united states army aviation center fort...

Distribution authorized to U.S. Government agencies and their contractors; Critical Technology August 10, 1999. Other requests for

this document will be referred to Department of the Army, PEO Aviation — Apache, SFAE-AV-AAH-LI, Apache Attack Helicopter,

Bldg. 5681, Suite 174, Redstone Arsenal, AL 35898. COMM (256) 313-4068 or DNS 897-4068.

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UNITED STATES ARMY AVIATION CENTER

FORT RUCKER, ALABAMA

May 2008

STUDENT HANDOUT

(LOT 11)

TITLE: AH-64D ELECTRICAL POWER MANAGEMENT SYSTEM (EPMS)

FILE NUMBER: 011-6249

This Package Has Been Developed For Use By: AH-64D Maintenance Test Pilot Course

Proponent For This Tsp Is: United States Army Aviation School

Fort Rucker, AL 36362

FOREIGN DISCLOSURE STATEMENT: This product/publication has been reviewed by the product developers in coordination with the Ft. Rucker foreign disclosure authority. This product is releasable to students from foreign countries on a case-by-case basis.

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TERMINAL LEARNING OBJECTIVE:

At the completion of this lesson you (the student) will:

ACTION: Troubleshoot the AH-64D Electrical Power Management System (EPMS).

CONDITIONS: Given an AH-64D helicopter, TM 1-1520-251-10, TM 1-1520-251-CL, and TM 1-1520-251-MTF, and a Soldiers’ Portable On-Line Repair Tool (SPORT) with TM 1-1520-APACHE/LONGBOW Interactive Electronic Technical Manual (IETM) software.

STANDARD: In accordance with TM 1-1520-251-10, TM 1-1520-251-CL, TM 1-1520-251-MTF, and TM 1-1520-APACHE/LONGBOW.

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INTRODUCTION:

The EPMS is perhaps the most important system on the AH-64D. Every subsystem on the aircraft requires electrical power for operation and monitoring. Without electrical power, the aircraft cannot navigate, communicate, engage targets or identify itself to friendly forces. The EPMS on the AH-64D is one of the most complex electrical systems found on any aircraft in the US Army inventory, and requires extensive knowledge to keep the system in an operational status. In the AQC course, the electrical system was broken down into types of power supplied: i.e., AC, DC, battery, and external power. In this lesson the system is referred to as the Electrical Power Management System (EPMS), and is broken into two systems, the primary and secondary distribution systems. This lesson will give you the skills and knowledge necessary in order to evaluate and functionally troubleshoot the EPMS. Let’s start by discussing the power distribution systems.

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A. Enabling Learning Objective 1

ACTION: Describe the AH-64D EPMS

CONDITIONS: Given a written test utilizing the IETM without the use of student notes or references.

STANDARD: In accordance with TM 1-1520-251-10 and TM 1-1520-APACHE/LONGBOW.

1. Learning Step/Activity 1

Describe the AH-64D EPMS

Figure 1. Electrical Power Management System Components

a. Electrical Power Management System (EPMS) Components.

(1) The EPMS generates, converts, regulates, distributes, controls, monitors, and

protects power throughout the AH-64D aircraft.

(a) The EPMS supplies Alternating Current (AC) Direct Current (DC) and battery

power to aircraft systems and subsystems.

(b) The EPMS can receive power from the aircraft generators, an Aviation Ground

Power Unit (AGPU), or battery power from the aircraft battery.

(2) When the aircraft Auxiliary Power Unit (APU) or engines are operating the mechanical

input from the main transmission is used to generate AC electrical power and provides

the AC to required aircraft components.

(a) The EPMS then converts the AC electrical power to DC

(b) The DC is provided to the required aircraft components.

(3) The EPMS consists of the following major components:

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(a) AC generators 1 and 2

(b) HPSM 1 and 2

(c) CBP 1 and 2

(d) ELC 1 and 2

(e) MIK

(f) FNC battery and charger

(g) R/TRU 1 and 2

(h) GCU 1 and 2

(i) External Power Receptacle and Monitor

Figure 2. Battery Components

(4) Battery components

(a) Fibrous Nickel-Cadmium (FNC) battery

a) The Fibrous Nickel-Cadmium (FNC) 24 Vdc battery is rated at 15 amp hours and at 80% charge, the battery will supply the normal flight battery loads for a minimum of 12 minutes.

b) It requires no maintenance and is composed of 20 cells that are individually sealed in a partial vacuum. This prevents the battery from venting any gasses or liquids. This configuration allows the battery to be installed in a compartment with other avionics equipment and can be shipped or stored in any position.

(b) The battery contains an internal heater, a heater temperature sensor and a

battery temperature sensor.

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1) The battery positive plates are coated with nickel oxide and the negative plates are coated with metallic cadmium.

2) The battery can withstand extremely high temperatures and high levels of vibration.

3) It maintains a steady output voltage even when being discharged at high currents and can be charged and discharged at a high rate current without causing permanent damage.

4) Battery heater

a) An internal battery heater eliminates the need for an external heater blanket and enables the battery to provide electrical power during

operation in temperatures down to -54 C (-65 F).

b) At -54 C, the heater can warm the battery sufficiently to enable the battery to supply normal aircraft load requirements within 30 minutes.

c) The battery heater temperature sensor provides over-temperature protection for the battery in the event the battery temperature sensor malfunctions

5) Battery temperature sensor

a) Provides a signal to the battery charger that is proportional to battery temperature

b) The battery temperature signal allows the charger to control the battery heater, based upon the internal temperature of the battery

Figure 3. Generator Components

(c) 45 KVA AC Generators (2)

1) Both generators are mounted on and driven by the accessory gear box of the main transmission. They are air-cooled units driven by a non-metallic,

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solid tooth spline adapter in the main transmission accessory gearbox at 12,251 or 12,373 revolutions per minute (rpm) based upon engine type, or at 12,200 rpm when driven by the APU.

2) The 45 Kilovolt-ampere (KVA) AC Generator converts mechanical energy to electrical energy and provides 115/200 Vac, 400 Hz, 3-phase, four-wire electrical power to the EPMS. Either generator is capable of supplying the total AC electrical power requirements for operating all systems.

3) The internal sections of the generator contain a Permanent Magnet Generator (PMG), a stationary and rotating exciter field along with stationary and rotating main field windings.

Figure 3. Generator Components

4) The generators are brushless units which are excited by a self contained

Permanent Magnet Generator (PMG) and provides power and control interface to the respective GCU.

5) The stationary exciter control field current induces AC voltage into the rotating exciter field.

6) The rotating exciter field voltage is rectified by the diode assembly and applied to the rotating main field.

7) The main rotating field induces 115 Vac into each of the main field stationary windings. The output is 115 Vac, 3-phase, 400 Hz. Current sensing transformers provide phase current inputs to the GCU for overcurrent protection.

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Figure 4. Generator Control Units Components

(d) Generator Control Units Components (GCUs)

1) The GCU continuously monitors the output voltage and provides voltage regulation, control and protection of its associated generator channel by varying the generator control to regulate the generator output to 115 ± 1.0 Vac.

2) Each GCU consists of:

a) A DC power supply for internal circuitry

b) A voltage regulator to regulate the AC generator output

c) Protection circuits and automatic control

d) Built-In-Test (BIT) circuitry for logic/sensing circuits

3) The GCU monitors and controls an integral Contactor Control Relay (CCR). The CCR provides power to the generator line contactor located in t

4) e respective HPSM. The GCU energizes automatically when the generator output is correct.

