Citation II Electrical Power System AST 473 Dr. Barnhart

Citation II Electrical Power Citation II Electrical Power SystemSystem

AST 473AST 473

Dr. BarnhartDr. Barnhart

Electrical System IntroductionElectrical System Introduction

The electrical system on the citation is The electrical system on the citation is divided into two separate systems:divided into two separate systems:1. DC- storage, generation, distribution and 1. DC- storage, generation, distribution and

monitoring.monitoring.2. AC- generation, distribution, monitoring2. AC- generation, distribution, monitoring

- There are also provisions for:- There are also provisions for:-Emergency-Emergency-GPU connection-GPU connection

DC- Principal Electric PowerDC- Principal Electric Power

2 Engine driven DC Generators- primary 2 Engine driven DC Generators- primary power sources.power sources.

Normal distribution- 3 left and 3 right buses Normal distribution- 3 left and 3 right buses connected by a TIE bus.connected by a TIE bus.– Allows either generator to power entire system Allows either generator to power entire system

(working in parallel sharing load)(working in parallel sharing load)*Hot battery and emergency buses- normally tied *Hot battery and emergency buses- normally tied

to main system but can be isolated to to main system but can be isolated to batterybattery or or External sources (ie. GPU for gnd. Ops).External sources (ie. GPU for gnd. Ops).

DC Power- BatteryDC Power- Battery

19 cell Ni-cad battery provides 24-volt power rated 19 cell Ni-cad battery provides 24-volt power rated to 39 amp-hours.to 39 amp-hours.

Located in tail-cone and has quick-disconnect Located in tail-cone and has quick-disconnect terminalsterminals

Always connected to hot battery bus.Always connected to hot battery bus. Ni-cads.- susceptible to excessive charging and Ni-cads.- susceptible to excessive charging and

overheat; as such, batt. Is limited to 3 eng. overheat; as such, batt. Is limited to 3 eng. Starts/hourStarts/hour

Battery isolated during GPU start to prevent Battery isolated during GPU start to prevent dischargedischarge

Battery Life- In good conditionBattery Life- In good condition

10 minutes to all buses10 minutes to all buses 30 minutes if only hot battery bus and 30 minutes if only hot battery bus and

emergency bus usedemergency bus used

Starter-GeneratorsStarter-Generators

2 each. 1 per engine mounted on accessory 2 each. 1 per engine mounted on accessory gearbox.gearbox.

Air Cooled, rated to 30 volts, DC regulated to 28.5 Air Cooled, rated to 30 volts, DC regulated to 28.5 volts, 400 amps.volts, 400 amps.

Capable of 50% overload to 600 amps. For 5 min. Capable of 50% overload to 600 amps. For 5 min. (starting)(starting)

Used as starters until 50% N2Used as starters until 50% N2 Distribution systems are in parallel- gens. Share Distribution systems are in parallel- gens. Share

load equally (+/- 10%) via an equalizer connection load equally (+/- 10%) via an equalizer connection between generator control units (GCU’s).between generator control units (GCU’s).

External PowerExternal Power

Receptacle- below left engine nacelleReceptacle- below left engine nacelle Power routed to hot battery busPower routed to hot battery bus Battery charges from GPU regardless of Battery charges from GPU regardless of

battery switch position.battery switch position. Ensure GPU regulated to 28.5v and btn. 800 Ensure GPU regulated to 28.5v and btn. 800

& 1,000 amps. Prior to connecting to A/C.& 1,000 amps. Prior to connecting to A/C.

External Power OperationExternal Power Operation

Connecting GPU:Connecting GPU:– Energizes external power relay which connects Energizes external power relay which connects

the external power unit to hot batt. Bus.the external power unit to hot batt. Bus.– Placing battery switch to BATT closes battery Placing battery switch to BATT closes battery

relay (on UN’s 0002 – 0626 emergency relay relay (on UN’s 0002 – 0626 emergency relay also closes) allowing DC external power to be also closes) allowing DC external power to be connected to the battery bus, emergency bus, connected to the battery bus, emergency bus, and left and right main buses.and left and right main buses.

External Power Operation- ctn.External Power Operation- ctn.

If either generator power relay is closed- external If either generator power relay is closed- external power relay deenergizes which removes external power relay deenergizes which removes external power from hot battery bus (prevents power from hot battery bus (prevents simultaneous airplane and GPU power).simultaneous airplane and GPU power).

