ATA24 bombardier q400 electrical power

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ATA 24

ELECTRICAL POWER

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Page 2© Jazz Aviation LP

Rev. 1.0 - Jan/2011

FOR TRAINING PURPOSES ONLY

ATA 24 - ELECTRICAL POWER

DC EXTERNAL POWER SYSTEM . . . . . . . . .48

Description . . . . . . . . . . . . . . . . . . . . 48

DC External Power Receptacle . . . . . . . . .50

Controls and Indications . . . . . . . . . . . . .50

EIS DC External Power Indications . . . . . . .52DC ELECTRICAL LOAD DISTRIBUTION . . . . . .54

Description . . . . . . . . . . . . . . . . . . . .54

28 VDC Circuit Breaker Panels . . . . . . . . .56

28 VDC Avionics Circuit Breaker Panel . . . . .58

AC VARIABLE FREQUENCY SYSTEM . . . . . . .60

Description . . . . . . . . . . . . . . . . . . . . 60

AC Generators . . . . . . . . . . . . . . . . . .64

AC Generator Adapter Plate . . . . . . . . .66

AC Generator Control Units (GCU) . . . . . . .66Voltage Regulation . . . . . . . . . . . . . .66

Control Of The AC Generator

Line Contactor . . . . . . . . . . . . . . . . 66

Protection. . . . . . . . . . . . . . . . . . .68

AC Control Panel . . . . . . . . . . . . . . . .70

AC Contactor Boxes . . . . . . . . . . . . . . .72

AC Contactor Box Contactors . . . . . . . . . .74

AC Generator Line Contactors . . . . . . . .74

External Power Contactors . . . . . . . . . .74

Galley Load Shed Contactors . . . . . . . .74

Controls And Indication . . . . . . . . . . . . .76

AC Voltage . . . . . . . . . . . . . . . . . .76

AC Load . . . . . . . . . . . . . . . . . . .76

AC GEN Caution Lights . . . . . . . . . . .76

AC BUS Caution Lights . . . . . . . . . . .78

AC GEN HOT Caution Lights . . . . . . . .78

External Power Receptacle . . . . . . . . . . .80

Table of Contents

EPGDS . . . . . . . . . . . . . . . . . . . . . . . 6

Description . . . . . . . . . . . . . . . . . . . . 6

BATTERY SYSTEM . . . . . . . . . . . . . . . . . 8Description . . . . . . . . . . . . . . . . . . . . 8

Main and Auxiliary Batteries . . . . . . . . . . .10

Battery Containment Vessel . . . . . . . . . . .12

Standby Battery . . . . . . . . . . . . . . . . . 14


Battery Load Indication . . . . . . . . . . . . 16

Battery Temperature Indication . . . . . . . .16

STBY BATTERY, AUX BATTERY,

MAIN BATTERY Caution Lights . . . . . . .18

STBY BATT HOT, AUX BATT HOT,MAIN BATT HOT Warning Lights: . . . . . .18

MAIN 28 VDC GENERATION SYSTEM . . . . . . .20

Description . . . . . . . . . . . . . . . . . . . . 20

DC Starter/Generator . . . . . . . . . . . . . .22

DC Generator Control Units (GCU) . . . . . . .24

Electrical Power Control Unit (EPCU) . . . . . .26

DC Control Panel . . . . . . . . . . . . . . . . 28

DC Transformer Rectier Units (TRU) . . . . . .30

DC Contactor Box . . . . . . . . . . . . . . . .32Standby Contactor Box . . . . . . . . . . . . .36


Caution Lights . . . . . . . . . . . . . . . . 40

APU 28VDC GENERATION SYSTEM . . . . . . .42

Description . . . . . . . . . . . . . . . . . . . .42

APU DC Generator . . . . . . . . . . . . . . .44





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External AC Power Protection Unit . . . . . . .80

Controls And Indications . . . . . . . . . . . . .82

ELECTRICAL LOAD DISTRIBUTION . . . . . . . .84

Description . . . . . . . . . . . . . . . . . . . . 84

115 VAC Variable FrequencyCircuit Breaker Panel . . . . . . . . . . . . .84

Operation . . . . . . . . . . . . . . . . . . . . 84




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Figure 23 – DC EXT. Power -

Control & Receptacle . . . . . . . . . . . . . .51

Figure 24 – EIS Indication - DC External Power .53

DC ELECTRICAL LOAD DISTRIBUTION

Figure 25 – DC Electrical Load Distribution . . .55Figure 26 – Left & Right DC Circuit

Breaker Panels. . . . . . . . . . . . . . . . . . 57

Figure 27 – 28 VDC Avionics C/B Panel . . . . .59

AC VARIABLE FREQUENCY SYSTEM

Figure 28 – AC Variable Frequency System . .61

Figure 29 – AC Generation - Normal Operation .63

Figure 30 – AC Generator . . . . . . . . . . . .65

Figure 31 – AC GCU Location . . . . . . . . . .67

Figure 32 – AC GCU . . . . . . . . . . . . . . .69Figure 33 – AC Control Panel . . . . . . . . . .71

Figure 34 – AC Contactor Box (ACCB) . . . . .73

Figure 35 – ACCB Contactors . . . . . . . . . .75

Figure 36 – AC Control and Indications . . . . .77

Figure 37 – Caution Lights . . . . . . . . . . . .79

Figure 38 – AC External Power

Receptacle and EPPU . . . . . . . . . . . . . . 81

Figure 39 – AC External Power - Controls and

Indications . . . . . . . . . . . . . . . . . . . . 83

ELECTRICAL LOAD DISTRIBUTION

Figure 40 – AC Distribution . . . . . . . . . . .85

List of Figures

EPGDS

Figure 1 – EPGDS Block Diagram . . . . . . . . 7

BATTERY SYSTEMFigure 2 – Battery System . . . . . . . . . . . . 9

Figure 3 – Main and Aux Batteries . . . . . . . . 11

Figure 4 – Battery Containment Vessel . . . . .13

Figure 5 – Standby Battery . . . . . . . . . . .15

Figure 6 – Controls and Indications . . . . . . .17

Figure 7 – Caution & Warning Lights - Batteries .19

MAIN 28 VDC GENERATION SYSTEM

Figure 8 – Main DC Generation System . . . . .21

Figure 9 – DC Starter Generator . . . . . . . . .23Figure 10 – DC Generator Control Unit (GCU) .25

Figure 11 – Electrical Power

Control Unit (EPCU) . . . . . . . . . . . . . . . 27

Figure 12 – DC Control Panel . . . . . . . . . .29

Figure 13 – Transformer Rectier Unit (TRU) . .31

Figure 14 – DC Contactor Box . . . . . . . . . .33

Figure 15 – DC Contactors . . . . . . . . . . .35

Figure 16 – STBY Contactor Box . . . . . . . .37

Figure 17 – Controls and Indications . . . . . .39

Figure 18 – Caution Lights . . . . . . . . . . . .41

APU 28VDC GENERATION SYSTEM

Figure 19 – APU Operation . . . . . . . . . . .43

Figure 20 – APU Starter/Generator . . . . . . .45

Figure 21 – Controls and Indications . . . . . .47

DC EXTERNAL POWER SYSTEM

Figure 22 – DC External - Schematic . . . . . .49




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THIS PAGE INTENTIONALLY LEFT BLANK




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The AC variable frequency generators make 115 VAC

three phase electrical power for AC systems that are

not frequency sensitive, such as deicing heaters,

fuel auxiliary pumps, the Standby Power Unit (SPU)

hydraulic pump and the galleys. They also energize theTransformer Rectier Units (TRU), which are part of the

Main 28 Vdc Generation System to supply 28 Vdc.

The Main 28 Vdc Generation System is energized by

theses sources:

Two engine driven starter/generators●

Two Transformer Rectier Units (TRU)●

Three NiCad batteries●

Auxiliary Power Unit (APU).●

EPGDS

The Electrical Power Generation and Distribution System

(EPGDS) supplies electrical energy to all electrical

equipment through an AC Variable Frequency System

and Main 28 Vdc Generation System.

The EPGDS does energy conversion, distribution,

storage, control, protection, monitoring, and indication.

Description

The EPGDS has these sub-systems:

Alternating current variable frequency●

Main 28 VDC generation●

Battery●

Auxiliary Power Unit (APU) 28 Vdc●

External AC ground power ●

External DC ground power ●

AC electrical load distribution●

DC electrical load distribution.●

The EPGDS has connections AC for and DC external

power while on the ground.