5) The GCU will connect the output of the generator to the respective AC bus when the generator output is correct and will automatically disconnect the

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generator in the event of a generator fault. The GCU will disconnect the generator output for these conditions:

a) Under voltage and Over voltage conditions

1 The 3-phase generator input to the HPSM is supplied back to the

GCU as a Point of Regulation (POR). This 3-phase input is full

wave rectified and reduced by a voltage divider network and an

under voltage and over voltage comparator inside the GCU.

2 If an over voltage of 125 ± 1.5 Vac occurs, the comparator output

is applied to an inverse time delay network. When the time delay

times out, the contactor control relay opens, which disconnects

the generator.

3 If an under voltage condition of 99.5 ± 0.5 Vac occurs for 200

±50 milliseconds, the comparator output is applied to an inverse

time delay network. When the time delay times out, the

contactor control relay opens, which disconnects the generator.

Under voltage protection is inhibited during an under frequency

or overcurrent condition.

b) Under frequency conditions

1 Phase A of the PMG is converted into a square wave signal by a

pulse-forming network inside the GCU that is used for under

frequency protection.

2 The output of the pulse-forming network is converted into a

sawtooth wave shape and applied to a comparator where it is

compared to a precision reference voltage.

3 If an under frequency condition of 365 to 380 Hz exists, the

output of the comparator triggers a timing logic, which after a 2 ±

l.0 second time delay opens the contactor control relay.

4 An under frequency inhibit is resident within the under frequency

protection circuit.

5 If the aircraft is in the air, input from the squat relay in the utility

relay panel disables the under frequency protection preventing

nuisance trips caused by main rotor RPM Nr droop.

c) Overcurrent conditions

1 The generator current transformer sensed input is connected to

a full wave rectifier inside the GCU where it is filtered and

applied to a comparator.

2 The resultant signal is compared to a precision reference

voltage. The output of the comparator is applied to an

overcurrent sensing logic.

3 When an overcurrent condition of 235 ± 5 amps is sensed, the

contactor control relay is opened and the generator is

disconnected via a time delay network in 5 to 7 seconds.

d) Differential current protection (feeder fault)

1 Differential current protection is provided by the Differential

Phase Current Transformer (DPCT) network. The network

consists of the generator output Current Transformers (CT)

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inside the generator, the load CTs inside the HPSM, and a

rectifier and comparator inside the GCU.

2 The outputs of the generator Current Transformers (CTs) are

routed to the GCU and to load current transformers inside the

HPSM.

3 The differential currents between the generator output current

transformers and the generator load current transformers are

connected to a full wave rectifier where they are filtered and

applied to a comparator.

4 The resultant signal is compared to a precision reference

voltage. The output of the comparator is applied to differential

current sensing logic.

5 When a differential current condition on any phase exceeds

16 to 25 amps for 45 ± 15 milliseconds, the contactor control

relay is opened via a time delay network.

e) There are 4-fault indicator lamps on the GCU adjacent to electrical connector J1. The following faults are monitored by a red indicator lamp:

1 Generator Fail (GEN) – under frequency/under speed

2 GCU Fail (GCU) – internal GCU fault

3 Bus Fail (BUS) – overload or short circuit

4 Feeder Fault (FF)

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Figure 5. High Power Switching Modules Components (1 of 4)

(e) High Power Switching Modules (HPSMs)

1) The HPSM provides power distribution, overcurrent sensing, and contactor switching logic for all AC, DC, and BAT/Emergency power requirements.

a) HPSM1 provides power to ELC1, CBP1, ECS 1, and the Fire Control Radar (FCR) major components.

b) HPSM2 provides power to ELC2, CBP2, ECS 2, and control logic for the aircraft battery charger.

2) Each HPSM is an LRU containing:

a) AC High Power Module (HPM) and an AC control module. The modules in HPSM1 are identical to the modules in HPSM2 except for the AC BUS TIE Contactor KA203, located in HPSM2.

1 AC bus bar – WA1 located in HPSM1, and WA2 located in

HPSM2

2 Six AC contactors

3 Current sensing for the contactors

4 Point of Regulation (POR) voltage monitoring that is fuse

protected

5 Differential fault current sensing capability for the respective

GCUs

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b) DC High Power Module (HPM) and an DC control module. The modules in HPSM1 are identical to the modules in HPSM2 except for the DC BUS TIE Contactor KD221, located in HPSM2.

1 Primary DC bus bar – WD1 is located in HPSM1, and

WD2 is located in HPSM2

2 There are two DC contactors (KD102 and KD103) in HPSM1 and

three DC contactors (KD202, KD203, and KD221) in HPSM2.

3 Primary BAT bus bar WB1 is located in HPSM1, and

WB2 is located in HPSM2

4 There are three Battery contactors (KB101, KB102, and KB103)

in HPSM1 and three Battery contactors (KB201, KB202, and

KB203) in HPSM2.

5 Hot battery bus bar WBP1 is located in HPSM1, WBP2 is located

in HPSM2.

a The hot battery bus bars are connected directly to the

battery.

b When the battery is installed and the battery connector is

connected, the ―hot‖ battery bus is powered.

c The MIK switch does not have to be in the BAT position for

the ―hot‖ battery bus to be energized.

6 Current sensing for the contactors

7 KD1D1 in HPSM1 and KD2D1 in HPSM2 are diodes that

connect the DC bus bar to the BAT bus bar for normal

operation and isolate the BAT bus from the DC bus when the

battery is selected to provide electrical power.

8 Voltage measurement points for the battery bus and R/TRU

outputs.

c) AC/DC/BAT control module

d) Provides AC/DC/BAT contactor control logic, Overcurrent protection, Power for the AC/DC/BAT coil drivers, and ELC DC/BAT data interface control

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3) Front panel circuit breakers and connections

a) HPSM1

1 ELC1 AC is a 3-phase, 35-amp circuit breaker. It provides

power and protection for bus WA3 inside ELC1.

2 FCR is a 3-phase, 15-amp circuit breaker. It provides power and

protection for major components of the Fire Control Radar

(FCR).

3 ELC1 DC is a 28 Vdc, 60-amp circuit breaker. It provides power

and protection for bus WD3 in ELC1.

4 PSP/LPRF is a 28 Vdc, 7.5-amp circuit breaker. It provides

power and protection for two FCR system components.

5 RFI is a 28 Vdc, 15-amp circuit breaker. It provides power and

protection for the Radio Frequency Interferometer (RFI)

processor.

6 MIK SW is a 28 Vdc, 2-amp circuit breaker. It provides power

and protection for input to the MIK switch.

7 HPSM1 CONT is a 28 Vdc, 7.5-amp circuit breaker. It provides

power and protection for control of DC power inside HPSM1.

8 COLD RFL is a 28 Vdc, 5-amp circuit breaker. It provides hot

battery bus power to the refuel panel.

9 CBP 3 BATT is a 28 Vdc, 25-amp circuit breaker. It provides

battery power to CBP 3 when installed.

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10 Five output terminals (labeled A , B , C , DC, and BAT),

mounted on the lower front panel, are wired directly to

corresponding input terminals on ELC1.

b) HPSM2

1 HPSM2 CONT is a 28 Vdc, 7.5-amp circuit breaker. It provides

power and protection for control of DC power inside HPSM2.

