System Review PTM CH-02 (Electrical) Flashcards
Electrical System Description
A DC Split Bus. During normal operations the left and right electrical buses are isolated from each other. The respective side generator, alternator, and battery power the associated side bus. A bus tie allows for the linking of the two systems.
Nosewheel Steering Accumulator
Requires battery power to bleed.
Transformer Rectifier Unit (TRU)
Each TRU is rated at 100A. The TRU converts alternator produced AC power to DC power to provide power to its respective EMER bus in the event of a generator failure.
In the event of a dual generator failure, either alternator will power the emergency buses using the selected TRU as long as the engine is still running and the BUS TIE is CLOSED.
The alternator can only power the windshield heat or provide emergency power through a TRU.
When a TRU is selected ON, windshield heat will no longer be available to the portions normally supplied by that alternator.
TRU Location
Two TRU are located one on each side of the nose bay compartment.
Primary Sources for Electrical Power
Left & Right engine driven starter generators
APU
Left & Right Engine driven alternator
EPU
Left & Right TRU (emer bus only)
Standby Battery location
Left nose compartment
Cabin Emergency Lighting Battery Packs locations
4 Total Two in the front of cabin two in the rear of the cabin.
External Power Connection Location
Right side aft fuselage.
ELT Battery Pack Location
Aft Bulkhead between cabin and baggage compartment.
APU DC Generator Location
Tail
Engine Driven generator and alternator locations
Respective engine compartment.
Battery Location
One on each side of aft fuselage in respective battery compartment.
Split Bus Safety and Protective Features
Only one generator is connected to a single bus system at any time.
* EPU overvoltage/undervoltage protection.
* Two separate distribution systems supply power.
* A malfunctioning power source cannot prevent the remaining power sources from furnishing power.
* Individual or collective disconnection of electrical power sources (including batteries) is available in flight.
* When either ENG FIRE PUSH button is pressed, the respective generator is deactivated.
* Generator overvoltage protection is provided at 35 ± 0.5 volts.
* All circuit breakers are push-to-reset type and cannot be reset if a fault is present in the circuit.
Bus Tie
Allows for opposite side battery to power bus.
The bus tie relay connects the left and right bus systems at the emergency buses.
Bus Tie Relay on the ground
On the ground the bus tie operates automatically. The relay closes for the following reasons:
A single primary power source is selected, or
An engine or APU start button is pressed.
Bus Tie Relay in flight
In flight, the bus tie operates manually. The bus tie may be closed for the following reasons:
A generator loss, or
An inflight engine or APU start.
Generator
Mounted on each engine accessory gear box. Each air-cooled generator provides primary power to the split bus system and is rated at 28 VDC and 300 constant amps.
When assisting the batteries during ground engine or APU starts, a generator supplies up to a maximum of 450 amps.
Transient current in excess of the constant 300 amps is allowed during the engine start and up to 2 minutes following start completion.
Generator Control Unit (GCU)
Provides numerous functions for regulating and protecting the generators and electrical system.
Alternator
Mounted on each engine accessory gear box. Each air-cooled alternator normally provides power to heat the windshields.
Main Aircraft Battery
Two standard 25-volt, 44-amp-hour, NiCad.
Each battery has a manual quick disconnect knob on the battery case.
The batteries provide power to all systems in flight for 20 minutes.
Batteries can supply the emergency buses for approximately 60 minutes if both L and R ELEC buttons are selected to EMER within 5 minutes of losing all generator power.
Battery Buses
Battery power is available to the respective battery buses with or without the cockpit L and/or R BATT button ON.
Batteries and Engine Start
With the bus tie closed, both main batteries assist in every engine or APU start. Bus tie closure is automatic on the ground, but in flight the bus tie must be manually closed. In-flight starter-assisted engine starts use battery power only.
DC/DC Converter
The DC/DC converter keeps the FADEC from experiencing a momentary voltage drop during engine start.
If the voltage drops below 24 VDC, the DC/DC converter will attempt to restore the voltage back to 24 VDC.
The converter will not reduce any voltages greater than 24 VDC.
Both converters are next to the aft J-Box.
Permanent Magnet Alternator (PMA) Location
Respective Engine compartment.
Permanent Magnetic Alternator (PMA)
The engine FADEC channels switch over from start bus power to their dedicated permanent magnet alternator (PMA) power sources at 25% N2 during start.
The FADEC can change back to start bus power if a PMA fault occurs.
Auxiliary Power Unit (APU)
Provides 28 VDC power to the entire aircraft electrical system.
Normally limited to 275 amps during ground and in-flight use.
Automatically limited to 275 amps during engine start.
The batteries supply the remainder of the current needed for engine start.
APU generator is interchangeable with the engine generators.
APU Power Distribution
APU generator provides electrical energy to the left emergency bus.