GPU unit should have reverse current protection. GPU unit should have reverse current protection. If not and unit is turned off while connected to A/C, If not and unit is turned off while connected to A/C, rapid discharge and battery damage can occur. rapid discharge and battery damage can occur. Disconnect GPU from airplane when not in useDisconnect GPU from airplane when not in use

Electrical DistributionElectrical Distribution

DC- distributed by 9 buses (fig. 2-6)DC- distributed by 9 buses (fig. 2-6) Main junction box (tail-cone compt.)- 2 main Main junction box (tail-cone compt.)- 2 main

DC buses, battery bus, and hot battery bus.DC buses, battery bus, and hot battery bus. Cockpit (pilot’s CB panels)- 2 main Cockpit (pilot’s CB panels)- 2 main

extension buses, two crossover buses and extension buses, two crossover buses and emergency bus.emergency bus.

Electrical Distribution ctn.Electrical Distribution ctn.

2 main DC buses are normally powered by rt. And 2 main DC buses are normally powered by rt. And left generators tied by the batt. Bus (can also be left generators tied by the batt. Bus (can also be powered from batt. Or GPU).powered from batt. Or GPU).

Hot batt. Bus- always directly connected to Hot batt. Bus- always directly connected to battery- normally powered by generators but may battery- normally powered by generators but may be by GPU.be by GPU.

Battery bus- sole function is a tie bus connecting Battery bus- sole function is a tie bus connecting hot battery , emergency bus, and two main DC hot battery , emergency bus, and two main DC buses (4 elements into 1 integral system).buses (4 elements into 1 integral system).


DC power from engine-driven generators- DC power from engine-driven generators- distributed to two main DC buses. Two main DC distributed to two main DC buses. Two main DC buses are paralleled through the battery bus by buses are paralleled through the battery bus by two 225-amp. Current limiters (connects each two 225-amp. Current limiters (connects each main bus to batt. Bus)main bus to batt. Bus)

Generator power routed through battery bus to hot Generator power routed through battery bus to hot batt. Bus by a batt. Relay and to emerg. Bus via batt. Bus by a batt. Relay and to emerg. Bus via the batt. Bus or hot batt. Bus depending on the batt. Bus or hot batt. Bus depending on position of BATT switch.position of BATT switch.


From each DC bus in tailcone- ext. bus provides From each DC bus in tailcone- ext. bus provides power dist. To components via switches and CB’s power dist. To components via switches and CB’s in cockpitin cockpit

L & R main ext. buses- located behind pilot’s and L & R main ext. buses- located behind pilot’s and co-pilot’s CB panels (respectively)co-pilot’s CB panels (respectively)

Left and right cross-over buses enable logical Left and right cross-over buses enable logical grouping of circuit breaker (i.e. L & R. fire grouping of circuit breaker (i.e. L & R. fire detection) providing power from opposite main detection) providing power from opposite main extension bus.extension bus.


Emerg. Bus- located at copilot’s CB panelEmerg. Bus- located at copilot’s CB panel Hot Battery bus powers:Hot Battery bus powers:

– Lights (cabin entrance, both baggage Lights (cabin entrance, both baggage compartments and emerg. Exit)compartments and emerg. Exit)

– Ignition- start onlyIgnition- start only– Voltmeter (batt. Switch in BATT. Or EMERG.), Voltmeter (batt. Switch in BATT. Or EMERG.),

LH/RH generator voltage regardless of BATT LH/RH generator voltage regardless of BATT switch position)switch position)

– Emerg. Nicad battery pack (generators/GPU Emerg. Nicad battery pack (generators/GPU online)online)

Emergency Bus DistributionEmergency Bus Distribution

The following are powered by the emerg. The following are powered by the emerg. Bus thus power is avail with batt. Switch in Bus thus power is avail with batt. Switch in the EMER. position:the EMER. position:– COMM 1COMM 1– NAV 2NAV 2– Copilot’s HIS (DG 2)Copilot’s HIS (DG 2)– Cockpit floodlightsCockpit floodlights– ON UN’s 0627 and on, also: cockpit speakers, ON UN’s 0627 and on, also: cockpit speakers,

copilot’s ADI, and rt. Pitot/static heat [682 and copilot’s ADI, and rt. Pitot/static heat [682 and on]on]

Electrical ControlElectrical Control

Battery switch and 2 generator switchesBattery switch and 2 generator switches Batt. Switch is 3 positions; BATT, OFF, and Batt. Switch is 3 positions; BATT, OFF, and

EMER.EMER.– Battery OFF- hot battery bus isolated from all Battery OFF- hot battery bus isolated from all

other busesother buses– Battery BATT- closes battery relay connecting Battery BATT- closes battery relay connecting

batt. To systembatt. To system– Battery EMER- only emergency energized Battery EMER- only emergency energized

closed- connects emerg. Bus to hot batt. Bus- closed- connects emerg. Bus to hot batt. Bus- powered by battery or GPU.powered by battery or GPU.

