Electrical Power Systems Flashcards
The Hawker is a primarily ___ aircraft.
DC
HS-125 Electrical Bus Codes: What does P, X, and S signify?
P: DC power
X: AC power
S: Split-bus power
What bus does the APU power?
The PS2 bus
What provides power for some avionics and navigation equipment?
Two inverters providing 115-volt AC power
What powers windshield heat, windscreen heat, and stall vane heat?
Two-engine driven alternators
What do the alternators power?
Windshield heat, windscreen heat, stall vane heat
Where are most of the electrical components located onboard?
Aft equipment bay
Where is the one location besides the aft equipment bay electrical components may be found onboard?
The main distribution panel in the vestibule area
How is power distributed onboard?
Through a split-bus system controlled via circuit breakers
Where are the circuit breaker panels located?
One panel behind the head of the SIC, one larger panel in vestibule, and additional panels in the aft equipment bay
What drives the electrical system onboard?
Two 28-volt, 300-amp (continuous, 400-amps for two minutes) starter-generators (with an additional starter-generator on the APU)
What is the battery arrangement onboard?
Two main batteries (24-volt, 28 amp-hour lead-acid) and four additional smaller batteries
Where are the batteries located and what are their function?
Aft equipment bay, primarily used to start APU/engines and provide emergency power
What items are on the Hot Battery Bus? (VREF)
Voltmeter
Rear Equipment Bay Light
Entry/Vestibule Lights
reFueling Panel
What are the batteries directly connected to?
The PE bus
BATT switch ON:
Uses power from BATT 1 to close emergency contactors, connecting BATT 1 and BATT 2 to PE bus
BATT switch EMERGENCY:
Closes emergency contactors, powers PE bus, batteries do NOT charge
Why do we need fully charged batteries prior to takeoff?
Guarantees the minimum 30 minutes of electrical power in the case of an emergency
What does the ISOLATE switch do?
Isolates the respective batteries from the system - it will neither be charged nor power anything
EXT PWR switch ON:
Allows ground power units to power the electrical system
EXT BATT switch CHG ON:
Allows onboard batteries to be charged from external ground power if available and EXT PWR is ON
What is the voltmeter used for?
Allows monitoring of voltage on selected battery or bus
How can you change what system you are monitoring on the voltmeter, and what systems/buses can be monitored?
Rotary switch under voltmeter - allows monitoring of BATT 1, BATT 2, PS1 bus, PS2 bus, PE bus, as well as an XFER position to check voltage of the 4 additional smaller batteries. Typically left in PE switch position.
What is located on each engine and the APU, providing DC power to the aircraft?
A 28-volt, 300-amp starter-generator
How are the starter-generators cooled?
Ram air inlets on the cowling for each engine
How do starter-generators function?
Initially act as starters (for the engines and APU), then automatically switches to acting as a generator
When does a starter-generator switchover to generating power?
Around 42.5% N2
What are Generator Control Units? (GCU)
Provide output stabilization and load equalization - generators share the load through a bus-tie, and the GCUs ensure that the generators are carrying their half of the load and providing proper output
What are the protections offered by a GCU?
Protection against reverse current flow, overvoltage, overexcitation (normal voltage is 28v)
How do GCUs control generators?
Directly controlling Generator Line Contactors (GLC), which allows power from the generator into the aircraft electrical system and stabilizes bus bars at 28.5-volts
What are bus-tie contactors?
Provides connection of the main bus bars (PS1 and PS2), allows load sharing to take place
Are bus-tie contactors automatic?
NO, must be manually closed via the spring-loaded BUS TIE switch, when first starting the aircraft the bus-tie must be manually latched every time (however opens automatically)
When would the bus-tie contactors automatically open?
In case of self-preservation due to under or over-voltage
What voltage would cause the bus-tie contactor to open?
When voltage reaches 29.5±0.5 volts or 24.5±0.5 volts
What allows for load sharing between the main bus bars?
An equalizing circuit
Generator Close Switches are located where?
The electrical services panel
Generator Control Switch to CLOSE:
Connects the respective generator to electrical system IF the GCU allows it
Generator Control Switch to TRIP:
Opens circuit, removing generator power from system; may happen automatically for self-preservation, may be moved manually to disconnect generators if needed
What are the ammeters for?
Dual purpose (may indicate loads on two different things), indicate load on respective generators for engines, range from 0-450 amps
Where is the ammeter for the APU generator?
APU Control Panel
What does the BATT pushbutton do when pressed?
Connects ammeters to batteries to show the charge rate of the batteries
What should the charge rate of the batteries be less than prior to takeoff?
The charge rate of the batteries should be below 20 amps prior to takeoff
What is shown if the BATT pushbutton is not pressed down when checking amperage?
The system or generator amperage is read instead
What does the 0-40 pushbutton do when pressed?
Rescales the ammeter from 0-450 amps to 0-40 amps for easier reading when checking battery amperage
How long does it typically take after engine start for the batteries to have an acceptable charge rate for takeoff?
Around 5-7 minutes after engine start
Where is the external power port located on the Hawker?
Right side fuselage, underneath the engine pylon
What connector is used for Ground Power Units?
Standard 3-pin, 28 volt DC-power receptacle
If using a GPU for engine start, what are the limitations of the GPU?
The GPU output capability must be 42kW (with a short term capability of 28-volts, 1500-amps), and a current limiter rated at 1,100-amps
What GPU is capable of powering the onboard systems?
A standard 28-volt battery cart
What happens if you attempt engine start with too weak of a power cart?
May damage electrical system onboard
In the cockpit, how is GPU power turned on and controlled?
Only the EXT PWR switched to ON - BATT switch does not need to be ON for electrical power to be supplied
How is AC power supplied onboard?
Two inverters in aft equipment bay - single-phase, 115-volt, 400Hz AC powering avionics and some navigation equipment
How do the inverters power the XS buses?
INV 1 normally powers XS1, INV 2 normally powers XS2, one inverter can power BOTH XS1 and XS2
How does the distribution of AC power work?
Automatic distribution, INV 1/2 switches provide manual control of inverters
How are the inverters started?
INV 1/2 switch must be held momentarily in START position (spring-loaded switch)
Maximum Battery Amps Before Takeoff (B1 and B2)
20 amps
Starter Limits
30 seconds on, 1 minute off. 30 seconds on, 1 minute off. 30 seconds on, 30 minutes off.
What is the maximum continuous generator load?
300-amps (transient load of 400-amps is permitted for two minutes maximum), active monitoring required
Can you reset tripped circuit breakers?
NO, unless deemed necessary for the safety of flight. If a reset is followed through with, only ONE attempt is allowed
What is the minimum battery voltage?
23 volts
What does a WHITE circuit breaker mean?
Unswitched PE function
What does a RED circuit breaker mean?
Related to the fire suppression system
What does a YELLOW circuit breaker mean?
Electric Pitch Trim
The batteries will maintain essential service during a dual generator failure for:
30 minutes maximum
When a generator is offline and the GEN FAIL and ELECT ^ annunciators are illuminated, the generator can be reinstated by:
Positioning the GEN switch to CLOSE for five seconds then releasing it
The battery-charging rate can be monitored by:
Depressing the BATT ammeter pushbutton
For engine starting, the ground power unit must produce
28 volts, 1,500 amps with 1,100-amp current limiter
Circuit breakers protecting unstitched PE circuits are marked to ease isolation in the event of smoke or fire with:
A white background
When either the BATT 1 CNTCTR or BATT 2 CNTCTR annunciator illuminates, it indicates that the respective:
Battery contactor or emergency contractor is open