2 ELC2 DC is a 28 Vdc, 60-amp circuit breaker. It provides power

and protection for bus WD4 in ELC2.

3 ELC2 AC is a 3-phase, 35-amp circuit breaker. It provides

power and protection for bus WA4 inside ELC2.

4 CBP 4 BATT is a 28 Vdc, 25-amp circuit breaker. It provides

battery power to CBP 4 when installed.

5 Five output terminals (labeled BAT, DC, C , B , and A ),

mounted on the front panel are wired directly to corresponding

input terminals on ELC2.

c) Both HPSMs have five internal tower terminals that provide a direct connection to the respective CBP bus bars. The terminals are

labeled BAT, DC, A , B , and C .


d) External wire terminals and all bus tie connections for AC power are located on the transmission side of the respective HPSM.

1 The AC module on each HPSM has:

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a Three terminals labeled GEN 1 (or GEN 2) PH A, PH B, and

PH C. Each terminal is connected directly to the

corresponding output terminal on the respective generator.

b Three terminals labeled AC1 (or AC2) TIE OUT, PH A, PH

B, and PH C. Each of the terminals is wired directly to a

corresponding terminal on the adjacent HSPM labeled AC2

(or AC1) bus TIE IN, PH A, PH B, and PH C.

c Three terminals labeled ECS, PH A, PH B, and PH C, are

wired to input terminals of the ECS 1 (or ECS 2)

compressor.

d The AC module of HPSM1 has three terminals labeled

GPU, PH A, PH B, and PH C that are connected to three

input terminal lugs from the external ground power

receptacle.

e The AC module on HPSM1 has three terminals labeled PH

A, PH B, and PH C. Each terminal is wired directly to the

corresponding input terminal on TRU 1.

f The AC module on HPSM2 has three terminals labeled PH

A, PH B, and PH C. Each terminal is wired directly to the

corresponding input terminal on TRU 2.

2 External wire terminals and bus tie connections for DC power

management is located on the transmission side of each HPSM.

a The positive (+) 28 Vdc regulated output from the respective

TRU is wired to a terminal on the DC module of each

HPSM. The terminal is labeled TRU IN.

b One terminal labeled BUS (tie out), located on the DC

module of HPSM2 is wired directly to a BUS (tie in) terminal

on the DC module of HPSM1.

3 Both HPSMs have five internal tower terminals that provide a

direct connection to the respective PCU bus bars. The terminals

are labeled BAT, DC, A , B , and C .

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(f) Circuit Breaker Panels (CBPs)

1) The CBPs provide circuit protection to meet system demands for AC, DC, and BAT/Emergency power requirements.

2) Each CBP is divided into three functional sections that provide power to the CBs. They are:

a) BAT

b) DC

c) AC

3) CBP1 supports various load demands primarily on the left side of the aircraft.

a) CBP1 receives battery power from HPSM1 through KB103 and distributes battery power on bus bar WB5 to aircraft loads requiring battery bus power.

b) CBP1 receives 28 Vdc power from HPSM1 through KD103 and distributes DC power on bus bar WD5 to aircraft loads requiring 25 amps or less.

c) CBP1 receives 115-volt 3-phase AC power from HPSM1 through KA105 and distributes AC power on bus bar WA5 to aircraft loads requiring 20 amps or less.

4) CBP2 supports various load demands primarily on the right side of the aircraft.

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a) CBP2 receives battery power from HPSM2 through KB203 and distributes battery power on bus bar WB5 to aircraft loads requiring battery bus power.

b) CBP2 receives 28 Vdc power from HPSM2 through KD203 and distributes DC power on bus bar WD5 to aircraft loads requiring 25 amps or less.

c) CBP2 receives 115-volt 3-phase AC power from HPSM2 through KA205 and distributes AC power on bus bar WA5 to aircraft loads requiring 20 amps or less.

5) CBP3 is not currently used.

6) CBP4 is not currently used.

Figure 9. Electrical Load Centers Components

(g) Electrical Load Centers (ELCs) Components

1) Each ELC provides circuit protection, switching control logic and power distribution for AC, DC, and BAT power to various aircraft loads.

a) ELC1 supports various load demands primarily on the left side of the aircraft.

1 ELC 1 receives battery power from HPSM1 through KB102 and

distributes battery power on bus bar WB3 to aircraft loads

requiring battery bus power.

2 ELC 1 receives 28 Vdc power from HPSM1 through KD102 (60

A) and distributes DC power on bus bar WD3 to aircraft loads

requiring 25 amps or less.

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3 ELC 1 receives 115-volt 3-phase AC power from HPSM1

through KA104 (35 A) and distributes AC power on bus bar WA3

to aircraft loads requiring 20 amps or less.

b) ELC 2 supports various load demands primarily on the right side of the aircraft.

1 ELC 2 receives battery power from HPSM2 through KB202 and

distributes battery power on bus bar WB4 to aircraft loads

requiring battery bus power.

2 ELC 2 receives 28 Vdc power from HPSM2 through KD202 (60

A) and distributes DC power on bus bar WD4 to aircraft loads

requiring 25 amps or less.

3 ELC 2 receives 115-volt 3 phase AC power from HPSM2 through

KA204 (35 A) and distributes AC power on bus bar WA4 to

aircraft loads requiring 20 amps or less.

2) Each ELC contains:

a) Circuit breakers

1 The CBs are linked in series with relays controlled by the System

Processor (SP) via the 1553B MUX data bus.

2 The CBs are grouped to the bus bar function that provides the

applicable power requirement, AC, DC, and BAT.

b) A Built-In-Test (BIT) for the respective ELC and HPSM.

1 The BIT in ELC1 tests ELC1 and HPSM1.

2 The BIT in ELC2 tests ELC2 and HPSM2.

3 BIT functions provide:

a HPSM fault analysis

b ELC fault analysis

c Status reporting via the MIL-STD-1553B data bus

d Diagnostic information reporting via the data bus

c) A 68020-processor board interfaced with the data bus to perform control functions, status reporting, fault analysis and diagnostic routines.

1 ELC1 communicates on MUX channel 1, address 13.

2 ELC2 communicates on MUX channel 1, address 14.

d) Two Input/Output (I/O) modules are used to provide all necessary processor interfaces other than MIL-STD-1553B.

e) Three SP-controlled relay modules for load switched, ground switched, or continuity switched relays.

1 During ELC initial power-up, all relays default to a predetermined

position, either opened or closed.

2 The relays change position only when commanded by the SP via

the MUX interface.

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3 If MUX bus transmission to the ELC fails, all the relays remain in

the last commanded position.

4 If control power to the ELC fails, all the relays return to a safe

default power-up position.

f) An internal DC power supply (PSU1), providing 5 Vdc and ± 15 Vdc for ELC electronics circuits.

g) The ancillary power supply (PSU2) generates additional power for secondary aircraft loads to include:

1 26 Vac phase A, B, and C references for the Flight Management

Computer (FMC), SP1 and SP2, WP1 and WP2, and the

stabilator synchros

2 10 Vac for ENG1 and ENG2 oil pressure reference transducers

and transmission transducers

3 10 Vdc for the Video Control Panel (VCP) and the Blade

Positioning Indicator Assembly (BPIA)

h) Five input terminals (labeled BAT, DC, A , B , and C ) are mounted on the upper left side of the front panel. Each terminal is wired directly to a corresponding output terminal on the respective HPSM front panel.