Note: The AC external power source does not supply

electrical power for engine starting.

The power is distributed by an electrical bus system.

It recongures when an electrical power source or bus

malfunction, by the automatic closing and opening of bus

tie contactors.




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EPGDS Block DiagramFigure 1 –




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The Battery system has these components:

Battery and Box, Main●

Vent and Drains, Main Battery●

Battery and Box, Auxiliary●

Vent and Drains; Auxiliary Battery●

Battery and Box, Standby●

Vent and Drains, Standby Battery.●

The contactors to connect the main and auxiliary

batteries are located in the DC Contactor Box (DCCB)

and the contactors that control the standby battery

operation are located in the Standby Battery Contactor

Box (SBCB)

The Multi-Function Display (MFD) electrical system page

and the caution and warning lights system show battery

system indications.

The Electrical Power Control Unit (EPCU) supplies

indication data through the two Input/Output Processors

(IOP1, IOP2) located in the Integrated Flight Cabinets

(IFC) to the Electronic Instruments System (EIS).

BATTERY SYSTEM

The battery system supplies aircraft engine start power,

emergency 28 Vdc electrical power to the aircraft DC

essential buses and to the No. 3 Standby Hydraulic

Pump.

Description

The battery power system of the aircraft has three

batteries and switching devices to supply electrical power

to the essential buses during emergency ight conditions.

The main, auxiliary, and standby batteries are connected

to the main feeder buses to receive a charging current.

The main and the auxiliary batteries also connected

to the main feeder buses to supply electrical power tostart the engines. During an engine start condition, the

standby battery is isolated from the main feeder bus,

but stays connected to the essential buses to maintain a

minimum voltage level on the essential bus.

The standby battery has a related battery power bus in

the right DC circuit breaker panel that is energized at all

times. The auxiliary and main batteries have a related

battery power bus in the left DC circuit breaker panel that

is energized when the AUX BATT or MAIN BATT toggleswitch is set to on.

The Engine and System Integrated Display (ESID)

system shows main 28 Vdc generation system electrical

indications




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Battery SystemFigure 2 –




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After a long discharge period, the initial charge current

can peak at 200 A. The current rapidly decreases as the

battery starts to charge.

During the discharge mode, the battery supplies electrical

power. The battery output voltage decreases as thecurrent load increases.

Note: The voltage at the battery terminals cannot be

used as an indication of the battery state of

charge.

The battery has nickel and cadmium (NiCad) plates with

potassium hydroxide electrolyte. The NiCad battery has

relatively constant voltage for most of the discharge

condition.

A main power positive and negative electrical connection

to the battery terminals is made with a power plug

connector attached to the case. The batteries have

two independent internal sensors that sense battery

temperature. A Resistive Temperature Device (RTD)

thermal sensor is used to measure the battery

temperature for an EIS indication and a bimetallic

temperature switch is used to sense a temperature

exceedance for a warning indication. The internal sensor

wires are routed through a circular connector attached tothe battery case.

The left lower nose compartment door must be opened

to access the main and auxiliary batteries. The auxiliary

battery is located aft of the main battery. It is secured to

the airframe in the nose compartment with tabs that are

part of the battery case cover.

Main and Auxiliary Batteries

The 40 A hour batteries have a rated discharge of 40

A for one hour. The discharge rate is not linear. The

capacity is usually less than the rated value when the

discharge current is more than the nominal value.

The left lower nose compartment door must be opened to

access the main and auxiliary batteries. The main battery

is located forward of the auxiliary battery. The batteries

are secured to the airframe in the nose compartment with

tabs that are part of the battery case cover. The case is

a steel box with a removable cover to give access for

inspection.

It also has a vent port that attaches to a tube that routes

the gas overboard through a containment vessel.

The main and auxiliary batteries are 40 A hour batteries

with an assembly of individual cells contained in a steel

case. Each cell is connected in series to make 24 Vdc at

the terminals. Solid copper bus bars are used to connect

the cells. They weigh 76.51b (34.7 kg) and are 10.25 in.

(260.4 mm) wide, 10.5 in. (266.7 mm) long and 9.7 in.

(246.4 mm) high.

The main and auxiliary batteries are self contained powersources that operate in the charge and discharge modes.

The main 28 Vdc generation system supplies electrical

power to the battery during the charge mode. The

amount of charge current is determined by the state of

charge and the internal resistance of the battery.




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Main and Aux BatteriesFigure 3 –




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Battery Containment Vessel

The left lower nose compartment door must be opened

to access the containment system. It is secured to the

battery shelf with three mounting screws.

The overow containment system protects the aircraft

structure and other parts from the corrosive battery

gases and uid.

Each battery has a vent port that attaches to a tube to

route its gases through a containment vessel overboard.

The electrolyte in the battery is potassium hydroxide and

water. The containment system has a bottle with a boric

acid and water wetted sponge to neutralize the battery

electrolyte.




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Battery Containment VesselFigure 4 –




Rev. 1.0 - Jan/2011



rated value when the discharge current is more than the

nominal value.

Note: The voltage at the battery terminals cannot be

used as an indication of the battery state of

charge.

The battery has nickel and cadmium (NiCad) plates with

potassium hydroxide electrolyte. The NiCad battery has

relatively constant voltage for most of the discharge

condition.

A main power positive and negative electrical

connection to the battery terminals is made with a

power plug connector attached to the case. The battery

has two independent internal sensors that sense

battery temperature. A Resistive Temperature Device

(RTD) thermal sensor is used to measure the battery

temperature for an EIS indication and a bimetallic

temperature switch is used to sense a temperature

exceedance for a warning indication. The internal sensor

wires are routed through a circular connector attached to

the battery case.

Standby Battery

The left upper nose compartment door must be opened

to access the standby battery. The battery is secured to

the airframe in the nose compartment with tabs that are

part of the battery case cover. The case is a steel boxwith a removable cover to give access for inspection.

It also has a vent port that attaches to a tube that routes

the gases overboard through a containment vessel. The

battery is a 17 or 40 A hour battery with an assembly

of individual cells contained in a steel case. Each cell

is connected in series to make 24 Vdc at the terminals.

Solid copper bus bars are used to connect the cells.

The 17 ampere hour standby battery weighs 38.5 Ib

(17.46 kg). It is 7.7 in. (195.6 mm) wide, 8.5 in. (215.9

mm) long and 9.75 in. (247.7 mm) high.

The Standby Battery is a self contained power source

that operates in the charge and discharge modes. The

main 28 Vdc generation system supplies electrical power

to the battery during the charge mode. The amount of

charge current is determined by the state of charge

and the internal resistance of the battery. After a long

discharge period, the initial charge current can peak at

200 A. The current rapidly decreases as the battery startsto charge.

During the discharge mode, the battery supplies electrical

power. The battery output voltage decreases as the

current load increases. The 17 A hour batteries have

a rated discharge of 17 A for one hour. The discharge

rate is not linear. The capacity is usually less than the




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Standby BatteryFigure 5 –




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symbol before the numbers is used to show an overload

condition of the battery. The symbol is out of view

when the load is less than 100 0/0. A - symbol shows a

discharge condition.

Battery Temperature Indication

The battery temperature indication shows the battery

temperature in degrees Celsius in white numbers. The

indication changes to yellow when temperature is more

than 50 and less than 65°C. If the temperature is more

than 65 °c, the indication will change to red.

Note: The Resistive Thermal Device (RTD) supplies

temperature data through the EPCU and

FDPS to the EIS.

Note: When the voltage or load data malfunctions, the

digits are replaced by white dashes

Controls and Indications

The battery toggle switch located on the DC control panel

is set to BATTERY MASTER position to let the standby,

auxiliary and main batteries energize the essential buses

if no other DC power source is available.

The battery toggle switches are set to STBY BATT, AUX

BATT, and MAIN BATT positions to let the standby,

auxiliary and main batteries connect to the main feeder

buses to receive a charging current.

Note: The BATTERY MASTER, AUX BATT, or MAIN

BATT toggle switch is set to on to energize the

battery power bus in the left DC circuit breaker

panel.

The MFD1 and MFD2 reversion switches located on

the ESID Control Panel (ESCP) are used to select the

electrical page on the multi-functional displays.


shows these battery system indications:

Load●

Temperature.●

The battery indication has a BATT title in white letters.The indication has MAIN, AUX and STBY titles in white

fonts to show the load and temperature of the main,

auxiliary and standby batteries.

