Over current relay for 50-200hz feeder

[pukar12345]

Hi All,

I have a feeder supplied from variable frequency drive (50 -200Hz). This feeder needs a overcurrent protection. But digital relays are not able to provide protection for varialbe frequencies (50-200)Hz.

Is electro-mechanical relay suitable for variable frequencies ? Or what other options to protect this feeder ?

 

[JG2828]

After a quick search on the internet I found this:

http://relays.tycoelectronics.com/datasheets/wd_ds.pdf

Take a look at the WD5051. "WD5051 AC current sensing relays provide current monitoring and protection in AC systems from 50 to 400 Hz."

 

[davidbeach]

Hang on a minute. A VFD running PWM on a x kHz carrier to produce a 200Hz input to a motor is putting out x kHz, not 200Hz. Why not just use the built in functions of the drive?

 

[PHovnanian]

I agree with davidbeach. The nature of a VFD's output could affect protection relays proper operation adversely.

Unless the VFD manufacturer has tested the operation of their product with a specific relay (or vice versa), you can't be certain that the two will play well together.

What leads you to believe that the VFD's built in protection is insufficient for your application?

 

[pukar12345]

Hi PHovanian / Davidbeach,

Thank you for valueable inputs. I was in same line with you guys to use the in built protection of VFD but client was insisting to put extra protection.

However, once you get 200Hz in your feeder,What is a problem to use WD5051 AC current sensing relays as suggested by JG2828.

 

[davidbeach]

Because you don't have 200Hz, you have somewhere in the 5-10kHz range. There is almost nothing other than the VFD that is producing the mess and the motor it is running that can make heads or tails of the noise and hash on the line.