Hobart 6921 Series User manual

OM-2040
062984
Revised 073188
Revised 093089
Revised 013190
Revised 022894
Revised 093095
OPERATION AND MAINTENANCE
MANUAL
with
ILLUSTRATED PARTS LIST
for
ENGINE DRIVEN GENERATOR SETS
90-kVA, 400-Hz, 115/200-V AC, 3-Phase Units
Series 6921 Series 6921A
Series 6922 Series 6922A
Series 6922B
100-kVA, 400-Hz, 115/200-V AC, 3-Phase Unit
Specification 7126-1
with
DEUTZ DIESEL ENGINE
Type DO 693-738
HOBART BROTHERS COMPANY
Ground Power Division
Troy, Ohio 45373 U.S.A.

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Safety Warnings and Cautions
CALIFORNIA PROPOSITION 65 - GASOLINE ENGINES. The engine exhaust
from this product contains chemicals known to the State of California to cause
cancer, birth defects or other reproductive harm.
CALIFORNIA PROPOSITION 65 - DIESEL ENGINES. Diesel engine exhaust
and some of its constituents are known to the State of California to cause
cancer, birth defects and other reproductive harm.
ELECTRIC SHOCK can KILL. Do not touch live electrical parts.
ELECTRIC ARC FLASH can injure eyes, burn skin, cause equipment damage,
and ignite combustible material. DO NOT use power cables to break load and
prevent tools from causing short circuits.
IMPROPER PHASE CONNECTION, PARALLELING, OR USE can damage
this and attached equipment.
Protect all operating personnel. Read, understand, and follow all instructions in
the Operating/Instruction Manual before installing, operating, or servicing the
equipment. Keep the manual available for future use by all operators.
1. General
Equipment that supplies electrical power can cause serious injury or death, or damage to other
equipment or property. The operator must strictly observe all safety rules and take precautionary
actions. Safe practices have been developed from past experience in the use of power source
equipment. While certain practices below apply only to electrically-powered equipment, other practices
apply to engine-driven equipment, and some practices to both.
2. Shock Prevention
Bare conductors, or terminals in the output circuit, or ungrounded, electrically-live equipment can fatally
shock a person. Have a certified electrician verify that the equipment is adequately grounded and learn
what terminals and parts are electrically HOT. Avoid hot spots on machine. Use proper safety clothing,
procedures, and test equipment.
The electrical resistance of the body is decreased when wet, permitting dangerous currents to flow
through it. When inspecting or servicing equipment, do not work in damp areas. Stand on a dry rubber
mat or dry wood, use insulating gloves when dampness or sweat cannot be avoided. Keep clothing dry,
and never work alone
IMPORTANT
WARNING
WARNING
WARNING
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a. Installation and Grounding of Electrically Powered Equipment
Equipment driven by electric motors
(rather than by diesel or gasoline engines) must be installed
and maintained in accordance with the National Electrical Code, ANSI/NFPA 70, or other applicable
codes. A power disconnect switch or circuit breaker must be located at the equipment. Check the
nameplate for voltage, frequency, and phase requirements. If only 3-phase power is available,
connect any single-phase rated equipment to only two wires of the 3-phase line. DO NOT
CONNECT the equipment grounding conductor (lead) to the third live wire of the 3-phase line, as this
makes the equipment frame electrically HOT, which can cause a fatal shock.
Always connect the grounding lead, if supplied in a power line cable, to the grounded switch box or
building ground. If not provided, use a separate grounding lead. Ensure that the current
(amperage)
capacity of the grounding lead will be adequate for the worst fault current situation. Refer to the
National Electrical Code ANSI/NFPA 70 for details. Do not remove plug ground prongs. Use correctly
mating receptacles.
b. Output Cables and Terminals
Inspect cables frequently for damage to the insulation and the connectors. Replace or repair cracked
or worn cables immediately. Do not overload cables. Do not touch output terminal while equipment is
energized.
