Citation ExcelDC Electrical System

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Narrative
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DC electrical power is used to control or operate many of the Citation Excel's systems. When the Citation Excel DC electrical system module is completed, the pilot will be familiar with the Citation Excel DC electrical distribution system, location and function of key components, electrical system controls, indications, and crew management of the DC electrical system during normal and failure modes. / Show the three-quarter view of a Citation Excel.
MAIN MENU:
  1. DC Electrical - General Description
  2. Battery Power
  3. Generator Power
  4. Optional Auxiliary Power Unit (APU)
  5. External Power
  6. Fault Protection and Load Shedding
  7. DC Emergency and Abnormal Operation
/ No audio on this page. Have the 7 categories to the left selectable.

DC Electrical – General Description

The Citation Excel DC electrical distribution system can receive power from 5 potential sources: the left engine driven generator, the right engine driven generator, an on-board battery, an optional auxiliary power unit generator or APU, and for ground operations, an external power source. / Show the three-quarter Citation drawing with the location of the generators in each nacelle, the battery in the behind the wing on the left side of the fuselage, APU in the right aft side of the tailcone and external power receptacle below the left engine pylon shown.
The DC electrical system is controlled by switches located on the left instrument sub-panel. These switches include a battery switch, two generator switches, two ignition and engine start switches and a starter disengage switch. The APU controls are located on a sub-panel forward of the right side circuit breaker panel if the optional APU is installed. / Show instrument panel and right side APU controls.
DC electricity is distributed to electrical components by supplying electricity through strips of metal strategically located in the aircraft called buses. The primary DC electrical buses are:
  • A BATTERY bus, which receives power from the battery or an external power unit.
  • The CROSSFEED bus functions primarily to connect the BATTERY bus, left hand FEED bus, right hand FEED bus, and the optional APU generator together.
  • Left and right GEN buses receive power directly from their respective generators.
  • Left and right SYS buses circuit DC power from the FEED buses to DC electrical components through controls and circuit breakers in the cockpit.
  • Left and right AVN buses circuit DC power from the FEED buses, to avionics.
  • EMER, EMER SYS, and EMER AVN buses, feed power to critical flight instruments and controls.
/ Show schematic [pg 2-5 in the Cessna book] and highlight the buses as they are mentioned.
DC electrical power is distributed to aircraft systems, avionics, and components through two circuit breaker panels in the cockpit and a J.-Box circuit breaker panel located in the tailcone.Circuit breakers are logically grouped in the cockpit. The left cockpit circuit breaker panel, located to the left of the pilot, includes primary aircraft systems and some basic flight instrument circuit breakers.The right circuit breaker panel located to the right of the copilot, contains avionics systems circuit breakers. / Show instrument panel and highlight breaker panels. Point to the tail cone area on a three-quarter view diagram of the plane.
System operation is monitored by two ammeters (1second pause), a voltmeter (1second pause), a battery temperature gauge (1second pause), red BATT O’TEMP and >160 annunciator segments,(1second pause), amber GEN OFF, L, and R caution annunciator segments, and amber AFT J-BOX, LMT, and CB annunciator segments. / Show instrument panel and highlight and enlarge instruments and annunciators as they are mentioned.
The ammeters display the load carried by each generator by measuring current flow from the respective GEN bus to the respective FEED bus. The indication on each ammeter during normal operation, should be within 10%. / Continue to show the instrument panel. Zoom out the ammeters and show each one indicating about 50 amps.
The voltmeter will indicate voltage from three buses. The VOLTAGE SEL switch is spring loaded to the BATT position and will indicate BATTERY BUS voltage if the battery switch is on. The voltmeter will indicate LH GEN BUS or RH GEN BUS voltage if the VOLTAGE SEL switch is moved to the L GEN or R GEN positions respectively. / Continue to show the instrument panel. The voltmeter will indicate 28 volts for the battery and 28.5 for the generator.

