B737-3 ATA 24 L3 e

ATA 104 LEVEL 3

Book No: B737-3 24 L3 E

Lufthansa

Lufthansa Base

Issue: Jan. 2000For Training Purposes Only

Lufthansa 1995Technical Training GmbH

Training ManualB 737-300/400/500

ATA 24ELECTRICAL POWER

For training purposes and internal use only.

Copyright by Lufthansa Technical Training GmbH.

All rights reserved. No parts of this trainingmanual may be sold or reproduced in any formwithout permission of:

Lufthansa Technical Training GmbH

Lufthansa Base Frankfurt

D-60546 Frankfurt/Main

Tel. +49 69 / 696 41 78

Fax +49 69 / 696 63 84

Lufthansa Base Hamburg

Weg beim Jger 193

D-22335 Hamburg

Tel. +49 40 / 5070 24 13

Fax +49 40 / 5070 47 46

TABLE OF CONTENTS

Page: i

ATA 24 ELECTRICAL POWER 1. . . . . . . . . . . . . . . .

24-00 GENERAL 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AC POWER PHILOSOPHY 2. . . . . . . . . . . . . . . . . . . . . . . . . . .

POWER SUPPLY 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ELECTRICAL POWER CONTROL PANEL 24. . . . . . . . . . . . . .

ELEC. CONTROL PANEL (NEW GENERATION) 26. . . . . . . .

ELECTRICAL POWER ANNUNCIATOR PANEL (M238) 32. . .

DC ANNUNCIATOR LIGHTS 34. . . . . . . . . . . . . . . . . . . . . . . . . .

AC BUS INDICATING LIGHTS 36. . . . . . . . . . . . . . . . . . . . . . . . .

GENERATOR MALFUNCTION LIGHTS 38. . . . . . . . . . . . . . . .

POWER SYSTEM TEST MODULE M400 40. . . . . . . . . . . . . . .

M 400 AC VOLTAGE / FREQUENCY METERING 42. . . . . . . .

M 400 DC VOLTAGE METERING 44. . . . . . . . . . . . . . . . . . . . . .

24-10 GENERATOR DRIVE / CSD 48. . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CSD SERVICING 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CSD WET PAD CAVITY 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DESCRIPTION OPERATION 56. . . . . . . . . . . . . . . . . . . . . . . . . .

CONSTAND SPEED DRIVE ADJUSTMENT 58. . . . . . . . . . . . .

24-20 AC GENERATION 60. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL 60. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AC GENERATOR / CSD 62. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF 64. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

AC GENERATOR / VSCF 66. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF SERVICING 70. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF WET PAD CAVITY 72. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GENERATOR BREAKER 74. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GENERATOR CONTROL UNIT 76. . . . . . . . . . . . . . . . . . . . . . . .

BUS TRANSFER 80. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TRANSFER RELAY CONTROL 82. . . . . . . . . . . . . . . . . . . . . . . .

AC POWER ANNUNCIATOR LIGHTS 84. . . . . . . . . . . . . . . . . .

DIFFERENTIAL PROTECTION CSD/GEN 86. . . . . . . . . . . . . .

DIFFERENTIAL PROTECTION VSCF 88. . . . . . . . . . . . . . . . . .

CURRENT TRANSFORMER (DIFF. PROTEC.) 90. . . . . . . . . .

DIFFERENCES CSD/GEN AND VSCF 92. . . . . . . . . . . . . . . . .

VSCF COOLING AND LUBRICATION 94. . . . . . . . . . . . . . . . . .

VSCF CONTROL 96. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF OPERATION 98. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF PROTECTION 100. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VSCF BIT TEST 102. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24-30 DC GENERATION 104. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL DESCRIPTION 104. . . . . . . . . . . . . . . . . . . . . . . . . . . .

TR-UNIT 106. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TR-UNIT SYSTEM 108. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BATTERY AND EXTERNAL DC POWER RECEPTACLE 110. .

BATTERY SYSTEM 112. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BATTERY CHARGER 114. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24-40 EXTERNAL POWER 116. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL AND PROTECTION 116. . . . . . . . . . . . . . . . . . . . . . . .

EXTERNAL POWER CONTACTORS 118. . . . . . . . . . . . . . . . . . .

GROUND SERVICE CONTROL 120. . . . . . . . . . . . . . . . . . . . . . .

BUS PROTECTION PANEL (BPP) 122. . . . . . . . . . . . . . . . . . . . .

24-50 ELECTRICAL LOAD DISTRIBUTION 124. . . . . . . . . . . . . . . . . . STANDBY BUS CONTROL 124. . . . . . . . . . . . . . . . . . . . . . . . . . .

STATIC INVERTER 126. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25-30 GALLEYS 128. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GALLEY POWER CONTROL 128. . . . . . . . . . . . . . . . . . . . . . . . . .

TABLE OF FIGURES

Page: ii

Figure 1 AC Power Philosophy 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 2 Elec. Power System - AC / DC Power Supply 5. . . . . . . . . Figure 3 Elec. Power System - Standby Power 7. . . . . . . . . . . . . . . . Figure 4 Location - Main System Components 9. . . . . . . . . . . . . . . . Figure 5 Location - External Power Panel P19 11. . . . . . . . . . . . . . . . Figure 6 Location - Forward Attendants Panel 13. . . . . . . . . . . . . . . . . Figure 7 Location - Main Power Breakers 15. . . . . . . . . . . . . . . . . . . . . Figure 8 Location - Panel P6 / M400 / M238 17. . . . . . . . . . . . . . . . . . Figure 9 Location / Interior - P6 Panel 19. . . . . . . . . . . . . . . . . . . . . . . . Figure 10 Location - AC Generator / VSCF 21. . . . . . . . . . . . . . . . . . . Figure 11 Location - AC Generator / CSD 23. . . . . . . . . . . . . . . . . . . . Figure 12 Electrical Power Control Panel (Upper) 25. . . . . . . . . . . . . . Figure 13 Elec. Panel (Upper - New Generation) 27. . . . . . . . . . . . . . Figure 14 Electrical Power Control Panel (Lower) 29. . . . . . . . . . . . . . Figure 15 Elec. Power Control Panel (Lower) cont. 31. . . . . . . . . . . . Figure 16 Electrical Power Annunciator Panel M238 33. . . . . . . . . . . Figure 17 M 238 DC Bus Indicating Lights 35. . . . . . . . . . . . . . . . . . . . Figure 18 M 238 AC Bus Indicating Lights 37. . . . . . . . . . . . . . . . . . . . Figure 19 M 238 Generator Malfunction Lights 39. . . . . . . . . . . . . . . . Figure 20 M400 Power System Test Module 41. . . . . . . . . . . . . . . . . . Figure 21 M400 AC Voltage / Frequency Metering 43. . . . . . . . . . . . . Figure 22 M400 DC Voltage Metering 45. . . . . . . . . . . . . . . . . . . . . . . . Figure 23 M400 AC Amperes Metering 47. . . . . . . . . . . . . . . . . . . . . . . Figure 24 CSD - Components 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 25 CSD - Servicing 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 26 CSD Wet Pad Cavity 53. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 27 CSD - Oil Cooler 55. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 28 Constant Speed Drive 57. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 29 CSD Adjustment 59. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 30 AC System Schematic 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 31 Engine Generator System Schematic 63. . . . . . . . . . . . . . . Figure 32 VSCF - General 65. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 33 VSCF - Block Diagram 67. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 34 VSCF Components 69. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 35 VSCF - Servicing 71. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 36 VSCF - Wet Pad Cavity 73. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 37 Generator Breaker 75. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 38 Generator Control Unit 77. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 39 Generator Control Unit Schematic 79. . . . . . . . . . . . . . . . . . Figure 40 Electrical Smoke Isolation 81. . . . . . . . . . . . . . . . . . . . . . . . . Figure 41 Transfer Bus Control 83. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 42 AC Power Annunciator Lights 85. . . . . . . . . . . . . . . . . . . . . . Figure 43 Differential Protection 87. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 44 VSCF Differential Protection 89. . . . . . . . . . . . . . . . . . . . . . . Figure 45 Diff. Protection Current Transformer 91. . . . . . . . . . . . . . . . Figure 46 Differenz CSD/GEN and VSCF 93. . . . . . . . . . . . . . . . . . . . Figure 47 VSCF Cooling and Lubrication 95. . . . . . . . . . . . . . . . . . . . . Figure 48 VSCF Control 97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 49 VSCF Operation 99. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 50 VSCF BIT Test 103. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 51 DC Power System Schematic 105. . . . . . . . . . . . . . . . . . . . . . Figure 52 DC Equipment Installation 107. . . . . . . . . . . . . . . . . . . . . . . . . Figure 53 DC POWER SYSTEM TR-Unit 109. . . . . . . . . . . . . . . . . . . . Figure 54 DC External Power Receptacle 111. . . . . . . . . . . . . . . . . . . . Figure 55 DC POWER SYSTEM Battery 113. . . . . . . . . . . . . . . . . . . . Figure 56 Battery Charger 115. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 57 External Power Schematic 117. . . . . . . . . . . . . . . . . . . . . . . . Figure 58 External Power Contactors 119. . . . . . . . . . . . . . . . . . . . . . . . Figure 59 Ground Service Control 121. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 60 Bus Protection Panel (BBP) 123. . . . . . . . . . . . . . . . . . . . . . . Figure 61 Standby Bus Control 125. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 62 Static Inverter 127. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 63 Galley Power Control 129. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 64 Automatic Galley Load Shedding 131. . . . . . . . . . . . . . . . . . .