3. Service and Maintenance
This equipment must be maintained in good electrical and mechanical condition to avoid hazards
stemming from disrepair. Report any equipment defect or safety hazard to the supervisor and
discontinue use of the equipment until its safety has been assured. Repairs should be made by qualified
personnel only.
Before inspecting or servicing electrically-powered equipment, take the following precautions:
a. Shut OFF all power at the disconnecting switch or line breaker before inspecting or servicing
the equipment.
b. Lock switch OPEN
(or remove line fuses) so that power cannot be turned on accidentally.
c. Disconnect power to equipment if it is out of service.
d. If troubleshooting must be done with the unit energized, have another person present who is
trained in turning off the equipment and providing or calling for first aid.
4. Fire And Explosion Prevention
Fire and explosion are caused by electrical short circuits, combustible material near engine exhaust
piping, misuse of batteries and fuel, or unsafe operating or fueling conditions.
a. Electrical Short Circuits and Overloads
Overloaded or shorted equipment can become hot enough to cause fires by self destruction or by
causing nearby combustibles to ignite. For electrically-powered equipment, provide primary input
protection to remove short circuited or heavily overloaded equipment from the line.
b. Batteries
Batteries may explode and/or give off flammable hydrogen gas. Acid and arcing from a ruptured
battery can cause fires and additional failures. When servicing, do not smoke, cause sparking, or use
open flame near the battery.
c. Engine Fuel
Use only approved fuel container or fueling system. Fires and explosions can occur if the fuel tank is
not grounded prior to or during fuel transfer. Shut unit DOWN before removing fuel tank cap. DO
NOT completely fill tank, because heat from the equipment may cause fuel expansion overflow.
Remove all spilled fuel IMMEDIATELY, including any that penetrates the unit. After clean-up, open
equipment doors and blow fumes away with compressed air.
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5. Toxic Fume Prevention
Carbon monoxide - Engine exhaust fumes can kill and cause health problems. Pipe or vent the exhaust
fumes to a suitable exhaust duct or outdoors. Never locate engine exhausts near intake ducts of air
conditioners.
6. Bodily Injury Prevention
Serious injury can result from contact with fans inside some equipment. Shut DOWN such equipment for
inspection and routine maintenance. When equipment is in operation, use extreme care in doing
necessary trouble-shooting and adjustment. Do not remove guards while equipment is operating.
7. Medical and First Aid Treatment
First aid facilities and a qualified first aid person should be available for each shift for immediate
treatment of all injury victims. Electric shock victims should be checked by a physician and taken to a
hospital immediately if any abnormal signs are observed.
Call physician immediately. Seek additional assistance. Use First Aid
techniques recommended by American Red Cross until medical help
arrives.
IF BREATHING IS DIFFICULT, give oxygen, if available, and have victim lie
down. FOR ELECTRICAL SHOCK, turn off power. Remove victim; if not
breathing, begin artificial respiration, preferably mouth-to-mouth. If no
detectable pulse, begin external heart massage. CALL EMERGENCY
RESCUE SQUAD IMMEDIATELY.
8. Equipment Precautionary Labels
Inspect all precautionary labels on the equipment monthly. Order and inspect all labels that cannot be
easily read.
EMERGENCY
FIRST AID
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Introduction
1. General
The following information is provided for the operator to familiarize himself with using the manual
properly. THE MANUAL MUST BE READ AND UNDERSTOOD BEFORE PERSONNEL ATTEMPTS
TO OPERATE, INSTALL, OR REPAIR THIS EQUIPMENT.
2. Scope
The manual covers a series of synchronous Motor-Generator Sets identified by the Specification
Numbers listed. A detailed description of the equipment and information covering operation,
maintenance, troubleshooting, repair, and overhaul is included.
3. Purpose
The manual provides information and instructions to guide and assist operator and maintenance
personnel in the proper use and maintenance of the equipment.
4. Contents
The Introduction is a List of Effective Pages which lists each page in the manual by its Chapter/Section,
and page number. Directly opposite each page number listing is a date which indicates whether the
page is original or revised.