Electrical ControlElectrical Control

When GPU not connected and gens. Are When GPU not connected and gens. Are online, placing battery sw. to OFF or EMER online, placing battery sw. to OFF or EMER isolates battery from any charging source isolates battery from any charging source (30 min. max.)(30 min. max.)

Gen. switch has 3 positions: GEN, OFF, and Gen. switch has 3 positions: GEN, OFF, and RESET.RESET.– In GEN position- GCU closes power relay & In GEN position- GCU closes power relay &

connects generator to main DC busconnects generator to main DC bus

Electrical Control ctn.Electrical Control ctn.

Generator switch:Generator switch:– In the OFF position- power relay will NOT close In the OFF position- power relay will NOT close

and generator assumes no loadand generator assumes no load– RESET- close the generator field relay if RESET- close the generator field relay if

opened.opened.– Engine Start buttons: activate a circuit to close Engine Start buttons: activate a circuit to close

the start relay- allows current to the hot batt. the start relay- allows current to the hot batt. Bus then to the starter/generator.Bus then to the starter/generator.

– Starter disengage button opens start relay- Starter disengage button opens start relay- manually terminates the start sequence.manually terminates the start sequence.

Electrical MonitoringElectrical Monitoring

DC system- monitored by voltmeter, 2 DC system- monitored by voltmeter, 2 ammeters, 2 GEN OFF annunciator warning ammeters, 2 GEN OFF annunciator warning lights a BATT O’TEMP warning light & batt. lights a BATT O’TEMP warning light & batt. Temp gauge (optional)Temp gauge (optional)

L/R GEN OFF annunciator- indicates an L/R GEN OFF annunciator- indicates an open power relay, if both lights are on the open power relay, if both lights are on the MASTER WARNING lights also flash.MASTER WARNING lights also flash.

Electrical MonitoringElectrical Monitoring

Voltmeter selector switch- permits Voltmeter selector switch- permits monitoring of voltage on the hot batt. Bus or monitoring of voltage on the hot batt. Bus or from a point btn. Each generator and its from a point btn. Each generator and its power relay.- spring loaded to BATT pos power relay.- spring loaded to BATT pos which indicates batt. Bus voltage.which indicates batt. Bus voltage.– Indicates highest of the source connected to Indicates highest of the source connected to

point being monitored (either gen. or batt point being monitored (either gen. or batt voltage)voltage)

– Will NOT read hot batt. Bus when batt. Switch in Will NOT read hot batt. Bus when batt. Switch in OFF.OFF.

Elec. Monitoring ctn.Elec. Monitoring ctn.

Ammeters- read current flow from their individual Ammeters- read current flow from their individual generators. During normal ops. Indication should generators. During normal ops. Indication should be = (+/- 10% of total load).be = (+/- 10% of total load).

BATT O’TEMP light on annunciator (and flashing BATT O’TEMP light on annunciator (and flashing MW light) comes on when batt. Temp = 145 deg. MW light) comes on when batt. Temp = 145 deg. F. At 160 deg. F light flashes. Optional temp. F. At 160 deg. F light flashes. Optional temp. guage goes to 180 deg. F.guage goes to 180 deg. F.

Engine start buttons- illuminate when respective Engine start buttons- illuminate when respective start relay is closedstart relay is closed

Electrical ProtectionElectrical Protection

2 GCU’s 2 GCU’s RegulateRegulate, , ProtectProtect, and , and ParallelParallel generators. Each unit controls the power generators. Each unit controls the power relay connecting the gen. to its main DC relay connecting the gen. to its main DC bus.bus.

GCU permits relay to close when cockpit GCU permits relay to close when cockpit generator switch is in GEN generator switch is in GEN AND AND gen. gen. output equals (within .3 v) or exceeds output equals (within .3 v) or exceeds system voltage.system voltage.

Electrical Protection ctn.Electrical Protection ctn.

Field relay- in the GCU either allows or prevents Field relay- in the GCU either allows or prevents field excitation within the generator.- If open the field excitation within the generator.- If open the field relay shuts off power relay solenoid (by field relay shuts off power relay solenoid (by opening gnd.) and opens the power relay.opening gnd.) and opens the power relay.