3) ELC1 and ELC2 distribute AC, DC, and battery power to aircraft loads through circuit breakers and relays that are connected in series.

a) The circuit breakers protect the wiring to the loads.

b) The relays apply and remove power to the loads as commanded by the SP.

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Figure 10. Transformer Rectifier Units Components

(h) Transformer Rectifier Units (TRUs) Components

1) The regulated TRUs convert 115 Vac 3-phase power into regulated 28 Vdc that is applied to the HPSM DC bus bars. Each TRU supplies a dedicated DC bus; however, it is capable of supplying the total DC electrical power requirements for operating all aircraft subsystems.

2) The 3-phase input wires from the HPSM are connected through the J1 connector on the upper right portion of the front panel.

3) The TRU is an AC-to-DC, 9.8-kilowatt, 350-amp, 28 Vdc regulated, self-cooling transformer rectifier unit.

a) Each regulated TRU has:

1 An input Filter used to remove voltage spikes induced by the

aircraft generators.

2 Silicon Controlled Rectifiers to control the AC voltage input to the

Wye-to-Wye rectifier.

3 A Wye-to-Wye Rectifier converts and rectifies each phase of the

incoming AC voltage.

4 A Halfwave Bridge Rectifier to convert the AC voltage to DC

voltage.

5 An Output Filter to remove voltage spikes from the DC voltage

provided to the aircraft.

a The positive output is connected to the HPSM

b The negative side is grounded to the aircraft structure.

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4) Current limiting protection is provided for overload or short circuit current is limited by action of the electronic control circuitry

5) A thermostatic switch provides overtemperature protection of the R/TRU by sensing the bridge rectifier heat sink temperature.

Figure 11. Power Control Units Components

(i) Power Control Units (PCUs) Components

1) The Apache Longbow Power Control Units consist of MIL-STD-1553B-interfaces to Load Centers for System Processor load status and control.

2) The PCU Subsystem Architecture consists of up to two load centers interfaced to the MIL-STD-1553B data bus on channel 1.

a) A PCU present wire input from each PCU into the SP allows the SP to configure the software so that it can handle multiple configurations.

b) Each PCU has its own 1553 interface.

1 PCU1 communicates on MUX channel 1, address 11.

2 PCU2 communicates on MUX channel 2, address 15.

3) The two optional non-redundant PCU Load Centers are designated as PCU1 and PCU2. Each PCU Load Center contains:

a) Load controllers for distributing power to SP controlled loads.

b) A MIL-STD-1553B MUX Bus Interface Unit for:

1 Receiving SP requests for power for the load controllers

2 Transmitting load controller status to the SP

3 Performing Built in Test on the EPMS

4) All PCU1 and PCU2 relays default to the off condition at aircraft power on.

5) When utilized, PCU1 relays will apply power to CBP 3 and PCU2 will apply power to CBP4 relays.

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Figure 12. Master Ignition Key Switch

(j) Master Ignition Key (MIK) switch: The MIK switch on the throttle quadrant is

used to apply either battery or external power to the aircraft.

1) External Power Receptacle

2) The external ground power receptacle provides the required connection for external power.

3) The external power receptacle has four large pins for phases A, B, C and ground, and two small pins for a DC signal.

4) The receptacle has a switch installed to monitor the position of the door. The switch is closed when the door is open and open when the door is closed.

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Figure 13. External Power Components

(k) External Power Monitor

1) The external power monitor ensures the external power source is providing proper voltage, frequency and phase to the aircraft.

2) The external power monitor is a line replaceable unit that contains monitoring circuits to monitor incoming external power.

3) The monitor contains a 26 Vdc power supply.

4) The monitor will output a 26 Vdc signal if the input power is correct.

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Figure 14. Battery Charger Components

(l) Battery Charger

1) The battery charger maintains the battery in a fully charged state and controls the battery heater in the battery.

2) The battery charger also monitors the status of the battery and battery charger, and reports detected faults to the SP.

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Figure 15. Utility Relay Panel Components

(m) Utility Relay Panel (URP)

1) The URP has two master reset switches to provide power reset for the EPMS.

2) These switches are used to reset contactor trips in HPSM 1 and HPSM 2 respectively when the contactors have tripped due to an overcurrent condition, and after a fault has been cleared.

Figure 16. Generator Reset Switch Components

(n) Generator Reset (GEN RST) Switch

1) The GEN RST switch allows the pilot to manually reset a generator that has been turned off by either crewmember via the Multipurpose Display (MPD).

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2) The GEN RST switch also allows reset of a generator disconnected by the GCU control and protection functions due to a malfunction.

NOTES

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Check On Learning

1 How long will the Fibrous Nickel-Cadmium battery supply the normal flight battery loads?

2 What do the Generator Control Units regulate generator output to?

3 What are the three functional sections that each CBP is divided into?

4 On which side of the aircraft does ELC1 support various load demands?

5 What do the four large pins on the external power receptacle provide?

6 What does the external power monitor ensure the external power source is providing?

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B. Enabling Learning Objective 2

ACTION: Describe the AH-64D primary power distribution system.




Battery and Battery Charger Operation

Figure 17. Battery Power Operation

a. The battery provides power when no other source of power is available. Bus bars WBP1 of

High Power Switching Module1 (HPSM1) and WBP2 of HPSM2 are energized whenever the

battery is installed and connected.

(1) KBP01 of HPSM1 provides power to the Cold Refuel (COLD RFL) panel.

(2) KBP02 of HPSM1 provides power to the Master Ignition (MSTR IGN) switch.

(3) KBP10 of HPSM1 provides battery power to HPSM1 control circuits and hold up

power to the SP 1 and Processor Select Panel (PSP).

(4) KBP20 of HPSM2 provides battery power to HPSM2 control circuits and hold up

power to the SP 2.

b. Relays KB101 of HPSM1 and KB201 of HPSM2 prevent the battery from supplying power to

WB1 of HPSM1 and WB2 of HPSM2 unless the MSTR IGN switch is placed in the BATT

position and the APU is not running.

c. When the MSTR IGN switch is in the BATT position, relays KB101 and KB201 close.

(1) The closed relays supply battery voltage to WB1 in HPSM1 and WB2 in HPSM2.

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(2) With battery power applied to WB1 and WB 2.

(a) HPSM contactors KB103 and KB203 are rated at 50 amps.

1) KB103 provides 24 Vdc power and overload protection to bus bar WB5 in CBP1 for distribution to BAT/Emergency circuit load requirements.

2) CBP1 provides 24 to PCU 1 when installed. PCU 1 in turn will provide BAT/Emergency power to CBP 3 as required when installed.

3) KB203 provides 24 Vdc power and overload protection to bus bar WB6 in CBP2 for distribution to BAT/Emergency circuit load requirements.

4) CBP2 provides 24 to PCU 2 when installed. PCU 2 in turn will provide BAT/Emergency power to CBP 4 as required when installed.

5) KB103 and KB203 are designed to trip when an overcurrent condition exists. They can be reset using the HSPM1 (or HPSM2) master reset switch located on the Utility Relay Panel.

(b) HPSM contactors KB102 and KB202 are rated at 30 amps.

1) KB102 provides 28 Vdc power and overload protection for bus bar WB3 in ELC1 for distribution to BAT/Emergency loads selected by the SP.

2) KB202 provides 28 Vdc power and overload protection for bus bar WB4 in ELC2 for distribution to BAT/Emergency loads selected by the SP.