The Table of Contents contains a list of all Chapters, Sections, and the principal paragraph titles within
each Section. The location of each listing is identified by Chapter/Section and page number. A
complete list of illustrations with their location is provided at the end of the Table of Contents.
The main text of the manual is divided into four Chapters as follows:
Chapter 1. Description/Operation
Chapter 2. Servicing
Chapter 3. Troubleshooting
Chapter 4. Illustrated Parts List
Each Chapter is divided into as many Sections as necessary. Sections are referred to by a combination
Chapter/Section number. Example, 2-3 refers to Chapter 2, Section 3.
5. Format
a. Paragraphing and Outlining
The material within each Section is divided into main subjects with applicable paragraph headings
and sub-headings as required. This method provides a means of identifying material for reference
purposes. For example;
(1) Control
a. A. Interior Panel
•(1) Protective devices
•(a) Overload relay
•(2) Contactors
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b. Page Numbering
Page numbers do not run consecutively throughout the manual. Each page is identified by the
Chapter/Section number in which it appears, and by a page number within the Chapter/Section.
Therefore, the first page in each Section is page 1. These identifying numbers appear in the lower,
outside corner of the page. Each page also bears a date located in the corner opposite the page
number. This date is either that of original issue, or of the latest revision. Any revision to the original
text is identified by a heavy black line in the left-hand margin. Illustrations follow a numbering system
similar to page numbering. The first Figure in each Section is Figure 1.
6. How to Use the Manual
a. General
This manual follows the format, rules and style proposed by members of the Air Transport
Association. Insofar as possible, information is grouped to help the user locate it quickly. All tables,
charts, diagrams, etc., as well as illustrations, are identified by Figure Number (i.e., Fig. 2) to avoid
confusion.
b. How to Locate Information
Refer to the Table of Contents for information required and where to locate it within the manual.
(1) Table of Contents
The Table of Contents provides information for easy location of all subjects contained within the
manual. The chapter and section numbers are together, e.g. 2-3, indicating Chapter 2, Section 3.
(2) List of Illustrations
The list of Illustrations follows the Table of Contents and includes the title, figure number, and
Chapter/Section, with page number location of the illustrations contained in the manual. Locate
the appropriate title in the List of Illustrations, refer to the Chapter/Section and page number
indicated.
(3) References
References are used throughout the manual. Both material in the text and illustrations may be
referred to in order to clarify or expand information and instructions. Portions of the text are
referred to by identifying the paragraph in which that material may be found. When referenced
material is located in the same Chapter/Section as the reference, only the paragraph
identification is given. For more information concerning references, refer to paragraph 5, A on
page 2.
Example:
(Ref. Para. 1, A) means the material is to be found in paragraph 1, A of the same
Chapter/Section.
When referenced material is located in another Chapter/Section, both the Chapter/Section
number and the paragraph identification are given.
Example:
(Ref. 1-2, Para. 1, A) means that the referenced material is located in Chapter/Section 1-2,
and identified by paragraph 1, A.
Components shown in illustrations, and illustrations themselves, are referenced in a similar
manner. When this type reference is made, the item number of the part and the Figure
number in which it appears are given.
Example:
(Ref. 2, Fig. 3) refers to item number 2 which appears in illustration Figure 3 of the same
Chapter/Section.
When the referenced Figure appears in another Chapter/Section, the reference will include
the Chapter/Section number.
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Example:
(Ref. 2-3; 1, Fig. 4) tells the user to refer to Chapter/Section 2-3, and to see item 1, in Figure
4.
Once a Figure number reference has been established for a series of instructional steps, the
Figure number is not repeated. Only the item numbers of parts involved are referenced.
For example, “Loosen screw (2, Fig. 6), slide out connector (4), and remove brush (6)”.
When an item is referenced without a figure number, it will always apply to the last preceding
Figure number mentioned in the text.
NOTE 1:The word See may appear in some references, as (See Fig. 2). It means exactly the same thing
as Ref., however, its usage is more direct and definite.
NOTE 2:When an “output cable” is mentioned in the manual, it refers to a multiconductor cable assembly.