If a short circuit or over-voltage is detected, the If a short circuit or over-voltage is detected, the field relay opens; also opens when engine fire field relay opens; also opens when engine fire switch is activated. Also a reverse current (10% or switch is activated. Also a reverse current (10% or >) or undervoltage opens the power relay.>) or undervoltage opens the power relay.


Circuits btn. Each main DC bus and its ext. Circuits btn. Each main DC bus and its ext. bus are protected by three 75 amp CB’s in bus are protected by three 75 amp CB’s in parallel on the CB panel.parallel on the CB panel.

A 35 amp. CB on each ext. bus provides A 35 amp. CB on each ext. bus provides protection btn. The ext. bus and the protection btn. The ext. bus and the crossover bus on the opp. CB panel.crossover bus on the opp. CB panel.

A 225 amp. Current limiter (CL or fuse) A 225 amp. Current limiter (CL or fuse) protects against system overload. When protects against system overload. When open, the elec. System splits into 2 halves.open, the elec. System splits into 2 halves.

Electrical Protection- CL’sElectrical Protection- CL’s

When one gen. pwr. Relay is closed the When one gen. pwr. Relay is closed the operator must protect the CL from the high operator must protect the CL from the high amps. During eng. Start.amps. During eng. Start.– The respective batt. relay automatically opens The respective batt. relay automatically opens

during eng. Start and closes after start seq.during eng. Start and closes after start seq.– When starting w/ GPU- batt. Disconnect relay When starting w/ GPU- batt. Disconnect relay

opens and removes batt from gnd- ensures batt opens and removes batt from gnd- ensures batt is not used for start (starting limits do not apply)is not used for start (starting limits do not apply)


If GPU output becomes excessive- If GPU output becomes excessive- overvoltage/overcurrent sensor opens the overvoltage/overcurrent sensor opens the ext. power relay & opens circuit to hot batt. ext. power relay & opens circuit to hot batt. Bus. Ext. pwr. Disable relays also Bus. Ext. pwr. Disable relays also disconnect the GPU from the hot batt. Bus disconnect the GPU from the hot batt. Bus whenever a pwr. Relay closes, bringing a whenever a pwr. Relay closes, bringing a gen. online.gen. online.

System OperationSystem Operation

During preflight place gen. switches to GEN During preflight place gen. switches to GEN for battery start or OFF for GPU startfor battery start or OFF for GPU start

Place batt. Switch to BATT and check for 24 Place batt. Switch to BATT and check for 24 – 25 min. voltage. Check lights and pitot – 25 min. voltage. Check lights and pitot heat then batt. Sw. to OFF.heat then batt. Sw. to OFF.

During exterior walk-around check for During exterior walk-around check for battery corrision/deterioriation, or other battery corrision/deterioriation, or other signs of overtemp.signs of overtemp.

System Operation ctn.System Operation ctn.

Prior to eng. Start verify switch positions & Prior to eng. Start verify switch positions & voltage.- batt. Sw. to BATT (allows pwr. voltage.- batt. Sw. to BATT (allows pwr. From main ext. bus to close the start relay From main ext. bus to close the start relay when START depressed)when START depressed)

Depressing START also activates the elec. Depressing START also activates the elec. Fuel boost pump. Arms the ignition, and Fuel boost pump. Arms the ignition, and activates the engine instrument floodlight activates the engine instrument floodlight (pwr. From emerg. Lighting nicad batt.)(pwr. From emerg. Lighting nicad batt.)

System Operation ctn. System Operation ctn.

When start relay closes (light comes on in START When start relay closes (light comes on in START button) hot batt. Bus pwr. Is connected to starter.button) hot batt. Bus pwr. Is connected to starter.

BTN. 8 & 10% N2, move throttle from idle cutoff, BTN. 8 & 10% N2, move throttle from idle cutoff, ignition activates via throttle pos. switch- grn. Lt ignition activates via throttle pos. switch- grn. Lt abv. Ign. Sw = pwr. To ign.abv. Ign. Sw = pwr. To ign.

Combustion should occur w/I 10 sec.- evidenced Combustion should occur w/I 10 sec.- evidenced by ITT rise. At approx. 38% (N2), start seq. by ITT rise. At approx. 38% (N2), start seq. terminates automatically:terminates automatically:– Elec. Boost & ign. Deactivate, start relay opens, Elec. Boost & ign. Deactivate, start relay opens,

floodlights extinguish all via a speed sensor on starterfloodlights extinguish all via a speed sensor on starter


Starter reverts to a gen. and GCU allows it to Starter reverts to a gen. and GCU allows it to come online (pilot initiated) after start termination come online (pilot initiated) after start termination and when gen. output = or > system. Voltage.and when gen. output = or > system. Voltage.

