Overvoltage during a VFD start
Overvoltage during a VFD start
(OP)
Hi,
We're doing a commissioning procedure over a 150kW (460Vac) conveyor. This motor have a VFD.
During the start (without load)we note an overvoltage on the 460Vac MCC that feeds the VFD.
It could be a problem on the transformer? or some kind of harmonics distortion that is causing this effect?
We're doing a commissioning procedure over a 150kW (460Vac) conveyor. This motor have a VFD.
During the start (without load)we note an overvoltage on the 460Vac MCC that feeds the VFD.
It could be a problem on the transformer? or some kind of harmonics distortion that is causing this effect?
RE: Overvoltage during a VFD start
Standard motor voltages are multiples of 115 Volts, standard system voltages are multiples of 120 Volts.
A 460 Volt rated motor is intended to be operated from a 480 Volt supply.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: Overvoltage during a VFD start
I doubt it was harmonic distortion.
RE: Overvoltage during a VFD start
Been there, doe that.
I have seen it in the field.
I have seen it in the lab.
I have put the scope on it in the lab.
Metering errors are common on unloaded wye-wye banks.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: Overvoltage during a VFD start
Is it a Line Regenerative VFD?
Do you perhaps have Power Factor Correction Capacitors connected to the MCC?
Details matter...
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Overvoltage during a VFD start
Here more details:
Motor voltage: 460Vac 50hz
MCC voltage: 480Vac
After discuss with our supervisor, we have more relevant information: the length of the cable from the VFD to the motor is about 580 meters. Due that the drive have a sinusoidal filter in order to minimize the capacitive effect on the equivalent circuit.
Cause this is a brand new area, no other equipment is running.
Is possible that this filter is contributing to the system become a pure capacitive?, cause at this moment there is no other motor (inductive load) running and the system is getting in resonance.
This could be possible?
Raul
RE: Overvoltage during a VFD start
I’ll see your silver lining and raise you two black clouds. - Protection Operations
RE: Overvoltage during a VFD start
RE: Overvoltage during a VFD start
Motor voltage: 460Vac 60hz
MCC voltage: 480Vac
Would be considered exactly right.
Both a 460 Volt motor and a 480 Volt MCC seem unusual for a 50 Hz system.
If that is a 60 Hz motor then 480 Volts is much too high for 50 Hz.
The filter should not affect the line voltage when the motor is not running and probably not when the motor is running.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: Overvoltage during a VFD start
The ONLY thing that a standard diode bridge front-end VFD can do to possibly affect the LINE side voltage is if it is resonating with capacitors on the line side bus, in which case the VFD would also be tripping on Over Voltage of the DC bus, probably first. If you have a capacitor bank on the 480V MCC bus, that is your problem. If it has a contactor to disconnect it from the bus, open that contactor and see if your problem goes away. If there is no contactor controlling your capacitor bank, that is the problem you must fix.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Overvoltage during a VFD start
Hi @jraef, the VFD is an active front end (ACS880-37). Based on your explanation there is no way that the sinusoidal output filter could being causing this overvoltage, right?
I'm in Brazil bringing support to our guys at site in Chile. I will ask them for more information including the confirmation of a capacitor bank on the MCC bus.
Thanks!
RE: Overvoltage during a VFD start
What burned exactly?
Resonating with capacitors is a possibility, but the VFD should have tripped on over-voltage if the voltage was reaching damaging levels.
RE: Overvoltage during a VFD start
At the same area we have a MV drive (ACS2000) with some fans in 480Vac that are feed by the same 480Vac bus, they have burned due this overvoltage. Also we have a crane that trips by overvoltage when the conveyor was running.
RE: Overvoltage during a VFD start
It’s one of the risks of enthusiastic salesmen selling a complex technology that really should have a qualified engineer looking at the entire situation. AFE drives are great, but WAY more complex than standard 6 pulse inverters.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Overvoltage during a VFD start
Yes we have some non-AFE drives on the same 480Vac bus. They are tripping due overvoltage when the ACS880-37 is running, also the main transformer is vibrating.
All this effect could decrease when the rest of the equipment begin to operate? There are a large number of inductive loads that are being commissioned.
RE: Overvoltage during a VFD start
Again, I stress the need for you to involve ABB in this discussion. Everyone that makes AFE drives has a "secret sauce" in their AFE algorithms and LCL filter designs so they all behave slightly different to specific situations. The best people to address yours are those that understand their own products.
I have been involved with several projects using Rockwell's PowerFlex 755T AFE drives and have had success simply adding Line Reactors to the other drives (which I felt should have been there anyway). But just because that worked on that brand is not a guarantee it is the right solution for the ABB drives. I put a Rockwell AFE drive into a pump station where there was an existing ABB ACS800-U37 AFE drive (the predecessor to the ACS880) and as soon as the Rockwell drive was powered on, the LCL filter in the ABB drive over heated and caught on fire!
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Overvoltage during a VFD start
With a true active front end drive there should be a large input inductor, of around 10% impedance (Z) and there may be a PWM filter in there too - parts of the "secret sauce". The active front end control must 'know' (be programmed with) the correct value of that inductor else the voltage boost to be performed across it may be divided between the inductor and the supply inductance (perhaps the MCC supply transformer) and in this case you would see the MCC volts rise.
And for the input harmonics to be very low, the DC link voltage may be around 110% x the normal dc link voltage of a diode rectified 480Vac supply (eg. 1.35 x 480V =648V) so around 720Vcc.
Another aspect you perhaps need to be concerned about is your motor. If you do have a boosted dc link voltage the PWM voltage will be higher and with the long cable run the motor insulation will be under greater stress.
RE: Overvoltage during a VFD start
Thanks @Drivesrock!, we are using a 1k class cable for the motor, but I didn't understood your comment, is possible that the drive could being supplying a higher voltage to the motor?
RE: Overvoltage during a VFD start