FIELD OF INVENTION :
The invention relates generally to manufacture of alternators for diesel-electric engines, and
particularly to the manufacture of a brushless alternator for 1400 HP diesel electric multiple
unit applications, which is compact and light in weight.
BACKGROUND AND PRIOR ART:
Indian Railway is manufacturing a self propelled 1400HP High Power Diesel Electric Multiple
Unit (HHP OEMU) consisting of one driving power car (OPe) and three Trailer Cars. The
driving power car (OPe) is powered with 1400HP on-board Oiesel Engine and AC/AC
transmission system. The engine, coupled to alternator is mounted in the longitudinal
direction on the floor of the power car. The alternator is used for providing power supply
on continuous basis as per OEMU application and operating site condition of temperature
range 0 deg to 55 deg C, humidity 40% to 100% , limit of noise, vibration, heat & exhaust
gases, heavy rainfall and flood water level of 178 mm above rail. It is also required that the
alternator shall deliver power for a maximum operating speed of 100 kmph.
In the driving power car, there is extreme shortage of space. Continuous efforts are there to
reduce the size of the machines, while ensuring that their performance is not compromised.

Moreover, the weight of any machine plays an important part because the weight has to be
continuously hauled by the DEMU throughout its operating life. The weight to be hauled by
an engine has direct bearing on its fuel consumption.
The application therefore needs an alternator which has reduced size and weight as
compared to the alternators for similar operations in the prior art.
The present invention seeks to overcome the above drawbacks of the prior art.
OBJECTS OF INVENTION :
It is therefore an object of the invention to provide a new type of brushless alternator,
suitable for self propelled 1400HP High Power Diesel Electric Multiple Unit (HHP DEMU)
application which has reduced size and weight.
Another object of this invention is to provide a brushless alternator for self propelled
1400HP High Power Diesel Electric Multiple Unit (HHP DEMU) application with the same
mounting arrangement and dimensions for easy replaceability.
A further object of the invention is to provide a brushless alternator with a tubular frame.

' Yet another object of the invention is to provide an alternator with a high power-to-weight
ratio.
SUMMARY OF THE INVENTION:
In line with the objects of invention, there is provided a new brushless alternator, in
particular for self propelled 1400HP High Power Diesel Electric Multiple Unit (HHP DEMU)
application which is applicable under various specified load conditions of traction at all
notches of the diesel engine.
The frame is of tubular construction, sturdy and light in weight. The frame, pedestal plates
and end-shields are designed such that the alternator can be easily assembled and
dismantled, if necessary. Lifting lugs are installed on the frame for lifting with a
conventional overhead hoist. A removable drip-proof, louvered cover in two halves encloses
the exciter and diode wheel.
The brushless alternator of the invention is of compact design with a high power to weight
ratio, and is suitable for coupling and aligning with diesel engine. A capsule type wound
stator is provided for the alternator. The alternator is provided with an auxiliary exciter
between the bearing arrangements for main alternator field excitation and has many
other features disclosed hereunder. The features have been achieved by optimised design
for achieving reqUired performance of the self propelled 1400HP High Power Diesel Electric
Multiple Unit (HHP DEMU).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates VI characteristic curve of the brushless alternator for 1400HP DEMU
according to the invention.
Fig. 2 illustrates sectional diagram of the invented brushless alternator displaying all the
components.
Fig. 3 illustrates outline diagram of the brushless alternator according to the invention
displaying mounting of the alternator.
Fig. 4 illustrates the difference between the alternator according to the present invention
and that of the prior art, shoWing the arrangement of exciter, diode wheel and bearing
assembly.
The invention will now be described in detail in an exemplary embodiment as depicted in the
accompanying drawings. There can however be other embodiments of the same invention,
all of which are deemed covered by this description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The bushless alternator according to the preferred embodiment, is rated at 980 KVA, 703V,
805 A at 1800 RPM.

