14.
Electrical Systems & Traction Alternator Design & Aux. System
Design
14.1
Locomotive Electrics- Basic AC-AC System:
The system basically uses diesel engine, alternator, rectifier, d.c. link,
invertor(s) and asynchronous motors. The alternator is directly coupled to the
diesel engine. The frequency of the alternator output varies with the speed of
diesel engine. The voltage is rectified and the power is fed through a d.c. link
to the invertor of the tractive system. Drive system uses asynchronous
motors. Asynchronous motor when used on railway vehicle has to be
supplied variable alternating voltage of variable frequency (VVVF). This is
accomplished by the invertor the input to which is d.c. voltage through d.c.
link. All AC-AC diesel locomotives employ this principle. The number of
invertors and the size of the alternator depends on the amount of energy to be
converted.
ENGINE
GENERATOR
INVERTOR
TRACTION
MOTOR
G
3~
=
M
3~
3~
The electronic control system ensures that the correct control inputs
are given to the invertor. It also controls and monitors the diesel engine, the
alternator and the other auxiliaries of the locomotive. It is the central control
unit which ensures that the locomotive operates optimally.
14.2 Main Alternator and Companion Alternator
Alternator is foot mounted with flange coupling with the engine.
Alternator TA17 is a 3 phase, 10 pole machine equipped with two
independent and interwoven sets of stator winding. It is basically two
generators in one - two sets of stator windings, permanently connected in
series, work with a rotating field common to both the windings in order to
provide a higher generator output voltage, which is a basic requirement of a
low current high voltage generator used on AC-AC locomotives.
The main alternator has a companion auxiliary generator CA 6 for
power supply to large auxiliaries. It is also the main excitation source for the
main alternator. The companion alternator is an electrically independent
machine and is mechanically coupled on the main shaft of the traction
alternator. The companion alternator rotor field is excited directly by auxiliary
supply of the locomotive (74+4 VDC). It receives the excitation current from
the auxiliary generator through slip rings located adjacent to the slip rings of
the main generator. The output voltage is directly proportional to the speed of
rotation but varies to some extent with change in alternator temperature and
load.
Both these alternators are forced air cooled. A dedicated blower
coupled to the engine crankshaft provides cooling to the Alternator / Rectifier
system. The air flow pattern has been depicted below.
Axial & Radial Cooling In EMD
Alternator
AIR FLOW
STS
STACKS
CORE
AIR FLOW
COMPANION ALTERNATOR
RECTIFIER
ALTERNATOR MAIN WINDING
14.3
Rectifier
AC output from the main alternator is supplied to air cooled rectifier.
The rectifier assembly consists of high current, high voltage silicon diodes
connected in 3 phase full wave bridge rectifier circuits. RC circuits are
connected to suppress the transients signal.
14.4
Traction Motor
The asynchronous motor with a squirrel cage rotor is the simplest of
all electrical machines. When fed by a 3- phase alternating voltage, a
magnetic field rotates in the stator. The speed of rotation of this field is directly
proportional to the frequency of the A.C. voltage. The rotating magnetic field
causes the rotor to turn at a slightly lower speed due to electric slip. This
difference in speed is responsible for the development of the torque.
The only winding fed with voltage in the asynchronous motor is housed
in stator. To prevent hot-spot developing in winding overhang, it is directly
ventilated. The winding is impregnated under vacuum. There are no exposed
metallic parts, so that excellent protection is assured. The rotor is squirrel
type, i.e. it consists of un-insulated copper bars joint to sturdy short-circuiting
rings. There is no commutator, sliprings, Brushgear or anything similar.
Following aspects are given primary importance while designing AC
traction motors :
 Vibrations and shocks from track
 Envelope dimensions - more torque packed in small space
 Reliability - TM subjected to different elements like movement of
locomotive, dirt heat & humidity
 Presence of transients
 Requirement of starting and road characteristics
14.5
Electrical Control Cabinet No. 1 (HVC)
Electrical control cabinet is for mounting of the following main
equipment :
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Main Control Panel
DC Link switch gear
Braking contactors
Circuit breakers
EM2000 computer chassis
EM2000 support hardware
GFC, GFD & IMGF
SCR bridge
Power supply for GTO1 & GTO2
TCC blower contactors - six numbers
IB1 ,IB2 , IBKBL1 , IBKBL2 transducers
Display Screen on ECC#1 door
Engine Control Panel
TMA transducer
74 V receptacles

The routine testing of HVC is an elaborate process . There is a
dedicated test station which is microprocessor controlled and
has the facility to check the important aspects related with
performance and reliability, viz., continuity of all the wires on the
cabinet and actual operation of the relays, switches and
contactors. All the test data is logged, abnormalities identified
and a printout is taken for undertaking the rectification work.