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ELECTRICAL POWERGENERAL

737-300/400/500

24-00

Page: 1FRA US/E ur 16.11.99

ATA 24 ELECTRICAL POWER

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Page: 2FRA US/F do 07.01.98

24-00 GENERALAC POWER PHILOSOPHY

Electrical power is generated by one generator on each engine and by oneAPU generator.Two different types of generators may be installed at the same time. They willhave no differences in system behavior and indication. Type 1: Each engine generator is connected to its respective engine

through a CSD which converts variable engine RPM to the constant speedneeded to produce 400 Hz used by the electrical system components.

Type 2: Each VSCF (Variable Speed Constant Frequency) Generator isdriven directly from the engine gear box, rotating at a variable speed. Thevariable frequency is converted to constant 400 Hz using a solid state, highpower inverter.

There are three basic principles of operation for the electrical system: 1. There is no paralleling of the AC sources of power. 2. The last source of power switched onto the system takes priority

and will automatically disconnect the existing source. 3. There is no automatic connection of electrical power sources. All

sources must be manually connected through the movement of a switch.

In flight each generator normally powers its own generator bus. If one genera-tor is inoperative, the APU generator may be used to power the inoperativegenerators bus.Each Generator system consists of a generator bus and a transfer bus. If thereis a failure of a generator bus, the associated transfer bus can be supplied au-tomatically from the powered generator bus. Each transfer bus has anassociated transfer relay which automatically selects the opposite generatorbus as a power supply if its normal generator bus fails and the transfer switchis in AUTO position.

The APU Generator can supply: On Ground:

AC GEN BUS 1, AC GEN BUS 2, TRANSFER BUS 1 and TRANSFERBUS 2

In Air:AC GEN BUS 1 or AC GEN BUS 2, TRANSFER BUS 1 and TRANFERBUS 2

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EXT AC BUS

EPC 1 EPC 2

APUGENERATOR

APUGB 1

APUGB 2

3 o115/200 V3 o115/200 V

3 o115/200 V

GB 2

3 o115/200 V

GB 1

MAINENGINEGEN No 1

MAINENGINEGEN No 2

EXTERNALPOWERUNIT

AC GEN BUS 1

NORMALLOAD

OFF

AC GEN BUS 2

NORMALLOAD

OFFNORMALALTERNATEALTERNATENORMAL

TRANSFER RELAY

AC TRANSFER BUS 1

ESSENTIAL LOAD ESSENTIAL LOAD

AC TRANSFER BUS 2

TRANSFER RELAY

Page: 3Figure 1 AC Power Philosophy

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Page: 4FRA US/F do/ur 07.01.98

POWER SUPPLY

AC POWER SUPPLYThe normal inflight configuration of the power system has engine generator 1connected to generator bus 1, main bus 1 and transfer bus 1. Generator 2 isconnected to generator bus 2, main bus 2 and transfer bus 2. These systemsare separate. In the event of an inoperative generator, the APU generator canbe connected to one of the generator busses thereby restoring full electricalpower.With the airplane on the ground and external power connected, placing theGround Power switch momentarily to ON will trip both engine generators andconnect external power to both generator busses simultaneously. When theAPU is operating, electrical power output of its generator can be connected togenerator bus 1 and/or generator bus 2 through the respective controlswitches. Whenever ground power is on both generator busses, and APU or anengine generator power is applied to one generator bus, ground power contin-ues to supply power to the other generator bus.The transfer busses normally receive their power from the respective generatorbus. If a generator bus loses power, the respective transfer bus will automati-cally receive power from the other generator bus. In addition the protectiveauto load-shedding circuit turns off all galley power.This feature ensures that the remaining generator will not be overloaded.The electrical system monitors itself for correct voltage, frequency, groundfaults in the generator or excessive current draw from any generator. If anymalfunction develops, the generator affected will be automatically disconnectedfrom its generator bus.

DC POWER SUPPLYPrimary DC power is supplied to the DC busses through transformer rectifierunits which are powered from the AC. TR-3 receives power from main bus 2and has a dual function. It is the primary power source for the battery bus andan alternate power source for both DC busses 1 and 2.TR-2 is also a backup power source for DC bus No.1 and TR-1 is also abackup power source for DC bus No.2.The TR-3 disconnect relay automatically opens at glide slope capture during aF/D or A/P ILS approach. This isolates the DC busses during approach in orderto prevent a single failure from effecting both navigation receivers and flight

control computers. The TR-3 disconnect relay can be opened manually forsmoke procedure with the BUS TRANSFER SWITCH in OFF position.TR voltage range is 24 - 30 V.The battery bus has two possible sources of power: the battery or batterycharger through the hot battery bus or from TR-3. Under normal operatingconditions, a relay controlled by the battery switch connects the TR-3 to thebattery bus. If TR-3 should fail the battery bus will automatically seek its powersource from the hot battery bus.Placing the Battery switch to OFF removes the ground for the controlling relaysand will cause the battery bus to lose power unless the electrical standbypower switch is in BAT position. With the electrical standby power switch inBAT, the hot battery bus will power the battery bus regardless of TR-3 output.The hot battery bus and the switched hot battery bus receive power from thebattery charger if a generator is operating or from the battery if AC power is notavailable. The hot battery bus remains powered at all times. The switched hotbattery bus is powered when battery switch is in ON position.

GROUND SERVICE BUSThe ground service bus is normally powered through generator bus 1. Whenthe airplane is on the ground and external power is connected, placing theGround Service Switch (located on fwd attendants panel) to ON will connectthe ground service bus directly to the external power source without energizingthe other airplane electrical busses. This bus contains most of the cabin lightingand other equipment needed for cleaning.

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BAT BUS

EXT PWR

DC EXT PWRRECEPTACLE

R41GEN PWRCONTROL

MANUALAIR

GRD

STANDBYPOWER OFF

R356

115V AC

115V AC

TRANSFORMERRECTIFIER 3

28V DCELEX BUS 2

STANDBY POWER

NORM

115V ACGEN BUS 1

28V ACBUS 1

115V ACELEX BUS 1

115V ACSTANDBY BUS

NORM

ALT GROUND

28V AC 28V AC

STATICINVERTER

TRANSFORMERRECTIFIER 1 BATTERY

28V DCBUS 1

28V DCELEX BUS 1

APU GENERATOR

APUGENERATOR

AUXILIARYPOWERUNIT 115V AC

GEN BUS 2

ALT

TRANSFER 2

115V AC

28V AC

BATTERYCHARGER

28V DC


28V DCBUS 2

115V ACELEX BUS 2

28V ACBUS 2

DISCONNECT

GENERATORBREAKER 1

BATTERY CHARGER

28V DCBATTERY BUS

115V ACMAIN BUS 1

115V ACMAIN BUS 2

STANDBY

TRANSFERBUS 1

TRANSFERBUS 1

GRD SERVICE

GRD SERVICE

TRANSFERBUS 2

TRANSFERBUS 2

CONTACTOR 1EXTERNAL POWER

BREAKER 1APU GENERATOR GENERATOR

EXTERNAL POWERCONTACTOR 2

BREAKER 2 BREAKER 2

RECEPTACLE

R1 BATTERY

GENERATOR2

R328

R37

HOT BAT BUS

GENERATOR1

R89

TRANSFER MANUAL

AUTO

115V AC


EXT AC BUS 1 AC EXT PWR

SERVICE

R6

R3 TRANSFER 1

BUSSES

TRANSFER

28V DC SWITCHEDHOT BAT. BUS

R9 TR 3

BUS

R4

BUSSES

R355BAT BUS

28V DCSTANDBY BUS

R389

CONTROLINVERTER

ENGINE 2ENGINE 1

POWER

R326

WDM 24-31-21BAT OVHT& APU STARTINTERLOCK

Page: 5Figure 2 Elec. Power System - AC / DC Power Supply

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STANDBY POWER SYSTEMThe standby power system consists of a 115 volt AC bus and a 28 volt DC bus.These busses power certain critical communication and navigation equipmentat all times. Normally, the standby busses are powered by Transfer Bus No. 1and DC Bus No. 1 respectively. If one of these busses lose it is power, the 115volt AC standby bus will be powered by the battery through a static inverter andthe 28 volt DC standby bus will be powered by the battery bus directly.A fully charged battery has sufficient capacity to provide power to essentialflight instruments, communication- and navigation equipment for a minimumof 30 minutes.Battery voltage range is 22-30 V.Automatic switching is provided from the normal power sources to the alternatepower source when the Standby Power Switch is in the AUTO position. If ei-ther the No. 1 DC Bus or the No.1 transfer bus loses power, both standbybusses automatically switch to the battery and battery bus.The automatic transfer of power from one bus to the other is an inflight featureonly. The air-ground safety sensor prevents the battery bus from powering thestandby busses when the airplane is on the ground. The function of the air-ground safety sensor may be bypassed by placing the Standby Power switchto BAT position.The standby busses may be deactivated with the Standby Power switch toOFF.New Generation:Both standby buses automatically switch to the battery and battery bus in airand in ground.

