FIELD OF THE INVENTION

The present invention relates to brushless exciters for power generators in power
generation industries. More particularly, the invention relates to a device for
mounting of Diode Wheels to an Exciter Rotor shaft after heating the diode
wheel at a temperature of around 300°C with accurate interference fit.
BACKGROUND OF THE INVENTION
EXCITATION SYSTEM: GENERAL DEFINITION
Equipment providing the field current of a machine, including all regulating and
control elements, as well as field discharge or suppression equipment and
protective devices.
In a Thermal Power Station, the exciter is the backbone of the generator control
system (Refer fig.l). It supplies dc magnetizing current to field windings of a
synchronous generator thereby inducing ac voltage and current in the generator
armature.
EXCITER
It is a source of electrical power, providing field voltage and current of a
synchronous machine and regulated by the excitation control. Basically two types
of excitation systems are used in the field :-
1) Brushless Excitation
2) Static Excitation

Brushless Excitation : This system comprises a shaft-driven AC exciter with
rotating diodes, a permanent magnet generator and an Automotive voltage
Regulator (AVR). This system is highly reliable with least maintenance and is
ideally suitable for gas turbine driven generators.
Static Excitation : This system consists of a rectifier transformer, a plurality of
thyristor converters, a field breaker and an AVR. This system is ideally suitable
where fast response is called for. This system is flexible in operation and needs
very little maintenance.
The amount of excitation required to maintain the output voltage constant is a
function of the generator load. As the generator load increases, the amount of
excitation increases.
One of the main components of a brushless exciter includes a Diode Rectifier
wheel which contains a wheel hub on which the silicon diodes are arranged in a
three-phase bridge circuit. This wheel is mounted to an exciter rotor shaft and
the wheel has interference fit with the shaft, therefore the mounting is carried
out by heating the diode wheel at a temperature of about 270°C. This operation
is very tedious and time consuming.
As per the existing practice, pedestals of different heights is used for mounting
the diode wheels at the exciter shaft, which is time consuming and risky for the
workforce.
There were chances that the diode wheels were slantly fitted thereby creating an
eccentricity in the center of gravity of the exciter rotor.

Since the exciter rotor is coupled with generator rotor, it rotates at 3000rpm.
Unbalance in an exciter rotor is the result of an uneven distribution of mass,
which causes the rotor to vibrate. The vibration is produced by the interaction of
an unbalanced mass component with the radial acceleration due to rotation,
which together generate a centrifugal force. Since the mass component rotates,
the force also rotates and tries to move the rotor along the line of action of the
force. The vibration will be transmitted to the rotor's bearings, and any point on
the bearing will experience this force once per revolution.
For example, if the mass of the diode wheels assembly is 1200 kg as per close
approximation and the rotor is rotating at 3000 rpm, the centrifugal force will be
in order of Mega Newton (MN) and such force can be damaging as the vibrations
will pass on to the bearing/rotor supports which under the influence of such
severe vibrations over prolong period may get de-rooted from there base and
creating catastrophic safety issues.
Following constraints were further noticed during the prior art process :
• More time consumption for the mounting.
• Less safety to workman.
• More workforce required to accomplish the operation.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a device for
mounting of Diode Wheels to an Exciter Rotor shaft after heating the diode
wheel at a temperature of around 300°C with accurate interference fit so that the
center of gravity of whole assembly (exciter rotor and diode wheels) lies on the
axis of exciter rotor.

Another object of the present invention to propose a device for mounting of
Diode Wheels to an Exciter Rotor shaft after heating the diode wheel at a
temperature of around 300°C with accurate interference fit which reduces cycle
time and eliminates any damage on the exciter shaft.
Another object of the invention is to propose a device for mounting of Diode
Wheels to an Exciter Rotor shaft after heating the diode wheel at a temperature
of around 300°C with accurate interference fit, in which the wheel hub of the
diode rectifier wheel being Shrink fitted achieves a precise contact with the
insulation layer provided between the diode wheel and the exciter rotor shaft.
A still another object of the invention is to propose a device for mounting of
Diode Wheels to an Exciter Rotor shaft after heating the diode wheel at a
temperature of around 300°C with accurate interference fit., in which the silicon
diodes are arranged in a three phase bridge circuit.
Yet another object of the invention is to propose a device for mounting of Diode
Wheels to an Exciter Rotor shaft after heating the diode wheel at a temperature
of around 300°C with accurate interference fit, in which a contact pressure
produced by a plate spring assembly is increased by the centrifugal force during
rotation.
A further object of the present invention is to propose a device for mounting of
Diode Wheels to an Exciter Rotor shaft after heating the diode wheel at a
temperature of around 300°C with accurate interference fit, which is safe to the
workforce and reduces the operational cost.