As illustrated in Fig 2, the stator core (3) is made of a plurality of one-piece low loss steel
laminations (2), stacked together to form a complete stator core construction with core
clamping plates (5) at both ends. The stator coils (1) are class "H" insulated, using the best
quality insulating material and inserted in stator slots.
Stator coils (1) of insulated copper are made on a former which are placed inside the slots in
core and connected to the form of a 3-phase winding. The stator coils, which have multiple
number of turns, are consolidated together before insertion in to the slots.
The 3- phase electrical connection of the stator winding is brought out for supply by
connection rings (9). Bus-bars (13) are bolted to these rings and connected to terminal box.
The alternator stator core (3) is built up of one-piece low loss steel laminations (2) which are
assembled under pressure to form the stator core. This stator core (3) is rigidly fixed on to
the frame (4) by means of a key.
The magnet frame (4) is of tubular construction, sturdy and light in weight. The frame and
end-shields (6,7) are designed such that the alternator can be easily assembled and
dismantled, if necessary. Eyebolts (8) are installed on the frame for lifting with a

conventional overhead hoist. A steel wrap-on cover of drip-proof construction encloses the
frame assembly. A removable drip-proof, louvered cover in two halves encloses the exciter
and diode wheel.
The rotor of the alternator has a shaft (14) proVided with a set of rim punching assembly
(15) with dovetail groove. The pole and coil assembly (16) is fitted in this dovetail groove.
Pole and coil assembly (16) comprises pole assembly made of sheet steel punching which
are retained from both ends by end plates . Field coils are assembled on pole assy. The pole
and coil assembly is locked in the dovetail of the rim punching assembly (15) by means of
tapered keys. All field coils are connected in series with copper connectors joined by bolting.
The rotor core is made from a plurality of rim punching, stacked together under pressure
and fitted on the shaft (14) with a key. The pole punching, of salient pole construction, is
stacked together to form a pole assembly.
The exciter consists of two basic component assemblies, the stator field assembly (12) and
the main rotor assembly comprising of the rotating exciter armature (18) and Diode Wheel
assembly (19). The exciter field assembly (12), consist of poles assembled along-with their
field coils and are bolted to the NDE end-shield (7). The exciter is mounted on shaft (14).

Exciter armature core is made of sheet steel lamination stacked together and armature coils
of enameled copper are placed inside the slots in core and joined together in the form of 3-
phase winding.
The exciter stator core made of sheet steel lamination, has a pole type configuration. The
exciter stator core laminations are stacked together and field coils are placed on the poles.
The Held coils are joined together in series by brazing the leads.
Diode wheel assembly (19) is mounted on the shaft (14) and the assembly consists of a full
wave rectifier bridge made of six semi-conductor devices mounted on aluminum heat sinks
and are retained in the heat-sink assemblies with retaining nuts & washers.
The diode wheel assembly and the exciter assembly (18) are sleeve mounted on the shaft
inside the magnet frame, before the bearing assembly NDE (11) for better stability and
negligible vibrations.
During operation of the alternator, the three phase voltage generated in the exciter armature
(18) is applied directly to the Diode wheel assembly (19). The forward polarity diodes
mounted on one heat-sink and the reverse polarity diodes on the other heat-sink are
connected to form a three phase, full-wave rectifier bridge. The Diode wheel assembly (19)
rectifies the alternating current supplied by the exciter armature (18).

Exciter current for the stationary field coils is supplied by the alternator through an excitation
control system at all eight notches. The alternator is designed with a self contained cooling
system which circulates cooling air through the machine. Ambient air is drawn into the
machine through louvered openings at the exciter end of the machine by a large capacity
blower mounted at the drive end. The warm air is exhausted to atmosphere through the
screened opening enclosing blower fan (17).
To achieve the object of making a compact alternator, the armature core length was reduced
considerably. The armature core length was reduced from 625 mm in earlier alternators to
425 mm, thereby reducing the core length by 32%. In consequence, to achieve the desired
output values, the flux density in stator teeth core, gap flux density on load, flux density in
rotor rim on load, maximum teeth flux density as well as the ampere-turns per pole had to
be increased.
It is known that increase in flux density has a direct fall-out of increased losses.
Therefore, an optimization had to be carefully conducted to allow the various flux densities
to be altered, keeping the stator and field copper losses within tolerance limits, so that the

