Supply
2ea 90KVA AC generators, 1ea 25KVA AC generator & 1ea 24V 25AH Sealed Lead Acid Battery are all examples of this.
What are the sources of internal electrical power?
Pressing this will illuminate with a SPLIT (amber) and the DC main buses will de-couple
What is the DC BUS PUSH BUTTON (DC BUS switch/indicator)?
This component disconnects the generator from its buses (generator contactor opens) if any of these conditions are detected and can not be corrected
1 Voltage regulation
2 Overvoltage
3 Undervoltage
4 Under frequency (on the ground only)
5 Current unbalance
6 Overcurrent
7 Differential current protection
What is the GCU (GENERATOR CONTROL UNIT)
This indicates that the AC Main busbars are coupled together and being supplied by a single AC power source
What does the green caption CPLD indicate when it is illuminated on the AC BUS switch/indicator on the Electrics Panel?
This system breaks the supply to the operating coil of the APU Ground Contactor, preventing the APU from connecting to the AC Main busbars, in flight
What is the WOW (Weight on Wheels)?
This indicates that the External Power access panel is open.
What does a green advisory caption AC EXT PWR displays on the SPSD mean?
Under this condition the DC Main busbars are coupled.
How are the Main DC busbars coupled/decoupled during normal operation?
This device checks external power for the following Correct supply voltage, frequency, phase sequence and correct aircraft AC system configuration
What is the External Power Control Unit
(EPCU)?
This indicates that AC Main busbars have been manually split and automatic coupling is disabled
What does it mean when the CPLD/SPLIT selector is
showing SPLIT (amber)?
Exceeding this will result in the caution APU GEN O/LD displays on the SPSD
What happens when you exceed 25KVA on the APU?
With loss of all AC power supply what power this is the only power available to Aircraft systems
What is Battery supplying the DC Essential and Battery busbars?
In the case of a feeder fault this will will rupture and split the DC Main busbars
What is the 150 amp DC fuse?
Each AC utility receptacle has one of these to protect against a ground fault.
What is the Ground Fault Interrupt device?
This indicates that one or more of the following have happened
• Battery is selected OFF,
• Battery voltage is below 16V, or
• One of the battery RCCBs has tripped.
What does the amber caption FAIL is illuminated on the BATT indicator on the Electrics Panel indicate?
This allows the APU AC Generator to be connected to the AC Essential busbars while the AC Main busbars are live and the EMERG/NORMAL switch is selected to EMERG.
What is the Dead Bus Sensing Relay?
Under this condition 2 A/C power sources can load share the same bus
What is no condition?
When the Voltage sensing units (VSU) sense the DC Main Bus bars have dropped below 25 volts they de-energize and the DC ESSENTIAL BUS CHANGEOVER CONTACTORS connect the DC essential bus bar to this
What is the Emergency TRU?
The gearbox is protected from AC generator seizure by this
What is a shear section on the Generator drive shaft?
This is the indication the operator will get when one or both of the DC Ess Bus Changeover Contactors are de-energised and the Emergency TRU is powering one or both DC Essential busbars.
What is a yellow caption EMR is illuminated on the DC BUS PUSH BUTTON (DC BUS switch/indicator) on the Electrics Panel?
These allows the AC Main busbars or APU AC Generator to distribute power to the AC Essential busbars.
What are AC Changeover contactors?
APU AC Generator on-line in either NORM or EMERG modes or both Main AC Generators on-line have priority over this
AC External Power
With the EMERG/NORM switch in this position and the APU supplying to only AC power the AC Main busbars are disconnected
What is EMERG?
The Essential busbar is protected from over-current fault by this device & a control/indication circuit breaker on the Generation Control Bus panel trips to indicate it has opened
What is the Remote Controlled Circuit Breaker (RCCB)?
This indication shows that external power is available, the AC EXT switch IS selected in and external power is ready to be automatically connected to the busbars, however a higher priority power supply is already supplying the aircraft.
What does is indicate when the green caption READY is illuminated on the AC EXT switch/indicator on the Electrics Panel?
In flight the APU as only power this these Buses will be powered
What are AC Essential busbars, the Emergency TRU will power the DC Essential and Battery busbars?