For next eng. Start- operating gen. assists battery. For next eng. Start- operating gen. assists battery. Operating eng. Must be steady at 49 – 50% N2. Operating eng. Must be steady at 49 – 50% N2.

Start sequence is repeated (pump, light, etc.) but Start sequence is repeated (pump, light, etc.) but this time both start relays close allowing generator this time both start relays close allowing generator assist (both start lights on). No generator assist assist (both start lights on). No generator assist capability when airborne via squat switch.capability when airborne via squat switch.


When one gen pwr. Relay is closed and the When one gen pwr. Relay is closed and the other is working as a starter- batt. Relay other is working as a starter- batt. Relay opens & interrupts circuit btn. Batt. bus and opens & interrupts circuit btn. Batt. bus and hot batt. Bus to protect the 225 amp. CL on hot batt. Bus to protect the 225 amp. CL on the side of the op. engine.the side of the op. engine.

All airborne starts are batt. Starts- this is All airborne starts are batt. Starts- this is required by certification regulations.required by certification regulations.

System Operation- GPU startsSystem Operation- GPU starts

Check GPU for 28V and 800 – 1,000 amps.Check GPU for 28V and 800 – 1,000 amps. Place gen. sw. in OFF until GPU removed. Place gen. sw. in OFF until GPU removed.

Otherwise when the 1Otherwise when the 1stst gen. comes online gen. comes online the GPU is automatically disconnected from the GPU is automatically disconnected from the hot batt. Bus & second start becomes a the hot batt. Bus & second start becomes a generator assisted start.generator assisted start.

Abnormal OperationAbnormal Operation

Battery Overheat can result from excessive Battery Overheat can result from excessive amount and charge rate, discharge, or internal amount and charge rate, discharge, or internal batt. Damage.batt. Damage.– If batt overheats it can “run away”. Batteries have If batt overheats it can “run away”. Batteries have

actually fallen through the bottom of some aircraft due to actually fallen through the bottom of some aircraft due to run away heating.run away heating.

– When overheat occurs- place batt. Sw. to EMER to When overheat occurs- place batt. Sw. to EMER to open batt. Relay removing it from charging- consult open batt. Relay removing it from charging- consult checklist. Ensure relay has opened by monitoring checklist. Ensure relay has opened by monitoring ammeter for a drop. & a min. voltage drop of 1 volt in ammeter for a drop. & a min. voltage drop of 1 volt in 30s to 2 min.30s to 2 min.

Abnormal OperationAbnormal Operation

If start sequence fails to terminate (starter lights If start sequence fails to terminate (starter lights and flood lights remain on etc.) depress STARTER and flood lights remain on etc.) depress STARTER DISENGAGE switch.DISENGAGE switch.

Monitor ammeters periodically for proper gen. Monitor ammeters periodically for proper gen. operation.operation.– If GEN OFF light comes on check voltmeter to see if If GEN OFF light comes on check voltmeter to see if

field relay or only power relay opened.field relay or only power relay opened.– Field relay trip indicated by near 0 voltage (can be Field relay trip indicated by near 0 voltage (can be

caused by short, temp. over-voltage, or actuation of caused by short, temp. over-voltage, or actuation of eng. Fire switch). Potential exists for reset.eng. Fire switch). Potential exists for reset.

Abnormal Operation- ctn. Abnormal Operation- ctn.

A tripped power relay can be caused by an under-A tripped power relay can be caused by an under-voltage or reverse current situation. If selected voltage or reverse current situation. If selected generator shows normal voltage; reset is not likley.generator shows normal voltage; reset is not likley.

Pulling 3 (75) amp. CB’s on pilot’s CB panel (left Pulling 3 (75) amp. CB’s on pilot’s CB panel (left main ext. bus) along with the 35 amp LH CB main ext. bus) along with the 35 amp LH CB PANEL breaker on the copilot’s CB panel PANEL breaker on the copilot’s CB panel (crossover bus from rt. Main extension bus) (crossover bus from rt. Main extension bus) disables the pilot’s CB panel if necessary.disables the pilot’s CB panel if necessary.

Abnormal Operation ctn.Abnormal Operation ctn.