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BAT BUS

EXT PWR

DC EXT PWRRECEPTACLE

R41GEN PWRCONTROL

MANUALAIR

GRD

STANDBYPOWER OFF

R356

115V AC

115V AC


28V DCELEX BUS 2

STANDBY POWER

NORM

115V ACGEN BUS 1

28V ACBUS 1

115V ACELEX BUS 1

115V ACSTANDBY BUS

NORM

ALT GROUND

28V AC 28V AC

STATICINVERTER

TRANSFORMERRECTIFIER 1 BATTERY

28V DCBUS 1

28V DCELEX BUS 1

APU GENERATOR

APUGENERATOR

AUXILIARYPOWERUNIT 115V AC

GEN BUS 2

ALT

TRANSFER 2

115V AC

28V AC

BATTERYCHARGER

28V DC


28V DCBUS 2

115V ACELEX BUS 2

28V ACBUS 2

DISCONNECT

GENERATORBREAKER 1

BATTERY CHARGER

28V DCBATTERY BUS

115V ACMAIN BUS 1

115V ACMAIN BUS 2

STANDBY

TRANSFERBUS 1

TRANSFERBUS 1

GRD SERVICE

GRD SERVICE

TRANSFERBUS 2

TRANSFERBUS 2

CONTACTOR 1EXTERNAL POWER

BREAKER 1APU GENERATOR GENERATOR

EXTERNAL POWERCONTACTOR 2

BREAKER 2 BREAKER 2

RECEPTACLE

R1 BATTERY

GENERATOR2

R328

R37

HOT BAT BUS

GENERATOR1

R89

TRANSFER MANUAL

AUTO

115V AC


EXT AC BUS 1 AC EXT PWR

SERVICE

R6

R3 TRANSFER 1

BUSSES

TRANSFER

28V DC SWITCHEDHOT BAT. BUS

R9 TR 3

BUS

R4

BUSSES

R355BAT BUS

28V DCSTANDBY BUS

R389

CONTROLINVERTER

ENGINE 2ENGINE 1

POWER

R326

WDM 24-31-21BAT OVHT& APU STARTINTERLOCK

Page: 7Figure 3 Elec. Power System - Standby Power

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THIS PAGE INTENTIONALLY LEFT BLANK

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CENTER-LEFT (P18)LOAD CONTROL

ACCESS DOORCOMPARTMENTELECTRONIC

GENERATOR

DC LINE (28V)AC LINE (3 PHASE)

RECEPTACLEPOWEREXTERNAL

NO. 1 (LH)

GENERATORAPU

NO. 2 (RH)GENERATOR

CENTER-RIGHT (P6)LOAD CONTROL

T-R UNIT NO. 3

T-R UNIT NO. 2

FWD

INVERTERSTATIC

CHARGERBATTERY

T-R UNIT NO. 1

BATTERY

ACCESS DOORCOMPARTMENTELECTRONIC

Page: 9Figure 4 Location - Main System Components

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Page: 10

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RECEPTACLE

EXTERNAL POWER PANEL P19

EXTERNAL POWERPANEL P19

Page: 11Figure 5 Location - External Power Panel P19

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Page: 12

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FORWARD ATTENDANTS PANEL

FORWARD ATTENDANTS PANEL

INOPINOP

GROUND SERVICESWITCH

Page: 13Figure 6 Location - Forward Attendants Panel

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Page: 14

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Page: 15FRA US/F do/ur 18.10.99 Page: 15Figure 7 Location - Main Power Breakers

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Page: 16

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Page: 17FRA US/F do/ur 18.10.99 Page: 17Figure 8 Location - Panel P6 / M400 / M238

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Page: 18

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Page: 19FRA US/F do/ur 18.10.99 Page: 19Figure 9 Location / Interior - P6 Panel

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Page: 20

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Page: 21FRA US/F do/ur 18.10.99 Page: 21Figure 10 Location - AC Generator / VSCF

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Page: 22

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Page: 23FRA US/F do/ur 18.10.99 Page: 23Figure 11 Location - AC Generator / CSD

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ELECTRICAL POWER CONTROL PANEL

DC AmmeterIndicates current of source selected by the DC Meter Selector Switch.

DC VoltmeterIndicates voltage of source selected by the DC Meter Selector Switch.

DC Meter Selector SwitchSelects DC source for DC Voltmeter and DC Ammeter.

Frequency MeterReads frequency of source selected by the AC Meter Selector Switch.

AC Voltmeter Indicates (Scale Range100 - 130 V) AC voltage selected by AC Meter Se-

lector Switch. Indicates (Scale Range 0 - 30 V) Residual Voltage of the selected Genera-

tor when the RESID VOLTS switch is pushed.

AC Meter Selector SwitchSelects the AC source for the AC Volt Meter and Frequency Meter. The posi-tion Test is for further measuring purpose.

Battery Switch ON (guarded position): With No. 2 AC Main Bus powered TR 3 provides

power to the Battery Bus. If No. 2 AC Main Bus is not powered, the BatteryBus receives the power via Hot Battery Bus

OFF: Battery Bus and Switched HOT Battery Bus are deenergized and Ex-ternal Power will be tripped from the airplane.

Galley Power Switch ON: The galleys are powered when the Generator Busses are energized. OFF: The galleys are deenergized.

Residual Volts SwitchPush to read residual voltage of Generator selected by AC Meter SelectorSwitch. The Generator Control Relay (Field Relay) must be tripped by the re-spective Generator Switch when the Engine is running. Caution: If respective GCR has not tripped, AC Voltmeter could be damaged.

Low Oil Pressure Light (amber)Illuminates when the respective CSD/VSCF oil pressure is below 120 PSI. Si-multaneously, the Master Caution Warning with ELEC Annunciator comes on.

High Oil Temperature Light (amber)Illuminates when CSD/VSCF oil temperature exceeds 157C. Simultaneously,the Master Caution Warning with ELEC Annunciator comes on.

Standby Power Switch AUTO (guarded position):

During normal operation DC Standby Bus is powered by DC Bus No. 1,AC Standby Bus is powered by the 115 Volt AC Transfer Bus No. 1. If either power source fails, the following switching will occur:- In Air: Battery Bus will be automatically connected to the DC Standby

Bus and the Battery to the Static Inverter in order to supply the ACStandby Bus.

- On Ground: No automatic transfer switching will occur. The StandbyBusses are deenergized.

OFF (unguarded center position) The Standby Busses are deenergized.

BAT (unguarded position)The Battery Bus supplies the DC Standby Bus and Static Inverter suppliesthe AC Standby Bus regardless of the BAT Switch position.

Standby Power OFF Light (amber)Illuminates when the AC Standby Bus is not powered.

Disconnect Switch (guarded and safetied)Disconnects the respective CSD from Engine actuation (VSCF will be discon-nected electrical only). Caution: Actuating is allowed only when Engine is running (min. Idle Speed).

Page: 24

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LOW OILPRESSURE

HIGH OILTEMP

LOW OILPRESSURE

HIGH OILTEMP

STANDBYPWR OFF

DISCONNECT DISCONNECT

OFF AUTO

STANDBY POWER

BAT

-0+

-50 +50DC

400

420FREQCPS

20

40DC VOLTS

120

30

AC

TR 2

TR 1

TR 3

TEST

BAT

BAT

BUS

GEN 2

APU GEN

TEST

GRD

GEN 1

PWR

OFF

ONON

OFF

BAT

GALLEYRESIDVOLTS

110

AC

VOLTS

1 2

PWRPWR

STBYSTBY

ELECTRICAL POWER CONTROL PANEL(UPPER) P5

INV

INV POSITON:

NOT ON OLD AIRPLANES

1 1DRIVE ALTERNATE INSTALLATION1

Page: 25Figure 12 Electrical Power Control Panel (Upper)

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ELEC. CONTROL PANEL (NEW GENERATION)

GeneralThe Panel consists of Alphanumeric Display, Fault Indicating Lights, RotarySelector Switches, BAT Switch, GALLEY Switch and MAINT Test Switch. Thepanel performs a self test on power-up. If there is a malfunction in the panelthat would prevent normal operation, the alphanumeric displays will show thefailure by the display of dashes in the associated meters. In the event that thefailure is in the display or the display driver, the alphanumeric display will showan unusual indication.

Alphanumeric DisplayThe Alphanumeric Display shows the Voltage, Frequency, and Amperage mea-surements. This display also shows the error messages associated with theELEC Fault Indicating Light.

Fault Indicating LightsThe Fault Indicating Lights are connected to the Master Caution and will makethe Master Caution light come on when one or more of these fault indicatinglights come on: BAT DISCHARGE

- The BAT DISCHARGE light will come on when the battery is in a di-scharge condition.NOTE: During an APU start, the BAT DISCHARGE light comes on, andthen goes off. This will not cause the MASTER CAUTION lights to comeon.

