Vfd

HI All,
Is it important to place a contactor relay before the VFD for powering up the VFD.

No

Yes it be important when need to switch off your Inverters also when there is Emergency..(i mean through Emergency PB)....

Gope_69 said:

Yes it be important when need to switch off your Inverters also when there is Emergency..(i mean through Emergency PB)....

Click to expand...

MCB on the Input can isolate the invertor (sized to invertor).

For emergency i would not have the contactor on the input to the invertor but put it on the output.

504bloke said:

MCB on the Input can isolate the invertor (sized to invertor).

For emergency i would not have the contactor on the input to the invertor but put it on the output.

Click to expand...

Dave
Seems to me if the contactor (or a shunt trip breaker) is on the input side of VFD then in emergency or a fault you would be deenergizing all of it (VFD motor etc). What is your reasoning to place contactor on VFD output side?

Dan Bentler

Surely with all the capacitors inside the vfd, it is better to cut off the output rather than the input. That way you are sure that all stored energy is cut off from the drive. The new danfoss drives do not need the high power removed in emergency. They have a special emergency circuit built in which meets ce directive

Glenwhere? said:

Surely with all the capacitors inside the vfd, it is better to cut off the output rather than the input. That way you are sure that all stored energy is cut off from the drive. The new danfoss drives do not need the high power removed in emergency. They have a special emergency circuit built in which meets ce directive

Click to expand...

Beat me to it, contactor on output of drive breaks all electronic circuits to the motor.

My old Ansaldo VFD's had a contactor prior to the drive. I am changing them to Powerflex 700VC drives which have a hardware enable digital input (I kept the contactor as the PLC performs some checks (ensures that the regen unit is fully working, etc) before pulling it in).
My E-Stop (Pilz safety relay) quickly ramps the drive to zero then disables the hardware enable, while the Ansaldo drives would quickly ramp down then remove power to the contactor.
I agree that I would not like to keep cycling the power to a vfd, but for a new installation (multiple drives, regen unit) I think I would use input contactors so the PLC is in control when power can be put to the drives instead of the main switch.

creativepaper said:

My old Ansaldo VFD's had a contactor prior to the drive. I am changing them to Powerflex 700VC drives which have a hardware enable digital input (I kept the contactor as the PLC performs some checks (ensures that the regen unit is fully working, etc) before pulling it in).
My E-Stop (Pilz safety relay) quickly ramps the drive to zero then disables the hardware enable, while the Ansaldo drives would quickly ramp down then remove power to the contactor.
I agree that I would not like to keep cycling the power to a vfd, but for a new installation (multiple drives, regen unit) I think I would use input contactors so the PLC is in control when power can be put to the drives instead of the main switch.

Click to expand...

Speaking of PowerFlex series, Allen Bradley DOES NOT recommend a contactor on the output side of the VFDs.
Just the input.
Though, I have done a few jobs where the contactor was placed on the output side and haven't had any issues.
And yes, the contactor is used in case of an Emergency stop condition where you should kill all power.

If you use the AB PF700, and use the contactor after the drive (which I prefer). I have found that it is also a good idea to break the Enable to the drive(hard wired) to bypass the decel ramp, or any DC injection used. Otherwise there is a lot of arcing going on in the contactor, and will weld the contacts together.

504bloke said:

MCB on the Input can isolate the invertor (sized to invertor).

For emergency i would not have the contactor on the input to the invertor but put it on the output.

Click to expand...

Not according to Mitsubishi you dont, it should be on the input side, end of story.

tragically1969 said:

Not according to Mitsubishi you dont, it should be on the input side, end of story.

Click to expand...

I never did like mitsubishi, plcs, software or drives! End of my story

I think it can be very hotly debated, and has been many times before.

I have seen recommendations that the contactor should be on the output side, and other recommendations that it should be on the input side.

For example, opening a contactor on the output side while the drive is running will in most cases cause the drive to trip because of overvoltage. It is also not "healthy" for the power electronics in the long run, despite it can withstand the overvoltage for a few times. AB VFDs are stated that they can withstand a contactor on the output side, but that doesnt mean you should simply cut the power while the drive is running.

For a contactor on the input side, I have seen recommendations that the contactor should not be switched on again until after a waiting time has expired (1 minute ?).

What I do is to have a contactor on the input side of the drive. The contactor is on as soon as the power is on and stays on as long as there is no E-stop. Additionally I have a waiting time in the PLC to not reengage the contactor too soon. This because one can imagine someone testing the E-stop repeatedly.

Modern drive have a 'E-switch' function incorporated.The latest SEW we use can remain powered up on an emergency cut-out.Using the proper connections , the output is considered save.

Eric

A few other items that need to be considered is how many drives are on the system. If there are more then 6 or 7, then contactors are needed to power up the drives in separate groups, otherwise, the inrush would be so great that the main breaker or fuses would be blown.

Another item to look at would be safety. If the contactors are put on the outfeed side, in order for it to be to code, you would need 2 contactors per drive. If the contactors were put on the infeed side, then you would need 2 contactors per group of drives.

We typically use the contactors on the infeed side in sets of 2 per code, but that is because our typical system that we build has 15 to as many as 80 total drives.