Creation: 01.31 - 2014
1-1-22
GPU - 406
the efficiency of the emissions reduction system. Exhaust temperature will increase as a part of the cleaning
process, and the “HIGH” Exhaust Temperature icon will appear. The “E.S.C.” icon will replace the water
temperature icon to show that exhaust system cleaning is taking place. The GPU operator will only receive this
notification if the engine is idling at the time of the exhaust system cleaning. If the cleaning process starts when
the GPU is delivering power, no notification will appear.
The GPU should not be shut down until the E.S.C. icon disappears.
E. Contactors
The GPU’s contactors are mounted on the relay panel, which is on the rear wall of the control
box. The contactors use a 24V control voltage, and they are driven directly by the GCM. The
GCM provides the logic for closing the contactors after the engine has ramped up. The GCM also
controls when the contactors need to open in the case of an aircraft rejecting the power delivered
by the GPU or when the delivered power enters a fault condition. The GCM can detect a stuck
contactor. If a contractor is determined to be stuck, either open or closed, voltage regulation will
stop and the engine will return to idle speed.
Note that for 90 KVA GPU’s, the 2
nd
contactor and output cable are optional.
(1) Load Contactor
When 400 Hz power is supplied to the aircraft, the aircraft returns a voltage signal to the GPU
through the E & F pins of the output cable and terminal block. This return signal is used to provide
a logical interlock for the GCM. Without this signal from the aircraft, the GCM does not allow the
contactor to stay closed. If the aircraft decides 400 Hz power is not within specification, it will cut
the return signal through the E and F pins, causing the GPU’s contactor(s) to open.
The output load contactor contains three main contact sets. The three main contacts conduct
three-phase AC generator output. Three-phase, 400 Hz generator output cables are connected
from the generator to the line side of the load contactor by passing through a set of current
transformers. From the contactor, power is brought to the aircraft via 400 Hz output cables (in
various lengths) and plugs.
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