Battery Power

The battery is located aft of the wing in a left side fuselage compartment. A connect/disconnect device links it to the battery bus. During the preliminary preflight inspection, ensure that the battery is properly connected. //// / Show the battery compartment, battery, and connect/disconnect device figure 2–2 in the manual. Point to the items as they are read. The student must click on the connector/disconnect device to continue.
The battery bus receives power from the battery and/or external power regardless of battery switch position. / ShowDC schematic with the battery bus powered.
Ram air cools the battery in flight. A ram air scoop located on the fuselage below and in front of the battery compartment directs cooling air through the battery case and around the battery. / Show a low angle shot of the RAM air scoop, battery compartment, and cooling air flowing through the battery compartment.
The red BATT O’TEMP and >160 degree annunciator segments monitor the temperature of the battery. If the battery reaches 145 degrees F [62.8 degrees Celsius], the BATT O’TEMP light illuminates and the red MASTER WARNING lights flash. If battery temperature continues to 160 degrees F [71.1 degrees Celsius], the BATT O’TEMP and >160 degree annunciator segments illuminate and the MASTER WARNING lights flash. The battery temperature gauge, located on the far right side of the instrument panel, should confirm the indication of the warning lights or indicate an impending over temperature warning signal. Please note: the BATT O’TEMP and >160 degree annunciator segments are disconnected if the optional lead acid battery is installed. However, the battery temperature gauge will function as previously described. / Show the annunciator panel and the master warning lights along with the battery temperature gauge. List the narrated temperatures on screen.
During the preliminary preflight inspection of the cockpit, check that the generator switches are in the OFF position if external power is to be used, or in the ON position for a normal battery or APU start. Momentarily place the battery switch to EMER //// and verify that the N1 indicators, RMU 1, and standby HSI are powered, and the landing gear indicator lights are illuminated. / Show the instrument panel and zoom in on the electrical switch panel figure 2-4, and the indications listed when the student moves the battery switch to EMER.
With the battery switch in the EMER position, the EMER, EMER SYS, and EMER AVN buses are powered from the battery bus. The battery, APU, or ground power unit may supply power to the battery bus. / ShowDC schematic and light the EMER, EMER SYS, and EMER AVN buses with the battery switch on EMER.
Place the battery switch to the ON position prior to accomplishing the Hot items/Lights check during the exterior preflight inspection. //// Be advised, battery power is limited. If a ground power unit is not used during the inspection, do the Hot items/Lights check as quickly as possible with the vapor cycle air conditioner OFF to conserve battery power. The battery is capable of powering the entire aircraft electrical system for approximately ten minutes. / Show the instrument panel and zoom in on the electrical switch panel figure 2-4. Prompt the student to move the battery switch to the ON position at the ////.
The battery voltage must indicate 24 volts minimum. If the indication is less than 24 volts, maintenance is required. / Show the instrument panel and zoom in on the voltmeter gauge figure 2-9 reading 26 volts.
When the battery switch is selected to BATT////, the battery isolation relay will close. Power flows through the battery isolation relay to the CROSSFEED bus and then to the left and right feed and SYS buses. The Emergency buses receive power from the CROSSFEED bus through the normally closed emergency power relay. / When you hit the purple slashes, stop, prompt the user to switch the battery switch to BATT. Show contactor closing. Use electrical zapper and color lines as appropriate with voice.
The BATTERY DISCONNECT switch allows the pilot to electrically disconnect the battery while in the cockpit. It is a red guarded switch forward of the left cockpit circuit breaker panel just above the MASTER INTERIOR switch. When the red guard is lifted and the BATTERY DISCONNECT switch is lifted to the BATTERY DISCONNECT position, //// the battery disconnect relay will open and disconnect the battery ground provided the battery switch is in the BATT position. CAUTION: since the battery disconnect relay is energized open, the battery will slowly discharge if the BATTERY DISCONNECT switch remains in the BATTERY DISCONNECT position with the battery switch in the BATT position. / Place the BATTERY DISCONNECT switch and schematic figure 2-3 in the manual on the screen. When the student selects the BATTERY DISCONNECT switch to BATTERY DISCONNECT, make switch and relay noises and show the battery disconnect relay energized open.
If the outside air temperature is below -10°C (+ 14°F) and the aircraft is cold soaked, it is recommended to use external power or warm the battery to -10°C (+ 14°F) or warmer. This temperature may be checked with the battery temperature gauge. Proper battery warmup may require extended application of heat to the battery. / Show the three-quarter Citation drawing with a thermometer dropping below -10°C (+ 14°F) and the location of the battery behind the wing on the left side of the fuselage and external power receptacle below the left engine pylon and an.
If generator power cannot be maintained in flight, the crew can manually shed sufficient electrical load to prolong battery life for approximately 30 minutes by performing the appropriate emergency procedures. / ShowDC schematic with the battery bus, EMER bus, both EMER AVN buses, and the EMER SYS bus powered.
LIMITATION: The battery is limited to three engine starts in one hour.
The following notes apply:
  • If this limitation is exceeded, a deep cycle including a capacity check must be accomplished to detect possible battery cell damage per the Maintenance Manual.
  • Three generator-assisted cross-starts are equal to one battery start.
  • If an external power unit is used for engine start, no battery cycle is counted. This is because the battery disconnect relay will open automatically and separate the battery from ground to prevent discharge during the start sequence when external power is used.
LIMITATION: If the BATT O’ TEMP light illuminates during ground operation (except for test), do not take off until after the proper maintenance procedures have been accomplished. / Summarize battery limitations on the screen.