Battery Load Indication

The battery load indication shows the battery load in

white numbers. The numbers show the battery output

load as a percentage of the total rated output. A +




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Controls and IndicationsFigure 6 –




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The battery system malfunctions are shown with these

caution lights:

STBY BATTERY●

AUX BATTERY●

MAIN BATTERY.●

STBY BATTERY, AUX BATTERY, MAIN BATTERY

Caution Lights

The STBY BATTERY, AUX BATTERY or MAIN BATTERY

caution lights come on to show that the battery is not

connected to its main feeder bus for charging.

The caution lights receive their signals from the related

contactor K25, K7 and K8.

The battery system malfunctions are shown with these

warning lights:

STBY BATT HOT●

AUX BATT HOT●

MAIN BATT HOT.●

STBY BATT HOT, AUX BATT HOT, MAIN BATT HOT

Warning Lights:

The STBY BATT HOT, AUX BATT HOT or MAIN BATTHOT warning lights come on to show that the battery

temperature is more than 71 °c. It goes out when the

temperature is less than 63°C.

The inputs to these warning lights come directly from the

bi-metal temperature switch located in each battery.




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Caution & Warning Lights - BatteriesFigure 7 –




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DCCB Contactors●

Standby Battery Contactor Box (8BCB)●

DC Current Transformers (DC CT)●

Current shunts.●


and the caution and warning lights system show main 28

Vdc generation system indications.

The direct current (DC) system operates in these modes:

Normal●

Protection●

Fault Tolerant●

Emergency●Diagnostics and Monitoring.●

MAIN 28 VDC GENERATION SYSTEM

The main 28 Vdc generation system makes and supplies

28 Vdc electrical power to the aircraft DC buses.

DescriptionThe main 28 Vdc generation system has two DC starter/

generators, one on each engine, and two Transformer

Rectier Units (TRU) to supply electrical power

independently to the left and right DC bus systems.

When a DC starter/generator or TRU malfunctions, the

main 28 Vdc generation system automatically connects

its bus to another serviceable electrical source for

continuous operation.

A DC external power receptacle and control circuitry

allows the system to be powered from an external power

source while the aircraft is on the ground.

Toggle switches located on the DC control panel in

the ight compartment give manual control of the main

28 Vdc generation system. The Engine and System

Integrated Display (ESID) system shows main 28 Vdc

generation system electrical indications.

The Main 28 Vdc Generation System has these units:DC Starter/Generators (GEN)●

DC Generator Control Units (DC GCU)●

Electrical Power Control Units (EPCU)●

DC control panel●

DC Transformer Rectier Units (TRU)●

DC Contactor Boxes (DCCB)●




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Main DC Generation SystemFigure 8 –




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the DC starter/generator with its output voltage until the

DC GCU starts regulation. When regulating, the DC GCU

supplies a modulated current to the DC starter/generator

to maintain a 28.5 Vdc output. The DC starter/generator

has stator and rotor assemblies contained in a cylindrical

shaped housing. The housing is made of a high iron

content material. It is part of the magnetic circuit for the

starter assembly.

The rotor assembly has a rotor winding that connects to

the xed input terminals on the machine housing through

a brush/commutator assembly. The machine housing

has 4 poles with a four brush block assembly to switch

the input or output current to the correct rotor winding.

The rotor is held at each end by ball bearings that are

mounted in the housing. The ball bearings are prelubricated with grease when installed and service is not

necessary until overhaul.

The DC starter/generator has a fan to supply a forced

air ow axially through it to cool the rotor and starter

windings, the commutator assembly, and the bearings.

Air is drawn from outside the nacelle through NACA vents

to keep the operating temperatures satisfactory. The

brushes that are used in the DC starter/generator have

optimum life when blast cooling is supplied by propellerthrust to lower their temperature.

The DC starter/generator electrical power circuit has a

4 pole shunt that operates at 12,000 rpm. The electrical

circuit of the DC starter/generator has interpole windings

to help the ux path between the stator and rotor to

increase generator efciency. The DC GCU supplies

a control current to the shunt eld winding of the DC

DC Starter/Generator

The DC starter/generator attaches to the accessory

gearbox with a Quick-Attach/Detach (QAD) adapter that,

once installed, stays attached to the gearbox when DC

starter/generator is removed. The DC starter/generatorconnects to the QAD with a V band clamp to secure the

assembly. The QAD has an opening that connects to an

airframe duct to exhaust cooling air outside of the engine

nacelle.

The torque force is transmitted to the DC starter/

generator through a splined shaft that connects to the

engine accessory gearbox. The DC starter/generator’s

drive shaft has a shear section that breaks to protect the

accessory gear box drive train from damage when toomuch torque is supplied.

The DC starter/generator is an electromagnetic machine.

When it rotates, it will change engine input mechanical

torque to output DC electrical power. In the starter mode,

it changes input electrical DC electrical power into a

mechanical output torque. The DC starter/generator

operation is controlled and monitored by the DC

Generator Control Unit (GCU).

The DC starter/generator is a four-pole, shunt connected,fully compensated DC generator with interpole windings,

brush commutation, and an internal cooling fan. It is

attached to the aircraft accessory gearbox.

The DC starter/generator has a permanent magnet

so that it can make output voltage without an external

excitation source. The output from the DC starter/

generator is sent to the DC GCU. The DC GCU supplies




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DC Starter Generator Figure 9 –




Rev. 1.0 - Jan/2011



voltage to maintain a constant voltage at the Point of

Regulation (POR) under different load conditions. The DC

starter/generator speed and voltage will increase when

the engine is operating. When the output voltage is more

than ±1 Vdc of the bus voltage, the DC GCU will cause

the bus contactor to connect the DC starter/generator to

its main feeder bus.

When the two main feeder buses are connected together

through K21 by a MAIN BUS TIE toggle switch selection

or EPCU reconguration, a signal is sent to each DC

GCU to make the DC starter/generators load share.

The DC GCU regulates the DC starter/generator’s output

and gives these protective functions:

Parameter Value

Over voltage 32.5

Differential Feeder Fault

Detection

75 A ±25 A

Bus Fault Detection 800 A

Parallel Load Sharing 10% rated current

starter/generator to control its output voltage. The

shunt eld winding current is amplied by the rotational

energy of the engine to make the rated output of 400 A

at 30 Vdc. The DC starter/generator terminal voltage is

monitored by the EPCU for CBIT functions.Inputs and outputs of the stator windings are given by

connections on the body of the DC starter/generator. Low

current connections are made with a circular connector

and high power output connections are made to studs

mounted on a terminal block. A bonding stud on the

housing of the DC starter/generator is used to connect it

to the airframe ground potential.

The DC starter/generator has a temperature switch that

closes a set of contacts when the temperature of the DCstarter/generator is excessive. It gives continuity through

two pins on the DC starter/generator connector to make

the DC GEN HOT indication come on in the caution and

warning lighting panel.

DC Generator Control Units (GCU)

The DC GCU controls the DC starter/generator start and

regulation modes. The DC GCU senses the DC starter/

generator speed and it stops the start mode when the

speed of the engine is more than 50%) NH. At the end of

the start mode, the DC GCU opens the bus contactor and

de-energizes the DC starter-generator.

When the DC GCU senses a voltage output from the

DC starter/generator, a eld control contactor in the DC

GCU switches from the eld build up circuits to a voltage

regulator circuit. The voltage regulator is a closed loop

control circuit. It adjusts the duty cycle of the exciter eld




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DC Generator Control Unit (GCU)Figure 10 –




Rev. 1.0 - Jan/2011



are supplied through output drives that use current

limiting for isolation.

The critical aircraft operating functions use circuits with

usually closed contactors to let the ight compartment

toggle switches control the main 28 Vdc generationsystem when the EPCU is de-energized.

The voltage and current data is supplied to the Electronic

Instruments System (EIS) through the Integrated Flight

Cabinets (IFC1, IFC2) for indication. The data supplied

for indication is not used for the control functions.

The EPCU has daughter printed circuit card assemblies

and a mother board contained in an aluminum enclosure.

The daughter printed circuit card assemblies connect to

a mother board that connects to interface connectors.The daughter circuit card assemblies connect to the

motherboard using thermal card guides for support and

thermal dissipation.

The EPCU is cooled by conduction through the mounting

feet of the unit to the airframe and by natural convection

through cooling holes near high power dissipation

devices. The high power devices are attached to heat

sinks on the circuit card assemblies that contact the

thermal card guides when it is installed.

The box enclosure has three connectors that connect

to the remaining part of the system. One connector is

used for the APU interface functions. A carrying handle

is provided for transporting the EPCU. The EPCU has

hard mounting points as an alternative to rack mounting.