3) KB102 and KB202 are designed to trip when an overcurrent condition exists. They can be reset using the HPSM1 (or HPSM2) master reset switch located on the utility relay panel.

4) Blocking Diodes KD1D1 of HPSM1 and KD2D1 of HPSM2 prevent the battery from supplying voltage to WD1 of HPSM1 and WD2 of HPSM2.

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Figure 18. Battery Charger Operation

d. Battery charger operation

(1) The Battery Charger maintains the battery in a fully charged state when 115 Vac is

available and the battery is not connected to the battery buses WB1 and WB2. Under

normal conditions, the battery is not connected to the battery buses when the MIK

switch is in the OFF or EXT PWR positions.

(2) CBP 2 provides the battery charger with 28 Vdc Battery Heater power.

(3) The battery provides 24 VDC to the battery bus and to the battery charger. The

battery charger monitors this voltage to determine the voltage level in the battery.

(4) ELC 2 provides an enable command to the battery charger. This enables the

automatic battery charging sequence.

(5) The Battery Charger monitors the temperature. Based upon battery internal

temperature the battery charger determines the level or percentage the battery is

charged.

(6) The main charging mode supplies a 15A current to charge the battery until the internal

temperature of the battery raises 5 ºC above the temperature at the start of the

charging period.

(a) The topping mode uses a 3A current to trickle charge the battery for 20 minutes

after the battery indicates a full charge condition.

(b) This ensures the maximum full charge status has been accomplished.

(7) The Battery Charger provides power to the battery heater assembly and controls

battery heating when required.

(8) The Battery Temperature Sensor provides internal battery temperature to the charger.

This allows the battery charger to control the heater based on temperature of the

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battery. The battery heater temperature sensor provides over temperature protection

in the event the battery temperature sensor malfunctions.

(9) The Battery Charger monitors the battery for Cell Imbalance. It compares the voltage

of the first 10 battery cells against the total voltage of the 20 battery cells.

NOTES

Check On Learning

1 When does the battery provide power?

2 What prevents the battery from supplying voltage to WD1 of HPSM1 and WD2 of HPSM2?

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3 Where does the battery charger 28 Vdc Battery Heater power come from?

4 Where does the battery charger get its enable command?

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AC Electrical Subsystem Operation

Figure 19. AC Electrical Subsystem Operation

a. CBP1 GEN 2 BKUP circuit breaker (CB315) and CBP2 GEN 1 BKUP circuit breaker

(CB422) provides 28 Vdc from the battery bus to the Generator Control Units (GCU) DC

power supply. This voltage enables the DC power supply to provide power to the GCU

circuitry as the generators are coming on line.

b. When an APU start is initiated, the System Processor (SP) issues a Contactor Control Relay

(CCR) INHIBIT signal to the Generator Control Unit (GCU) which prevent the generators

from coming online (applying power to the HPSM) until the Auxiliary Power Unit (APU)

reaches 95% of it's normal operating speed (NG), at which time the SP removes the CCR

INHIBIT signal.

c. The rotating Permanent Magnet Generator (PMG) produces a field current that induces a 22

Vac, 3-phase, voltage into the stationary PMG when rotated by the accessory gearbox in the

main transmission. The APU or the engines drive the accessory gearbox.

d. Circuits of the GCU DC Power Supply rectify the AC voltage from the Stationary PMG Field

to a DC voltage.

(1) The DC voltage operates the switching logic of the GCU to enable its operation.

(2) It also powers the overcurrent protection circuits to prevent too much current from

damaging the GCU and to the GCU AC Voltage Regulator.

e. The GCU AC Voltage Regulator monitors the output of the generator via the Point of

Regulation (POR) input to pins 42, 44, and 47 of connector P1021 (this does not occur until

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there is an output from the Stationary Main Field). Based upon these inputs, the GCU

controls the generator output by controlling the amount of current flow through the Stationary

Exciter Control Field windings.

f. The Stationary Exciter Control Field current produces a magnetic field that induces an AC

voltage into the Rotating Exciter Control Field.

(1) The amount of current through the Stationary Exciter Field, which is controlled by the

GCU AC Voltage Regulator, determines the strength of the magnetic field induced.

g. The amount of voltage induced is dependent upon the strength of the magnetic field. The

output of the Rotating Exciter Field is rectified to a DC voltage by a diode assembly inside

the generator and applied to the Rotating Main Field.

h. The Rotating Main Field current flow produces a magnetic field that rotates inside the coils of

the Stationary Main Field windings, causing each of the three main windings, Phase A,

Phase B, and Phase C, to produce 115 Vac, 400 Hz.

i. Phases A, B, and C of the Stationary Main Field are connected to T1, T2, and T3 of the

generator. T1, T2, and T3 are connected to terminals A, B, and C of the HPSM respectively

and T4 is connected to terminal E, aircraft ground.

(1) The output of the three Current Transformers (CTs) is applied to the Rectifier

Comparator/Differential Phase Current Transformer (DPCT) Loop and the generator

load current transformers located in the HPSM.

(2) The HPSM full wave rectifier provides filtering and applies the output to the Rectifier

Comparator/DPCT Loop.

j. Control and protection functions of the generator are provided by the GCU and are fully

automated.

(1) The GCU monitors the generator output for over voltage and under voltage, under

frequency (which is inhibited by an input from the Squat Switch during flight), over

current, and differential current conditions.

(2) If any of the monitored systems fail, the GCU will trip the generator offline.

k. When the GCU senses that generator output is within acceptable limits, the GCU will

connect the generator output to the AC bus by energizing the CCR contactor.

(1) When the CCR contactor closes, DC voltage is applied to KA101 of HPSM1.

(2) As discussed earlier, when the APU reaches 95% of it's normal operating speed (NG),

the SP removes the CCR INHIBIT signal.

l. When KA101 of HPSM1 and KA201 of HPSM2 are energized, one set of normally open

contacts close to connect the generator 115 Vac, 3-phase, 400 Hz output to bus WA1 of

HPSM1 and WA2 of HPSM2.

(1) One set of normally closed contacts open, interrupting the bus ties between HPSM1

and HPSM2.

(2) WA1 supplies power to Environmental Control System1 (ECS1) and Fire Control

Radar (FCR).

(a) WA2 supplies power to ECS2 and if installed, the Rotor Blade De-Ice system.

m. WA1 supplies voltage to WA3 and WA5 of HPSM1 and Regulated/Transformer Rectifier

Unit1 (R/TRU1). WA2 supplies voltage to WA4 and WA6 of HPSM2 and R/TRU2.

(1) External circuit breakers KA104 and KA204 are rated at 35 amps.

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(a) KA104 provides power to bus bar WA3 in ELC1 for distribution to AC loads as

directed by the SP.

(b) KA204 provides power to bus bar WA4 in ELC2 for distribution to AC loads as

directed by the SP.

(2) Internal contactors KA105 and KA205 are rated at 100 amps.

(a) KA105 provides power to bus bar WA5 in CBP1 for distribution to AC loads that

require circuit protection.

(b) KA205 provides power to bus bar WA6 in CBP2 for distribution to AC loads that

require circuit protection.

