Hawker 800 XP, Pilot Training Manual

Page: 146 / 504

Any fault detection and opening of the GLC
takes the generator off line and lights the GEN
FAIL and MWS ELECT annunciators. An at-
tempt to reinstate can be made by holding the
a s s o c i a t e d G E N C L O S E / T R I P s w i t c h t o
CLOSE for five seconds and then release.
NOTE
With external power on the aircraft,
closure of the GLC is inhibited.
Bus-Tie Contactor
The bus-tie contactor splits the main bus bars
in the event of power supply failure or mal-
function. The mechanically latched contac-
tor is manually controlled by a spring-loaded
BUS TIE CLOSE/OPEN switch or automati-
cally opened by the voltage-sensing unit in
overvoltage or undervoltage conditions.
With the bus-tie contactor open, bus bars PS1
and PS2 are split, and the generator-equaliz-
ing circuit is open. Additionally, a supply is
connected to light an amber BUS TIE OPEN
annunciator and ELECT annunciator on the
MWS panel. With any airplane generator con-
nected to the bus-bar system, the “close” coil
can be operated by positioning the BUS TIE
switch to CLOSE. This selection connects a
supply from bus bar PE via the generator line
contactor to close the bus-tie contactor.
With the bus-tie contactor closed, the BUS
TIE OPEN light goes out, the main bus bars
are linked together, and the generator-equal-
izing circuit is completed.
The equalizing circuit ensures equal load shar-
ing between generators when the systems are
paralleled and serviceable.
The voltage-sensing unit opens the bus-tie con-
tactor automatically when an overvoltage or
undervoltage condition occurs on the main bus
bar. The unit incorporates sensing circuits which
close a pair of contacts when the voltage exceeds
29.5 ±0.5 volts or falls below 24.5 ±0.5 volts.
Time-delay circuits in the voltage-sensing unit
prevent the bus-tie contactor from being oper-
ated by transients.
With PS1 and PS2 bus bars split, the service-
able channel restores to 28 volts. The unser-
v i c e a b l e c h a n n e l m a y b e s w i t c h e d o f f
automatically by the operation of the GCU
overvoltage or reverse-current protection de-
vices. Alternatively, the unserviceable chan-
n e l c a n b e s w i t c h e d o f f m a n u a l l y b y
positioning the associated GENerator control
switch to TRIP. With the unserviceable gen-
erator off line, positioning the BUS TIE switch
to CLOSE closes the bus-tie contactor.
Overvoltage Protection
The GCU overvoltage protection device op-
erates to open the generator field circuit when
generator terminal voltage is 32.5 volts or
above. At the same time, the GLC is signaled
to open and thus disconnect the generator from
the associated bus bar (PS1 or PS2).
Generator Control Switches
A three-position GENerator control switch, la-
beled “CLOSE/TRIP,” is connected into each
generator circuit. (See Figure 2-17.) The switch,
spring-loaded to the center position, can be
2-18
FOR TRAINING PURPOSES ONLY
HAWKER 800 XP PILOT TRAINING MANUAL
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Figure 2-17. Generator Controls and
Indicators