What can cause coil whine, quite high pitched, around alto-soprano level, when grid returned, and as inverters started to charge. What I was able to observe was the L2 phase frequency dropping from 50.1Hz to 48Hz, but it was probably more intense than that as the multis disconnected the grid quickly. They attempted to charge several times until I lowered input max current from 40Amps to 29 Amps. There are 6 x 5kVA multi 1s in 3 phase config. Grid voltage was stable between 237V and 242V. Ive not noticed our grid frequency drop before, this is a first, and it only happened on 1 phase.
The VRM records don't reveal anything that Incan see but have included a few shots.
Could this be or become a severe problem? Should I report it to the utility?
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