NOTES

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Check On Learning

1 What happens when the APU Power Takeoff clutch energizes at 60% APU speed?

2 Where does the GCU AC Voltage Regulator monitor the output of the generator?

3 What provides the control and protection functions of the generator?

4 What does the GCU monitor the generator output for?

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Transformer Rectifier

Figure 20. DC Electrical Subsystem Operation

a. DC electrical subsystem operation

(1) When the primary bus bar WA1 (and WA2) is energized, 115 Vac 3-phase from

KA102 in HPSM1 (and KA202 in HPSM2) is routed to TRU 1 (and TRU 2).

(a) The 115 Vac 3 phase power is applied to the input filter. The cooling fan also

receives 15 Vac 3 phase power to provide ambient air across the TRU internal

components for cooling.

(b) The input filter acts to buffer the generator from noise produced by the three-

phase transformer

(c) The neutral point controller’s three-phase electronic control circuitry produces

blanking and firing waves to the Silicon Controlled Rectifiers (SCRs), which

provide the required current paths for exciting and resetting the transformer

core.

1) In this manner, the input ac supply voltage is varied in the transformer primary and the resultant rectified output of the transformer secondary is closely regulated to a constant 28 Vdc, regardless of input line voltage fluctuations or the DC connected load.

2) As the DC connected load is increased beyond the R/TRU’s rated capacity, the SCRs are maintained in full conduction and overload current is provided at reduced DC output voltages.

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(d) Embedded in the transformer primary inputs are three SCRs configured in a

delta arrangement. The 115 Vac output from the SCRs is provided to the wye-

to-wye transformer rectifier

(e) The wye-to-wye rectifier converts all three phases of the 115 Vac to 28 Vac and

provides it to a half wave bridge rectifier.

(f) The Halfwave Bridge Rectifier converts the 28 Vac to 28 Vdc and provides it to

the output filter.

(g) The output filter, filters the 28 Vdc to limit the output ripple voltage providing a

clean 28 Vdc power back to the HPSM.

(h) A thermal switch in the TRU provides an overtemperature indication. The switch

activates when TRU internal temperature exceeds approximately 190°F.

1) In the event that an overtemperature condition exists, sense inputs inhibit the electronic control circuitry.

2) The SCR firing waves are blanked, by turning off all SCRs and a fail signal is enunciated to the EPMS.

3) As a result, the ac input contactor to the R/TRU is opened. The de-energized dc bus is automatically disconnected from the non-operating R/TRU and transferred to the operating R/TRU by the secondary dc bus tie

(i) The HPSM provides the 28 Vdc it its internal circuitry and to the appropriate

ELC.

(j) The Point of Regulation (POR) sense input voltage taken at the input to the ELC

and is used to regulate the input voltage to that TRU.

1) This regulator maintains a constant 115 Vac to the rectifier to maintain the output voltage at 28 ± 0.5 Vdc.

2) The rectifier converts the 115 Vac input to 28 ± 0.5 Vdc output. An internal filter smoothes voltage spikes and removes noise from the output.

(k) The output of TRU 1 closes the KD101 contactor control relay. When contactor

KD101 is energized the output of TRU 1 is connected to the primary DC bus bar

WD1 in HPSM1.

(l) The output of TRU 2 closes the KD201 contactor control relay. When contactor

KD201 is energized the output of TRU 2 is connected to the primary DC bus bar

WD2 in HPSM2.

(m) Each of the TRUs operates independently of each other and can support all DC

voltage requirements if necessary.

(2) Circuit breaker panel DC power

(a) WD1 also provides 28 Vdc to WD5 of CBP1 through a 150-amp circuit breaker

(KD103).

(b) WD2 also provides 28 Vdc to WD6 of CBP2 through a 150-amp circuit breaker

(KD203).

(c) KD103 (or KD203) is designed to trip when an overcurrent condition exists.

They can be reset using the HPSM1 (or HPSM2) master reset switch located on

the utility relay panel.

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(3) CBP 1 distributes the DC requirement to PCU 1 when installed. PCU 1 in turn will

provide DC power to CBP 3 as required when installed.

(4) CBP 2 distributes the DC requirement to PCU 2 when installed. PCU 2 in turn will

provide DC power to CBP 4 as required when installed.

(5) ELC DC power

(a) WD1 also provides 28 Vdc to WD3 of ELC1 through a 60-amp circuit breaker

(KD102). KD102 provides 28 Vdc power to bus bar WD3 in ELC1 for

distribution to DC loads selected by the SP.

(b) WD2 also provides 28 Vdc to WD3 of ELC2 through a 60-amp circuit breaker

(KD202). KD202 provides 28 Vdc power to bus bar WD4 in ELC2 for

distribution to DC loads selected by the SP.

(6) WD1 provides power to the Programmable Signal Processor (PSP)/Low Power Radio

Frequency (LPRF) and Radar Frequency Interferometer (RFI) systems.

(7) The Remote Controlled Circuit Breaker (RCCB) rated at 75 amps and is also

connected to the BUS (tie) terminal on the DC/BAT module of HPSM1.

(a) The RCCB supplies power to the AN/ALQ-144A(V)3 Infrared Jammer (IRJAM)

Countermeasures Set and is mounted at the top left of HPSM1, on the aft side

of the canted bulkhead.

(b) Primary control of the RCCB is provided by a 28 Vdc circuit breaker labeled IR

JAM CONTRL. The circuit breaker is rated at 1 amp and located on CBP1.

(8) When the R/TRUs are producing an output, blocking diodes KD1D1 and KD2D1

polarity allow 28 Vdc to be applied to bus bars WB1 and WB2.

(9) WB1 provides 28 Vdc to WB3, WB5 and to the open contactor of KB101 and WB2

provides 28 Vdc to WB4, WB6 and open contactor of KB201.

(10) The HPSM will not allow the battery contactors KB101 and KB201 to close when the

voltage on WB1 and WB2 is above 26 Vdc.

NOTES

Check On Learning

1 What moves ambient air across the TRU internal components for cooling?

2 What temperature activates the thermal switch in the TRU to provide an overtemperature indication?

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3 What does the Remote Controlled Circuit Breaker supply power to?

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External Power

Figure 21. External Power Subsystem Operation

a. External power subsystem operation

(1) If either generator is connected to the EPMS when external power is connected, the

external power will be automatically disconnected from HPSM1.

(2) If an attempt is made to apply external power when either generator is on the line, the

EPMS will not accept the external power input.

(3) The external power subsystem connects the 115-volt, 400-cycle, 3-phase AC external

power, normally supplied by an Aviation Ground Power Unit (AGPU), to the EPMS for

distribution to aircraft systems, and components requiring AC power.

(a) Power is applied to External Power Monitor (EPM) and to the normally open

contactors of KA121 of High Power Switching Module1 (HPSM1).

(b) Distribution of external AC power by the EPMS is identical to normal generator

operation.

(4) The EPM evaluates the incoming power for correct voltage, frequency, and phasing.

It also rectifies a portion of the incoming power into a 28 Vdc signal.

(a) Correct voltage for each phase (110–121 Vac).

(b) Correct frequency (385–415 Hz).

(c) Proper phase relationship of A-B-C.

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(d) If the voltage, frequency, and phasing are correct, the external power monitor

develops a 28 Vdc signal. This signal is routed through the AFT AVN BAY circuit

breaker to pin F in the ground power receptacle.

(e) If the AGPU connector is seated correctly, the signal is looped out through pin E

of the receptacle and routed to P435 pin J of the Master Ignition (MSTR IGN)

switch.

(5) When the MSTR IGN switch is placed in the EXT PWR position, the 28 Vdc is routed

to HPSM1 as a close command to energize the External Power Contactor KA121.