TR UNIT- The TR UNIT light comes on for any one of these reasons:

Any TRU fails on the ground, or TRU 1 fails in flight, or TRU 2 and TRU 3 fail in flight

ELEC Light- The ELEC light will come on for these fault messages:

STAT INV INOP-The Static Inverter is defective.

BAT CHGR INOP-The Battery Charger is defective.

GEN1 FAULT-A fault exists in the NO. 1 VSCF Generator.

GEN2 FAULT-A fault exists in the NO. 2 VSCF Generator.

STBY BUS XFER FAULT-The AC Standby Bus is on a source other than that selected by the pilot.

BAT BUS XFER FAULT-The Battery Bus is on a source other than that selected by the pilot.

INTERFACE FAILURE-The P5-13 panel programming pins are not connected correctly.

If the faults occur while the airplane is in the air they will be stored and theELEC light will not come on until 30 seconds after the airplane is on theground.The intermittent faults (indicated by an I after the fault message) and theELEC light can be cleared by the MAINT Test switch. NOTE: Except for the Generator No. 1 and No. 2, the faults cannot be clearedby the MAINT button when the fault condition still exists.

Recall/Reset Test SwitchThe RECALL/RESET switch is used to control the initiation of the Display Test,the display of any maintenance messages, and the erasure of the maintenancemessage memory. NOTE: The AC and DC selector switches must be in the TEST position andairplane on the ground for the RECALL/RESET switch to be operable.The Display Test is initiated when the RECALL/RESET switch is operable andis pressed for the first time. The Display Test will exercise all of the elements inthe alphanumeric display to allow the operator to verify the functionality of thedisplay. The Display Test is terminated automatically after a complete test cycleor when the RECALL/RESET switch has been pushed during the Display Test.Maintenance Messages, if any exist, are displayed after the Display Test. Thefirst message will automatically be displayed. Push the RECALL/RESET switcheach time after the Display Test to see the subsequent messages. Push theRECALL/RESET switch after the last message and an informational messageto clear the fault messages will be displayed.The Maintenance Messages will be removed when the RECALL/TEST buttonis pressed and held for approximately 6 seconds.

Page: 26

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TEST

INV

GEN2APU GEN

GEN1

GRDPWR

STBY PWR

ACDC

ON

GALLEY

OFFOFF

ON

TR3

TR2TR1

DISCHARGEBAT

TR UNIT ELEC

AC VOLTSDC VOLTS

CPS FREQDC AMPS

BAT

BATBUS

STBY PWR

TEST

RECALL/RESET

BAT

Page: 27Figure 13 Elec. Panel (Upper - New Generation)

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Drive Temp SwitchSelector Switch with 2 positions (RISE / IN) for Generator Drive Oil Tempera-ture Indicator.

Generator Drive Oil Temperature IndicatorDisplays the temperature of the oil used in the CSD / VSCF. RISE (outer scale)

- Displays the temperature of the In and Out flowing oil within the CSD /VSCF.

IN (inner scale)- Displays the oil temperature entering the CSD / VSCF (Normally moni-

tored).

Ground Power Available Light (blue)Illuminates when External Power Plug is plugged and Voltage is available.

Ground Power SwitchThe GRD PWR switch has 3 positions: Momentary ON - OFF and springloaded to the center position. ON: Ground Power available and Battery Switch in ON position

- If Ground Power has no fault, EPC 2 and ECP 1 closes.- If Ground Service Switch has been switched to ON before, it will trip to

OFF position.- If both Engine Generators supply the airplane, the following switching

sequence will occur: GB No. 2 trips and EPC No. 2 closes GB No. 1 trips and EPC No. 1 closes

OFF:- Both External Power Contactors will be tripped.

AC AmmeterDisplays the Load of the respective Generator

Bus Transfer SwitchThe Bus Transfer Switch has 2 positions. AUTO (guarded):

- Allows automatic transfer of Transfer Bus to the Generator Bus on theopposite side, when the respective Generator Bus fails.

OFF:- No power transfer switching of the Transfer Bus to the opposite Genera-

tor Bus possible, when the respective Generator Bus fails. (Smoke Pro-cedure).

- The TR 3 Disconnect Relay is open and eliminates the parallel switchingof DC Bus No. 1 and DC Bus No. 2.

Transfer Bus Off Light (amber)Illuminates when the respective Transfer Bus is not powered. Simultaneously,the Master Caution Warning with ELEC Annunciator comes on.

Bus Off Light (amber)Illuminates when the respective Generator Bus is not powered. Simultaneously,the Master Caution Warning with ELEC Annunciator comes on.

Generator Off Bus Light (blue)Illuminates when the respective Generator does not supply the Generator Bus.

APU Generator Off Bus LightIlluminates when: The APU reaches the normal RPM after starting ( Garret APU 95 %,

APS 2000 APU 98 % ) and the APU Generator does not supply anyGenerator Bus.

The APU stops automatically because of a shut down signal and the APUStart Switch is not in the OFF position.

Page: 28

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RISE RISE

DRIVE CAN BERECONNECTED

ONLY ONGRD

40

0 80 120160

30

2010

4080 120

160

30

2010

0

IN

GEN DRIVEOIL TEMP

GEN DRIVE

C C

RISEDRIVE TEMP

OIL TEMP

IN IN

MAINTLOW OIL

PRESSURE FAULTOVERSPEED

B AA A

Electrical Power Control Panel(LOWER) P5

Page: 29Figure 14 Electrical Power Control Panel (Lower)

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Generator SwitchThe Generator Switch has 3 positions: Momentary ON / OFF and springloaded to center position. OFF:

- Trip signal to respective GCR and GB.- The associated generator is disconnected from its bus.

ON:- Close signal to the respective GCR (if tripped).- Trips associated EPC and APU GB and closes the GB (if voltage is cor-

rect).

APU Generator SwitchThree position switch, spring loaded to the center position. OFF: Trip signal to APU GCR (if both switches are switched to OFF), trips

the associated APU GB. ON: Closes APU GCR (if tripped), trips the respective ENG GB or EPC and

closes the associated APU GB.NOTE: When airplane is in AIR, the APU Generator can be switched either onGEN BUS No. 1 or GEN BUS No. 2., because of load limitations.

APU AC AmmeterIndicates the APU Generator load.

Page: 30

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RISE RISE

DRIVE CAN BERECONNECTED

ONLY ONGRD

40

0 80 120160

30

2010

4080 120

160

30

2010

0

IN

GEN DRIVEOIL TEMP

GEN DRIVE

C C

RISEDRIVE TEMP

OIL TEMP

IN IN

MAINTLOW OIL

PRESSURE FAULTOVERSPEED

B AA A

Electrical Power Control Panel(LOWER) P5

Page: 31Figure 15 Elec. Power Control Panel (Lower) cont.

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ELECTRICAL POWER ANNUNCIATOR PANEL (M238)

GENERALThe Electrical Power Annunciator Panel M238 is located in a well of the P6panel in the Cockpit entrance way and faces aft. It is used for the indication ofpower on the individual AC and DC Busses and indication of Faults which tripthe Generator Control Relays.The M238 is divided into three sections: AC Bus Lights (neon type) DC Bus Lights (white) Malfunction Lights (white)

There are to switches on the M238: ERASE (S1)

- The latched Malfunction Lights can be deleted when switch is beingpushed (except MT-Light)

INDICATE/TEST (S2)Three position switch, spring loaded to the center position.- INDICATE:

All DC Bus Lights illuminate, when DC Busses are powered.- TEST:

Light Test for DC Bus Lights and Malfunction Lights.

Page: 32

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M238 LOCATION

DC BUS

INDICATION LIGHTS

AC BUS

INDICATION LIGHTS

MALFUNCTION LIGHTS

(COVERED)

Page: 33Figure 16 Electrical Power Annunciator Panel M238

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DC ANNUNCIATOR LIGHTSThe Lights on the Annunciator Lights Module M238 illuminate when power ison: DC Bus No.1 DC Bus No. 2 DC Standby Bus External Power T-R Unit is energized T-R Unit No. 3 has output power

The INDICATE/TEST switch S2 on the module must be set to INDICATE forthe lights to illuminate.When the INDICATE-TEST switch is set to TEST, all lights except EXT PWRTR are grounded and connected to the 28-Volt DC Bat Bus. The EXT PWR TRlight, which is always connected to Bus Protection Panel, is grounded. Thisverifies that all lamps on the M238 module are operable.

