Guideline required for MFAC relay

[kaspor]

Hello

Can anyone provide any guidance or reference material for how to correctly size (if required) the stabilizing resistor that comes with the high impedance MFAC relay in bus differential applications? I have looked everywhere and cannot find anything.

 

[che12345]

'..Can anyone provide any guidance or reference material for how to correctly size (if required) the stabilizing resistor that comes with the high impedance MFAC relay in bus differential applications?'
1. Do you mean MFAC 14/34 GEC High impedance differential relay?
In my collection GEC Modular protective relays publication Section 3 , page 191-3 state Metrosil characteristics, arrangement etc...
2. I can furnish the data/information if that is what you are looking for.
Che Kuan Yau (Singapore)

 

[kaspor]

Yes the MFAC. The manual for the MFAC talks about a stabilizing resistor and the standard sizes available but no literature on how to size it.

Do you have any material you can share?

 

[cranky108]

I did at one time, but I have not seen one of those relays in over a decade. But there is a paper somewhere.
I thought they no longer made those.

 

[che12345]

@ Mr kaspor (Electrical)(OP)18 Sep 24 11:32
Yes the MFAC. The manual for the MFAC talks about a stabilizing resistor and the standard sizes available but no literature on how to size it.
Please see attachment. Hope it is useful.
Che Kuan Yau (Singapore)

 

[cranky108]

The metrosil size would be based on the maximum energy to be dissipated for an internal fault. Calculate that, then purchase the size metrosil.

 

[Peter85]

Hi! Sizing a stabilizing resistor for a high impedance MFAC relay in bus differential applications can be tricky. Typically, the relay manufacturer should provide guidelines or a calculation method for determining the correct size based on system parameters like CT ratios, maximum fault current, and the relay’s voltage setting. If you haven’t already, I’d recommend checking with the manufacturer’s technical support team or documentation. You might also find helpful information in IEEE or IEC standards related to differential protection schemes.

 

[che12345]

@ Mr. kaspor (Electrical)(OP)18 Sep 24 11:32
' Yes the MFAC. The manual for the MFAC talks about a stabilizing resistor and the standard sizes available but no literature on how to size it'.
In addition to my a earlier post dated 19th inst. 02:49, you may like to look into the publication "GEC protective relays application guide" page 262-3 which touch on "...by increasing the R[sub]R[/sub], the spill current can be below any specified relay setting... the series-connected resistor is the Stabilizing resistor ...."
Che Kuan Yau (Singapore)