FIELD OF INVENTION
The present invention relates to a device to protect contact pins of Turbo-
generator rotor field current lead during mechanical test run. More particularly,
the invention relates to a protective device which provides support to the contact
pins against bending due to centrifugal forces.
BACKGROUND OF THE INVENTION
Conventionally the rotors of large size Turbo-generators are assembled inside the
stator at test bed and mechanical, open circuit and short circuit test runs are
performed. Out of these, open circuit and short circuit tests require feeding the
field current to rotor by means of a test shaft assembly. This test shaft assembly
houses the contact pins of field lead of rotor and protects them. However,
mechanical test run is usually done without assembling of test shaft assembly to
save test bed time. Therefore, contact pins of the field current lead of rotor,
which extend beyond the rotor end, require to be protected against large
centrifugal forces at 3000 rpm, the operating speed of turbo-generator rotor.
Therefore need was felt for invention of a device which could protect the contact
pins against centrifugal forces and be easily mounted on exciter side face of
generator rotor.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a device to protect contact
pins of Turbo-generator rotor field current lead during mechanical test run,
which is capable of protecting the contact pins against centrifugal forces at 3000
rpm, the operating speed of turbo-generator rotor.

Another object of the invention is to propose a device to protect contact pins of
Turbo-generator rotor field current lead during mechanical test run, which
ensures mechanical test run without assembling of test shaft assembly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further features and advantages of the invention become clear from the
following description and drawings.
Fig.1 - It shows the protection device with its mounting arrangement on Turbo-
generator rotor.
Fig.2 - It shows the flow diagrams of testing process at test bed before and
after the invention and the testing time cycle reduction as a result of the
invention
Fig.3 - It shows an element mesh plot in a finite element model of protection
device.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
A protection device is developed to provide support to contact pins against
bending due to high speed (3000 rpm) centrifugal forces. The design of
protection device is worked out using finite element analysis. The same
protection device can be used for protection of contact pins in case of
250/600/660 MW Turbo-generator rotors due to similar geometries involved in
their assemblies. The device for protection of contact pins can be mounted easily
onto the exciter end face of Turbo-generator rotor by means of bolts using same

holes as used for coupling generator rotor to exciter rotor at thermal power
station.
The protection device is made using plate of high strength insulating material.
The protection device has broadly shape of a thick circular plate with
appropriately drilled holes to house the contact pins and bolts for its own
assembly on the exciter end face of rotor shaft (See Fig.1).
The protection device can be mounted easily onto the exciter end face of Turbo-
generator rotor by means of bolts using same holes as used for coupling
generator rotor to exciter rotor at thermal power station. These holes are match-
marked from rotor on the protection device.
The design of protection device has bee developed and optimized using Finite
Element Analysis technique (See Fig.3).
The design of protection device has been analyzed for stresses using Finite
Element Analysis on ANSYS package.
Considering circular symmetry, Finite Element model of two sectors, with suitable
loads/boundary conditions has been made to generate the analysis for full disc
having given number of sectors. Analysis of stresses in the model (see Fig.3) has
been done for the running condition of 3000 rpm as well for overspeeding
condition of 3600 rpm. Different design variants have been analyzed, using
parameters like thickness and material properties of plates, to optimize the
performance of the design.
Adequate factor of safety has been ensured with respect to the yield strength of
material of the protection device under all loading conditions.

Referring to Fig.1, the protection device 1 is designed similar in shape to a thick
circular plate. The thickness of circular plate used is 70mm which is sufficiently
high to support contact pins without bending. Its material is carefully chosen as
a high strength insulating material with low density reducing self centrifugal
stresses. The material used is epoxy glass laminate (fabric base).
It is provided with accurately machined holes 2 for snugly supporting contact
pins 6, made of high conductivity copper alloy.
These contact pins are assembled at the ends of insulated current carrying field
leads, 5.
The insulated current carrying field leads are fitted in the bore of rotor shaft 7.
The protection device 1 is also provided with circular recess 8, matching in close
tolerance to the spigot at the end face of generator rotor.
The protection device 1 is also provided with a number of holes, matching with
coupling holes at exciter end face of rotor shaft.
The protection device 1 is assembled with the rotor shaft 7 using high strength
alloy steel screws 3 and bushes 4 through these holes. 14 Nos. of screws (3) in a
pitch circle diameter fix the device (1) with the rotor shaft (7). The diameter of
the circular plate used is 600mm.
The protection device is to be assembled carefully ensuring that all contact pins
fit snugly in the holes provided for them. Also all bolts for assembly (of high
strength alloy steel) are to be tightened adequately and locked by tab washers.
Speeding up and down should be done gradually and steadily.

BENEFITS OF INVENTION
The following benefits would result from the subject invention:
1. Possibility of carrying out mechanical test run of generator without
assembly of test shaft and brush gear.
2. Saving of Test Bed assembly time of about three days for each generator
set tested (see Fig.2), by enabling parallel execution of assembly of test
shaft with brush gear and job of leak test on generator casing and gas
filing.
3. The invention is used during the testing of several 250 mw Turbo-
generators and also for 600 MW Turbo-generator.
4. The same protection device can be used for 250 MW, 600 MW and 660
MW Turbo-generator rotors by virtue of its standardized sizing.
The protection device for 250/600/660 MW Turbo-generator rotor contact pins of
field current lead has the following provisions.
■ Snugly supporting of contact pins against centrifugal forces at operating
speed of 3000 rpm
■ Circular recess matching with spigot at the end of Turbo-generator rotor
■ Holes matching with rotor end face for assembly
■ High strength bolts and bushes suitable for assembly onto rotor
The use of this device for protecting the contact pins enables the mechanical test
run of 250/600/660 MW Turbo-generator rotors at test bed without assembly of
slip ring shaft and brush gear.

WE CLAIM
1. A device (1) to protect contact pins of Turbo-generator rotor field current
lead during mechanical test run comprising;
a circular plate (c);
Characterized in that,
the said plate is provided with holes (2) for snugly supporting the contact
pins (6) assembled at the ends of insulated current carrying field leads (5)
fitted in the bore of rotor shaft (7) when the plate (c) is provided with
circular recess (8) for matching in close tolerance to the spigot at the end
face of generator rotor wherein the device (1) is assembled to the rotor
shaft (7) by screws (3) and bushes (4) through the holes (8)
2. A device (1) as claimed in claim 1, wherein the thickness of the circular
plate (c) is 70mm being sufficiently high to support contact pins without
bending
3. A device (1) as claimed in claim 1, wherein the material of the circular
plate (c) is epoxy glass laminate (fabric base),
which is a high strength insulating material with low density.
4. A device (1) as claimed in claim 1, wherein 14 numbers of screws (3) in a
pitch circle diameter fix the device (1) with the rotor shaft (7)
5. A device (1) as claimed in claim 1, wherein the diameter of the circular
plate is 600mm.

A device to protect contact pins of Turbo-generator rotor field current lead
during mechanical test run consists of a circular plate (c) which is provided with
holes (2) for snugly supporting the contact pins (6) assembled at the ends of
insulated current carrying field leads (5) fitted in the bore of rotor shaft (7) when
the plate (c) is provided with circular recess (8) for matching in close tolerance
to the spigot at the end face of generator rotor, wherein the device (1) is
assembled to the rotor shaft (7) by screws (3) and bushes (4) through the holes
(8).