The software for the test station is written in HP Basic. EM
2000 Modules, which are not mounted at this stage, are
therefore not tested at EMD. The cabinet complete is
despatched to DD , London, OT.
14.5.1 Design Aspects Of ECC#1
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Ventilation Engineering of the cabinet has been done based on
the cooling requirements of major components, e.g. power
chassis , EM2000 , SCR Bridge Assembly. Main duct has been
constructed along the wall sided which branches to supply air to
the components.
The panel is modular so as to facilitate quicker assembly.
The cabinet is pressurised to avoid ingress of dust etc. A
pressure of 2 to 3” of water gauge is maintained.
No electro pneumatic contactors are used on this cabinet.
Components and cables of a common electrical circuit are
grouped together (e.g. GFC, GFD, RE2 , RE32, CA32 and the
SCR Bridge) in order to reduce EMC interference.
14.5.2 Electrical Cabinets 2 & 3
Electrical cabinet number two and three are smaller cabinets than the
HVC. These cabinets consist of the following components:
Cabinet# 2.

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Auxiliary Generator circuit breaker
ST & STA contactors - for starting of engine.
RE11 & RE12
BCASM - Battery Charging assembly
Provision for Shunt DC
DVR - Digital Voltage Regulator
Inductor L4,5,6
Air Filter
Cabinet# 3 (AC Cabinet)





146
Cooling fan contactors -six numbers
Terminal Boards
MRPTs- Main reservoir pressure transducer
DIP80 - Diode Panel and CMUX hardware for multiplexing
Air Filter
EM 2000
EM2000 is a modern locomotive computer control system. The
system, has effectively replaced the outdated electronic and IC-based
control systems used earlier. Some of the basic features of the system,
inter alia, are
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
Significant reduction in number of control modules
Better fault detection of components
Self diagnostics and self tests to aid in troubleshooting
Memory archive and data snap shot
The main computer chassis contains the following modules
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One CPU module which uses a 32 bit Motorola 68020 16 Mhz
microprocessor
Three Digital Input/Output (I/O) modules ( DIOs)
One communication module (COM)
One Analogue to digital and digital to analogue module ( ADA)
One memory module ( MEM )
The computer chassis is split in the middle by a metal partition.
The right houses the high speed data modules, CPU, MEM and COM.
The left side houses the I/O handlers, i.e., ADA and DIOs. On the front
of all the above modules, Fault LEDs are mounted on the face plate.
These LEDs illuminate for a couple of seconds as part of the ‘power up’
diagnostic routine. These are tripped by watchdog timer faults,
database errors or through certain other conditions satisfied in the
software.
14.6.1 CPU Module
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CPU Module is the brain of the entire computer system. which
processes all incoming locomotive parameters and controls
locomotive responses to derive the operating characteristics. It
contains the following hardware
32 bit Motorola 68020 16.5 Mhz microprocessor with a math coprocessor for enhancing the speed and efficiency of information
processing
Motorola 68881 floating point co-processor running at 16.5 M Hz
512 KB ‘flash prom’ memory storage which can be easily
reprogrammed in the field with the aid of laptop computer
communicating through an RS 232 port or through special module
called MMB. While the time required to load a programme from
MMB is approximately 15 seconds, the same through laptop
computer is 15 minutes. The programme storage can be upgraded
to 1 MB.
128 KB static RAM for data storage, which can be upgraded to 1
MB
64 K B static dual port RAM for inter processor communication .
6840 Programmable timers which are use for periodic inputs and
out puts.
RS232 Serial port with programmable baud rates.
RS422 Serial port with programmable baud rates. One of these
port is dedicated to the display unit.
CPU module plays a very active role in SCR gating sequence as it
sends the weak gate signals to the FCD and receives information from the
zero cross detection circuit on the FCF so that it knows what phase angle
to fire at to achieve desired alternator excitation.
14.6.2 Digital Input /Out Put (I/O) Modules
The digital inputs and output to and from EM2000 are handled by
three such modules. Each module has 24 input channels and 26 output
channels. This module works as an interface between locomotive’s 74
VDC control system and the computer’s 5 VDC system.
The DIO input channels are either +74 VDC or 0 VDC signals
depending upon the relay/contactor status, picked up or dropped out. The
DIO output channels, in turn, depend upon the logic built-up, either +74
or 0 VDC, so as to pickup or drop out the relay/contactor by supplying the
gating power to the field effect transistor.
Multiplexing is a selective monitoring process through which several
inputs may be monitored through the use of only one input channel. In
other words not all inputs need be monitored constantly.
14.6.3 Communication Module
All the computers on board i.e. EM2000, Sibas 16, electronic brake
computer etc. need communication with each other. The two traction
computers SIBAS 16 communicates to each other and to EM2000. The
link carries all sorts of the information which, inter alia, could be data
ranging from torque requests, feed backs to contactor requests and
acknowledgements to fault annunciation etc.