Generator Power

A Starter/Generator is mounted on each engine accessory case and turns at a proportionate speed to the engine N2. The Starter/Generatoracts as a starter to spool up the engine during the start sequence and acts as a generator once the engine is operating. They are each rated for 300 camps at 30 volts. / Show the location of each Starter/Generator on the aircraft.
Engine fan bypass air is ducted to the generators for cooling. A lower nacelle exhaust port completes the cooling cycle and allows this generator cooling air to be discarded into the air stream. / Show the flow of fan bypass cooling air through the generator and out the exhaust port.
The generator control unit (GCU) is a critical part of the power generating system and serves a number of functions:
  1. Voltage regulation. The GCU maintains generator output voltage at 28+ or -0.3 VDC.
  2. Generator relay control. When the generator switch is released from reset to on, generator voltage is applied to the GCU, which sends a line signal to close the generator relay.
  3. Overvoltage protection. The GCU’s over excitation circuits disconnect the faulty generator from the system.
  4. Load sharing. When both generators are on line, each GCU compares the two generator output voltages and regulates its generator output voltage to match the other generator.
  5. Reverse current protection. If either generator voltage drops to low, it may begin to draw current from the system. The faulty generator’s GCU will sense reverse current and open the generator relay, removing it from the system.
  6. Safety shutoff switch. If an ENGINE FIRE switchlight is pressed in order to suppress an engine fire, the GCU will automatically trip the associated generator relay – taking the generator off line.
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  1. Show voltmeter and selector switch. If you want you can make the selector active. Meter should show the proper voltage (28)
  2. Bring back the left gen switch. Move it to reset .5 seconds (gen relay opens) release back to on (gen relay closes).
  3. Show voltmeter w/right gen selected. Increase to 32 volts. Trip gen relay and illuminate lights. Change color to operating generator.
  4. Show voltmeter, move selector switch from left generator to right gen (both 28 volts).
  5. Reset colors to 2 generators operating. Show voltmeter left gen selected, show voltage drop below 28, gcu opens gen relay, show lights, change to one gen operating current.
  6. Show the ENGINE FIRE switchlights on the glareshield from pg 8-3 that shows the annunciators. Show one light illuminate. Also the DC electrical schematic [normal system] and show the corresponding generator shut down. All buses will then be powered by the remaining generator.

