Earth leakage relay for individual Roller Table Motors (in Steel Plant) which are driven by VVVF drive in a group drive mode

[duttaa1]

Customer is asking for individual motor earth fault / leakage protection for roller table application in a steel plant. These motors are of small  KW rating ( around 5.5kW) and several motors are fed by a single VVVF drive . 

In case we use standard earth leakage relays with CBCT at outgoing of each motor  , then the relays will malfunction due to PWM output ( non sinusoidal AC ) leading CBCT core saturation. 

What is the solution ? 

[Araceli_Monje]

@Pete_Vivers , could anybody from your team look at this request related to protection for small motor and provide the reply?, thx.

[NeiB · Accepted solution]

Hi @duttaa1 ,

Hope you are very well.

Regarding your question, it is not usual to have a RCD device downstream due to the signal restriction as you mentioned. Mainly because if the intention is to protect the motor against an insulation fault, a good VSD should provide this protection as a standard.

I recommend that you check the VSD installation guide to confirm which are the manufacturer indications for this type of protection.

Just for instance, our VSD offer ALTIVAR brings this information on its installation manual and in this case the RCD should be installed upstream of VSD as you can see at the FAQ below:

https://www.se.com/au/en/faqs/FAQ000184975/ 

Let´s see if someone else can share their experience with us.

Best Regards,

Neide