A five-conductor (A, B, C, N, and E or F) cable is required when delivering power directly to an
aircraft. A four-conductor (A, B, C, and N) cable may be used on a single output machine when
delivering power to a distribution box.
7. Customer Service
If you have any questions concerning your Hobart Power Systems Group equipment, you are invited
to contact our service department by mail, telephone, or FAX.
Write: Hobart Brothers Company
Airport Systems Group
Service Department
Troy, Ohio 45373, U.S.A.
Telephone: [phone] (Service)
[phone] (Parts)
FAX: [phone]
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Table of Contents
SUBJECT CHAPTER/SECTION PAGE
SAFETY WARNINGS
INTRODUCTION
CHAPTER 1. DESCRIPTION/OPERATION
SECTION 1. DESCRIPTION 1-1 1
1. General 1-1 1
2. Special Features 1-1 6
A.ProtectiveMonitor .............................. 1-1............6
B.Pull-outTrays .................................. 1-1............6
C.VoltageRegulator............................... 1-1............6
D.TestCircuitry................................... 1-1............6
E.ElectricGovernor ............................... 1-1............6
F. Transformer-Rectifiers (Optional) . . . . . . . . . . . . . . . . . . 1-1 . . . . . . . . . . . . 6
3. Optional Equipment 1-1 6
A.QuickStartKit.................................. 1-1............6
4. Canopy 1-1 6
5. Engine, Generator and Controls
Assembly 1-1 7
A. BasicEngine .................................. 1-1............7
B. EngineManufacturer’sEquipment ................ 1-1............7
C. HobartEngineEquipment........................ 1-1............7
(1) Electric governor system 1-1 7
(a) Magnetic pickup 1-1 7
(b) Control unit 1-1 7
(c) Actuator 1-1 7
(2) Air Cleaner 1-1 9
(3) Exhaust System 1-1 10
D. Generator ..................................... 1-1...........10
E. ControlBoxAssembly .......................... 1-1...........11
(1) Generator control tray (see Figure 8) 1-1 11
(a) Resistors 1-1 11
(b) Generator output monitors (meters) 1-1 12
(c) Meter and line switches 1-1 12
(d) Receptacle connector 1-1 12
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SUBJECT CHAPTER/SECTION PAGE
(e) Tray 1-1 12
(f) Manual voltage control 1-1 12
(g) Excitation-deenergization relay 1-1 12
(2) Protective relay tray (Figure 9) 1-1 12
(a) Sensing modules 1-1 12
(b) Memory and time delay module 1-1 14
(c) Indicating lights 1-1 14
(d) Plug interlock relay 1-1 14
(e) Test bank switch 1-1 14
(f) Resistor 1-1 14
(g) Fuse-interlock relay 1-1 14
(h) Connector 1-1 14
(j) Auxiliary underfrequency relay 1-1 14
F. EngineControlPanel(Fig.10) 1-1....................... 16
(1) Engine Instruments 1-1 16
(a) Ammeter 1-1 16
(b) Oil Temperature Gage 1-1 16
(c) Oil Pressure gage and oil
pressure switch 1-1 16
(d) Hourmeter 1-1 16
(2) Engine and generator controls 1-1 16
(a) Fuse 1-1 16
(b) Engine-generator control switch 1-1 16
(c) Contactor control switch 1-1 16
(d) Indicating lights 1-1 17
(e) Fuel gage and blocking diodes 1-1 17
(f) Cold weather starting aid
control (Optional) 1-1 17
(g) Engine stop control 1-1 17
(h) Air cleaner indicator 1-1 17
(j) Test receptacle connector 1-1 17
G. VoltageRegulator 1-1 ....................... 19
(1) Controls 1-1 20
(2) Protection 1-1 20
(3) Components (See Fig. 12) 1-1 20
H. Power Module Panel Assembly . . . . . . . 1-1. . . . . . . . . . . . . . . . . . . . . . . . 20
(1) Load contactor 1-1 20
(2) Current transformers 1-1 20
(a) Ammeter current transformers 1-1 20
(b) Line-drop current transformers 1-1 20
(c) Overload current transformers 1-1 21
(3) Overload module 1-1 21
(4) Rectifier 1-1 23
6. Test Box 1-1 23
A. Description(SeeFig.14) ............ 1-1........................ 23
B. TheoryofOperation................ 1-1........................ 23