The EPCU has an interface panel with two push-button

The DC Generator Control Unit (GCU) contains the

voltage regulation and protection circuits for the DC

starter/generator. Printed circuit cards, discrete power

semiconductors, and electromechanical contactors are

put in an aluminum box without the need for convectioncooling through the box.

The DC GCU is cooled by conduction through the

chassis mounting locations and by convection of air over

the surface of the box. Power dissipating components

in the DC GCU are attached to chassis heat sinks to

transfer heat to it. Electrical connections are made with

a single connector that is attached to the end of the DC

GCU enclosure.

Electrical Power Control Unit (EPCU)

The EPCU manually or automatically controls the

operation of some contactors in the main 28 Vdc

generation system. It manually controls contactors by

ight compartment toggle switch selections.

For example, a manual external DC power selection

causes the EPCU to close the external power contactor.

Automatic functions are used to reduce pilot work load

and to start protective functions that cannot tolerate thetime delay associated with a pilot selection. For example,

the EPCU automatically causes the external power

contactor to open when an over voltage condition is

sensed. Digital logic control is used as the primary control

of the main 28 Vdc generation system. Analogue to

digital circuits in the EPCU changes the analogue inputs

to digital format to control the system. The output signals




Rev. 1.0 - Jan/2011



Electrical Power Control Unit (EPCU)Figure 11 –




Rev. 1.0 - Jan/2011



double throw switch. The toggle lever is connected to

a mechanism located in the body of the switch that

moves in the opposite direction as the toggle lever. The

wires from the receptacle connector are connected to

the switch terminals with lugs except the bus fault reset

toggle switch that has solder wire connections. The

toggle switches are attached to the backing panel with

mounting nuts and lock washers.

switches and a digital display on its front face to access

fault codes.

The Electrical Power Control Unit (EPCU) records main

28 Vdc generation system fault conditions. It has an

interface panel on its front face to look at the fault codes

DC Control Panel

The DC control panel is attached to the overhead console

using four DZUS fasteners. The fasteners and a bonding

wire are directly connected to the chassis to make a

ground continuity connection between the backing panel

and the aircraft structure.

The DC control panel gives manual control of the main

28 Vdc generation system. It has these toggle switchesto control the systems:

Batteries●

DC starter/generators●

External DC power ●

Main feeder bus tie●

Bus fault reset.●

The DC starter/generator, standby, auxiliary, and main

battery toggle switches are positive break, two pole,

double throw, toggle switches. The battery master toggle

switch is a four pole, double throw switch.

The main bus tie and DC external power toggle switches

are positive break, single pole, double throw toggle

switches and the main bus tie toggle switch has a

locking mechanism that locks the selection to the set

position. The bus fault reset toggle switch is a four pole,




Rev. 1.0 - Jan/2011



DC Control PanelFigure 12 –




Rev. 1.0 - Jan/2011



a maximum of 10 seconds. The AC generator output

voltage is reduced proportionally with the frequency to

prevent damage to the TRU.

No active control to connect or disconnect the TRU from

the AC generator is necessary. A short circuit in the TRUor related aircraft wiring will open its 3 phase AC circuit

breaker.

The TRU has a thermal sensor to automatically control

the cooling fan. The cooling fan draws in ambient air and

exhausts it outside the aircraft through a ange on the

TRU attached to an airframe duct. If the TRU overheats,

the thermal sensor supplies a signal to the caution and

warning lights system.

DC Transformer Rectier Units (TRU)

The TRU are located in the nose of the aircraft. They are

accessed by opening the upper right nose compartment

door. The TRU enclosure has a rectangular shape, with

the cooling air ow driven from the front face along thelength of the enclosure to the rear face, where provision

is included to attach ducting for routing of the hot exhaust

air. The cooling air is forced through the unit using a fan

mounted in the TRU at the front face. This fan is powered

from within the TRU without the need for external

activation and is thermostatically controlled so as to

only be operational when the unit requires cooling. The

enclosure provides for mounting by incorporating four

hard mounting feet that bolt to the aircraft structure.

The Transformer Rectier Unit (TRU) is a self contained,

solid state power conversion device that changes 115

VAC variable frequency AC electrical power to 28 Vdc

electrical power.

The TRU receives three phase 115 VAC power through

a circular connector on the front face of the enclosure.

The output 28 Vdc power is available through positive

and negative studs also located on the front face of the

enclosure.The TRU supplies an indication of its status for indication

in the ight compartment through the EPCU.

The TRU stays energized during AC generator under

frequency and under voltage condition. When the

frequency and voltage are decreased because of AC

generator under speed operation during propeller

feathering, the TRU stays connected to the load for




Rev. 1.0 - Jan/2011



Transformer Rectier Unit (TRU)Figure 13 –




Rev. 1.0 - Jan/2011



The DCCB contains these components:

Diodes●

Current transformers●

DC circuit breakers●

Protective fuses●

DC starter/generator bus tie contactors, K1 and K2●

Main feeder bus tie contactor, K21●

Secondary feeder bus tie contactor, K22●

Secondary/main feeder bus tie contactors, K5 and K6●

DC external power contactor, Kg●

Battery bus tie contactor, K7 and K8.●

DiodesDiodes are electronic devices that are used to isolate the

direct current power sources.

Current Transformers

Two current transformers, identied CT1 and CT3,

located in the DCCB, are used to sense the current

ow in the main feeder buses. The main feeder current

transformers supply current data to the EPCU differential

current sense circuits. Each current transformer

assembly is a toroidal (ring-type) current transformers.

The cable from each phase of the system is passed

through a toroid. A multi-pin connector is used to make

electrical connections between the toroids and the other

components. The toroidal current transformers are

contained in an aluminum case and have mounting holes

that are not symmetrical to prevent improper installation.

DC Contactor Box

The DC Contactor Box (DCCB) is installed in the nose

compartment and is secured to the airframe with six

mounting bolts. It weighs 76 Ib (34.47 kg) and it is 47.5

in. (1.2 m) long, 9.2 in. (233.7 mm) high and 16 in. (406.4mm) wide.

The DCCB’ is not a Line Replaceable Unit (LRU). It

does not require replacement unless it is damaged. The

components in the DCCB are easily accessed when its

covers are removed. The components in the DCCB give

control and distribution of the DC power source from the

two DC starter/generators transformer rectier units, main

and auxiliary batteries, or DC external power source.

The DC Contactor Box (DCCB) assembly is used todistribute and control the main 28 Vdc electrical power.

The DCCB contains monitor and protection components

in a protected environment. The box has covers to allow

access to the internal Line Replaceable Units (LRU). The

electrical power connections between contactors in the

DCCB is made with bus bars. They are attached by a

mounting plate assembly that secures the bus bars in the

DCCB. Standard cable is used to make the connections

between the mounting plate assembly and the boxconnectors. The DCCB has circuit breakers to protect

the feeder cables that are routed directly to the aircraft

equipment or to the circuit breaker panels in the ight

compartment. The DCCB cover must be removed to get

access to the circuit breakers.




Rev. 1.0 - Jan/2011



DC Contactor BoxFigure 14 –




Rev. 1.0 - Jan/2011



DC Circuit Breakers

The circuit breakers are installed in the DCCB to protect

the feeder cables that are routed to the circuit breaker

panel in the ight compartment. Protective Fuses: Two

fuses are installed in the DCCB to protect the feedercables that go to the loads. A 100 A fuse protects the

ECS recirculation fan and a 150 A fuse protects the TRU

and the secondary feeder bus tie contactor, K22.

DC Contactors

The contactors are attached to the bus bars with

mounting screws and to a connector with two mounting

screws.

Each contactor has 400 A single pole, single throwcontact arrangement with 2 sets of 5 A auxiliary contacts.

Coil windings are used to move the contact arms.

The DC contactors in the DC contactor box connect the

DC electrical sources to the main and secondary feeder

buses.




Rev. 1.0 - Jan/2011



DC ContactorsFigure 15 –




Rev. 1.0 - Jan/2011



The SBCB contains these components:

Diode, CR 6, CR7, CR8●

Circuit Breakers●

DCMP power contactor, K23●

Main Bus contactor, K25●

Essential Bus contactor, K24.●

Diodes

Diodes are electronic devices that are used to isolate the

direct current power sources. A 100 A diode is located in

the SBCB. It is connected between the standby battery

and the left essential distribution bus. The diode allows

power to reach the essential bus but prevents the left

essential bus from being the source of power.