SUMMARY OF THE INVENTION
Accordingly there is provided a device for mounting of Diode Wheels to an
Exciter Rotor shaft after heating the diode wheel at a temperature of around
300°C with accurate interference fit, comprising;
a base plate (1) on which an assembly of a first set of large diameter hollow
pipes of (2) and a second set smaller diameter hollow pipes(3) is assembled;
Stud (11) is assembled on the base plate (1) through threaded portion to guide
the coupling face of exciter shaft to sit on the surface of base plate (1); the first
set of our four pipes of larger diameter (2) on which the Diode wheels are placed
during mounting; a plurality of other four pipes of smaller diameter (3) which will
be mounted on first set of pipe during assembly of second diode wheel; a
plurality of spacers (7) for guiding and clamping of Diode Wheels from the top
with the help of hexagonal nut (12); a plurality of disc (4), disc (5) and studs (8)
for assembly of said both sets of the pipes (2 and 3); and guide Block (6) for
guiding the Diode wheels is placed in stud (9) and rests on pipe of smaller
diameter (3) when first diode wheel is mounted; wherein the base plates have
four holes at four corners for screw assembly (10) used to level the base (1) of
the mounting device, the same screws (10) is also used for lifting of mounting
device as a whole, wherein said first set of four hollow pipes (2) of larger
diameter is welded on the base plate (1), wherein the second set of four hollow
pipes of smaller diameter (3) are assembled on the first set through a stud (8)
and disc (5), wherein the disc (4) and disc (5) of two different sizes are used in
the device, and wherein the exciter rotor shaft is inserted in vertical position into
the diode wheel.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Excitation system
Figure 2 -shows a mounting device assembled with hollow pipes, stud, screw
assembly, nut, disc, pipe and spacers.
Figure 3 - shows the base plate on which the hollow pipes are welded.
Figure 4 - shows an assembled device according to the invention.
Figure 5 - shows spacer used in the device.
Figure 6 - shows stud used in the device.
Figure 7 - shows disc used in the device.
Figure 8 - shows guide block used in the device.
Figure 9 - shows diode wheel to be mounted on exciter shaft
Figure 10 - shows the device during mounting of diode wheel.
Figure 11 - shows exciter rotor shaft on which the diode wheel is to be
mounted.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The present invention is described in detail with reference to the accompanying
drawings, in which preferred embodiments of the invention are shown. The
present invention may, however be embodied in many different forms and
should not be constructed as limited to the illustrated embodiments set forth
herein. These illustrated embodiments are provided so that this disclosure will be
through and complete and will convey the scope of invention to those skilled in
art.

The present invention is related to the manufacturing of Exciters assembly of
600/660/700/800 MW rating. Major assemblies for manufacturing of Exciters
comprises:
1. Rectifier Wheels
2. Three-phase pilot Exciter
3. Cooler
4. Metering and supervisory Equipment
The invention made is used in the mounting of Rectifier Wheel (Diode Wheel) on
the Exciter Rotor shaft. Rectifier wheel is one of the vital component of Exciter
with main function for rectification of the three phase high frequency AC output
of exciter. The DC current from rectifier wheels is fed via conductors to the
center of the rotor shaft and carried out by a filed lead core bar in the hollow
shaft area under the bearing journal which is then applied to the Turbogenerator
filed winding.
To overcome the prior art disadvantages of mounting which resulted in deviation
in alignment of diode wheel on the shaft and time consuming activity, a
mounting device (fig. 2) is provided which comprises :
a. Base Plate (Item 1)
b. Hollow Pipe of larger diameter (Item 2)
c. Hollow Pipe of smaller diameter (Item 3)
d. Disc (Item 4)
e. Disc (Item 5)
f. Guide Block (Item 6)
g. Spacer (Item 7)
h. Stud (Item 8)

