Contactor Between VFD and AC 3 Phase Induction Motor

Modern transistor PWM VFDs don't leak. That was only an issue for older Current Course Inverters that used SCRs on the output. hardly anybody does that any more.

I am attaching the start up method i.e. inverter for 132 kW motor. You will notice that contactor is used between inverter and motor, where as it is recommended that contactor should not be used in the ckt. moreover you will notice that 2 inverters are used instead of 1 inverter.

From the looks o that, the Inverters are there for redundancy and the contactors isolate one inverter from the other. No problem with that arrangement really, other than the cost... Someone must have had some bad experiences with VFDs in the past and insisted on a back-up unit being installed and wired ready to go just in case one failed. Is the process this is controlling extremely critical?

yes! the process seems to be critical as the humidified air is used in the paint shop of the automobiles and they cant afford 132 kw blower motor to stop at any cost as this blower is suppling the humidified air to the booths and certain temperature has to be maintained when painting of the automobiles is in progress.

But they still only have one blower and one motor! If it were that critical, complete redundancy would be my choice. That way you can also alternate the motors so that wear and tear is evenly distributed and each one lasts longer. This seems like a half-baked attempt.

If the same VFD is controlling more than one motor, then one might have to go for individual contactors at the out of the VFD to each motor to enable to isolate only one motor for any maintenance/inspection, etc.

Otherwise, for stand-alone VFD-Motor set-up, output side contactor is not necessary. It would rather create more harm (switching surges) tahn help. I would prefer an input isolation contactor instead.

I agree, but there are specific safety regulations and/o corporate practices that insist on an output contactor, maybe because if residual energy storage in the capacitors. I actually don't like it myself, I'm just acknowledging that the requirement exists.

Mr.Salahuddin Zia - After having gone through all your threads it seems that you are out there on Energy Audits (particularly electricity) and it seems that you have little experience in this"Energyv Audit" field and practically none in the boiler/steam field. You are out requesting electricial data / reports from members on hatchery/gum/etc., and very recently you started a couple of inter-related energy efficiency threads. Basically you are getting your homework done from us.

Who are you? What is the name of your Company?

I will appreciate you being really honest in your reply before anyone of us proceed further.

If you do not wish to disclose the name of your Company then it will not be difficult to find out too.