DC Circuit Breakers

The circuit breakers are installed in the DCCB to protect

the feeder cables that are routed to the hydraulic DCMP

and circuit breaker panel in the ight compartment.

DC Contactors

The contactors are attached to the bus bars with

mounting screws and to a connector with two mounting

screws. Each contactor has 400 A single pole, singlethrow contact arrangement with 2 sets of 5 A auxiliary

contacts. Coil windings are used to move the contact

arms. The DC contactors in the standby contactor box

connect the standby battery to the hydraulic DCMP and

battery buses in the ight compartment.

Standby Contactor Box

The Standby Contactor Box (SBCB) is installed in the

nose compartment or aft fuselage compartment and

is secured to the airframe with four mounting bolts. It

weighs 14 Ib (6.35 kg) and it is 12.1 in. (307.3 mm) long,5.9 in. (150 mm) high and 12.03 in. (305.56 mm) wide.

The Standby Contactor Box (SBCB) energizes the No.

3 hydraulic system DC Motor Pump (DCMP) and battery

buses in the ight compartment. The SBCB has monitor

and protection components in a protected environment.

The box has a cover to allow access to the internal Line

Replaceable Units (LRU).

The electrical power connections between contactors in

the SBCB is made with bus bars. They are attached by amounting plate assembly that secures the bus bars in the

SBCB. Standard cable is used to make the connections

between the mounting plate assembly and the box

connectors. The SBCB uses three circular connectors to

interface with the other aircraft system components in the

main 28 Vdc generation system. The SBCB has circuit

breakers to protect the feeder cables that are routed

directly to the aircraft equipment or to the circuit breaker

panels in the ight compartment. The SBCB cover mustbe removed to get access to the circuit breakers.

The SBCB is not a Line Replaceable Units (LRU). It

does not require replacement unless it is damaged. The

components in the SBCB are easily accessed when its

covers are removed. The components in the SBCB gives

control and distribution of the DC power source from the

standby battery.




Rev. 1.0 - Jan/2011



STBY Contactor BoxFigure 16 –




Rev. 1.0 - Jan/2011



DC Voltage Indication

The DC voltage indication shows the DC essential, main,

and secondary bus voltage in white numbers.

DC Starter/Generator and TRU Load Indication

The DC starter/generator load indication shows the DC

starter/generator output load. The numbers show the DC

starter/generator output load as a percentage of the total

rated output. A 1.00 indication is used to show 1000/0.

A + symbol before the numbers shows an overload

condition of the DC starter/generator or TRU. The +

symbol is out of view when the load is less than 100%

NOTE: When the voltage or load data malfunctions,

the digits are replaced by white dashes.

•


When the aircraft engines are operating with no external

AC and DC power connected, and the DC starter/

generator toggle switches located on the DC control

panel are set to GEN 1 and GEN 2, the DC starter/generators are connected to their related DC main feeder

buses for operation.

The DC starter/generator toggle switches are set to the

OFF position to de-energize the DC generators and reset

latched functions in the DC GCU. The bus fault toggle

switch is set to BUS FAULT RESET position to reset

latched functions in the EPCU.

The MFD1 and MFD2 reversion switches located on

the ESID Control Panel (ESCP) are used to select theelectrical page on the multi-functional displays.

The electrical page shows these DC starter/generator

indications:

Essential, main, and secondary bus voltages●

DC starter/generator loads●

TRU loads.●

The DC voltage indication has a DC BUS L and DC BUS

R title in white fonts to show the voltage of the essential,main, and secondary buses. The DC load indication has

a DC GEN1 and DC GEN2 title in white fonts to show the

load of the DC starter/generators and it has a TRU1 and

TRU2 title in white fonts to show the load of the TRU.




Rev. 1.0 - Jan/2011







Rev. 1.0 - Jan/2011



DC BUS Caution Light

The DC BUS caution light comes on to show that the

EPCU has recongured the main 28 Vdc generation

system because of a source or bus fault condition. If the

bus fault is reset, the indication will go out. The cautionlight receives its input from the EPCU.

#1 DC GEN HOT, #2 DC GEN HOT Caution Light

The #1 DC GEN HOT or #2 DC GEN HOT caution light

comes on to show that the generator temperature is more

than 160 of (71.1 °C) and goes out when the temperature

is less than 155 of (68°C). The two caution lights receive

their inputs directly from the bimetal thermal sensor in

each starter/generator.

L TRU HOT, R TRU HOT Caution Light

The L TRU HOT or R TRU HOT caution light comes on

to show that the TRU has overheated. The two caution

lights receive their inputs directly from the TRU.

Caution Lights

The main 28 Vdc generation system malfunctions are

shown with these caution lights:

#1 DC GEN●

#2 DC GEN●

L TRU●

R TRU●

DC BUS●

#1 DC GEN HOT●

#2 DC GEN HOT●

L TRU HOT●

R TRU HOT.●

#1 DC GEN, #2 DC GEN Caution Light:

The #1 DC GEN or #2 DC GEN caution light comes on

to show that the generator is not connected to its bus

because of a source fault condition, the DC starter/

generator toggle switches are set to the OFF position, or

external DC power is energizing the left and right main

feeder buses. The caution lights receive their inputs from

the left GCU and right GCU.

L TRU, R TRU Caution Light

The L TRU or R TRU caution light comes on to show

that the a secondary feeder bus is not energized by its

related TRU because of a source fault condition or the

AC generator toggle switches are set to the OFF position.

The caution lights receive their inputs from the EPCU.




Rev. 1.0 - Jan/2011



Caution LightsFigure 18 –




Rev. 1.0 - Jan/2011



Description

The APU 28 Vdc generation system supplies 28 Vdc

electrical power from a APU DC generator to these

buses:

Left and right main feeder buses●Left and right secondary feeder buses●

Left and right main distribution buses●

Left and right secondary distribution buses●

Left and right essential buses.●

if there is an overload condition the EPCU will open the

APU contactor K26.

The APU 28 Vdc generation system is continuously

monitored by the EPCU. When a malfunction is sensed, it

disconnects the APU power from the aircraft buses.

The APU 28 Vdc generation system has passive and

active protection. The APU 28 Vdc generation system

uses circuit breakers and fuses for passive protection

so that a malfunction condition will not cause damage

to the aircraft wiring. The circuit breakers and fuses are

protection devices that open the circuit during excessive

current ow conditions.

Unlike fuses, circuit breakers can be reset without having

to be replaced. The APU 28 Vdc generation system uses

the EPCU and GCU to automatically control the APU

contactor for active protection so that a fault condition will

not cause damage to the aircraft wiring. The automatic

functions do not need a manual selection from the ight

compartment.

APU 28VDC GENERATION SYSTEM

The APU 28 Vdc generation system makes and supplies

28 Vdc electrical power to the aircraft 28 Vdc buses.

The APU supplies 28 Vdc to the main, essential and

secondary DC buses while the aircraft is on the ground.

The annunciator switches located on the APU control

panel in the ight compartment give manual control of the

APU 28 Vdc generation system.

The Engine and System Integrated Display (ESID)

system shows 28 Vdc generation system electrical

indications. After the APU is started, the APU DC

generator is available to supply power in parallel with

the batteries to assist start the aircraft engines. The APU

generator is connected to the right main feeder bus andautomatically cross ties to the left main feeder bus to

supply 28 Vdc electrical power to the DC buses.

The APU 28 Vdc electrical power system has these

components:

Generator, APU DC●

Unit, APU DC Generator Control●

Transformers, DC Current●

Shunt, Current.●




Rev. 1.0 - Jan/2011



APU OperationFigure 19 –




Rev. 1.0 - Jan/2011



APU DC Generator

The APU DC generator is attached to the APU gearbox

and has a fan to supply a forced air ow axially through

it to cool the rotor and starter windings, the commutator

assembly, and the bearings. Air is drawn from outside

the APU bay through NACA vents to keep the operating

temperatures satisfactory.

The APU DC generator is an electromagnetic machine.

When it rotates, it will change engine input mechanical

torque to output DC electrical power. In the starter mode,

it changes electrical input power into a mechanical output

torque. The APU DC generator operation is controlled

and monitored by the APU DC Generator Control Unit

(GCU).

The APU DC GCU supplies the APU DC generator with

its output voltage until the APU DC GCU starts regulation.

When regulating, the APU DC GCU supplies a modulated

current to the APU DC generator to maintain a 28.5 Vdc

output. The APU DC generator supplies information

to the APU DC GCU for system protection through

tapping of the interpole winding voltage. This voltage

is proportional to generator current and is continuously

monitored by the APU DC GCU to sense unusual currentlevels.