7. Dual Output Machine 1-1 24
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SUBJECT CHAPTER/SECTION PAGE
SECTION 2. PREPARATION FOR USE,
STORAGE, OR SHIPPING 1-2 1
1. Preparation for Use 1-2 1
A. General .................................1-2...................1
B. Inspection/Check.........................1-2...................1
C. InstallingOutputCables ...................1-2...................2
(1) Three-phase, AC output cable
assembly installation. 1-2 2
(2) Transformer-rectifier (T-R) cable
assembly installation 1-2 3
2. Preparation for Storage 1-2 3
A. General .................................1-2...................3
B. TemporaryStorage .......................1-2...................3
C. LongTimeStorage(Over30days)...........1-2...................4
3. Preparation for Shipment 1-2 4
SECTION 3. OPERATION 1-3 1
1. General 1-3 1
2. Operating the Generator Set 1-3 1
A. Pre-startInspection.......................1-3...................1
B. Normal Engine Starting Procedures . . . . . . . . . . 1-3. . . . . . . . . . . . . . . . . . . 1
C.ColdWeatherEngineStartingProcedures.....1-3...................4
D. Preparation for Power Delivery
(NormalAutomaticVoltageControl).......1-3...................4
E.PowerDelivery(AutomaticVoltageControl) ...1-3...................5
F. Preparation for Power Delivery (Manual
VoltageControl) .......................1-3...................6
G. PowerDelivery(ManualVoltageControl).....1-3...................6
H. DiscontinuePowerDelivery ................1-3...................6
J. StoppingtheEngine ......................1-3...................6
3. Transformer-Rectifier Operation 1-3 6
A. DirectCurrentPowerDelivery...............1-3...................6
B. SimultaneousOperationof28.5-VT-R’s......1-3...................7
C. Simultaneous 28.5-V DC and
115-VACPowerDelivery.................1-3...................7
D. Simultaneous 112-V DC and 115-V AC
PowerDelivery.........................1-3...................7
4. Test Box Operation 1-3 7
5. No. 2 Output Operation 1-3 8
A.PowerDelivery............................1-3...................8
B.DiscontinuePowerDelivery.................1-3...................9
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SUBJECT CHAPTER/SECTION PAGE
CHAPTER 2. SERVICING
SECTION 1. MAINTENANCE 2-1 1
1. General 2-1 1
2. Inspection 2-1 1
3. Lubrication 2-1 1
A. General ................................ 2-1.................. 1
B. ACGenerator ........................... 2-1.................. 1
C. GeneratorControls....................... 2-1.................. 1
D. Trailer ................................. 2-1.................. 1
E. Engine ................................. 2-1.................. 5
(1) Lubrication schedule 2-1 5
(2) Oil specification 2-1 5
(3) Oil viscosity 2-1 5
(4) Change engine oil 2-1 5
(5) Change oil filter element 2-1 7
F. EngineAccessories ...................... 2-1.................. 7
(1) Starter 2-1 7
4. Air Cleaner Service 2-1 8
A. CartridgeRemoval ....................... 2-1 ................. 8
B. CartridgeInstallation ..................... 2-1 ................. 9
5. Engine Fuel 2-1 9
A. Quality ................................. 2-1.................. 9
6. Generator Maintenance 2-1 9
A. Cleaning ............................... 2-1.................. 9
B. Adjustment ............................. 2-1.................. 9
7. Drive Belts 2-1 9
A. FanBelts ............................... 2-1.................. 9
B. CheckBeltTension....................... 2-1.................. 9
C. AdjustingAlternatorBeltTension........... 2-1................. 10
D. Belt Replacement . . . . . . . . . . . . . . . . . . . . . . . . 2-1 . . . . . . . . . . . . . . . . . 10
8. Service Helps 2-1 10
A. Wiring ................................. 2-1................. 10
