|
1. General
A. The electrical power system is a network consisting of three, 3-phase, 400 cycle 115/200 volt,
generating and interconnecting bus arrangements. Electrical power is supplied from isolated
generators located on each engine and from an APU generator of the same rating in the tail
cone (Fig. 1). Single phase transformers are used to reduce a portion of this power to 28 volts
ac, and transformer rectifiers fed from the 3-phase bus connections are used to furnish 28 volts
dc. A battery is installed in the lower forward section to furnish emergency power to certain
critical loads when the basic sources are de-energized.
B. The generating system consists of the two main ac load busses energized by two isolated
brushless generators each driven by a constant speed drive (CSD). In the event of generator
failure, selected loads carried by that generator are automatically relayed to the other running
generator by means of two transfer bus relays. An identical generator driven by the auxiliary
power unit turbine may be used in flight as well as on the ground to supply 3-phase 400-cycle
power when necessary. Provisions are made for connecting conventional ground power
supplies to external power receptacles. A 3-phase receptacle near the nose wheel well on the
lower right side of the body is used for external dc power and those airplanes provided with a
external dc receptacle, the receptacle is located below the battery in the lower equipment bay
and is used for external dc power (Fig. 1). None of the three generators on the airplane can be
operated in parallel with others or with a 3-phase ground supply. The APU generator speed is
controlled by a mechanical governor in the turbine fuel line. Engine-driven generator speed is
controlled by a mechanical governor in each CSD.
C. A generator control unit (GCU) is provided to regulate and control each of the three generators.
They perform the following functions:
(1) Regulation of the average of the three phase voltages which may exist at the end of the
generator feeders, (considering an estimated length of 50 feet).
(2) Provision of excitation power for normal, overload, and fault conditions by means of a
transformer rectifier unit within the GCU and connected to the generator output through
boost current transformers used in conjunction with the transformer rectifier.
(3) Provision of adjustment for generator no-load voltage. (The point of adjustment is marked
to show the direction of rotation required to lower or raise the line-to-neutral voltage
between 110 and 120.)
(4) Limitation of power input to the generator shaft to 160 horsepower, by means of a current
signal supplied to the regulator in the GCU by three current transformers. (This power limit
is based on a generator efficiency of 77%.)
(5) Protection from abnormal system conditions such as overvoltage, undervoltage,
differential current, overcurrent, overfrequency or underfrequency. An anticycling
protection feature within the control system prevents cycling of the system when fault
conditions exist, and the manual switches in the control cabin are held in the ON position.
D. Control of the electrical system is more automatic than for systems which may be operated in
parallel. Since the generators in the system cannot be operated in parallel, control of the
transfer bus is automatic, so that the operating generator is transferred to pick up bus loads of
the tripped generator when that generator stops functioning. The transfer bus contactor has a
magnetically held relay with a "center-off" position. The transfer bus control has a preferred
source, with the control circuit so arranged that transfer of power under normal operating
conditions should not occur. The right and left generator breakers and bus tie breakers, the
APU generator breaker and the external power contactor are all electrically interlocked and
automatically trip the operating source of the bus when another source is switched to this bus.
2 Operation
A. With the airplane on the ground, all engines shut down, external 3-phase power connected to
the receptacle, and if the power source is of the correct voltage, (with no negative sequence
voltage condition) then the external power contactor (EPC) will close when the ground power
(EP) switch is placed on the ON position.
NOTE: Placing the ground power switch to ON sends a trip signal to the APU generator
breaker (GB) and to engine generator breakers No. 1 and 2 (GBl-GB2).
With the APU generator powering the airplane, closing the ground power switch (EP)
will trip the APU GB and allow the external power contactor (EPC) to close. The bus
tie breakers (BTB) will close, connecting external power to the load buses (Fig. 2).
The dc power for closing the EPC and BTBs is supplied from a transformer-rectifier
(T-R) unit in the bus protection panel (BPP). The transformer-rectifier provides dc
power for control and protection when ac power is connected to the external power
receptacle. If external power goes into an undervoltage, overvoltage, or negative
sequence voltage condition, the EPC will be de-energized.
B. With the airplane on the ground, all engines shut down, all generator control relays (GCR's)
closed, and power being supplied to the main buses through both BTB's from the APU, if
engine No. 1 is started (and a few seconds allowed for its generator to come up to speed and
voltage), the No. 1 generator breaker (GB) will not close and take over generator bus No. 1
until No. 1 generator control switch is placed in the ON position, and No. 1 BTB is tripped. Then
No. 1 GB automatically closes and No. 1 generator supplies the No. 1 main bus. If APU power
is removed from the airplane before the No. 2 engine is started, power will be lost to the No. 2
load bus. When the No. 2 engine is started, it will automatically take over the No. 2 load bus
when No. 2 generator control switch is placed in the ON position. The same sequence will hold
if external power is being used instead of the APU (Fig. 3).
C. With neither airplane engine running, the APU GCR closed, APU generator voltage and
frequency correct, the external power contactor (EPC) tripped, either left or right APU control
switch in the ON position, the APU GB will close (Fig. 4). Closing the APU GB connects the
APU generator to the TIE BUS (Fig. 2). When the left and/or right APU control switch is placed
in the ON position, the associated BTB closes and APU power is connected to the No. 1 and/or
2 main bus. Control and protection of the APU is provided by the APU generator control unit
(GCU). The BTB's wil1 close with power from the APU GCU or from the battery. The BTB's wil1
trip when the APU GB is tripped or when either APU switch is momentarily placed in the OFF
position. The APU generator will shut down automatically when the APU turbine is shut down.
The APU generator field is de-excited by momentarily placing both APU control switches in the
OFF position if APU generator is powering both buses.
D. When the APU generator is supplying power to a main load bus through its associated BTB
and an engine is started, the BTB will be tripped when the generator control switch is placed in
the ON position and the voltage and frequency are correct. When the BTB is tripped, the
engine-driven generator will be automatically connected to the bus and the differential
protection switching relays (DPR's) will be de-energized. When the engine is shut down, the
engine-driven generator will reach an underfrequency condition, thereby tripping the GB and
disconnecting the generator from the load bus. When the generator reaches an undervoltage
condition, a time delay is started. After 7 seconds the GCR will automatically trip and de-excite
the field. Momentarily placing the generator control switch in the OFF position will also trip the
GCR and GB.
E. When both No. 1 and 2 generators are supplying power to the main load buses, No. 1 and 2
GB's will be closed. Transfer buses No. 1 and 2 will be energized with bus transfer relays No. 1
and 2 both in the normal position (Fig. 5). Bus transfer switch S2 on forward overhead panel
must be in the AUTO position. Should generator No. 2 stop functioning, loads supplied from the
No. 2 transfer bus will be automatically transferred to the No. 1 generator. This is accomplished
by energizing the alternate coil of the No. 2 bus transfer relay through normally closed contacts
of No. 2 GB. A time delay permits the circuit to mechanically clear previous connections before
the No. 2 bus transfer relay closes. A similar sequence takes place should generator No. 1 stop
functioning instead of No. 2. Lights on the forward overhead panel P5 indicate when the buses
are de-energized. Should generator No. 1 or 2 be connected to the No. 1 and 2 main load
buses respectively with the bus transfer switch S2 in the OFF position, No. 2 or 1 transfer bus
OFF light respectively on the overhead panel will be on, indicating that transfer buses No. 1 or
2 are de-energized
| 
IP卡
狗仔卡
发表于 2011-6-13 12:15:47
分享
收藏
提升卡
置顶卡
沉默卡
喧嚣卡
变色卡
显身卡
发表于 2011-7-30 19:59:13