Rev. 1.0 - Jan/2011



APU Starter/Generator Figure 20 –




Rev. 1.0 - Jan/2011



The PWR FAIL caution light on the APU CONTROL panel

and the APU caution light on the CAWP also illuminates,

and the APU shuts down.

NOTE: The FAIL caution light on the APU CONTROL

panel and the APU caution light on the CAWPwill not illuminate if the PWR push-button is

not set, except when the re protection control

amplier has calculated an APU shutdown.

The MFD ELECTRICAL system page has a digital display

of the APU load. The digital display of the APU load in a

white box gives an accurate APU generator load value.

An APU GEN label, in white identies the APU generator

load indicator. A LOAD unit is also shown in blue with the

indication.

The numbers for the digital display of the APU generator

load change from .00 to +1.99 in 0.01 power unit

increments. A + symbol before the numbers shows an

overload condition. The numbers relate to the APU

generator load as a percentage of the maximum rate.

If there is an open or short circuit between the APU

current shunt and the EPCU, the digital display of the

APU generator load indicator will show .00.


The APU CONTROL panel has the GEN control for

the APU 28 VDC generation system. The APU starter/

generator is connected to the DC buses when the

conditions are as follows: APU is operating●

EXT PWR toggle switch power is not set●

GEN switchlight is pushed.●

The GEN switchlight is set to the off position to reset the

related APU DC GCU.

The GEN ON light on the APU CONTROL panel

illuminates when the generator is connected to the right

main feeder bus. The APU contactor K26 has connectedthe APU generator to the right main feeder bus.

The WARN caution light in the APU control panel

illuminates when contactor K26 does not connect the

generator to the right main feeder bus. The WARN

caution light will also come for conditions that are not

malfunctions as follows:

The ON/WARN switchlight is not set●

External DC power is energizing the right main feeder●

bus.

NOTE: The WARN caution light will not illuminate

if the PWR switch is not set. The GEN

OHT caution light on the APU control panel

illuminates when the APU DC starter/generator

temperature is more than 166°C (330°F).




Rev. 1.0 - Jan/2011







Rev. 1.0 - Jan/2011



The DC external system has protective functions to

prevent damage to the system The DC external power is

continuously monitored for the fault conditions that follow:

Correct polarity●

Over voltage●Under voltage.●

The faults are isolated to give continued operation.

DC EXTERNAL POWER SYSTEM

The DC external power system supplies 28 VDC

electrical power to the main 28 VDC generation system.

28 VDC electrical power is supplied through a DC

external power receptacle to let an external power sourceenergize the main 28 VDC generation system when

the aircraft is on the ground and the engines are not

operating.

DC external power supplies 28 VDC electrical power

through a line contactor to the left DC electrical load

distribution systems. The EPCU controls the line

contactor. The toggle switches on the DC CONTROL

panel give manual control of the DC external power

system.Description

The DC external power operates when the conditions are

as follows:

BATTERY MASTER toggle switch is set to energize●

the EPCU

DC external power is set.●

External power contactor Kg is energized by the EPCU

and DC starter/generator contactors K1 and K2 areprevented from operating as well as APU contactor K26.




Rev. 1.0 - Jan/2011



DC External - SchematicFigure 22 –




Rev. 1.0 - Jan/2011



DC External Power Receptacle

The DC external power receptacle is located in the left

nose fuselage. The DC external power receptacle is a

high power electrical connector. The unit has two large

gauge pins to carry the DC current and one smaller pinfor interface control.


The DC CONTROL panel has the EXT PWR control for

the DC external power system. OVERHEAD CONSOLE

The DC external power is connected to the DC buses

when:

Good external DC power is connected to the aircraft●

The BATTERY MASTER toggle switch on the DC● CONTROL panel is set

The EXT PWR toggle switch on the DC CONTROL●

panel is set.




Rev. 1.0 - Jan/2011



DC EXT. Power - Control & ReceptacleFigure 23 –




Rev. 1.0 - Jan/2011FOR TRAINING PURPOSES ONLY


EIS DC External Power Indications

The MFD ELECTRICAL system page has a DC external

power message. The EIS ELECTRICAL systems page

shows a DC EXT PWR ON message when the:

DC external power voltage is more than 22 VDC and●less than 31 VDC

DC EXT PWR toggle switch is set●

DC external power is energizing the left and right●

buses.






EIS Indication - DC External Power Figure 24 –






DC ELECTRICAL LOAD DISTRIBUTION

28 VDC electrical power is distributed through the circuit

breaker panels in the ight compartment to services.

Some distribution is done at the standby battery and DC

contactor boxes.

Description

28 VDC electrical power is supplied through circuit

breakers in the DC contactor box to the left and right 28

VDC circuit breaker panels.

The left and right 28 VDC circuit breaker panels supply

power to the avionics circuit breaker panel. 28 VDC

electrical power is supplied through circuit breakers in

the standby contactor box to the left and right 28 VDCcircuit breaker panel and main hydraulic system NO.3.

The DC electrical load distribution system are the:●

28 VDC circuit breaker panels●

28 VDC avionics circuit breaker panel.●






DC Electrical Load DistributionFigure 25 –






28 VDC Circuit Breaker Panels

The left and right 28 VDC circuit breaker panel is installed

in the ight compartment on the left and right side of the

pilot’s and copilot’s seats.

CAUTION: DO NOT LET THE CIRCUIT BREAKERPANEL TOUCH THE ADJACENT SIDE

WINDOW. WHEN YOU INSTALL THE

CIRCUIT BREAKER PANEL, IT IS EASY

TO PUT A SCRATCH IN THE SIDE

WINDOW. THIS WILL CAUSE DAMAGE

TO THE SIDE WINDOW.






Left & Right DC Circuit Breaker PanelsFigure 26 –






28 VDC Avionics Circuit Breaker Panel

The DC avionics circuit break r panel is installed in the

ight compartment above and aft of the left 28 VDC

circuit breaker panel.

CAUTION: DO NOT LET THE CIRCUIT BREAKERPANEL TOUCH THE ADJACENT SIDE




WINDOW. THIS WILL CAUSE DAMAGE

TO THE SIDE WINDOW.

The DC avionics circuit breaker panel gives distribution

for the main 28 VDC generation system.






28 VDC Avionics C/B PanelFigure 27 –






and controls the AC generator line contactors. The AC

variable frequency system also has current transformers

in the AC contactor boxes and AC generators to measure

A, B, and C phase current.

The toggle switches on the AC CONTROL panel give

manual control of the AC variable frequency system.

NOTE: 115 VAC three-phase electrical power is

also supplied through an AC external power

receptacle to let an external power source

energise the AC variable frequency system

when the aircraft is on the ground and the

engines are not operating

The AC variable frequency system units are the:

AC generators● AC generator adapter plate●

AC GCU●

AC CONTROL panel●

AC contactor boxes●

AC contactor box contactors.●

The MFD, ELECTRICAL system page and the CAWP

show AC variable frequency system indications.

AC VARIABLE FREQUENCY SYSTEM

The AC variable frequency system supplies 115 VAC

three-phase electrical power to the AC electrical load

distribution system.

The AC variable frequency system supplies electricalpower to AC systems that are not frequency sensitive,

such as:

De-icing (heaters)●

Fuel (auxiliary pumps)●

Hydraulic (standby power unit)●

Galleys.●

The AC variable frequency system also interfaces with

the Main 28 VDC generation system to supply electricalpower to the transformer rectier units (TRUs) that are

additional sources of DC electrical power.

Description

The AC variable frequency system has a left and right

system with cross-tie capabilities. Two engine driven AC

generators supply 115 VAC three-phase electrical power

through AC generator line contactors to the left and right

AC electrical load distribution systems.

It is not possible to connect the two AC generators

in parallel. The AC generator line contactors have a

centre off position to make sure that the AC generator

is disconnected before it is connected to the opposite

side (break before make). This is necessary because

variable frequency AC generators are used. The AC

GCUs regulate its related AC generator’s output voltage

C C O






AC Variable Frequency SystemFigure 28 –

ATA 24 ELECTRICAL POWER






active protection. Circuit breakers and fuses are used for

passive protection.

The AC GCUs are used to control the AC generator

line contactors for active protection. The AC variable

frequency system uses the EPCU for CBIT. The AC

variable frequency system also uses AC GCUs for

initiated built in test.

