Bill said:
You don't use a thermostat with an anti-condensation heater.
So true! A "thermostat controlled anti-condensation heater" is an oxymoron...
Think about it; the idea is to ALWAYS hold the temperature of the protected electrical equipment above ambient, no matter how high the ambient, and a thermostat would defeat the very purpose of the anti-condensation heater.
Anecdote:
One of the very well insulated metal-clad switchgear buildings at a transformer station in Toronto had healthily-sized anti-condensation heaters in the swgr cubicles, and on hot midsummer days when the outdoor temperature in the shade was 35°C the indoor temperature at that station could rise to 40-45°C - which was quite an incentive to expedite the completion of a station inspection. The protected equipment did however last for years and years.
As to the question in the OP: it depends on what other measures are undertaken to mitigate this concern...
Is the station structure an older one of poured concrete, block or brick? Or is it perhaps a newer one with a metal building envelope? The surrounding thermal mass can have a profound effect upon how quickly the internal temperature of the building changes, and therefore to what degree condensation can or does occur on the generator windings.
Is the plant run-of-the-river such that some units are always in operation 24/7, or does the plant operate using peaking/ponding such that a large number of units are in operation during the day and none are in service overnight? The latter case will cause much greater building internal temperature fluctuations than in the former...and in the latter, leap-frogging the units operated and closing the generator air dampers shortly before shutdown and keeping them closed until shortly after start-up can trap a good portion of the thermal energy in the windings and preclude or at the very least minimize the likelihood of condensation.
Do the units disperse their heat to the interior of the building with the building's internals subsequently rejecting heat to the ambient environment, or do the units reject heat directly out-of-doors?
More information yields better answers...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
