Thanks for your message.
Our problem is not during the engine starting, but when the aircraft arrives to the terminal: we connect the plug to the aircraft while the APU is running.
There is a light marked "available" next to the aircraft socket. Instead of lighting, it flashes, and the pilot...
We have installed a new 400 Hz power supply (static converters from Axa Power).
We receive Embraer, Bombardier, Airbus A320 and Boeing 737.
All aircraft connecting to this power supply have no problem, except the Embraer 170 and 190.
Did anybody have a similar problem and may know the reason...