Drive Protection

I am putting in a new ac motor and drive and need to know what protection if any I need. The drive and motor will be 5 hp ac and from the output of the drive to the motor is about 10 feet. Do I need one of the reactor transformers after the drive? Do I need VFD cable? Do I need anything on the input side of a drive this small? This will be the only drive in the system and the motor is drive rated.

I would prefer not to use anything on input or output of drive if possible due to space limits and costs.

Also it will be a allen bradley 750 drive if that helps.

Regulations are probably different in the US, but down here in Australia this is how it would be commonly wired.

3 Phase Incoming --- Motor Protection Circuit Breaker --- Line Contactor (this may not be necessary) --- VSD --- Shielded 3 Phase Motor Cable --- Isolator --- Shielded 3 Phase Motor Cable --- Motor

Assuming this is 460V, the only issue to settle is whether the drive has an internal input reactor or equivalent. If it doesn't, I'd add a 3% input line reactor and run the motor leads in conduit. That's all.

If you are in a research facility or hospital or some other location where EMI and RFI are big concerns, then run the motor leads in shielded cable.

This is a an industrial facility and I will have to run flex from the motor to drive under 10 feet. Will this be ok to run in liquid tight conduit?

How can I find out if the allen bradley 750 drives have a built in input reactor?

This is a 460 setup.

if it is to operate as per your previous post, I would advise on adding a braking resistor and use the DC injection braking facility also

Tim,

Bare Bones - You are required to properly protect the drive with a suitable circuit breaker or fuse on the input side. So long as you properly setup the drive to protect the motor(by entering the motor nameplate amps), you don't need fuses or overloads or additional protection on the output.

Input Reactor - not required by code. Placing a reactor on the input side of the drive helps to minimize noise that the drive would reflect back onto your power system. Some places use isolation transformers to feed their drives instead. Some places do not use anything. The drive will work fine without either, but since I don't know anything about your facility, I'd recommend using one or the other. It's also a slippery slope to go from "just one drive" to several...

Output Reactor - typically used when the distance from the drive to the motor is long. Doesn't sound like that's the case here.

First, I don't see anything in your posts that would indicate any type of braking so there is probably no need for a brake chopper, brake resistors, or even DC injection braking.
Second, it's ok to run the motor leads in flex or sealtite for such short distances but be sure that there is a continuous copper ground bond wire from the motor frame to the drive frame. You cannot depend upon conduit and certainly not flex or sealtite for an effective ground at the high frequencies present on the motor leads.
Third, the AB sales people have to be able to tell you if an input reactor is standard on their own product. If there is a built-in reactor, you would not want to add more externally.
Fourth, at 5hp 460V, there is no chance of repairing the drive if it goes bad. In view of that, I would recommend using plain old Class J fuses on the input. Semiconductor fuses are expensive and hard to find and why protect against collateral damage in the drive when the first failure will doom the drive anyway. I don't start using semiconductor fuses until the drive is large enough to be repairable and that's around 75hp 460V these days. (My bosses would croak if they knew I said that!)

sorry DickDv
his other post suggested a a ccut to length system
the OP wanted to avoid using an encoder.
He said he is replacing an old DC motor drive with an AC drive.
I have assumed, maybe incorrectly, that it is this one