HV Switchyards - Bus bar protection with numerical relays 2

[RRaghunath]

Normally, we are not comfortable with low / medium impedance bus bar protection schemes for HV switchyards though the RADSS of ABB has been in service for so long proving the dependability of the low/medium impedance bus bar protection schemes.

All those comprehensive numerical bus bar protection relays available in the market seem to be offering only low impedance bus bar protection.

Do you find any problem with the concept of High impedance bus bar protection using Alstom numerical relays such as KCGG or P122 (or ABB relays type SPAE or any other make relays, for that matter)?

I have worked with KCGG relay based bus bar protection scheme for 220kV switchyard. With regard to relay P122, I heard the same has some problems when tested with transients and was not acceptable at that point of time.

Thanks in anticipation.

 

[DiscoP]

The last I heard (about a year ago) was that the P122 is tested for up to 4 circuits, but not guaranteed beyod that (I'd check that with Areva if I were you), but the KCGG is OK.

SEL have a relay - SEL587Z. I do not know much about it - only from what I have seen on their website but it looks suitable.

All the other numerical busbar relays I know of are low impedance schemes.

I still prefer the electromechanical relays for this application.

 

[xabproject]

Dear RRN,

Why "we are not comfortable with low/medium imp BBP for HV Switchyards"? What decides the 'comfort level'?

I my opinion the high imp type does not suit the situations where the 'ever increasing size of the switchyard (distances from CTs to the relays)' imposes incredible CT parameters such as KPV, Rct, Imag etc. That apart, the CT secondary 'major' leads have to be some fanciful sizes such as 2X25sqmm - finding a suitable terminal block in the CT Kiosk will be a challenge some times! Whereas, the low/med imp BBP demands very modest CT parameters and hence will be most suitable in 'large' layouts. Markets produce/favor what is in demand - think of all those 42 bay, 37bay layouts you did needing 'so many' Bay Units and 'so many more' Central Units.

If you are still with 4/5 bay layouts with the Relay room at 50m distance or some compact GIS layouts you can drop this reasoning and go ahead with the hi-imp BBP. Low imp BBP sellers will sell their products elsewhere!