(6) When contactor KA121 energizes, one set of normally closed contacts open, and one

set of normally open contacts close.

(a) The closed contacts connect 3-phase, 115 Vac external power through the

normally closed contacts of KA101 to WA1 of HPSM1.

(b) WA1 supplies power to ECS1 and FCR. KA103 of HPSM1 applies AC voltage

through the normally closed contacts of KA201 to WA2 of HPSM2.

(c) WA2 supplies power to ECS2 and if installed, the Rotor Blade De-Ice system.

(7) WA1 supplies voltage to WA3 and WA5 of HPSM1 and R/TRU1.

(8) WA2 supplies voltage to WA4 and WA6 of HPSM2 and R/TRU2.

(9) A module within the R/TRU monitors the input voltage and provides control signals to

an internal voltage regulator.

(a) This regulator maintains a constant 115 Vac to the rectifier; thus maintaining the

output voltage at 28 ±0.5 Vdc.

(b) The output is used to close contactor control relays KD101 of HPSM1 and

KD201 of HPSM2 and is also applied to WD1 and WD2.

(c) WD1 provides power to the PSP/LPRF and RFI systems.

(10) WD1 also provides 28 Vdc to WD3 of ELC1 and WD5 of CBP1 and WD2 provides 28

Vdc to WD4 of ELC2 and WD6 of CBP2.

(a) In the event a R/TRU fails, the bus tie contactor KD221 of HPSM2 allows the

operational R/TRU to power the DC buses of the failed R/TRU.

(b) This is an automatic function. Contactor KD221 cannot energize if the R/TRUs

are producing an output, blocking diodes KD1D1 and KD2D1 apply both R/TRUs

are operating (KD101 and KD201 energized).

(11) When the R/TRUs are producing an output, blocking diodes KD1D1 and KD2D1 apply

28 Vdc to bus bars WB1 and WB2. If the R/TRUs are not producing an output,

KD1D1 and KD2D1 prevent the battery from supplying voltage to WD1 and WD2.

(12) WB1 provides 28 Vdc to WB3, WB5 and to the open contactor of KB101. WB2

provides 28 Vdc to WB4, WB6 and open contactor of KB201.

(13) The HPSM will not allow the battery contactors KB101 and KB201 to close when the

voltage on WB1 and WB2 is above 26 Vdc.

NOTES

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Check On Learning

1 Where is the external power receptacle located?

2 What happens if either generator is connected to the EPMS when external power is connected?

3 What happens if an attempt is made to apply external power when either generator is on the line?

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C. Enabling Learning Objective 3

ACTION: ACTION: Describe the AH-64D secondary power distribution system.




Bus Tie Operation

Figure 22. Bus Tie Operation

a. Bus tie operation

(1) Once online, the aircraft generators can be disconnected by:

(a) Normal aircraft shutdown procedure using under frequency protection

(b) MPD generator off selection by either crewmember

(c) A fault condition

(2) No. 1 generator inoperative or offline

(a) KA103 will trip when generator 1 is off (bus tie is occurring) and there is an

overcurrent condition of 100 amps on WA1.

(b) When GEN1 is disconnected via crewmember action or a malfunction, primary

contactor KA101 is de-energized. When KA101 de-energizes:

1) The normally open contacts open to disconnect GEN1 from WA1.

2) The normally closed contacts close to complete the bus tie circuit.

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(c) KA201 remains closed as in normal operation and powers bus bar WA2. The

normally closed contacts of KA203 bus tie contactor route AC power to bus bar

WA1 through the normally closed contacts of the external power contactor

KA121, and the normally closed contacts of KA101.

(3) No. 2 generator inoperative or offline

(a) KA203 will trip when generator 2 is off (bus tie is occurring) and there is an

overcurrent condition of 100 amps on WA2.

(b) When crewmember action or a malfunction disconnects GEN2, primary

contactor KA201 is de-energized. When KA201 de-energizes:

1) The normally open contacts open to disconnect GEN2 from WA2.

2) The normally closed contacts close to complete the bus tie circuit.

(c) KA101 remains closed as in normal operation and powers bus bar WA1. The

normally closed contacts of KA103 Bus Tie contactor route AC power to bus bar

WA2 through the normally closed contacts of KA201.

(4) When TRU 2 is operating and TRU 1 is not:

(a) KD201 closes normally and connects the output of TRU 2 to bus bar WD2.

(b) KD221 BUS (tie) contactor closes and connects the output of TRU 2 to bus bar

WD1 in HPSM1.

(5) When TRU 1 is operating and TRU 2 is not:

(a) KD101 closes normally and connects the output of TRU 1 to bus bar WD1.

(b) KD221 BUS (tie) contactor in HPSM2 closes and connects the output of

TRU 1 to bus bar WD2 in HPSM2.

b. Operator controls

(1) The generators are disabled (disconnected from the AC bus) when selecting the

GEN1 or GEN2 pushbuttons on the MPD system (SYS) page. Once selected, the

generator will be turned off and the pushbutton will be barriered.

(2) If a generator is disconnected from the AC bus by crewmember MPD selection or

automatically by the GCU, it may be reset using the generator reset (GEN RST)

switch on the pilot check overspeed test/generator reset panel.

(a) Momentarily placing the switch in either GEN1 or GEN2 position will command

that GCU to connect the generator to the AC bus if there are no generator faults.

(b) If faults are present, the generator will remain off-line.

NOTES

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Check On Learning

1 How are the aircraft generators disconnected once they are online?

2 What occurs when either GEN1 or GEN2 pushbuttons are selected on the MPD system page?

3 What is used to reset the generators once they have been tripped?

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D. Enabling Learning Objective 4

ACTION: ACTION: Describe the AH-64D EPMS MOC.



1. Learning Step/Activity 1 EPMS

Describe the AH-64D EPMS MOC

a. The EPMS MOC is contained in TM 1-1520-APACHE/LONGBOW (Interactive Electronic

Technical Manual – IETM). It is designed to check electrical system operation using both

external and aircraft power.

REFER STUDENTS TO THE IETM AND PERFORM THE EPMS MOC USING AIRCRAFT TAIL NUMBER 03-5378

NOTES

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Check On Learning

1 Why is it important to verify that the EXT PWR INTLK circuit breaker is closed?

2 EXT PWR advisory is displayed on the UFD. What does this message confirm?

3 Why is it important to turn the ECS off before resetting the HPSM contactors?

4 When we reset the HPSMs, what is one indication that the HPSM RESET is functional?

5 EXT PWR advisory is not displayed on the UFD. What does this confirm?

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E. Enabling Learning Objective 5

ACTION: Describe the AH-64D built-in-test (BIT) functions.




Describe the AH-64D built-in-test functions

a. There are three built-in tests for the EPMS, the PBIT, the CBIT, and the IBIT.

Figure 23. BIT Logic Block Diagram

b. The EPMS utilizes Power-on BIT (PBIT), Continuous BIT (CBIT), and Initiated BIT (IBIT)

(1) PBIT occurs immediately after application of aircraft power.

(a) The SP monitors the health status of the EPMS.

(b) Detected faults are reported to the SP. At the completion of PBIT, the SP

begins CBIT.

(2) CBIT runs continuously after the PBIT has been completed.

(a) Each ELC monitors the health of the respective HPSM via discrete monitor

signals. Detected failures are reported to the SP as a function of the CBIT.