During the normal mode of operation, the AC GCU

controls the related AC generator line contactor to

connect the AC generator to the related AC bus.

NOTE: The two AC GCUs monitor the condition of

the opposite AC GCU. When an AC GCU

senses that the opposite AC generator is not

serviceable, it then controls the AC generatorline contactor to connect the bus to the

serviceable AC generator.

The galley load shed contactors are controlled by

auxiliary contacts in the AC generator line contactors.

The two galley load shed contactors are automatically

closed when the AC buses are energized by the two AC

generators or external power.

The alternating current variable frequency system modes

of operation are:

Airborne (normal)●

External AC power.●

The AC variable frequency system operates in thenormal mode when:

Two engines are operating and the propeller is not●

feathered

External AC power is not set●

GEN 1 and GEN 2 toggle switches on the AC●

CONTROL panel are set.

The AC generators are by monitored by the AC GCUs to

automatically control the operation of the AC generator

line contactors. If a fault is sensed, the AC generator

line contactors are opened or closed to automatically

recongure the system. The fault is isolated from the

remaining part of the AC variable frequency system to

give continued operation.

The AC variable frequency system has protective

functions to prevent damage to the AC generators

when there is a fault. The AC variable frequency system

continuously monitors for the following fault conditions:

Source●

Bus.●

The source and bus faults are isolated and the part of

the system that continues to operate is automatically

recongured to give continued operation. The AC

variable frequency system has passive protection and







AC Generation - Normal OperationFigure 29 –







the generator cooling oil. Inputs and outputs of the stator

windings are supplied through interface connections

on the body of the AC generator. The low current

connections are made with a circular connector and the

high power three-phase output connections are made

with studs attached to a terminal block.

A bonding stud is also attached to housing of the

AC generator. The generator also has a bimetallic

temperature sensor that closes a set of contacts and

gives continuity through two pins on the interface

connector when the temperature of the machine is too

much.

A three-phase current transformer is attached in the

neutral lines of the windings to give current data to the

AC GCU.

NOTE: The AC generators output rating is 45 KVA.

The rst stage of the AC generator is a Permanent

Magnet Generator (PMG). It has a magnet to make

output power without the need for an external excitation

sources. The three-phase output from the PMG is

supplied through the AC GCU to the second stage eld.

The second stage is the exciter.

NOTE The generator also has a generator positivevoltage output signal so that the terminal

voltage of each phase at the generator can be

monitored by the EPCU for CBIT functions.

AC Generators

The AC generators are attached to the propeller

reduction gearboxes of the engines with V-clamps around

the quick attach/detach (QAD) adapter plates and the

AC generator mounting anges. The QAD adapters stay

attached to the reduction gearboxes.

CAUTION: YOU MUST CORRECTLY ALIGN THE

FLANGE OF THE AC GENERATOR WITH

THE QAD ADAPTER PLATE. IF YOU DO

NOT DO THIS, YOU CANNOT INSTALL

THE V BAND CLAMP AND YOU CAN

CAUSE DAMAGE TO THE EQUIPMENT.

The generator receives a supply of pressurized oil from

the reduction gearbox to cool and lubricate the internalcomponents. Oil is transferred from the gearbox, through

the QAD adapter, to the generator using transfer tubes.

These tubes are sealed with O-rings at each end to

prevent oil leakage. Oil enters the shaft and is sprayed

outward to cool the windings and lubricate the bearings.

The used cooling oil then goes under gravity to the

bottom of the generator where it is collected in the sump.

A scavenge port is located in the sump. The engine

scavenge pump extracts the oil and returns it to theengine.

The generator is a three-stage machine, with

electromagnetic coupling between stages. (It does not

have slip rings and brushes). Each stage in the machine

has of a rotor and stator segment along its length. The

rotor is supported in the machine by ball bearings at

both ends. The bearings are lubricated and cooled by







AC Generator Figure 30 –







The AC GCUs give the functions that follow:

Voltage regulation●

Control of the AC generator line contactors●

Protection●

Control of the AC generator and AC bus caution lights●CBIT.●

Voltage Regulation

The AC GCU supplies power through a voltage regulator

circuit to the exciter windings of the AC generator to start

generator output when the conditions are as follows:

The related GEN 1 or GEN 2 toggle switch on the AC●

CONTROL panel is set

AC GCU senses that the AC generator is at the●correct operating speed.

The voltage regulator gives a constant voltage at the

POR under different load and speed conditions. An

average of the individual three-phase outputs are

used for regulation. The AC GCU also uses current

transformers in the system to continuously monitor the

AC generator current and limit the current if the output is

more than the permitted limits.

Control Of The AC Generator Line Contactor

When a stable output is sensed by the AC GCU, it closes

the related AC generator line contactor to connect the AC

generator to the related AC bus.

It closes the opposite AC generator line contactor to

connect the AC generator to the opposite AC bus if the

opposite AC GCU or AC generator is not operating.

AC Generator Adapter Plate

There are two quick attach/detach QAD adapter plates

installed on the aircraft, one for each AC generator. The

QAD adapter plate is not removed when an AC generator

is removed.

The QAD adapter plate has two transfer tubes to supply

engine oil to the AC generator. The QAD adapter plate

has an O-ring and the transfer tubes also have O-rings

and retaining clips. The QAD adapter plate gives an

interface between the AC generators and the reduction

gearbox of the engines.

AC Generator Control Units (GCU)

The two AC GCUs are installed under the fuselage

oor in the centre of the aircraft. The AC GCU is a fully

enclosed, non-hermetically sealed unit. A connector

is attached to one end of the AC GCU enclosure to

interface with the electrical power generation and

distribution system (EPGDS).

The AC GCU has an Initiated Built In Test (lBIT) function

to check the status of the unit. The unit is cooled by

conduction through the chassis and support bracket and

by convection air over the surface of the box. Power

dissipating components in the unit are attached tochassis heat sinks to minimize the thermal resistance

of the cooling circuit and give correct operating

temperatures.







AC GCU LocationFigure 31 –







NOTE: If an undervoltage and bus fault condition

is sensed at the same time, the overcurrent

protection function will occur.

Differential Current

The AC generator is de-energized and the related ACgenerator line contactor is opened by the AC GCU when

the differential current on any phase is more than 20 A.

Underfrequency

The AC generator is de-energized and the related AC

generator line contactor is opened by the AC GCU when

the AC generator frequency is less than 300 Hz. It will

automatically reconnect the AC generator when the

frequency is more than 320 Hz.

This will occur only if the system was not previously

disconnected by a different protective function. As the

AC generator frequency goes below 340 Hz, the output

voltage decreases relative to the frequency until the AC

generator is disconnected at 300 Hz

NOTE: When the condition lever is set to START &

FEATHER, the AC generator is de-energized

and disconnected from the bus because the

AC generator speed to too low for operation.The AC generator will automatically reconnect.

The operating AC GCU senses this condition through a

TRANSFER REQUEST [TR] signal. This signal is active

when there is no need for transfer and is removed when

there is a need.

If AC external power is supplied to the aircraft, a signalis supplied to the AC GCU to energize the Y coil of the

AC generator line contactor to give external AC power

system operation.

Protection

To prevent damage to the AC generators, the AC GCUs

have the protective functions that follow:

Overvoltage●

Undervoltage●Differential current●

Underfrequency●

Bus fault.●

Overvoltage

The AC generator is de-energized and the related line

contactor is opened by the AC GCU before the voltage

is more than approximately 125 VAC. This protective

function is sensed in a period of time that is inverselyproportional to the size of the sensed overvoltage

condition.

Undervoltage

The AC generator is de-energized and the related line

contactor is opened by the AC GCU before the voltage is

less than approximately 100 VAC.







AC GCUFigure 32 –







AC Control Panel

The AC CONTROL panel is attached to the overhead

console with four DZUS fasteners.

The toggle switches are identied as:

GEN 1●

GEN 2●

EXT POWER.●

The three switches have an OFF label to show their off

position. The AC CONTROL panel gives manual control

of the AC variable frequency system.







AC Control PanelFigure 33 –







output current of the AC generators to the EPCU for AC

electrical load indications in the electronic instrument

system (EIS).

Two current transformers, identied as CT2 and

CT5, supply total generator output current of the AC

generators to the AC GCUs for differential currentsensing (protection). When an AC bus is energized by the

opposite AC generator, CT3 or CT6 is also used.

AC Contactor Boxes

K1 and K3 are installed in the left-hand side ACCB, and

K2 and K4 are installed in the right-hand side ACCB.