APU generator will power both bus systems provided the bus tie is closed.
The bus tie automatically closes on the ground with APU generator power only.
The APU generator and the left engine generator cannot be online at the same time.
Priority logic uses the left engine generator and places the APU generator in an off-line status.
If the APU generator switch is ON, the APU generator automatically comes online if the left engine generator goes off line.
External Power Unit
EPU must be regulated to 28.5 and 30.0 VDC with maximum amperage of 1,500 amps for engine starts.
EXT Power
The button has two positions: AVAIL and ON.
The white AVAIL light indicates that the EPU is connected and voltage is within acceptable range.
Power is supplied to the Right EMER Bus.
EIS Group
The area is divided into two columns representing the left and right electrical bus systems.
During normal operation, the digital displays will be colored green.
In an abnormal condition the digits will turn to inverse video amber or inverse video red.
Invalid data is presented as amber dashes.
Battery Voltage & Amperage EIS Group
A negative sign (-) in front of the corresponding number indicates the battery is being discharged. The absence of the symbol indicates the battery or batteries are being charged by the generator(s) or EPU.
Generator Switches
The L GEN, R GEN and APU GEN toggle switches on the cockpit ELECTRICAL panel have three positions: ON, OFF and RESET.
Generator Switch On Position
Enables the GCU to place the respective generator online by closing the generator relay. Automatic generator control for voltage regulation/protection, and bus connections is enabled.
Generator Switch Off Position
Commands the GCU to open the respective generator relay and place the generator off line.
Generator Switch Reset Position
Commands the GCU to attempt a generator reset in the event of a fault.
Generator Relay
With the engines running and generators operating, the generators are connected directly to the left and right generator buses. Placing the L (or R) GEN toggle switches to the ON position closes the left and right generator relays.A
Generator Power
Supplied to the left and right main buses when the respective generator relay is closed. Placing the L (or R) GEN toggle switch to the OFF position opens the relay, disconnecting the respective generators from the main DC buses.
APU Generator
Provides power to the left emergency bus when selected ON. The APU generator will not provide power to the buses if the left engine generator is online.
TRU Buttons
The buttons have two positions: ON and OFF. When a TRU button is selected ON, alternator power is directed to the associated left or right emergency DC bus. In the OFF position, alternator power is used for windshield heat.
AVN Button
The buttons have two positions: ON and OFF. Avionics power is distributed from the left and right electrical buses through the left and right avionics relays, which are activated open and closed with the AVN buttons.
ELEC NORM/EMER Buttons
NORM—With the switchlights displaying NORM (and the generators online), the generators are powering their respective buses and charging the respective battery.
The electrical relays have the ability to automatically open and close as commanded by start logic.
EMER—When the relay is open, the button illuminates the amber EMER indication.
The relay can be manually opened by placing the button to EMER. Manually selecting a button to EMER opens the electric relay and illuminates the DC EMER BUS L and/or R on each PFD.
Interior Button
The left and right interior relays are simultaneously opened and closed with the single two-position INTERIOR button.
Interior Button ON
Closes the interior relays and supplies power to both interior buses and the cabin J-Box circuit breakers. All cabin equipment and appliances are powered except cabin emergency lighting.
Interior Button OFF
Opens the interior relays and depowers the cabin J-Box and its equipment. Cabin EMER LTS, PAX SAFETY, and cabin ENTRY lights are unaffected by the INTERIOR button.
Must be selected OFF for battery-only APU or engine starts on the ground.
Engine Start with Interior Button ON
If the first engine start is with batteries only, the interior buses are shed until the engine generator comes online and power is restored to the buses. Engine starts assisted with a generator or EPU do not shed the interior buses.
Interior Electrical Logic
Automatically opens the respective interior relay following the loss of an engine generator.
Opening the relay sheds the respective interior bus and reduces the load on the battery.
Dual generator failure opens both relays and sheds the left and right interior buses.
BATT Buttons ON
Closes the relay and connects the respective battery bus to the emergency bus.
BATT Buttons OFF
Opens the relay and disconnects the respective battery bus from the emergency bus.
Open Battery Relay
Triggers Amber CAS
BATT Button Off due to overtemperature condition
Battery Off CAS message is White
APU Fire System Protection
Batteries must be installed and the BATT buttons in the ON position, or the aircraft generator(s) must be operating, prior to and during all APU operations.
Bus-Tie Relay Button On-Ground
Pressing the button has no effect on relay operation while on the ground.
Bus-Tie Relay ON-Ground Logic (Closed Position)
Either L START or R START button on the ENGINE control panel is pressed.
The APU START button is pressed.
A single power source is online (APU or engine generator or EPU).
Bus-Tie Relay ON-Ground Logic (Open Position)
Engine start is complete (57-59% N2) unless that generator is the only one online.