14.6.4 Analogue To Digital And Digital To Analogue Module
It is responsible for converting analogue input signals to digital signal
for processing the data and digital information from the CPU into an
analogue signal that is required by the receiving device (external
ammeters). It has within it 

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Differential analogue inputs
Hall effect transducer current inputs
General purpose frequency inputs
measurements
for
period
&
frequency
14.6.5 Memory (Archive Memory) Module
This module holds dynamic locomotive parameters and archive data
that are required to remain intact even in case of power failure. It has one
128 KB battery backed static RAM . which can be upgraded. The amount
of data stored with each fault is substantial. For selected faults such as
ground relay, data is stored from each of the 5 seconds before the
occurrence of the fault.
14.6.6 Panel Mounted Modules
Many other modules, called panel mounted modules, belonging to the
EM2000 control are directly mounted to the rear panel of the HVC. These
modules are-
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14.7
Analogue signal conditioner modules- ASC 300- scales and filters
analogue signals.
Firing control driver - FCD 300 - amplifies SCR gate signals to control
the CA6 output for main alternator field.
Firing control feedback - FCF 300 - scales three phase companion
alternator frequency feedback
Voltage amplifying module- VAM 300- trainline 24 T interface for slow
speed pace setter control ( optional for GT46MAC)
Trainline filter - TLF 300- scales and filters digital data from trainline
signals.
Power Supply
EM2000 control system requires different power supply and conditioner
modules which are mounted in the Power Chassis. These modules
are-
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14.8
PSM 300 module for Power supply of +5V DC - the main power supply
for EM2000
PSM310 module for +12VDC PSM 320 module for Power supply of +15VDC - for feed back circuits
like hall effect transducer devices & analogue circuits viz. magnetic
speed pickup
PRG300 power regulator is the power conditioner for the PSM modules
and functions properly even with the voltage variation within 20-95
VDC. It regulates the output voltage between 64-77 VDC when the
input voltage is between 25-68VDC. If the input is beyond this range,
there is a variation in the output within the acceptable limit.
Development Of Software
The software for EM2000, or any sophisticated computer system, is
developed by EMD in the following stepsDevelopment of Sales Specification
Finalization of System Specification
Development of Software Specification
Actual Software Code Writing
Software Test
A locomotive characterisation report, which identifies the exact type of
the equipment used, defines all the functions and indicates the value of all the
parameters, is issued by the Product Engineering group. This report forms
the basic locomotive document and the foundation on which the entire
software of the locomotive is built up.
14.9
Locomotive Performance & Train Run Simulation
EMD has developed versatile computer simulation programme for train
run simulation and offers this service to all its customers on commercial basis.
14.10
Thyristors, GTOs And AC Motor Control
The thyristor offers immense advantages like compactness, high
reliability, excellent time response and low loss. An added advantage of using
thyristors in power converters for drive control is the easy manner in which
they can be adopted for sophisticated feed-back schemes. As a result,
microprocessor control of thyristor-drive systems can provide great
operational flexibility.
GTO thyristor or the ‘gate turn-off thyristor’ is referred to briefly as
‘GTO’. It is a four-layer silicon semiconductor device and is an improvement
over the normal, slow devices used in line commutated converters into
increasingly faster devices with better dynamic characteristics by refining the
gate geometry.
GTO allows fast turn-off with a negative current impulse by means of
the gate alone, which is not possible with the conventional thyristor. This
results in simplification of the converter circuitry.
A three-phase inverter system with variable voltage and frequency
output, is achieved by using GTOs for speed/torque control of 3-phase
asynchronous motor.
14.11 Pulse-Width Modulation
INPUT CONVERTER
D C L I N K C A P.
Six load carrying thyristors and six free wheeling diodes are the
basic ingredients of three phase bridge inverter circuit. A DC-link capacitor is
added for stabilising the DC-link voltage and supplying of magnetising
reactive power required for induction motor.
+
+
+
M
3~
+
+
+
V O L T. - S O U R C E I N V E R T E R
PWM INVERTER CIRCUIT
FIG-7
Amplitude and frequency setting take place solely by the principle of
pulse width modulation (PWM). The max. possible amplitude of the phase-tophase output voltage Uv depends on the magnitude of the DC link voltage
Ud such that,
Uv = 0.78 Ud
This method of voltage control of an inverter is known as pulse-width
modulation.