B. ControlBoxTrays ....................... 2-1................. 10
(1) Tray removal 2-1 10
(2) Tray installation 2-1 11
C. GeneratorExciter ........................ 2-1................. 11
(1) Preparation for exciter removal. 2-1 11
(2) Exciter removal: 2-1 11
(3) Exciter installation: 2-1 11
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SUBJECT CHAPTER/SECTION PAGE
D. EngineControlPanel .....................2-1..................11
(1) Tilt out engine control panel 2-1 11
(2) Reinstall engine control panel 2-1 12
9. Transformer-Rectifier Maintenance 2-1 12
SECTION 2. INSPECTION / CHECK 2-2 1
1. General 2-2 1
2. Engine 2-2 1
A. Fuel(SeeFig.1fortimeschedules)..........2-2...................1
B. Lubrication..............................2-2...................1
C. V-Belts .................................2-2...................1
D. ExhaustSystem..........................2-2...................1
3. Electrical System (12-V DC) 2-2 1
A. Lights ..................................2-2...................1
B. Fuses ..................................2-2...................1
C. WiringandConnections ...................2-2...................4
4. Electrical System (115-V AC) 2-2 4
A. MonitoringInstruments....................2-2...................4
B. IndicatingLights..........................2-2...................4
C. ProtectiveModules........................2-2...................4
D. WiringConnections.......................2-2...................4
5. Inspection of Transformer-Rectifiers 2-2 4
SECTION 3. ADJUSTMENT/TEST 2-3 1
1. General 2-3 1
2. Generator Set Test 2-3 1
A. Pre-operationTestProcedures .............2-3...................1
(a) Flashing exciter field using test box. 2-3 1
(b) Flashing exciter field without test box. 2-3 4
B. OperationalTestProcedures ...............2-3...................5
3. Generator Set Adjustment 2-3 9
A. GeneratorAdjustment.....................2-3...................9
B. GeneratorControlAdjustments.............2-3...................9
(1) Adjust manual voltage control, variable resistor. 2-3 9
(2) Adjust 400-Hz voltage regulator 2-3 9
C. BasicEngineAdjustments .................2-3...................9
(1) Exhaust valve adjustment. 2-3 9
(2) Exhaust valve bridge adjustment. 2-3 9
(3) Fuel injector timing adjustment. 2-3 9
(4) Idle speed, speed limiting, and
overspeed adjustments. 2-3 9
D. Alternatorandfanbeltadjustment ..........2-3..................10
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SUBJECT CHAPTER/SECTION PAGE
E. ElectricGovernorSystemAdjustment....... 2-3................. 10
(1) Actuator linkage adjustment 2-3 11
(2) Magnetic pickup adjustment 2-3 11
(3) Governor Control Unit Adjustment 2-3 13
(4) Magnetic pickup signal 2-3 13
4. Generator and Exciter Test 2-3 15
5. Diode Test 2-3 15
6. Test and Adjustment of Transformer-
Rectifiers 2-3 16
7. Additional Tests for Dual Output Units 2-3 16
CHAPTER 3. TROUBLESHOOTING
SECTION 1. TROUBLE SHOOTING
PROCEDURES 3-1 1
1. General 3-1 1
2. Trouble Shooting Chart (Figure 2) 3-1 1
A.Description.............................. 3-1.................. 1
B. Use of the Trouble Shooting Chart . . . . . . . . . . 3-1 . . . . . . . . . . . . . . . . . . 1
3. Equipment for Troubleshooting 3-1 2
4. Safety - WARNING: 3-1 2
5. Parts Replacement 3-1 2
6. Test Values 3-1 2
7. Checking Connections and Leads 3-1 3
8. Electric Governor Trouble Shooting 3-1 3
9. Engine Trouble Shooting Procedures 3-1 3
A. General................................. 3-1.................. 3
B.LocatingaMisfiringCylinder............... 3-1.................. 3
C. CheckingCompressionPressure........... 3-1.................. 4
D. Interpretation of Compression
PressureRecords........................... 3-1.................. 4
