AC brake interference

[lostcontrol]

Hi Team,
We have had an old VSD fail (15+ years old) & replaced it with a modern inverter.
The brake on this motor is AC as opposed to a DC which we see mostly these days.
When the replacement VSD is started, an earth leakage fault is triggered. When this detection is disabled, the fault is changed to high DC link.

The brake appears to operate ok electrically & mechanically.
If the brake is released manually, the VSD operates as expected with no issues.

We don’t think it is a bad brake as visually & audibly, it looks good.
Current conclusion is the modern electronics are more sensitive & less output filtering are the issue, but even still it should not fault like this


Any thoughts.?

 

[widelto]

Can you disconnect your brake from the drive ?
can you use a digital output from the drive that only comes on when speed is less than 3 hertz for example and use a relay to energize your brake. ?

 

[lostcontrol]

The brake is controlled from the PLC (not idea I know..)
When electrically isolated at cabinet and motor end, then manually released all is good.
Have tried to energise brake, wait 2-3 sec then start VSD as well as the opposite of starting VSD then energising brake .
Same occurrence in all instances

 

[JesperMP]

Electromechanical brakes on AC motors usually have a DC coil.
And the motor manufacturer usually supply a small AC to DC rectifier that fits into the terminal box on the motor. You just connect 2 motor leads to the rectifier and this operates the brake coil.

When you say that the new motor has an AC brake instead of a DC brake, are you sure that it is not with the abovementioned rectifier unit ?

Post photos of the motor name plate and of the inside of the motor terminal box.


edit: I am guessing that the original brake was ordered without the rectifier, because the designer did not want to connect from a VSD to the rectifier. Instead it meant that a separate direct DC supply to the brake coil was needed.

 

[lostcontrol]

Electromechanical brakes on AC motors usually have a DC coil.
And the motor manufacturer usually supply a small AC to DC rectifier that fits into the terminal box on the motor. You just connect 2 motor leads to the rectifier and this operates the brake coil.

Yep, that is for DC brakes for sure. This motor does not have a rectifier in the terminal block though ( that is obvious, but will double check..)

When you say that the new motor has an AC brake instead of a DC brake, are you sure that it is not with the abovementioned rectifier unit ?

Motor is existing, is the VSD that is new. I will 95% sure as the manufacturer states they can do AC or DC brakes.

Post photos of the motor name plate and of the inside of the motor terminal box.

Motor photo attached. Will try & get one of the terminal block

 

[JesperMP]

I meant a close-up of the name plate.

 

[JesperMP]

I will 95% sure as the manufacturer states they can do AC or DC brakes.

It could be that the VSD simply has an output for controlling an external relay that activates the brake, AC or DC.

Make and type no of the VSD ?

 

[lostcontrol]

sorry my bad, see attached

 

[JesperMP]

Unfortunately the brakes data is not included on the motor name plate.
Is there a second name plate only for the brake ?
Maybe on the cover over the brake/ventilator end ?
Any marking on the brake itself ?
Any information in the old decomentation for the control system. What voltage did the old system send to the brake ?

 

[lostcontrol]

I will have to check what/if the brake has anything
The voltage is 400 I am pretty sure as have not identified a rectifier anywhere, as well as the nerimotor site says AC or DC brakes available

 

[GaryS]

the Brake should always be controlled directly by the VFD
that way if there is fault the brake is set to hold the load
the power for the brake can be Ac or DC either way you need a separate contactor for brake
the way you describe it PLC controlling the brake you run the risk of dropping he load before the VFD ca get power to the motor, and if the VFD Faults the brake could be held on and again drop the load

DC power brakes are better than AC powered they pull in and release quicker
DC also has the advantage that you can reduce the voltage after the brake pulls in the brake coils don't overheat
if you do it right you never have to replace anything on the brake

 

[lostcontrol]

Yes, I am aware of what is best practice etc.
This post was more about why is the VSD faulting when the brake is electrically engaged, when it appears to be operating correctly.
This application has a high ratio gearbox, so when the brake is released the load does not move until it is encouraged to move (manually or commanded)

When this occurs, there is zero movement of the motor before the VAD trips.

 

[Steve Bailey]

Assuming this is an electrically released brake, does the brake get its power from the motor leads or is there an independent power source for it. If it is powered by the motor voltage and the VFD is operating in volts/Hz mode, the voltage level at low speed may not be enough to release the brake. The previous drive may have provided for a boost to release the brake at low speeds.

 

[lostcontrol]

There is a separate cable & contactor for the Berkeley from the switchboard.
The brake appears to release fine when the contactor is manually activated as can turn the motor by hand

 

[chelton]

There is a separate cable & contactor for the Berkeley from the switchboard.
The brake appears to release fine when the contactor is manually activated as can turn the motor by hand

Have you tested for any connection between the brake and the motor wiring? The star points haven't accidentally been tied together? Assuming 3Ø brake.