i. Stud (Item 9)
j. Screw Assembly (Item 10)
k. Stud (Item 11)
I. Nut hex (Item 12)
Four hollow pipes of larger diameter (item 2 of Fig. 2) are welded on the base
plate (Item 1 of figure 2) and another four hollow pipes (item 3 of Fig. 2) are
assembled on the hollow pipes of larger diameter (2). They are assembled
through studs with threads on the whole length (item 8 of fig.2). Disc (item 5) is
welded on the top of pipe (item2) and another disc (item 4) is welded on the top
and bottom of pipe (item 3).
Screw assembly (10) are used to level the base (1) of the mounting device. The
same is also used for lifting of mounting device as a whole.
Stud (item 11) is assembled on the base plate (1) through threaded portion to
guide the coupling face of exciter shaft to sit on the surface of base plate (1).
Guide Block (6), Spacer (7) and Hexagonal nut (12) are used to guide and mount
the diode wheel. Guide Block (6) is placed in stud (9) and rests on hollow pipe of
smaller diameter (3) when first diode wheel is mounted.
Spacer (7) is used to clamp the diode wheel from the top with the help of
hexagonal nut (12).
Diode wheels (figure 9) which are to be mounted on the exciter rotor shaft
(figure 11) are placed on the pipe assembly as shown in figure 10. Exciter rotor
shaft is inserted in vertical position into the diode wheel and then it is allowed to

cool down so that the diode wheel can achieve its shrink fit within a tolerable
limit of alignment of diode wheel with respect to exciter shaft.
After shrink fitting of first diode wheel (non-driving end side) the assembly of
exciter rotor (in vertical position) and first diode wheel is taken out from the
mounting device by lifting the assembly vertically.
For second diode wheel mounting, the hollow pipes with smaller diameter (3) are
removed and then guide Block (6) will rest on pipe of larger diameter.
Now, for shrink fitting of second diode wheel, the pipes (item 3) are removed
and second diode wheel is placed on the pipes (item 2) and then again exciter
shaft is brought into vertical position into it and allowed to shrink fit.
This procedure has led to keep facial and axial runouts of diode wheels with
respect to exciter shaft within the allowed limits and time cycle is also reduced
with limited manpower in comparison to previous practice.

WE CLAIM :
1. A device for mounting of Diode Wheels to an Exciter Rotor shaft after heating
the diode wheel at a temperature of around 300°C with accurate interference
fit, comprising :
- a base plate (1) on which an assembly of a first set (2) and a second set
(3) of hollow pipes is assembled;
- Stud (item 11) is assembled on the base plate (1) through threaded
portion to guide the coupling face of exciter shaft to sit on the surface of
base plate (1).
- the first set of our four pipes of larger diameter (2) on which the Diode
wheels are placed during mounting;
- a plurality of other four pipes of smaller diameter (3) which will be
mounted on first set of pipe during assembly of second diode wheel
- a plurality of spacers (7) for guiding and clamping of Diode Wheels from
the top with the help of hexagonal nut (12);
- a of the Patent Act. disc (4), disc (5) and studs (8) for assembly of said
both sets of the pipes (2 and 3); and
- a guide Block (6) for guiding the Diode wheels is placed in stud (9) and
rests on pipe of smaller diameter (3) when first diode wheel is mounted;
- a plurality of Screw assembly (10) are used to level the base (1) of the
mounting device. The same is also used for lifting of mounting device as a
whole.
wherein the base plates have four holes at four corners, wherein said first set
of four pipes of larger diameter (2) is welded on the base plate (1), wherein
the second set of four pipes of smaller diameter is assembled on the first set

through a stud (8), wherein the disc of two different sizes are used in the
device, and wherein the exciter rotor shaft is inserted in vertical position into
the diode wheel.
2. The mounting device as claimed in claim 1, wherein nine studs of same size
but different length are used during the whole assembly.