Page: 34

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STBY DC IND

STBY BUS

STBY

P6-5 CIRCUIT BREAKER PANEL

DC BUS INDICATION

28V DC

STBY

BATT

TR 3

BAT

BAT BUS

TR NO. 3

BUS NO. 2

BUS NO. 1

INDICATE

M238 ANNUNCIATOR LIGHTS MODULE (P6)

G7 BUS PROTECTION PANEL (P6)

NORMAL

FAULT

S2

OA

DC BUS PWR ON

OC

NO.1 NO.2

GEN 1NO.1 NO.2 TR3 FF MT

TREXT PWR

BATT HV LV

ERASE

INDICATE

TEST

AC BUS

R2

S2TEST SWITCH

W

NO.2

TREXT PWR

NO.1

TEST

INDICATE

DC BUS INDICATION

DC BUS INDICATION

DC BUS INDICATION

DC BUS INDICATION

28V DC

TR 328V DC

BUS 228V DC

BUS 128V DC

DC BUS PWR ON

IS ATTACHEDEXTERNAL POWER28V DC WHEN

W W

W W

W

S1

Page: 35Figure 17 M 238 DC Bus Indicating Lights

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AC BUS INDICATING LIGHTSThe neon lights illuminate when phases A and C of their AC Busses are pow-ered.Each light is connected directly to a circuit breaker on its respective bus and alllights are connected to a common ground.The Lights are covered by a hinged panel which can be opened when a quickopening device is released.NOTE: The indicators for Voltage, Frequency and Amperes are normallyswitched to the phase B.

Page: 36

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L27

L29

L28

L26

L25

L24

L23

L22

L21

L20

L19

OA STBY

AC BUS PWR ON

OA

OC

115V ACSTANDBYBUS

AC INDICATION

AC INDICATION115V ACTRANSFERBUS 2

AC INDICATION

AC INDICATION115V ACMAIN BUS 2

AC INDICATION

AC INDICATION

115V ACMAIN BUS 1

AC INDICATION

AC INDICATION115V ACTRANSFERBUS 1

AC INDICATION

AC INDICATION115V ACGROUNDSERVICEBUS

AC STANDBY BUSINDICATION

NO. 1 NO. 2 NO. 1TRANS

NO. 2TRANS

GRDSVC

STBY

AC BUS INDICATION LIGHTS

AC BUS PWR ON

OC

OA

OA GRD SVC

OC GRD SVC

TRANS

TRANSTRANS

TRANS

P6-4 CIRCUIT BREAKER PANEL M238 ANNUNCIATOR LIGHTS MODULE (P6)

TRANSFER BUS 2 C

TRANSFER BUS 2 A

TRANSFER BUS 1 C

TRANSFER BUS 1 A

GRD SERVICE C

GRD SERVICE A

BUS NO. 2 C

BUS NO. 2 A

BUS NO. 1 C

OA NO. 1

OC NO. 1 OC NO. 2

OA NO. 2 OA NO. 1

OC NO. 1

OA NO. 2

OC NO. 2

BUS NO. 1 A

Page: 37Figure 18 M 238 AC Bus Indicating Lights

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GENERATOR MALFUNCTION LIGHTS

GeneralThe white Malfunction Lights (4 for each generator) are controlled by double-coil relays inside the GCUs.The lights show the reason for tripping of the Generator Control Relay.

OperationAll lights have 28 Volt DC Battery Bus power available (provided the batteryswitch is in ON). A ground will be connected within a GCU by energizing thetrip coil of the applicable fault light relay.If the trip coil of the relay has been energized, it will be latched in the Trip posi-tion by a permanent magnetic latch, and can only be released by energizingthe reset coil. The only possibility for energizing the reset coils and deleting theFF, HV and LV lights is by pushing the ERASE button.The only possibility for energizing the reset coil and deleting the MT lights is byswitching the respective GEN Switch to the ON position.The ERASE button has no effect on the MT lights.Reasons for indication: High Voltage (HV): Voltage > 130 V Low Voltage (LV): Voltage < 100 V Feeder Fault (FF): Overcurrent or Differential Protection (VSCF Fault) Manual Trip (MT): Generator Breaker Switch to OFF or CSD Disconnect

Switch to Disconnect position.

Page: 38

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/

/

STBY

UNIT 2 (P6)

CONTROL UNIT (P6)G5 APU GENERATOR

G4 GENERATOR CONTROL

M238 ANNUNCIATOR LIGHTS MODULE (P6)

G3 GENERATOR CONTROL UNIT 1 (P6)

RESET

TRIP

RESET

TRIP

DC BUS PWR ON

OC

OA

INDICATE

TEST

ERASE

STBYSVCGRD

TRANSNO. 2

TRANSNO. 1NO. 2NO. 1

AC BUS PWR ON

APUGEN 2GEN 1

LVHV

MTFF

LV

MT

HV

FF

LV

MT

HV

NO. 1 NO. 2 TR3

TREXT PWR BATT

FF

S1

S2

CONTROLMANUAL

FEEDER FAULT

PROTECTIONDIFFERENTIAL

VOLTAGEUNDER

VOLTAGEOVER

BUSBATTERY28V DC

INDICATE

TEST

APU

GEN 2

GEN 1

ERASE

BATDC BUS INDICATION

P6-5 CIRCUIT BREAKER PANEL

MANUAL TRIP

HIGH VOLTAGE

ON

OFF

DC

DC

RESET

DC

TRIP

G-3SAME AS

INTERNALS

G-3SAME AS

INTERNALS

S2TEST SWITCH

INDICATORS1SWITCH

ERASE

FF

HV

MT

W

LV

FF

HV

MT

LV

FF

HV

MT

LV

LOW VOLTAGE

W

W

W

W

W

W

W

W

W

W

W

.

Page: 39Figure 19 M 238 Generator Malfunction Lights

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POWER SYSTEM TEST MODULE M400

GeneralThe Power System Test Module M400 is a switch panel for testing the airplanepower system with current transformer selecting relays and portable meterjacks. It permits measuring DC voltages and current values, and AC voltages,current values and frequency at various electrical system component connec-tions throughout the electrical system. The module is at the top of the load con-trol center panel P6. Calibrated portable meters may be connected to checkthe accuracy of meters on the pilots overhead panel P5.The system test operation consists of selecting various combinations of set-tings on the two switches (S1 and S2) in M400 and observing the meters onP5. The DC and AC rotary switches on pilots overhead panel are turned toTEST position for meter readings of DC volts, AC volts, and frequency. Gener-ator ammeter readings are depend on the position of S2 switch; voltmeter andfrequency meter readings depend on the position of S1 and S2 switches.When M400 is not being used, S2 have to be set to position B.

M400 LOCATION

Page: 40

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POWER SYSTEM TEST

A

BCD

EF G

H

123

4

5

6 78

DCAC

PART NO.SER. NO.

S 1S 2

JACKS FOREXTERNALMEASURING

Page: 41Figure 20 M400 Power System Test Module

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M 400 AC VOLTAGE / FREQUENCY METERINGAdditional test points may be selected from combinations of the two M400 se-lector switches S1 positions 1 - 3 and S2 position A - F. When the AC MeterSelector Switch is in the TEST position, the additional values can be displayedon the Frequency and AC Voltmeter on P5-13. These test points may also beselected for reading AC Volts and Frequency on portable meters connected tothe M400 Test Module AC jacks J1 and J2 (independent of AC Meter SelectorSwitch position).The following outputs can be checked: Main Bus 1 / 2 Transfer Bus 1 / 2 External Power Bus Ground Service Bus

