Synchroscope failure question

[IdahoSpud]

Back in the 1980's, when I was a young pup in Admiral Rickover's propulsion program...

We were told to always take the synchroscope out of service after using it, lest it "burn out". I took it on faith that failure to de-energize this meter would result in damage (even though none of the other electrical meters seemed to be burdened with this problem).

Today I find myself in a more modern facility where synch check relays and synchronizing relays perform the task of synchronizing, yet we have to leave these circuits out of service at all times until we are actually ready to synch, for fear of burning out the legacy analog meter.

Question: Is there *any* truth to the idea that a synchroscope is going to be ruined if left on? Common sense seems to suggest otherwise.

 

[MikeHalloran]

If one generator is off and one is running and the syncroscope is connected, it spins, fast, right? The bearings may not be up to extended operation.



Mike Halloran
Pembroke Pines, FL, USA

 

[IdahoSpud]

Hi Mike, Thanks for the quick reply!

I am at a power station, and the line side bus is the Western US electrical grid, while the incoming bus is the generator. Here are my observations and thoughts.

When the generator is offline, the synchroscope doesn't move because the grid is at 60 Hz and the generator is de-energized. The line side windings are live (maybe - see below), but the slip between line and bus is so vast that it is impossible to create a rotary motion.

When the generator is synchronized, incoming and line voltages are the same because the breaker is shut, and so there no voltage differential to create rotary motion.

What I have observed is that the synchroscope needle only moves for a very brief period, within a very limited set of circumstances. The generator must have the field flashed (which occurs at 95% speed), and the generator needs to be very close to synchronous speed, but not synchronized. You only see movement on the scope for 1-2 minutes at the very most during a normal start-up.

However, it was always my understanding that the meter would burn out in an electrical sense, rather than suffer from a mechanical failure.

Lastly, I am reasonably confident that if the synchroscope were prone to some sort of electrical failure, the manufacturer (GE) would use the supplied modern digital circuitry to remove it from service until it was actually needed, in order to protect it.

 

[rasevskii]

Synchronizing circuits are usually designed not to be energized continually, due overheating of the coils in the scope and associated resistance units, if applied.

There is also no reason to have the syn circuits remain energized after the CB has closed. In well designed systems there has to be a selector system that selects the circuits to be synced and disconnects these circuits afterward, manually or automatically.

rasevskii