alternator can deliver its rated output at an acceptable overall efficiency. The following table
of comparison provides the various values.
As a result, the total weight of the machine was reduced from 4920 Kg to 4040 Kg, which
works out to be 17.88%.
The overall length of the alternator was also reduced from 2430 mm in the prior art to 1953
mm, which is a reduction of 19.62%.
The compact alternator in accordance with the invention is provided with a smaller cooling
fan having 750 mm dia as compared to 940 mm in the prior art. This has resulted in
reduction of noise level of the machine from 110 dB to 101 dB.
Referring to Fig. 4, the exciter of the alternator is provided inside the stator frame (4) before
the bearing NDE (11), in contrast with the exciters of similar alternators of prior art, which
were placed outside the stator frame, after the bearing on NDE side. This has contributed to
reduction in the length of the machine. The same holds true for the diode wheel assembly.
Fig. 3 shows the mounting arrangement of the alternator. It has been ensured that the
alternator has the same mounting dimensions as of the earlier alternators so that the latter
can easily be replaced by the invented alternator.

We claim:
1. A brushless alternator for 1400 HP diesel electric multiple unit applications
comprising of:
stator core (3) made of a plurality of one-piece low loss steel laminations (2)
which are assembled under pressure to form the stator core, the core being fixed
rigidly on to the magnet frame (4) by means of a key;
a plurality of stator coils (1) of copper with class H insulation placed inside the
slots in stator core (3) and connected to form a 3-phase winding;
a magnet frame (4) of tubular construction which is sturdy and light in weight
provided with end-shields (6,7) and eyebolts (8);
a rotor comprising of a plurality of rim punching (15), stacked together under
pressure and fitted on the shaft (14) with a key, pole and coil assembly (16) being
fitted in the dovetail groove provided on the rim punching assembly (15);
an exciter mounted on shaft (14) comprising of stationary stator field assembly
(12) and rotating armature assembly (18);
a diode wheel assembly (19) mounted on shaft (14); and
a blower fan (17) mounted on shaft (14) and enclosed within the said magnet frame,
characterized in that the alternator can deliver its rated output with 17.88% lower
weight and 19.62% lower length compared to similar alternators of prior art.
2. The brushless alternator as claimed in claim 1, wherein the core length has
been reduced by 32% compared to prior art.

3. The brushless alternator as claimed in claim 1, wherein the exciter is placed
inside stator frame before bearing on NDE side (11).
4. The brushless alternator as claimed in claim 1, wherein the diode wheel
assembly (19) is placed inside stator frame before bearing on NDE side (11).
5. The brushless alternator as claimed in claim 1, wherein the noise level of the
machine has been reduced fromllO dB to 101 dB by reducing the diameter of the fan
(17) from 940 mm to 750 mm.
6. The brushless alternator as claimed in claim 1, wherein the 3-phase winding of
the stator coil is brought out for supply by connection rings (9), which are connected
to the terminal box through busbars bolted to the rings.
7. The brushless alternator as claimed in claims 1 and 6, wherein the terminal box
has separate boxes for power and control terminals.

A compact and light weight brushless alternator for 1400 HP diesel electric multiple
unit applications is disclosed. It has stator core (3) made of a plurality of one-piece
low loss steel laminations (2) assembled under pressure. The stator core and the
core is fixed rigidly on to the magnet frame (4) by means of a key. Stator coils (1) of
copper with class H insulation are connected to form a 3-phase winding. It has
magnet frame (4) of tubular construction which is sturdy and light in weight provided
with end-shields (6,7) and eyebolts (8). The rotor comprises of a plurality of rim
punching (15) stacked together under pressure and fitted on the shaft (14) with a
key. Pole and coil assembly (16) are fitted in the dovetail groove proVided on the rim
punching assembly (15). An exciter mounted on shaft (14) comprises of stationary
stator field assembly (12) and rotating armature assembly (18); A diode wheel
assembly (19) and a blower fan (17) are mounted on shaft (14), enclosed within the
said magnet frame (4). The alternator can deliver its rated output with 17.88% lower
weight and 19.62% lower length compared to similar alternators of prior art.