The amber GEN OFF L and/or R annunciator segments indicate that the respective generator is offline and generator relay is open. When one generator trips offline, the respective GEN OFF L or R annunciator segments flash. This in turn causes the amber MASTER CAUTION RESET lights to flash. When both generators trip offline, both GEN OFF L and R annunciator segments flash which causes the amber MASTER CAUTION RESET and red MASTER WARNING RESET lights to flash. / Show the annunciator panel and the MASTER CAUTION RESET and MASTER WARNING RESET lights.Illuminate the appropriate annunciator segments and lights consistent with the narration.
For battery starts and under all normal flight conditions, the generator switches should remain in the ON position. Depressing either engine start button closes the respective start relay and provides DC power to the engine starter////. A white light in each starter button indicates power on the contacts of the respective start relay////. Power to close the solenoid start relays and energize the ignition is available when the battery switch is in the BATT position. Automatic ignition sequencing takes place with both engine ignition switches in the NORM position. The starter operation is terminated when the speed sensor in the generator control unit removes power from the start relay. The automatic start sequence can be terminated at any time by pushing the cockpit STARTER DISENGAGE switch, located between the start buttons. This will open the start relay and halt the start sequence. After the engine is running during the start sequence, the starter/generator changes to generator operation. / Show instrument panel with both generator switches ON. Place the start switches on the screen. When the student selects the left button ON, make engine-starting noise, then halt when the words “Power to close” appear. Show left starter button turn white when it is selected and leave white until the words “start button light”.
Highlight the Starter Disengage button.
When the Generator Control Unit senses that the generator is ready to produce power, the operating generator will power the system. The GEN relay closes and supplies power to the respective feed bus. Current will then flow from the feed bus through the CROSSFEED bus, battery isolation relay and battery bus to provide battery charging. / Show schematic and power routing. Close the generator relay and illuminate the system with generator power using the zapper
The airplane is capable of cross starting an engine from an operating generator. Both the battery and the operating generator will provide power to the second Starter/Generator. On cross-starts, the operating engine must be at idle. Start the second Engine. //// Both start relays close when the second start is initiated. Power is routed through the battery bus to the other Starter/Generator. As a result, both the left and right starter buttons illuminate. Please note that whenever one generator relay is closed and the other Starter/Generator is energized as a starter, the battery isolation relay opens, interrupting the circuit between the battery bus and the CROSSFEED bus. This protects the 225–ampere current limiter on the side of the operating engine generator by interrupting a parallel path of power. Once the Generator Control Unit senses that the generator is capable of providing proper power, the generator relay will close. The second generator will share the load with the operating generator. / Show instrument panel. When the student selects the right starter button, show both left and right buttons illuminating white. Show schematic with power routing to the right Starter/Generator and sequence consistent with the narration. Label the screen “AIRPLANE ON THE GROUND”
When the airplane is in flight, the start switch activates the same circuits as a ground start except that only the associated start relay closes, not both. The generator–assist capability is disabled by the squat switch, allowing only battery power for the start. This isolates the start circuit from the operating generator, the 225-ampere current limiters, and the buses as required by certification regulations. / Show schematic and power routing. Label the screen “AIRPLANE IN FLIGHT”
When both engine driven generators are online with both 225 amp current limiters intact and the battery switch in the BATT position, the voltmeter will indicate the same system voltage in all three voltage selector positions. / Show the instrument panel. The voltmeter will indicate 28.5 volts for the battery and 28.5 for each generator as the VOLTAGE SEL switch is moved to each position.
Before takeoff, the electrical system generator voltage can be checked under no load and high load conditions. Begin with the battery switch on, both 225 amp current limiters intact, and both engine driven generators online. Turn the left generator off. //// The right generator high load voltage will be indicated with the voltage selector in the BATT position. //// The left generator no load voltage will be indicated when the voltage selector is placed in the L GEN position. //// Turn the left generator on //// and confirm that both generators are sharing the load. //// Turn the right generator off. //// The left generator high load voltage will be indicated with the voltage selector in the BATT position. //// The right generator no load voltage will be indicated when the voltage selector is placed in the R GEN position. //// Turn the right generator on //// and confirm that both generators are sharing the load. / Show the electrical switches, voltmeter, voltage selector, ammeters, and electrical schematic. Highlight the switches for the student to click on to continue consistent with the narration and show the electrical schematic indications consistent with the narration.
LIMITATION: the starter is limited to three engine starts in 30 minutes with a 90 second rest period between start cycles.
LIMITATION: the electrical is limited to 200 amps per generator during ground operations. Transients up to 250 amps are permissible up to four minutes.
LIMITATION: the generator load limit in flight is 300 amps. / Summarize generator limitations on the screen.

Optional Auxiliary Power Unit (APU)