14.12 Locomotive Cables, Wire Running And Layout
GT46MAC locomotive employs mainly the Exxon cables. The cables used on
this locomotive are classified into following categories:
 Category 0 These are used in the circuits with extremely high
potential requiring increased creepage distances.(DC link cables)
 Category 1These are used in the circuits of high potential and high
current levels ( Generator , Traction Motors and Battery Trunk Lines to be
routed through cleats)
 Category 2 These are used in the circuits of AC voltage and high
current DC voltage (conductors larger than AWG#12, not including traction
circuit)
 Category 3 These are used in locomotive control logic wiring
(typically 74 V DC including all electro mechanical devices)
 Category 4 Low voltage and energy control signal lines ( shielded
multi conductor cables, and signals below 24 V)
 Category 5 Specific conductors requiring independent routing
(communication radio antenna cabling, or high energy unfused
conductors)
14.13 Locomotive Cabling:
 All the cables which are to be laid out on the underframe are performed
with end lugs, connectors, sockets provided. For this purpose there is a
separate section consisting of the wire measuring and cutting table, end
shearing machine for preparing the ends and crimping of the lugs. The
bigger size lugs are made in house using metallic tubes on a lug making
machine, others are bought out from trade.
 The cabling on the underframe is done in the belly up position (in the overturned position)
 The cable layout has been so planned that all the cables are planned to
run on only one side of the underframe i.e. on the left side in the belly up
position looking from the short hood side.
 Brackets for the rubber cleats are welded to the underframe before the
laying of cables is started and are located through out the length of the
underframe.
 The power cables are laid first followed by the control cables. For the
control wires running between EM2000 and Traction Control Cabinet use
is made of special channel having EMI protection and runs on the top
corner through out the length of U/frame.
 The cleats used are of BUNA-N rubber. Special clamps for smaller
diameter cables are used which have a rubber lining to prevent the
damage of insulation of cable due to vibrations and prevention from
grounding.
 Splicing of the power cable going into the traction motor is done to avoid
running of large number of cables from TCC and the exposed joints are
covered using heat shrinkable silicon rubber boots.
 Cutouts on the underframe are already provided for the cables and no oxy
cutting of the underframe is done at all during the cabling stage.
A separate wire running list as per zone, wire category and wire tag is
prepared and circulated to the shop to give details of wire running from source
to destination. The wire running list is derived from the locomotive schematic
as soon as the same is ready.
14.14 Electrical Schematics
The schematic of GT46MAC consists of two major parts - EMD
schematics and Siemens schematic. The schematic conventions followed by
EMD and Siemens are different.
The major equipment covered by the two sections of schematic are as
underEMD schematic - EMD manufactured or vendor supplied equipment
viz. alternator - rectifier, locomotive computer, electrical control cabinets
including all switches, contactors and relays, auxiliary machines, safety and
alarm circuits, third party equipment like radar etc.
Siemens schematic - Siemens manufactured equipment viz. inverter
and inverter control equipment, traction computer and traction motors.
The EMD schematic is built around the main block diagram of the
electrical equipment of the locomotive. The schematic is a representation of
the hard wiring along with the connection/termination details of the equipment.
All the computer/microprocessor modules, which control the operation of the
hardware like relays, contactors etc., have been represented as a block. The
logic used by EMD is not known.
All the electrical sub-assemblies like ECCs, control consoles etc. have
been allocated a zone identification. This schematic also explains the various
wiring nomenclature used in the EMD schematic. For locating any item, the
equipment locator chart provided in the schematic can be used which
identifies location based on the zone in which the equipment in question lies
on the locomotive and schematic sheet no. along with the location on the
schematic sheet. Similarly, the circuit for any function like engine cooling
control, engine governor control, traction motor bearing temperature probe
etc. can be located easily in the schematic by using an alphabetical index. In
addition, locator charts based on digital & analogue input/output functions
employed on EM 2000. A chart detailing the location of various switches and
circuit breakers as well as the sequence of operation of main interlock contact
of the switches is also provided in the schematic.
The schematic is very versatile and the category, size and specification
of any wire can be read straightaway from the connecting points. In addition,
details of all plugs and receptacles are also provided clearly indicating the
used & potential free pin numbers. Details of terminal boards are also given
with internal & external connections with locomotive wire numbers.
The schematic can be divided into three strings of control viz. Battery
(i.e. on battery side & past battery knife switch), local control (PA / NA string)
& control (13T/4T string). The schematic shows the interfacing with the
inverter cabinet (TCC1 & TCC2) and other third party.
The Siemens schematic has been drawn by Siemens and is annexed
to the EMD schematic. As indicated earlier, this schematic is meant largely for
inverter and inverter control equipment, traction computer and traction
motors. The schematic gives the details of the arrangement of GTOs along
with other devices like anti parallel diodes, snubber capacitors and resistors
etc. The protection circuits including the hard and soft crowbar circuits for
protection of GTOs, have been shown in the schematic. The interface and
connections to the SIBAS traction computer have also been shown.
14.15 Integration Of Electrics With Engine And Other Mechanical
Systems
The following mechanical aspects which are closely linked or interfaced
with the electrics of the locomotive are 
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Coupling of alternator with engine
Torque requirement of the engine and starter motor requirement
Engine cooling system interface with EM 2000
Engine cooling fan design and air circuit