AC Drives Wiring

georgeofthejungle02 · Oct 27, 2004

Hello:
I've seen some drive wiring where they have a disconnect switch, fuses, then main contactors on the 600VAC 3phase input line. This contactor is energized when the drive doesn't have any fault conditions and this contactor is fed from 120VAC control. Thus, when there is a fault, the contactor opens up and cuts off the 600VAC line into the drive.
My question is, is this a common practice or needed?
And also, for AC drives in general, in particular for the PowerFlex700, where is the on board circuitry getting its power from? Is it from the 120VAC control power or the 600VAC line power?
Thanks.
George

DickDV · Oct 27, 2004

Most AC drives power their control circuitry from the internal DC bus which is, in turn, powered from the input AC.

As far as a contactor that drops open when the drive faults, no, that is not a common practice. Most drives display the fault code or English word description of the fault on their keypad and that benefit is lost when when the power is removed.

Most drives also have a fault log which saves the most recent faults but, with instant power loss on fault, some processors may be so slow that the log record is not completed before the power goes away. In that case, even the log entry is lost. Not good from a troubleshooting standpoint.

Rube · Oct 27, 2004

George, the answers to these questions are drive specific and will be covered in the drives manuals. I know AB 160s, 1305s, and 1335s like the overloads between the drive and motor and most every other control etween supply and drive. Most drives are like this. The AB 160 and PowerFlex 4 drive has an onboard power supply to bump supply voltage down to the 12 volts to its terminal board.

elevmike · Oct 27, 2004

georgeofthejungle02 said:
Hello:
I've seen some drive wiring where they have a disconnect switch, fuses, then main contactors on the 600VAC 3phase input line. This contactor is energized when the drive doesn't have any fault conditions and this contactor is fed from 120VAC control. Thus, when there is a fault, the contactor opens up and cuts off the 600VAC line into the drive.
My question is, is this a common practice or needed?

As Dick said this may not be common pratice, but for us it is.. We also install a fault contactor in all of our soft starter applications. On open delta wiring (soft start) the fault contactor isolates the back end from the line. We typically cycle the fault contactor. That is we pick the contactor before initiating the soft start, then drop it after dropping the run signal to the soft starter.

It all depends on the application...

BobB · Oct 27, 2004

That is we pick the contactor before initiating the soft start, then drop it after dropping the run signal to the soft starter.

Agreed. We call it an isolation contactor. If there is a surge of power when the drive is off, the surge does not reach the drive. In fact some of our suppliers in Ozz recommend that this be done to protect the drive.

In front of the contactor I noemally place a motor circuit breaker rather than a normal circuit breaker. Better magnetic range.

DesertDog · Oct 27, 2004

The driver can make a difference as well. Step-7 5.2 scrolled (not always correctly) with the Microsoft Intellamouse driver but not the standard Microsoft driver or the Logitech driver.

Ajdonally · Oct 29, 2004

A Canadian opinion for the newguy...

As a rule here all VFD have input contactors. The majority of VFD systems we sell have 3 contactor bypass.

In the case of a VFD fault, we do not open the input contactor. I'm curious as to why that would be done.

We leave the VFD powered up..it will show the operator or service technician what the fault is safely.

If the VFD has a fault and the power is removed, then the service tech is likely to power it back up in their investigation....and that may cause collateral damage.

Happy Halloween!

Aj

CaseyK · Oct 30, 2004

I haven't seen the contactor fault drop out either.

All drives I've seen are either small ones in a machine, with no contactor, or the 3 contactor inverter bypass panel (a couple of threads on these out there).

I prefer the inverter bypass panel, but then, I like to make them.

regards.....casey

georgeofthejungle02 · Nov 1, 2004

Hello AJ:
I am waiting for an answer from AB to confirm, on a fault condition dropping out the 600VAC line will not shut off your fault screens if the on board electronics are powered from the 120VAC. But if this is not the case, then yes you are right, the HMI fault displays will be deactivated as well.

georgeofthejungle02 · Nov 2, 2004

The PF 700 Drive electronics get its voltage from the 600VAC.
Thus opening the main 600VAC input with a contactor that works off the drive's fault signal will deenergize the entire drive and you won't be able to see what caused the faults.

Doug_Adam · Nov 2, 2004

I have only used a few brands of VSD, with SEW being the most common.
However, with the few I have seen, the control can be powered either from the 3 phase input, or from an external supply, usually 24V.
Generally, they have an internal power supply and an external connection. If you don't connect the external supply, all I/O will be powered off the internal supply.

You sometimes need to read the manual carefully.

If you wanted the contactor to drop out due to the fault, but still be able to read the fault list, connect the external power, wire the contactor from this, and program as appropriate.

Hope this helps,

Doug

AC Drives Wiring

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