Page: 42

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737-300/400/500

24-00


420400

380

FREQCPS

A

B

C

1

23

A

A

A A B C

A B C

A B C

B

B

C

C

C

110

100 130

120

ACVOLTS

300

AC DC

876

54

3 21

HGF

ED

C BA

MAIN BUS 2 XFR BUS 2

MAIN BUS 1 XFR BUS 1MAIN BUS 1 XFR BUS 1MAIN BUS 1 XFR BUS 1

A

BC

D

SERVICE BUS

115V ACGENERATOR 2

115V ACEXTERNALPOWER

FREQUENCY METER

TEST

APU GEN

MODULE

STBY PWR

GND PWR

GEN 1

APU GEN

GEN 2

TEST

GRDPWR

GEN 2GEN 1

STBYPWR

FEDCBA

3

2

1

PO

SIT

ION

OF

M40

0 S

W S

1 POSITION OF M400 SWITCH S2

EXT PWREXT PWRGND SVCEBUS

GND SVCEBUS

GND SVCEBUS

XFR BUS 2MAIN BUS 2 XFR BUS 2MAIN BUS 2

NC

NCNC

RESIDVOLTS

POWER SYSTEM TEST MODULE (P6)M400

NC

BC

D

E

F G

H

BC

J2

E

F

D

E

F G

G

H

A

H

CIRCUIT BREAKER PANELP6-4

AC INDICATIONSTBY

STANDBY BUS

AC INDICATIONGENERATOR 1

115V ACGENERATOR 1

APU GENERATOR AC INDICATIONAPU GENERATOR

AC INDICATIONGENERATOR 2

AC INDICATION

AC INDICATION115V ACMAIN BUS 1

AC INDICATION

AC INDICATION

AC INDICATION

AC INDICATION

J1

AC INDICATION

AC INDICATION

MAIN BUS 2 AC INDICATION

AC INDICATION

AC INDICATION

115V ACAC INDICATION

AC INDICATION

AC INDICATION

AC INDICATION

CIRCUIT BREAKER PANELP6-12

BUS PROTECTION PANEL AC

NC

NC

A

115V AC GROUND GND SERVICE C

GND SERVICE B

GND SERVICE A

C

B

A

AC VOLTMETER

RESIDUAL VOLTS SWITCH

S957 AC METER SELECTOR SWITCH

P5-13 ELECTRICAL POWER METERS

S1 WAFER SWITCH

POWER SYSTEM TEST

TRANSFER BUS 2 C

TRANSFER BUS 2 B

TRANSFER BUS 2 A

BUS NO 2 C

BUS NO 2 B

BUS NO 2 A

TRANSFER BUS 1 C

TRANSFER BUS 1 B

TRANSFER BUS 1 A

BUS NO 1 C

BUS NO 1 B

BUS NO 1 A

B

B

B

S2 WAFER SWITCH

TRANSFERBUS 2

TRANSFERBUS 1

115V AC

115V AC

115V AC

115V AC

J1 J2

Page: 43Figure 21 M400 AC Voltage / Frequency Metering

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737-300/400/500

24-00


M 400 DC VOLTAGE METERINGAdditional test points may be selected from combinations of the two M400 se-lector switches S1 positions 1 - 8 and S2 position A - C. When the DC MeterSelector Switch is in the TEST position, the additional values can be displayedDC Voltmeter on P5-13. These test points may also be selected for readingDC Voltage on portable meter connected to the M400 Test Module DC jacks J3and J4 (independent of DC Meter Selector Switch position).The following outputs can be checked: Generator Field of the three Generators (2 - 10 VDC) DC output of the three GCUs (min. 22VDC) Close signals of the four GBs (min. 22 VDC) Close signals of the both EPCs (min. 22 VDC)

Page: 44

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737-300/400/500

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STBY PWR0

2040

DC VOLTS

APU MODULESYSTEMS ANDP5-4 AC

7

6

5

4

3

2

1

CBA

EPC 2

EPC 1

APU GB 2

CLOSE COIL

CLOSE COIL

CLOSE COIL

CLOSE COILCLOSE COILCLOSE COILENG GB 1 ENG GB 2 APU GB 1

GCU DCGCU DCAPUNO. 2

GCU DC

APUNO. 2

NO. 1

GEN FIELDGEN FIELDGEN FIELDNO. 1

M400 S2 SWITCH POSITION

M40

0 S

1 S

WIT

CH

PO

SIT

ION

P5-13 ELECT, METERS, BATTERY & GALLEY POWER PANEL

DC VOLTMETER

SWITCHSELECTORS956 DC

BAT BUS

BAT

TR1

TEST

TR2

TR3J4J3

S1S2

J3J2J1 J4

S2 WAFER SWITCH

M400 POWER SYSTEM TEST MODULE (P6)

S1 WAFER SWITCH

P8-1 ENGINE & APUFIRE CONTROL PANEL

APU

BREAKER 1 (P6)APU GENERATOR

BREAKER 2 (RIGHT SIDEENGINE GENERATOR

NOSE WHEEL WELL)

NOSE WHEEL WELL)BREAKER 1 (RIGHT SIDEENGINE GENERATOR

BREAKER 2 (P6)APU GENERATOR

CONTACTOR 1 (RIGHTEXTERNAL POWER

SIDE NOSE WHEEL WELL)

SIDE NOSE WHEEL WELL)CONTACTOR 2 (RIGHTEXTERNAL POWER

CONTROL UNIT 1 (P6)G3 GENERATOR

CONTROL UNIT 2 (P6)G4 GENERATOR

NO. 1 GEN

NO. 2 GEN

SIGNALGCR CLOSE

FIELD

SIGNALGCR CLOSE

FIELD

H

GF

E

D

C B

A

D

B

GEN

GEN 1

GEN 2

S8 ENG 1

S9 ENG 2

CLOSE SIGNAL

CLOSE SIGNAL

CLOSE SIGNAL

CLOSE SIGNAL

CLOSE SIGNAL

CLOSE SIGNAL

UNITCONT

FIRE SW

FIRE

NORMAL

76

85

4

32

1

UNITCONT

FIRE SW

FIRE

NORMAL

C

76

85

4

32

1

UNITCONT

FIRE SWS10 APU

FIRE

NORMAL

CONTROL UNIT (P6)G5 APU GENERATOR

SIGNALGCR CLOSE

FIELDAPU GEN

76

85

4

3

2

1

STBY PWR

BAT

POWER SYSTEM TEST

ABC

DE

F GH

123

45

6 78

DCAC

TR 1TR 2

TR 3

TESTBUS

BAT

Page: 45Figure 22 M400 DC Voltage Metering

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737-300/400/500

24-00


AC AMPERES METERINGThe three AC Ammeters on P5 overhead panel for the two engine generatorsand the APU generator normally read the phase B line current. Each of theAmmeters senses current using one of the metering transformer windings in itsline current transformer assembly in the ceiling of the electrical electronicscompartment.The Ammeter can read phase A, B or C current by selecting positions of theswitch S2 on the Power System Test Module M400 in the P6 panel.For each Ammeter the connection from the line current transformer windings tothe Ammeter is made through contacts of three relays inside M400 module.The relative positions of the relays are controlled by switch S2.If the switch is in position A or D relays K1 and K2 are energlzed and the phaseA windings are connected to all three Ammeters.If the switch is in position B, E, G or H all three relays are relaxed and thephase B windings are connected to all three Ammeters. B is the normalposition. Please verify this position when you leave the cockpit !If the switch is in position C or F relay K2 and K3 are energized and the phaseC windings are connected to all three Ammeters.

CURRENTTRANSFORMER

CURRENTTRANSFORMER

CURRENTTRANSFORMER

T7 T9 T8

Page: 46

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737-300/400/500

24-00


B

A

C

B

A

C

B

A

C

K3

M400 POWER SYSTEM TEST MODULE (P6)

T7 CURRENT

T8 CURRENT

TRANSFORMERASSEMBLY

TRANSFORMERASSEMBLY

TRANSFORMERT9 CURRENT

DC BUS

K2

P5-4 AC SYSTEM GENERATOR AND APU MODULE

200

15010050

AMPERES

AC0

AMMETER

200

15010050

AMPERES

AC0

AMMETER

APU GENERATOR

GENERATOR 2GENERATOR 1

C B C B

C B C B

C B C B

A

A

A A

AAC

876

54

3 21D

A

POWER SYSTEM TEST

S2 WAFER SWITCHP6-5 CIRCUIT BREAKER

C B

A

H

G200

15010050

AMPERES

AC0

A

BCE

F GH

DC

AMMETER

S2 SWITCH POSITION

FEDCBA

F

E

ASSEMBLY

GENERATORENGINE 2

GENERATORENGINE 1

(STA 285, RBL 50)LOWER 41-CEILING

BUS 128V DC

BUS 1INDICATION

PANEL

D

K1

READINGMETER

AMMETERGEN 1

AMMETERGEN 2

AMMETERAPU GEN

GENERATORAPU

Page: 47Figure 23 M400 AC Amperes Metering

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ELECTRICAL POWERGENERATOR DRIVE

737-300/400/500

24-10


24-10 GENERATOR DRIVE / CSDGENERALThe purpose of the engine generator drive (constant speed drive - CSD), is toconvert the variable speed of the engine (accessory gearbox) to a constantspeed (6000 RPM) for the driven generator to produce ac power at constantfrequency. The constant speed drive is located on the left side of the engine,on the front of the accessory gearbox. The CSD is a hydromechanical trans-mission using hydraulic trimming and mechanical controls to govern the outputrotational speed.Located on the CSD are: oil inlet and outlet connection with temperature bulbs wet spline cavity fill valves main electrical connector and harness vent valve mount low oil pressure switch (LOP) oil quantity sight glass disconnect solenoid output pad drain (generator side) charge filter with dif-

ferential pressure Indicator drain plug (reservoir) case drain and magnetic drain plug governor adjustment reset handle

On the input end of the CSD is a QAD (Quick Attach Detach) flange for CSDattachment to the QAD ring on the gearbox. On the opposite face are 12 studsfor the generator attachment.

Page: 48

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737-300/400/500

24-10


(6 oclock

RESETHANDLE

position)

GENERATORATTACHMENTSTUDS (12)

MAINELECTRICALCONNECTORAND HARNESS VENT

VALVE

SIGHTGLASS

LOW OILPRESSURESWITCH

DISCONNECTSOLENOID

WET SPLINESERVICE PORT

QAD RINGLOCKBOLT

WET SPLINESERVICE PORT

DRAIN PLUG(RESERVOIR)

OIL OUTLETCONNECTION

GOVERNORADJUSTMENTCOVER

OIL INLETPORT

CASE DRAIN ANDMAGNETIC CHIPDETECTOR

CHARGEFILTER

OUTPUTPAD DRAIN

DIFFERENTIALPRESSUREINDICATOR

DOWN

Page: 49Figure 24 CSD - Components

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737-300/400/500

24-10


CSD SERVICING

GeneralThe CSD sight glass has different ranges for the oil level on the left and rightengines. This is because the left and right engines are at different angles. Theoil quantity of the CSD is 10.7 pints. The oil quantity of the external system is2.75 pints.The total oil quantity for a dry CSD oil system is 13.45 pints for eachengine.The oil level shown on the sight glass of a disconnected CSD can show moreoil than there is. Expanded air can push the oil from the oil cooler into the CSD.To get an accurate indication of the oil level, fill the CSD and look at the sightglass again. Leakage of the seal in the CSD will let oil flow from the CSD to thespline cavity. A defective input shaft seal will cause these indications: The oil level in the CSD will decrease. The oil level in the spline cavity will increase.

