Voltage Imbablance

[powerqualitycc]

Re: Voltage Imbablance

Nearby capacitor banks have been known to cause bus overvoltage trips on drives. When the capacitor closes in there is a momentary short circuit (microseconds) then a ringing transient will occur (usually only lasting about 1/2 cycle). This is normal to the operation of caps and a 3% line reactor in front of the drive will dampen the problem. To verify this you would need a power quality analyzer that is capable of capturing waveforms with at least a 64 micro second response time.

The power quality engineer should be able to tell if you have a bad neutral connection if the connection is upstream of the monitor. Otherwise it was most likely an event on one phase of the 3 phase distribution system. This will cause the other two phases to swell, momentarily while the fuse blows and opens the faulted circuit.

 

[Sebbe]

Re: Voltage Imbablance

Sorry to steal the post, but I am seeing a similar problem. I am using a 11kW VFD with a triplex pump (piston) connected to the motor. When using standard "wall" power it works flawlessly, but when I try to hook it up to a 24kW generator it trips on overvoltage when I start to load the VFD. Does anyone have a suggestion why and how this is?
Thanks for any help!
Sebastian

 

[comaqc]

Re: Voltage Imbablance

This is quite an interesting thread for me as it relates somehow to my own problems with my induction heaters group of power supplies. While my system is fed from 208 WYE transformer secondary, I see that JNH has reported possible DC bus swings caused by phase unbalance in a circuit which sees primarily a constantly balanced load from a 3 phase rectifier input. For a lack of not having found any explanations for the two weeks long series of random failures of our induction power supplies, I blame phase unbalnce as the culprit causing the overvoltage surge suppressors installed on each power supply to kick in and blow a fuse. I'll certaily be following this thread for informantion.
JNH, may you will get lucky like me and have the problem resolve itself without any definite action on your part. Our 61 induction heaters have been running without problems for 8 days now. The only recorded change done to the system was to readjust the air gaps on each workcoil to meet our specs. This action has a direct impact on our DC bus voltage, but our engineer had checked it to within acceptable maximum range when he was trouble shooting the system when it was failing.
I do not sleep well on this issue as I know that what disapeared without knowing the root cause of the problem might come back to haunt us.