APU start sequence is complete (50% APU rpm).
A primary power source is active on both bus systems.
In-flight Bus Tie
The bus tie relay does not open or close automatically in flight and must be activated manually by the crew.
In-flight Bus Tie Closed CAS Message
If the bus tie is manually closed with a generator active on both bus systems, the BUS TIE CLOSED CAS message appears. The message changes to amber after 5 minutes from the time a generator is active on both sides.
In-flight Bus Tie Automatically Opens
If manually closed in flight, the bus tie relay does not automatically open unless a major overcurrent occurs. A bus tie relay that has been forced open cannot be closed until a total aircraft electrical power down is accomplished.
EXT PWR Button
If the appropriate voltage is supplied to the aircraft from a EPU, the AVAIL annunciation displays. If the EXT PWR button is then pressed and the external power contactor closes, the ON annunciation displays. External power is then supplied to the right emergency bus to be distributed throughout the aircraft electrical system.
AVAIL Light
Indicates external power is connected and voltage is within range. This annunciation does not monitor amperage. When the AVAIL light extinguishes, power is not available (external power may be disconnected).
STBY PWR Switch
The switch has three positions: ON, OFF, and TEST.
STBY PWR Switch ON
Powers the standby bus and the standby instruments initialize.
Power Supplied:
Through right electrical bus power.
The standby battery (in the left nose compartment) will provide power if the right electrical bus fails or if neither main electrical bus power is available. The illumination of the amber light, next to the switch, indicates that the standby battery is powering the standby system. The standby battery is charged from the left emergency bus. This allows it to be constantly charged during use if normal power is available on the left side, or if a TRU is powering the left emergency bus.
STBY PWR Switch OFF
The standby instrument bus is not powered.
STBY PWR Switch TEST
The spring-loaded position tests the standby battery system circuitry. Illumination of the green light for at least 10 seconds indicates a successful test.
BATT Temperature
Battery temperature is monitored at all times, but displayed only on the electrical synoptic page.
Battery Over Temperature Conditions
A battery temperature > 63°C will change the readout color to white on red. It will also trigger the BATTERY O’TEMP L and/or R CAS message, cause the MASTER WARNING button to flash and produce a “Battery Overtemp” aural warning. Once the MASTER WARNING is reset, if the temperature continues to climb above 71°C, the warnings will appear again. The temperature display will change to black on amber with battery temperatures < -20°C. Three amber dashes indicate invalid data.
Circuit Breaker Groups
Three major CB panel groups are in the Latitude aircraft:
Aft J-Box CB panels
Cabin J-Box CB panels
Cockpit CB panels
Aft J-Box CB Panels
Electrical power is distributed via a system of relays, buses and circuit breakers in the aft J-Box on the forward wall of the baggage compartment. The top two circuit breaker panels are accessed through two doors. The bottom set of panels are covered to protect them from possible baggage damage.
Aft J-Box Contains
Left and right battery buses
Left and right emergency buses
Left and right start buses
DC/DC converters
Left and right main electrical buses
Left and right main avionics buses
APU generator bus
EPU electrical bus
Cockpit extension buses via cables and current limiters.
Aft J-Box Monitored Circuit Breakers
Specific circuit breakers in the aft J-Box are monitored and if tripped will result in the REMOTE CB TRIPPED CAS message. These circuit breakers cannot be reset in the air and aircraft systems must be monitored to see the effect of the tripped circuit breaker.
Cabin J-Box
Contains two interior electrical buses and circuit breakers. Nonessential cabin equipment such as cabin lighting, the Cabin Management System (CMS) and other equipment receive power when the cockpit INTERIOR button is in the NORM position.
Cockpit CB Panels
Labeled in columns and rows to aid the crew in locating a circuit during a malfunction.
Divided into three sections:
Avionics
Electrical
Emergency/Standby
Minimum Voltage for Engine Start
Indicated by green digits on the EIS.
Engine Start Order
Either Engine maybe started first.
Generator Switch Location for Engine Start
ON for all engine starts.
Battery Participation in Engine Start
With the bus tie closed, both batteries participate in every engine start except windmilling.
ELEC Relay(s) during Start
Open temporarily during the engine start sequence and close when the engine is self-sustaining (engine starter is not being driven). This occurs during cross generator starts in order to isolate the main electrical bus from electrical power fluctuations.
PCB Start Logic Prioritization
Engine start with EPU power: EPU assists the batteries.
Engine start with APU generator power: APU assists the batteries.
Engine cross generator start: Generator assists the batteries.
Engine start batteries only: The batteries are used if none of the previous primary sources are available.
Lavatory Service
Requires the right battery be connected for fill operations.
Nosewheel Steering Accumulator
Requires batteries connected in order to bleed system.
