VFD starting several motors
VFD starting several motors
(OP)
Dear All,
I would like to know your pros and cons for using only one VFD for starting several motors. The application had four 350 hp 8 pole 3-phase motors involved and once the VFD starts the first motor then the second one is started using the VFD and so on. The problem here is some of these motors fail frequently, even since commissioning with factory motors.
Motors was rewound by several EASA´s workshops using Inverter duty materials and procedures.
Thanks for your inputs
Petronila
I would like to know your pros and cons for using only one VFD for starting several motors. The application had four 350 hp 8 pole 3-phase motors involved and once the VFD starts the first motor then the second one is started using the VFD and so on. The problem here is some of these motors fail frequently, even since commissioning with factory motors.
Motors was rewound by several EASA´s workshops using Inverter duty materials and procedures.
Thanks for your inputs
Petronila
RE: VFD starting several motors
- Cheaper, maybe.
Cons
- Only 1 VFD so if it gives issues everything is down or you start the motors full-voltage.
- Much more complex, need all the interlocking and switching. Can be harder to lockout and to work on one motor while others are running.
RE: VFD starting several motors
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD starting several motors
RE: VFD starting several motors
Can you tell us what the failures of the motors have been - the reports by the repair shops? Also, what is the application?
If there is not a synchronizing of the VFD output frequency and phase with the mains supply with paralleling of VFD output with the mains for a short time for the transfer - for a bumpless operation (I think a project special feature by integrators requiring extra electrical equipment) - then there will be a 'bump' transfer.
The VFD output should be stopped and the output contactor opened then the bypass contactor closed. This takes a little time so the motor rotor could be much slower in rpm (and therefore frequency not forgetting slip) than the mains frequency. How much it slows down could depend on the application.
At the moment of closing the bypass contactor there will be a current inrush. Now this can depend on the delay time as the magnetic field in the motor may or may not have died and there is the question of the difference in phase angle. There have been some threads on this before, try https://www.eng-tips.com/viewthread.cfm?qid=187116.
If you are transfering the motors from VFD to mains constantly and have high current inrushes, you may be, basically, exceeding the number of starts per hour and your motors are failing for that reason as opposed to not (or were not) inverter duty motors?
Drivesrock
RE: VFD starting several motors
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