E. CausesofLowCylinderPressure........... 3-1.................. 5
F. FuelFlowTest(seeFig.7)................. 3-1.................. 4
10.Illustrations 3-1 5
11. Troubleshooting Transformer-
Rectifiers (T-R’s) 3-1 5
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SUBJECT CHAPTER/SECTION PAGE
CHAPTER 4. ILLUSTRATED PARTS LIST
SECTION 1. INTRODUCTION 4-1 1
1. General 4-1 1
2. Purpose 4-1 1
3. Arrangement 4-1 1
4. Explanation of Parts List 4-1 1
A. Contents................................4-1...................1
B. PartsListForm ..........................4-1...................1
(1) “FIGURE-ITEM NO.” Column 4-1 2
(2) “HOBART PART NUMBER” Column 4-1 2
(3) “NOMENCLATURE” Column 4-1 2
(4) “EFF” (Effective) Column 4-1 2
(5) “UNITS PER ASSEMBLY” Column 4-1 2
SECTION 2. MANUFACTURER’S
CODES 4-2 1
1. Explanation of Manufacturer’s
(Vendor)CodeList 4-2 1
SECTION 3. PARTS LIST 4-3 1
1. Explanation of Parts List Arrangement 4-3 1
2.Symbols and Abbreviations 4-3 1
SECTION 4. NUMERICAL INDEX 4-4 1
1. Explanation of Numerical Index 4-4 1
CHAPTER 5. OPTIONAL EQUIPMENT
CHAPTER 6. MANUFACTURER’S LITERATURE
UNUSUAL SERVICE CONDITIONS
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TITLE = Chapter 1. Description / Operation
Section 1. Description
1. General
The Hobart generator sets covered by this manual are designed to provide power for maintenance and
startup of aircraft having 115/200-V AC, 3-phase, 400-Hz electrical systems. Five different series of
generator sets are covered by this manual. All generator sets in these series are driven by a Deutz
Diesel engine. Within the five different series of generator sets, 28 specifications of generator sets have
90-kVA, 400-Hz output power ratings. One specification, Specification Number 7126A has a 100-KVA,
400-Hz output power rating.
Generator sets are identified by a Specification Number which includes the Series Number and a dash
number suffix
(i.e. -1, -2, etc.) . The suffix number indicates either the mounting design of the generator
set and/or one or more other major distinguishing features. Refer to the identification chart within this
section l to identify a particular unit.
Generator sets are commonly referred to as “ground power units”, however, the equipment will be
identified in the manual as generator sets. Generator output power is principally used for operation of an
aircraft’s electrical equipment when the on-board generators are not operating. For voltage and current
requirements, physical dimensions, weight and general output characteristics of a typical generator set
covered by this manual, refer to Figure 2.
Refer to Fig. 1 for identification of the main components . The equipment is a combination
motor-generator unit mounted on a welded steel frame. A superstructure supports the control box,
motor switch, load contactors, and other equipment. The output terminal is located to the rear at the
engine end, and the input panel is located to the front at the motor switch end. Right and left are
determined by standing at the rear and facing the machine. A sheet metal housing, or canopy, protects
electrical components. Removable panels and covers provide access for servicing and maintenance.
OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
February 28/94 Chapter 1-1
Revised Page 1

1. Voltage Panel & Contactor
Access Door
2. Engine Exhaust Pipe
3. Battery Storage Compartment
4. Alternator & Motor Starter
Access Door
5. Air Filter Access Door
6. Fuel Fill Pipe
7. Lights
8. Canopy
9. Left Side Engine Access Door
10. Output Receptacle
11. Engine Controls & Panel
Access Door
12. Window
13. Trailer Hitch
14. Trailer Frame
15. Lifting Yoke
Generator Set
Figure 1
OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
Chapter 1-1 February 28/94
Page 2 Revised