Also, when installed, K5 is in the left ACCB and K6 is in

the right ACCB.

CT1, CT3, and CT5 are installed in the left-hand side

ACCB, and CT2, CT4, and CT6 are installed in the

right-hand side ACCB. Connectors are attached to the

enclosure to interface with the EPGDS.

There are two ACCBs installed on the aircraft. The units

have additional components:

AC generator line contactors, K1 and K2●

External power contactors, K3 and K4●

Galley load shed contactors, K5 and K6 (optional)●

Stand by power unit (SPU) contactor, installed in the●

right hand side ACCB

Internal cable assemblies and rigid bus bars●

Circuit breakers and fuses for output protection●

Circuit breakers for heaters in the propellers anti-icing●

system

Current transformers, CT1, CT2, CT3, CT4, CT5,●

CT6.External Power Protection Unit (EPPU), installed in●

the right-hand side ACCB

The current transformers in the ACCBs monitor the

current for phase A, B, and C of the AC generator for

indication and protection. Two current transformers,

identied as CT1 and CT4, supply total generator







AC Contactor Box (ACCB)Figure 34 –







They also have auxiliary contacts to control the galley

load shed contactors, K5 and K6.

Galley Load Shed Contactors

The galley load shed contactors, K5 and K6, are

50A Three-Pole Single Throw (3PST), normally opencontactors.

They have one coil winding to move the contact arms to

connect the galley buses to the AC buses.

The galley load shed contactors are only energized

when:

The two AC buses are energized by the two AC●

generators

The two AC buses are energized by the external AC● power.

AC Contactor Box Contactors

The contactors in the left-hand side and right-hand side

ACCBs attach directly to rigid bus bars.

AC Generator Line Contactors

The AC generator line contactors, K1 and K2, are 150A

Three-Pole Double Throw (3PDT), centre off contactors.

They have two coil windings, identied as X and Y, to

move the contact arms to connect the AC buses to

the related or the opposite AC generator. They also

have auxiliary contacts to control the galley load shed

contactors, K5 and K6.

NOTE: The contactor arms also move to the Y

position when the external AC power is used.

NOTE: The X position of the bus contactor is

controlled by the related AC GCU and the Y

position is controlled by the opposite AC GCU.

External Power Contactors

The external power contactor, K3 and K4, are 100A

3PDT, contactors. They have one coil winding to move

the contact arms to connect the AC buses to the AC

external power receptacle.

The external power contactors are only energized when

the conditions are as follows:

Good external AC power is supplied●

EXT PWR toggle switches on the AC CONTROL●

panel are set






ACCB ContactorsFigure 35 –






If there is an open or short circuit to ground potential

between the AC bus and the EPCU, the related digital

display of the AC generator voltage will show 0.

AC Load

The load part of the AC generator voltage and loadindicator shows an indication for the digital display of the

AC generators phase A, B, and C.

The numbers for the digital display of the AC generator

load change from .00 to +1.99 in 0.01 power unit

increments. A + symbol before the numbers shows

an overload condition. The numbers relate to the AC

generator load as a percentage of the maximum rate.

AC GEN Caution Lights

The #1 AC GEN or #2 AC GEN caution light illuminates

when the associated generator (GEN1 or GEN2) is not

connected to its bus.

The #1 AC GEN or #2 AC GEN caution light will also

illuminate for conditions that are not malfunctions as

follows:

The AC GEN1 or AC GEN2 toggle switch is set to the●

OFF position●

External AC power is energizing the Land R AC●buses.

If a source fault is sensed, the AC generator line

contactors K1 and K2 will not connect the AC GEN to the

115 VAC BUS.

Controls And Indication

The AC CONTROL panel has the controls for the AC

variable frequency system:

GEN 1 toggle switch●

GEN2 toggle switch.●

The AC generators are connected to the AC buses when

the:

Two engines are operating and the propeller is not●

feathered,

EXT PWR toggle switch power is not set, and●

GEN1 and GEN2 toggle switches are set.●

The GEN1 and GEN2 toggles switches are set to the

OFF position to reset the related AC GCU.

The MFD ELECTRICAL system page has an AC

generator voltage and load indicator with a digital display

for voltage and load.

AC Voltage

The voltage part of the AC generator voltage and load

indicator shows an indication for the digital display of the

AC generators phase A, B, and C.

If there is an open or short circuit between the ACgenerator current transformer and the EPCU, the digital

display of the AC generator load indicator will show .00.

The numbers for the digital display of the AC generator

voltage change from 0 to 249 in 1 volt increments.






AC Control and IndicationsFigure 36 –






AC BUS Caution Lights

The R AC BUS or L AC BUS caution light illuminates

when there is an overcurrent condition on the 115 VAC

BUS for more than seven seconds.

The caution light will go out if the associated toggleswitch is set to the OFF position.

AC GEN HOT Caution Lights

The #1 AC GEN HOT or #2 AC GEN HOT caution

light in the CAWP illuminates when the AC generator

temperature is more than 166°C (330°F).





Rev. 1.0 - Jan/2011


Caution LightsFigure 37 –





Rev. 1.0 - Jan/2011


External Power Receptacle

The AC external power receptacle is located in the right

nose fuselage. The unit has four large gauge pins to

carry the three-phase AC current and two smaller pins for

interface control.

It gives the interface connection between external AC

power source and the aircraft.

External AC Power Protection Unit

The external AC power protection unit is located in the

right AC contactor box. It is attached with screws. The

AC external power protection unit monitors the quality

of the input power to the AC external power receptacle

and prevents connection of the power to the aircraft

distribution system if the power is not satisfactory.

It monitors the parameters for:

Undervoltage, 106 VAC●

Overvoltage, 124 VAC●

Underfrequency, 370 Hz●

Overfrequency, 450 Hz●

Phase Rotation.●





Rev. 1.0 - Jan/2011


AC External Power Receptacle and EPPUFigure 38 –





Rev. 1.0 - Jan/2011


Controls And Indications

The AC CONTROL panel has the EXT PWR control

for the AC external AC power system. The external AC

power is connected to the AC buses when the:

Good external AC power is connected to the aircraft,● and

BATTERY MASTER toggle switch on the DC●

CONTROL panel is set, and

EXT PWR toggle switch on the AC CONTROL panel●

is set.

The MFD ELECTRICAL system page has an AC external

power message. The EIS ELECTRICAL systems page

shows an AC EXT PWR ON message when:

AC external power voltage is more than 106 VAC●and less than 124 VAC, frequency is more than 370

Hz and less than 450 Hz, phase rotation is phase

A, phase B, then phase C, and AC EXT PWR toggle

switch is set, and

AC external power is energizing the left and right 115●

VAC buses.





Rev. 1.0 - Jan/2011


AC External Power - Controls and IndicationsFigure 39 –





Rev. 1.0 - Jan/2011


CAUTION: DO NOT LET THE CIRCUIT BREAKER

PANEL TOUCH THE ADJACENT SIDE




WINDOW. THIS WILL CAUSE DAMAGETO THE SIDE WINDOW.

Operation

Three-phase, 115 VAC variable frequency electrical

power is supplied through three 50 A circuit breakers on

the Land R AC contactor box to the 115 VAC variable

frequency circuit breaker panel.


power is supplied through three 35 A circuit breakers onthe L and R AC contactor box to the propellers anti-icing

system


power is supplied through three 60 A circuit breakers on

the R AC contactor box to the main hydraulic systems 1

NOTE: The left part of the AC electrical load

distribution is described. The right part is

similar.

ELECTRICAL LOAD DISTRIBUTION


power is distributed through a circuit breaker panel in the

ight compartment to electrical loads. Some distribution

is done at the AC contactor boxes.

Description

Phase A, phase B, and phase C 115 VAC electrical

power is supplied through circuit breakers in the left and

right AC contactor boxes to:

115 VAC variable frequency circuit breaker panel●

Propellers anti-icing system●

Main hydraulic system No.1.●

The AC electrical load distribution has an 115 VACvariable frequency circuit breaker panel. Circuit breakers

(CB) in the 115 VAC variable frequency circuit breaker

panel and AC contactor box protect the wires in the AC

variable frequency system.

115 VAC Variable Frequency Circuit Breaker Panel

The 115 VAC variable frequency circuit breaker panel is

installed on the rear ight compartment bulkhead above

and aft of the right 28 VDC circuit breaker panel. It has

circuit breakers attached to the panel. Panel markings

identify the buses and circuit breakers.




© J A i ti LP AC DistributionFigure 40

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ATA24 bombardier q400 electrical power