CSD Oil Level Check Push the vent valve cap on the top of the CSD to remove the internal pres-

sure. Look at the oil level in the sight glass on the CSD.

- If the oil level is above the top of the applicable range, drain some of theoil from the CSD.

- If the oil level is below the bottom of the applicable range, add oil to theCSD.

CSD Fill ProcedureMake sure that you have the correct oil for the CSD. Refer to the marker on theCSD to find the oil that is in the CSD. Remove the cap from the case pressure-fill valve. Connect the coupling of the service cart to the case pressure-fill valve. Set the pressure from the service cart to 5 - 40 psi.

CAUTION: DO NOT PUT TOO MUCH OIL INTO THE CSD. TOO MUCHOIL WILL CAUSE THE CSD TO BECOME TOO HOT ANDCAUSE DAMAGE TO THE GENERATOR DRIVE.

Fill the CSD until the oil level increases to the bottom of the applicablerange on the sight glass.

- Stop for five minutes.NOTE: The time will let the oil level become stable.

Look at the oil level in the sight glass on the CSD.- If the oil level is below the bottom of the applicable range, add oil to the

CSD.- If the oil level is above the top of the applicable range, drain some oil

from the CSD. Remove the coupling from the case pressure-fill valve and install the cap.

Page: 50

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737-300/400/500

24-10


VIEW LOOKING AFT

FAN CASE

SCAVENGEFILTER

CSDOIL COOLER(FAN AIR STREAM)

CSD PRESSUREFILL PORT

CSD

SIGHT GLASSFILL VALVEPRESSURE

Page: 51Figure 25 CSD - Servicing

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24-10

Page: 52FRA US/F ur 19.10.99

CSD WET PAD CAVITY

GeneralBetween the CSD and the Engine Accessory Gearbox is the Wet Pad Cavitylocated. It contains oil to lubricate the CSD Input Spline.The Wet Spline Pressure Fill Port is on the CSD. A standpipe attached to theEngine Accessory Gearbox limits the oil level in the Wet Pad Cavity during ser-vicing.

Wet Pad Cavity Servicing Step 1

- Check oil level in the wet pad cavity by removing overflow drain cap onengine gearbox and allow oil to flow from standpipe indicator inside thecavity. When oil stops flowing spline cavity is filled to proper level. If ex-cessive oil flows, check CSD seals for oil leaking into the wet spline cav-ity.

Step 2- To bring oil to overflow level, pump oil from service cart through spline

cavity fill check valve on CSD until it begins to flow from the standpipe.Oil quantity is 2 pints (0,95 Liter).

Step 3- Allow exess oil to flow from standpipe, then replace overflow drain cap

on engine gear case.

Page: 52

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Page: 53FRA US/F ur 19.10.99

ACCESSORYGEARBOX

SPLINE CAVITYSTANDPIPE INDICATOR CAPDRAIN & OVERFLOW

WET PAD CAVITY

SPLINE CAVITYFILLPORT

OIL OUTFLOW

INPUT SPLINE

VENT TOENGINEDRAINS

WET PADCAVITY

STANDPIPE

WET SPLINE CAVITY DRAIN PLUG(REMOVE ONLY WHEN DRAININGWET SPLINE CAVITY)

OVERFLOW DRAINREMOVE SEAL FITTING CAPWHEN FILLING CAVITY

Page: 53Figure 26 CSD Wet Pad Cavity

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737-300/400/500

24-10


Oil CoolerThe CSD oil cooler is used for cooling the oil from the CSD.It is located in an opening on the right hand side of the engine fan duct.The cooler is a small oil/air heat exchanger using fan air. A pressure relief valveis installed in the cooler assembly. On the outlet fitting is an HIGH OIL TEM-PERATURE switch installed.During engine operation, hot oil from the CSD passes through the cooler; fanair provides the cooling for the oil. If the cooler becomes blocked on the oilside, a pressure relief valve cracks open at 50 psi differential pressure and isfully open at 90 psi differential pressure allowing oil to bypass the cooler core.

CSD Line Filter (Scavenge Filter)The Line oil filter collects contamination from the oil. This prevents damage tothe CSD and oil cooler.The line filter has a pop-out button. The pop-out button extends when the oilpressure becomes to high. This is an indication that the oil filter element is fullof contamination and will not let the oil flow through it.The line oil filter is on the fan case at the 5 o clock position.

Page: 54

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737-300/400/500

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POP-OUTINDICATOR

HOUS-ING

FILTERLINE OIL

CSD LINE FILTER(SCAVENGE FILTER)

CSD LINE FILTER(SCAVENGE FILTER)

CSD COOLER

OIL-OUT

BOLT AND WASHER(TYPICAL, 8 PLACES)

GASKET

FWDHIGH OILTEMPERATURESWITCH

OIL-INPORT

PORT

BY-PASSVALVE

CSD OILCOOLER

ENGINE FANCASE

VIEW LOOKING AFT

Page: 55Figure 27 CSD - Oil Cooler

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737-300/400/500

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DESCRIPTION OPERATION

Hydraulic SystemThe constant speed drive consists of two positive displacement axial slipperpiston-type hydraulics units and mechanical axial geared differential which per-forms the speed summing function. One hydraulic unit is of fixed displacementand the other one is a variable displacement type.The hydraulic system consists of the charge pump, the scavenge pump andthe charge relief valve. The charge pump is located in the system between theall-attitude reservoir and the transmission. It supplies oil to the hydraulic units,governor, control piston and the lubricating system. The charge pump forcesthe oil through the charge filter which incorporates a differential indicator (notused). Connected to the charge line is a low oil pressure switch which operatesat 120-160 psi. The scavenge pump is located in the system between thetransmission sump and the external oil cooler. The scavenge pump picks uplube oil and internal leakage and pumps it through the external oil cooler intothe all-attitude reservoir

GovernorThe governor is a spring-biased, flyweight operated sleeve valve. It functionsto control porting of charge oil to the control cylinder. The rotating sleeve valveis driven by the output gear and hence is responsive to transmission outputspeed. Flyweights pivoted on this sleeve move a valve stem located within thesleeve against the bias of a spring. The valve allows Increasing or decreasingoil pressure application to the control cylinder which in turn controls the variabledisplacement hydraulic unit.

DisconnectThe disconnect solenoid is activated by 28 volt dc from a guarded switch onthe P5 panel. The normally closed contacts of the switch connect a ground tothe disconnect solenoid; thus both sides of the coil are grounded to prevent thepossibility of voltage pickup and inadvertantly tripping the CSD. A second sec-tion of this switch - provides 28 volt dc to the trip coil of the generator controlrelay, tripping off the generator field. The CSD re-connection is by an externalreset handle.NOTE: Diconnect of the CSD is allowed only, when Engine is running. Re-con-nect is allowed only, on a stopped Engine.An overrunning clutch is provided in the output shaft permitting the generator tomotor freely at rotational speeds above that of the drive output.

Temperature MonitoringHeat produced by the transmission is absorbed by the oil in the unit and dissi-pated in an oil cooler at the fwd end of the engine. The hot oil passes throughan external filter (Scavenge Filter) then trough the cooler.Two variable resistance temperature bulbs measure the oil temperature on ei-ther side of the oil cooler. One bulb measures the input oil temperature to theCSD and is read on a meter on P5 panel. A switch on the panel alters the cir-cuit to include the oil out temperature bulb so that the meter can indicate therise in oil temperature through the CSD.Normal temperature rise of the oil through the transmission is about 10 0C atcontinuous full load with an inlet oil temperature of about 80 0C - 90 0C (Nor-mal) at normal input speeds. The oil in the transmission serves as a lubricant,as a coolant and as the hydraulic medium of the drive.The oil returning from the cooler is deaerated in a swirl chamber in the reser-voir. If the temperature of the oil reaches 157 0C a thermo switch in the in-linecloses illuminating the HIGH OIL TEMP light on the P5 panel.A vent valve is provided to prevent negative pressure and retain positive pres-sure. Oil quantity is indicated by a sight gage.

