differents parts of the system.

Good Luck

What are your trip thresholds?

VFD's tend to be intrinsically electrically noisy. I have seen too sensitive settings cause nuisance tripping. However, I have also seen the power conversion section start leaking current through the devices, especially as they get hot. With junction temperatures at 100C they will often have 10 x the leakage cold. With an imbalance in devices you may get asymmetrical phase loading and this erroneously picked up as a ground fault.

You can often help isolate the problem by using independent metering on the ground returns to actually measure the ground current and move through the system until you find its origin.

And then there was the system where the isolation transformer ground fault kept alarming and the VFD kept tripping. It was thought the transformer only fed the drives, but there was a high pressure lamp on the system that had gone to ground. The transformer alarmed, and the drive shutdown on its ground fault detection.

Happy hunting gremlins.

You could have a problem with wire degridation or insulation overheating during operation. Have you tried to use earth leakage monitoring?

Pls check your cable inside the motor terminal box, there's a posibility that the cable insulation is leaking.

Suggestion:

1. insulate motor cable which is directly touching the terminal block

2. run and observed unit operation, check parameters and temperature etc.

Dear,

there are always a faults behind every trippings.

earth fault means one of your phase is touching the earth. If you assume that motor & drives are ok even in hot conditions, ( does tripping occure after a definite time of operations ? ) check for the connections - of cable. - near cable gland, there might be a cut.

I agree with the answers mentioning current leakage / current unbalance due to heating for about 10-12 Hrs as in your case. We faced similar problem with our VFDs. We provided a separate fan to cool the enclosure to overcome heating which solved our problem. Another problem we faced was dust entry into VFD panels. When we cleaned the cards properly, we could avert tripping without any reason for a much longer time.

hv u checked the connection of ur CT cos if ur CT is connected in reverse order it can cause ur equipment to trip on earth fault

Wheather the cooling system in proper in drive room if not then first of all check the cooling system.In zinc plants mostly there dust is cunductive in nature. so provide the separate room arrangement for the drive panels .then this type of problem will rectify.

if ur drives tripped earth fault so its not started.how at any cost.

May be some where is wrong.chcked ur earthing its proper or not.

if any control circuit in loop that may be chance to triped the drives.

checked the gland of Motor cable.May be its due to vibration and noise spikes.

that welding Machine was connected neare the area with out pricosion.

checked the insulation of inside termination.

Dear Mr.rameshchandsharma1

I want to supplement for the details furnished by Mr.Carl Pugh, pertaining to EARTHING.

I also faced a similar problem. In your case the system has worked for 12 Hours. In my case NOT even 30 Minutes. Every expert I called, came and checked and declared installation is OK, but the problem continued.

Finally other expert came and after checking, he advised to remove 6 swg. G.I., Earth wire and provide EARTHING FLAT 3 TIMES OF THE RECOMMENDED CAPACITY - then the problem did not arise or repeat.

It cannot be concluded that the problem is solved, siince at that point of time load reached was 60% only and it is to be seen at full load.

Now after increasing the EARTHING FLAT to 3 times of the Recommended value - HOW the Problem GOT REDUCED/SOLVED - IS TO BE UNDERSTOOD.

I request the CR4 MEMBERS to share their Experience in this matter, and can explain how increasing earth flat size helped to solve the problem.

Rajeswari.