Buszone Isolator Parity Alarm: Any Ideas 2

[warickwrx]

Hi

I have a ASEA 2BZ1 bus zone scheme protecting two busbars being zone 1 and zone 2, there is currently an isolator parity alarm being generated but the manual is not very clear what might be generating this alarm. I am thinking it's just the auxiliary contacts from one of the isolators but not sure..................any ideas

 

[Marmite]

I don't have any knowledge of that particular relay, but my guess is that your isolators use a pair of auxiliary contacts, NO and NC to indicate open or closed status. ie 2 bit indication. The valid binary outputs from the aux switches could be 10 and 01 as the NO and NC contacts change over. If you have 00 or 11 then you get an alarm.

Regards
Marmite

 

[warickwrx]

Hi

I somehow think this cannot be the case as the isolators can be linked to both zones at once or independently with bus coupler open, or if one has both sets of isolators open then the alarm should also not be up as technically that bay is isolated and out of service. perhaps it requires a current input along with the senarios you suggested.

 

[Marmite]

I think you misunderstood what I meant.
What I was suggesting is that rather than relying on a single auxiliary contact to indicate whether your disconnector is open or closed, ie a single auxiliary contact opens and closes to reflect the operation of the primary contacts, it is possible that your system uses two contacts to increase reliability. A single contact would be at risk of open circuit fault or sticking contacts.

eg Primary contacts open - Aux Switch 1 open, Aux switch 2 closed
Primary contacts closed- Aux switch 1 closed, Aux switch 2 open

This gives 01 & 10 as the only valid combination.
If the combined outputs are 00 or 11 they are invalid and the relay alarms.

Regards
Marmite

 

[warickwrx]

Hi, yes I had a look at the scheme drawings you are correct, it uses to isolator contact input states for each isolator. The one bay was showing a 00 instead of a 10 like you suggested.