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737-300/400/500

24-10


SCAVENGEPUMP

CHARGEPUMP

POPOUT

CHARGEPRESSURE SW( 120 PSI )

CHARGE RELIEFVALVE( 250 PSI )

( 3 PSI )

( 20 PSI )

OIL OUTFLOW TOWET PAD CAVITY

SPLINECAVITYPRESSUREFILL CHECKVALVE

CASEDRAIN &MAGNETICPLUG

SUMP

OUTTEMPBULB

PRESS FILL PORTSCAVENGEFILTER

INTEMPBULB

RESERVOIRGRAVITY FILL PORT

T

CONTROLPRESSURE

SUPPLY CHARGEPRESSURE

RETURN OIL

TOGENERATOR

DRIVE

AXIAL GEARDIFFERENTIAL

4300 - 8600 RPM

FIRE

WARN

PUSH TO RESET

MASTER

CAUTIONPUSH TO RESET

ELEC

RISE RISE

40

0 80 120160

30

2010

4080 120

160

30

2010

0

IN

GEN DRIVEOIL TEMP

GEN DRIVE

C C

RISE

DRIVE TEMP

OIL TEMP

IN IN

LOW OILPRESSURE

HIGH OILTEMP

LOW OILPRESSURE

HIGH OILTEMP

STANDBYPWR OFF

DISCONNECT DISCONNECT

OFF AUTO

STANDBY POWER

BAT

1 2

6000 RPM

HIGH OILTEMPBULB

ANDVACUUMVALVE

TO PUMPSAND GOVERNOR

INPUT SPLINEIN ACCESSORY

GEAR BOX

FREQUENCYADJUSTMENTSCREW

RESET HANDLE

DISCONNECT

FLYWEIGHTGOVERNOR

FROMGEAROUTPUT

PUMP MOTOR

TO SUMP

TOLUBEJETS

SCAVENGE

FILTERCHARGE

RESERVOIR

OIL COOLER

VENT

Page: 57Figure 28 Constant Speed Drive

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737-300/400/500

24-10


CONSTAND SPEED DRIVE ADJUSTMENT

GeneralThe governor in the CSD ensures that the output speed to the generator ismaintained at 6000 RPM corresponding to electrical frequency of 400 Hz. If thefrequency is out of this range the governor can be adjusted.

This is a procedure to adjust the output speed of the constant speed drive.There is a short test before the adjustment procedure. This will make sure thatthe CSD is only out of adjustment and not unservicable.You can adjust the con-stant speed drive governor to change the output frequency of the generator.The permitted generator output frequency is 400 5 Hz (400 4 Hz during ad-justment). The constant speed drive is on the accessory gearbox at the 8oclock position.Make sure that the frequency meter on the P5-13 panel is accurate. Supply engine generator power (Ref 24-22-00/201). Permit the CSD to

operate for three minutes to become warm. Turn the AC meters switch on the P5-13 panel to the applicable GEN 1 or

GEN 2 position. Put electrical loads on the AC buses. Use lights, air conditioning, fuel boost

pumps, and hydraulic pumps. Make sure that the frequency meter on the P5-13 panel shows 400 5 Hz. If the frequency is not in the limits, adjustment is necessary. Write down the

frequency value. Remove the electrical loads that you applied before (lights, air conditioning,

fuel boost pumps, and hydraulic pumps). Make sure that the frequency meter on the P5-13 panel shows 400 5 Hz.

Replace the CSD if the conditions that follow occur: (Ref 24-11-11/401) The frequency is not stable. The frequency goes out of the limits and stays out when you apply or re-

move the loads.Remove the engine generator power (Ref 24-22-00/201).

Adjust the CSD Output Speed Make sure that the engine is stopped (Ref 71-00-00/201). Remove the adjustment cap to get access to the adjustment screw. Re-

move the two screws and washers from the adjustment cap on the CSD.Pull the adjustment cap away from the CSD.

Adjust the CSD output speed to get a frequency of 400 4 Hz. Put a screw-driver into the adjustment screw slot.

Push in and turn the screwdriver until the adjustment screw engages thegovernor adjustment screw.

Turn the adjustment screw clockwise to increase the frequency, or turn itcounterclockwise to decrease the frequency.

NOTE: One full turn of the adjustment screw will change the frequency byapproximately 14 Hz. Supply engine generator power (Ref 24-22-00/201). Make sure that the frequency meter on the P5-13 panel shows 400 4 Hz. If the frequency is not in limits, adjust the CSD again until the frequency is

OK.

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GOVERNORADJUSTMENTSCREW

GOVERNORADJUSTMENTSCREW

O-RING

ADJUSTMENT CAP

NORMAL CONDITION ENGAGED CONDITION

ADJUSTMENTSCREW

ADJUSTMENTCAP

DISCONNECTRESETT-HANDLE

1 TURN = 14 Hz

-0+

-50 +50DC400

420FREQCPS

20

40DC VOLTS

120

30AC

TR 2

TR 1

TR 3

TEST

BAT

BAT

BUS

GEN 2APU GEN

TESTGRD

GEN 1

PWR

OFF

ONON

OFF

BAT

GALLEYRESID

110

AC

VOLTS

PWR PWRSTBYSTBY

1000

130

VOLTS

Page: 59Figure 29 CSD Adjustment

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ELECTRICAL POWERAC GENERATION

737-300/400/500

24-20

Page: 60HAM US/E do/ur 11.11.99

24-20 AC GENERATION

GENERALThe ac generation system consists of generators, manual controls, generatorcontrol relays (GCR), generator control units (GCU), main power circuit break-ers (GB) and annunciator lights.

AC Generator with CSDA rotating electromagnetic field causes the output voltage - three phase electri-cal power at 115 volts and a constant frequency of 400 Hz- to be induced in thestationary generator armature. The engine-driven generators are driven byCSDs. A complete generator assembly consists of an ac exciter generator, arotating rectifier and a main generator.

AC Generator/VSCF (Variable Speed Constant Frequency)The VSCF is interchangeable with the CSD and generator assembly. TheVSCF gets power from a variable speed shaft on the accessory gearbox on theengine. It converts this to three phase electrical power at 115 volts and aconstant frequency of 400 Hz.

Generator Manual ControlsManual controls and monitoring devices for the electrical power system are onthe forward overhead panel P5. The switches for latching contactors are mo-mentary. There is an ac ammeter for each engine. The ac voltmeter and fre-quency meter monitor various systems as determined by the selector switchesbelow the meters.

Generator Control Relay (GCR)The GCR, located in the generator control unit, energizes the generator field.The GCR and the generator field circuit are normally closed. The GCRs maybe opened or closed by the GEN switches on the pilots forward overheadpanel P5 or opened by signals from the GCU protection circuits.

Generator Control UnitThe purpose of the generator control unit is to provide excitation, control andprotection functions for the generator system. The three GCUs are located inthe right front of the P6 panel.

Each of the GCUs (and also the bus protection panel - BPP) contains a trans-former rectifier unit (TRU). The TRU converts the 3-phase ac power to 28 voltdc power for the control and protection circuits during normal system operation.If the ac power is not available or the TRU has failed, the power for the controland protection circuits is available from the switched hot battery bus. Withthe battery switch in ON position the switched hot battery bus is con-nected to the three GCUs and the BPP as a back-up power for each of the TRunits.

Generator BreakerThe generator breakers connect the 115 volt ac, 400 Hz, 3-phase power to thedistribution system from the engine and APU generators.

Annunciator LightsThe annunciator lights indicate the situation of the ac system and the genera-tors.

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Page: 61HAM US/E do/ur 11.11.99

CL = CLOSE SIGNAL

TR = TRIP SIGNAL

EPC 1 EPC 2

APU GB 1 APU GB 2

EXTPWR

APUGEN

GB 2GB 1

FROM GCU 2 FROM GCU 1

XFERRLY 1

XFERRLY 2

Page: 61Figure 30 AC System Schematic

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AC GENERATOR / CSD

GeneralA rotating electromagnetic field causes the output voltage to be induced in thestationary generator armature. This rotating field is excited by an integral acexciter, in which the output is converted to dc by rectifiers in the generator rotorshaft. The engine-driven generators are driven by CSDs. A complete generatorassembly consists of an ac exciter generator, a rotating rectifier and a maingenerator. The ac exciter consists of a six-pole stationary dc field and a rotat-ing armature.

OperationThe operation of the unit is as follows:(1) The exciter field is supplied dc power from the voltage regulator. Thiscauses a three-phase voltage in the exciter armature. The ac voltage is recti-fied and fed to the ac generator rotating field. This field generates the useful acoutput voltage in the ac generator stator.(2) The exciter stator has a shunt field winding connected between terminals Fand A.(3) Current supplied by the voltage regulator to the shunt field winding providesexcitation for the exciter generator. The current controls the exciter output tothe main ac generator. The shunt field winding consists of two wires wound inparallel in six series coils mounted on the six main poles. The coils are alter-nately reversed in polarity over the six poles, on one end both insulated wiresare connected to a common F terminal. On the opposite end, one wire is con-nected directly to the A terminal and the other wire is connected through athermistor to the A terminal.

Temperatur CompensationThe thermistor, mounted on the exciter frame, has an inverse temperature re-sistance characteristic. The high resistance at low or normal ambient tempera-ture blocks current flow in one of the parallel wires and causes the overallshunt field resistance to be about that of the remaining single wire. At thehigher temperature resulting from normal operation, the resistance of eachsingle wire increases to approximately double. At the same time, the resistanceof the thermistor drops to a negligible value permitting approximately equal cur-rent to flow in each wire. The combined resistance of the two parallel wires athigher temperatures is approximately equal to that of the single wire at lowtemperature, temperature compensation is thereby provided.

Permanent Magnets (PM)Six permanent magnets are mounted on the exciter frame between the six sta-tor poles. These magnet

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