Reverse Power Trip...Advice

| We have a standby generator, that also runs in Triad periods. At the start | of the triad period, the generator starts up, synchronises with incoming | mains, switches on it's circuit breaker to supply power, then the mains | circuit breaker switches off and disconnects mains. | At the end of the triad period, generator synchronises with mains power, | switches on incoming circuit breaker, switches off it's own breaker then | shuts down.

A "closed transition".

| This has been working well for a number of years, until last week. At the | end of the triad period, when the generator has synchronised and switched on | the mains breaker, within seconds the reverse power relay in the mains | breaker trips.

Obviously something is failing.

| Also noted that when running on mains power, site current draw is about 400 | Amps. When running on generator only, site current draw is about 500 Amps. | Generator voltage is not much different from DNO voltage, load is the same | under both scenarios.

How reactive are those 400 and 500 amps?

| Appreciate if someone can advise on why all of a sudden we are getting | reverse power trips. | Also, an explanation on the higher current draw when running on generator. | I suspect something may be wrong with the generator, load sharing, governor,

A more reactive load and the way the amps are measured?

In order to avoid a reverse power situation for the mains, the generator should unload immediately after the main breaker shuts. This is probably built into the automatic test 'triad' profile. But if the signal for loading/unloading is broken, the generator may stay at load after shutting the mains breaker, causing the RP trip.

Does the generator governor operate in an isochronous or 'droop' mode? When in parallel with the mains, it should probably be in droop. If it switches back and forth based on breaker line-up, check the aux contacts responsible for this. If the generator stays in isochronous mode after the mains breaker shuts, it will load up the generator significantly trying to raise mains frequency. That would trigger the mains rev.power trip in short order.

As to the current difference, some ideas (in no particular order) come to mind. Calibration / CT ratios between the two ammeters? If these are readings when the 'opposite' power supply is off-line, then they reflect the

*load* current and either your load is changing or you have a calibration/CT issue. If these are readings while the two sources are paralleled, then they aren't very meaningful as reactive/real load can be shared between the sources in all sorts of different ways.

One other thought about current readings, if this is a three-phase set-up, are you looking at all three phases? If only reading one phase, is it the same phase? Don't know what your loads are, but maybe you should check to see if the generator is putting out the proper voltage on all three phases, if one phase is open on the generator, current on the other phases will change.

daestrom