(b) The SP monitors the health status of the EPMS by monitoring the BIT status

from the ELCs.

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(3) IBIT can be initiated by either crewmember from the DMS IBIT page by first selecting

the ACFT/COMM page, then choosing EPMS 1 or EPMS 2.

(a) ELC1/2 provides IBIT for both ECS1/2 and HPSM1/2. Once IBIT is initiated, the

ELC will clear all latched faults and determine if any faults still present.

(b) If a fault is detected in the generation and conversion subsystem, the fault is

reported and recorded. The fault does not cause the subsystem to be turned

off.

(c) The generation and conversion subsystem has the following BIT attributes:

1) The faults are generated within 2-5 seconds after aircraft power is applied.

2) Once a fault is set, it remains on for at least one second. It remains until the logic to reset it is met.

3) When the system powers on, all faults are initialized by resetting them.

(d) IBIT cannot be initiated if any one of the following conditions exists:

1) The aircraft is airborne.

2) An engine start or ignition override is in progress.

3) An APU start or stop is in progress.

4) A manual generator trip is in progress.

5) A fuel boost operation is in progress.

6) A zeroize function is in progress.

7) A change of fuel crossfeed position is in progress.

Figure 24. UFD Warnings, Cautions, Advisories

c. EPMS BIT displays

(1) Warnings

(a) There are no warnings associated with the electrical system

(2) Cautions

(a) Generate a caution tone and illuminates the caution segment on the Master

Warning/Master Caution panel.

(b) Are displayed in UFD caution message area

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Figure 25. DMS and DMS Fault Pages (1 of 3)

(c) Are displayed on the DMS page in the ADVISORY section and on the DMS

WCA page

Figure 26. UFD and DMS Page

(3) Advisories

(a) Are displayed in the UFD advisory message area

(b) Are displayed on the DMS page ADVISORY area

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Figure 27. DMS and DMS Fault Pages (2of 3)

(4) Faults

(a) Are displayed on the DMS page in the FAULT area

(b) Are displayed on the DMS Fault page

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EPMS Caution/Advisory/Fault Messages

a. If a failure occurs in the ELC, there is a possibility that a system could lose power. If the

failure occurs in the HPSM, power would not be lost because of the cross tie capability.

Figure 28. DMS and DMS Fault Pages (3 of 3)

b. Fault messages

(1) Approximately 180 fault messages can be identified and displayed on the DMS page

and DMS Fault page. A partial listing of the electrical system faults will be discussed.

Refer to the IETM for the complete listing.

(2) Electrical power generation and conversion system

(a) GENERATOR1 FAIL–Generator1 has been detected as failed

(b) GENERATOR2 FAIL–Generator2 has been detected as failed

(c) GCU1 FAIL–GCU1 has failed. The fault is determined by BIT inside the GCU

and is reported to the HPSM1 via the discrete output. ELC1 monitors the fault

via direct input from HPSM1 and transmits the fault to the SP.

(d) GCU2 FAIL–GCU2 has failed. The fault is determined by BIT inside the GCU

and is reported to the HPSM2 via the discrete output. ELC2 monitors the fault

via direct input from HPSM2 and transmits the fault to the SP.

(e) RECT1 FAIL–indicates R/TRU1 is not connected to DC bus1 because it is

overheated and/or has no DC output. ELC1 monitors the fault via direct input

from HPSM1 and transmits fault status to the SP.

(f) RECT2 FAIL– indicates R/TRU2 is not connected to DC bus2 because it is

overheated and/or has no DC output. ELC2 monitors the fault via direct input

from HPSM2 and transmits fault status to the SP.

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(g) BATTERY FAIL–indicates the battery has failed the BIT and is not being

charged. ELC2 monitors the battery through the battery charger and transmits

the BATTERY FAIL status to the SP.

(h) CHARGER FAIL–indicates the battery charger has failed the bit and is not

charging the battery. ELC2 monitors the battery charger and transmits the

CHARGER FAIL status to the SP.

Figure 29. ELC Block Diagram

(3) Electrical power distribution system fault types

(a) ELCs

1) ELC relay faults

a) ELC relay faults are reported when the ELC detects a mismatch between the commanded state and the monitored state of the relay.

b) Most of the software controlled ELC relays will report a fault if the circuit breaker is out and the relay is commanded to provide power. The ELC detects that the voltage is not present and it fails the relay.

c) The failure message displayed on the MPD shows the circuit breaker label in quotes.

2) ELC SRU failures

a) The card level failures reported by the ELC are the results of many low level tests.

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b) Each of the tests has been isolated to one or more of the SRUs in the ELC.

c) ELC faults can not cause ELC SRU failures to be reported.

d) ELC SRU level failures are repaired first.

3) MUX bus failures

a) The ELC does not respond to a MUX bus channel command

b) The ELC did not complete IBIT normally.

Figure 30. EPMS Block Diagram.

(b) HPSM contactor faults

1) HPSM contactor faults can be caused by a failure in the HPSM or external failures. Therefore, each of these faults will require the maintainer to isolate the cause of the fault.

a) CONTACTOR TRIPPED indicates the contactor has tripped open or a failure has occurred in the HPSM. They are set only if the contactor is supposed to be closed.

b) CNTCTR MISSING PHASE indicates a missing phase or a failure in the HPSM.

c) HPSM SRU FAIL

1 The card level failures reported by the HPSM via the ELC are the

results of many low level tests.

2 Each of the tests has been isolated to one or more of the SRUs

in the HPSM.

3 For every SRU failure, there will be a HPSM contactor failure.

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4 HPSM faults cannot cause HPSM SRU failures to be reported.

5 HPSM SRU level failures are repaired first.

d) HPSM Contactor Failures

1 The contactor level failures reported by the HPSM via the ELC

are the results of tests on each contactor.

2 Each HPSM contactor failure has been isolated to the HPSM but

not necessarily to a specific SRU in the HPSM.

3 A single contactor failure, may cause two HPSM SRU failures to

be reported.

4 HPSM faults cannot cause HPSM contactor failures to be

reported.

5 HPSM contactor failures and SRU failures are repaired first.

Figure 31. UFD

(4) EPMS UFD displays

(a) Caution

1) GENERATOR1 FAIL–Generator1 has been detected as failed

2) GENERATOR2 FAIL–Generator2 has been detected as failed

3) RECT1 FAIL–indicates R/TRU1 is not connected to DC bus1 because it is overheated and/or has no DC output. ELC1 monitors the fault via direct input from HPSM1 and transmits fault status to the SP.

4) RECT2 FAIL– indicates R/TRU2 is not connected to DC bus2 because it is overheated and/or has no DC output. ELC2 monitors the fault via direct input from HPSM2 and transmits fault status to the SP.

(b) Advisory

1) BATTERY FAIL–indicates the battery has failed the BIT and is not being charged. ELC2 monitors the battery through the battery charger and transmits the BATTERY FAIL status to the SP.

2) CHARGER FAIL–indicates the battery charger has failed the bit and is not charging the battery. ELC2 monitors the battery charger and transmits the CHARGER FAIL status to the SP.

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NOTES

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Check On Learning

1. What types of built-in tests are available for the EPMS?

2. When is the EPMS PBIT initiated?

3. When is CBIT initiated?

4. What conditions inhibit the initiation of the electrical system IBIT?

5. Which component monitors the health of the respective HPSMs to the SP?

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