NOTE: when the three 75 amp. Main bus NOTE: when the three 75 amp. Main bus breakers are pulled, the crossover bus to breakers are pulled, the crossover bus to the opposite CB panel is also disabled.the opposite CB panel is also disabled.

Failure of a 225 amp CL after start can be Failure of a 225 amp CL after start can be detected during the gen. check after eng detected during the gen. check after eng start.start.– When one gen. sw. is in OFF the other gen. When one gen. sw. is in OFF the other gen.

should pick up the entire load (as indicated on should pick up the entire load (as indicated on the ammeter). If this does not happen it the ammeter). If this does not happen it could could mean a failed CL.mean a failed CL.

Abnormal Operation ctn.Abnormal Operation ctn.

If the previous occurs and the gen. on the If the previous occurs and the gen. on the side with the failed limiter is selected to OFF side with the failed limiter is selected to OFF the buses on that side lose pwr and the the buses on that side lose pwr and the opposite-side MW light illuminates steady opposite-side MW light illuminates steady and and cannotcannot be reset. be reset.

This is most easily detected by looking for This is most easily detected by looking for off flags in the instruments. DO NOT fly in off flags in the instruments. DO NOT fly in this condition. this condition.

AC powerAC power

AC power provided via two static inverters AC power provided via two static inverters powered by the main DC system.powered by the main DC system.

AD is distributed via two buses: 115v and AD is distributed via two buses: 115v and 26v.26v.

AC power protectionAC power protection

Power source to inverters protected by the Power source to inverters protected by the CB’s on the left and rt. CB panels.CB’s on the left and rt. CB panels.

Inver switching relay and inverter fail Inver switching relay and inverter fail warning light are both protected by an AC warning light are both protected by an AC sw. CB. In the rt. CB panel. This CB sw. CB. In the rt. CB panel. This CB provides pwr. For: AC FAIL light, autopilot provides pwr. For: AC FAIL light, autopilot disengage light/horn, go-around button, and disengage light/horn, go-around button, and inverter switch.inverter switch.

AC power protection ctn.AC power protection ctn.

AC not available from the No. 2 inverter AC not available from the No. 2 inverter when the AC switch CB is disengaged. If when the AC switch CB is disengaged. If the No. 2 inverter is on line when the CB is the No. 2 inverter is on line when the CB is tripped, the inverter sw. must be moved to tripped, the inverter sw. must be moved to inv. 1 to restore AC.inv. 1 to restore AC.

AC power- ControlAC power- Control

Control sw. is grouped with the avionics Control sw. is grouped with the avionics master power sw. It has 3 positions: INV 1, master power sw. It has 3 positions: INV 1, OFF, and INV 2.OFF, and INV 2.

System is monitored by one red AC FAIL System is monitored by one red AC FAIL light- illuminates for a loss of AC power on light- illuminates for a loss of AC power on the 115-VAC bus due to any number of the 115-VAC bus due to any number of reasons: loss of DC, voltage fluctuations, reasons: loss of DC, voltage fluctuations, etc. Since this light is a red annunciator it etc. Since this light is a red annunciator it trips the MW lightstrips the MW lights

AC power OperationAC power Operation

One inverter is sufficient to provide all AC One inverter is sufficient to provide all AC needs on board. It is recommended that the needs on board. It is recommended that the inverters be used equally.inverters be used equally.

Place switch in either the INV 1 or INV 2 Place switch in either the INV 1 or INV 2 positions which supplies a ground path for positions which supplies a ground path for the inverter (#1 or #2) circuit; power is the inverter (#1 or #2) circuit; power is supplied to the switching relay, energizing it supplied to the switching relay, energizing it and thus AC pwr. From the inverter is and thus AC pwr. From the inverter is directed to the AC pwr. Buses.directed to the AC pwr. Buses.

AC power- Abnormal ops.AC power- Abnormal ops.

If one inverter should fail, simply select the If one inverter should fail, simply select the other inverter and continue normally.other inverter and continue normally.

If both inverters fail (unlikely) the battery If both inverters fail (unlikely) the battery switch must be placed in EMER to allow an switch must be placed in EMER to allow an integral inverter in the copilot’s vertical gyro integral inverter in the copilot’s vertical gyro to provide emergency AC power to the to provide emergency AC power to the copilot’s CDI needle on VOR mode.copilot’s CDI needle on VOR mode.

THE ENDTHE END

Documents

Citation II Electrical Power System AST 473 Dr. Barnhart