FIELD OF INVENTION
The invention relates to a turbo-generator operation in a power plant. In
particular, the invention relates to the insulation constraints in turbo-generator
bearings encountered during installation of the generator. More particularly, the
invention relates to a method for removal of trapped chips between the bearing
pedestal and foundation frame to achieve desired insulation resistance of the
bearing in a turbo generator. The invention further relates to a corresponding
device for implementation of the method.
BACKGROUND OF THE INVENTION
In a turbo-generator, the outboard bearing is electrically insulated to prevent
flow of shaft currents from the rotor to the earth through the lube oil film formed
between the white metal and the journal contact surface. The high currents that
flow through this smaller areas of contact have the potential to damage the
white metal of the bearing beyond repair, if the shaft currents are continued to
flow across the oil film for prolonged periods. In view of these problem. It is
necessary to maintain required insulation resistance value between the bearing
housing and earth.
Shaft voltages are normally induced in a generator rotor due to i) asymmetry in
the magnetic circuit of generator ii) build up of static charge within the shaft ill)
capacitative coupling of voltage in static excitation systems.
To achieve a required Insulation resistance value, the following measures are
generally taken during assembly of the bearing housing i) insulating the bearing
pedestal to the anchoring bolts of the assembly of the foundation frame, ii)
insulating the bearing pedestal seating surface to foundation frame, iii)
Insulating the lube oil piping flanges, and iv) insulating guide pin holes.
Insulating the guide pin holes is carried out at site after completing the assembly
and alignment of the generator. The guide pins are assembled to locate the
bearing pedestal lower-half with respect to the foundation frame. These are
drilled at site through transferring from bearing pedestal bottom holes. During
the process of drilling, the generator chips of different sizes and shapes flow
which get trapped between the pedestal and the foundation frame. It is a quite
difficult task to completely remove the chips in spite of using compressed air or
applying vacuum. It takes a considerable time and efforts to remove the left-over
chips. Thus, chip-removal poses a serious disadvantages to achieve the required
insulation resistance value between the bearing housing and earth which
interalia largely affects the process of final box-up on completion of generator
installation work.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for removal of
trapped chips between the bearing pedestal and foundation frame to achieve
desired insulation resistance of the bearing in a turbo generator, which
eliminates the disadvantages of prior art.
Another object of the invention is to propose a device for removal of entrapped
steel chips between the bearing pedestal and foundation frame to achieve
desired insulation resistance of the bearings in turbo generators.
SUMMARY OF THE INVENTION
A steel tube of suitable size, less than the dowel pin diameter is inserted into the
tapped pin hole. A plurality of GI wires of 1mm dia are inserted into the dowel
hole. On raising the tube and at the same time pushing the bunch of wires
allows the wires to take a bend in different directions. The wires are pushed with
the help of one hand while other hand keeps the tube in position. The bent wires
are then rotated in the groove between the closing sheet (see Fig 2) and
insulating plug., the trapped chips become loose during rotation of the GI wires.
The wires along with the pipe are then with drawn from the dowel hole. A bent
tube is inserted into the above gap where the chips are laying loose now and
compressed air is blown through it. This process removes all the trapped chips.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : Shows the assembly of dowel pin between bearing pedestal and the
foundation frame.
Figure 2 : Shows the drilling of hole for dowel pin.
Figure 3 : Shows the formation of chips in the gap formed between the dowel
holes and the closing sheet
Figure 4 : Shows a first components (8) of the device attached to the taper pin
hole with galvanized iron steel wire strands of 1 mm diameter.
Figure 5 : Shows a second component (10) of the device with its farther end
(end that is placed towards chips) bent.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
In accordance with a preferred embodiment of the present invention, there is
provided a method to address the issue of chip removal that make the insulation
resistance value zero, other than attempting to remove the same through
applying vacuum or compressed air etc. The invention positively eliminates the
source of the problem and ensures the design requirement.
A tapped pin hole (6) is made in the foundation frame (1) and an insulation plug
(20 is driven into the frame (1). After completing the machine assembly, the hole
(5) for dowel pin is transferred from the bearing housing (3) to the foundation
frame (1).
A recess (12) is provided below each dowel hole (5) and each anchor bolt hole in
the foundation frame (1). These recesses are closed with steel sheets (4) by
welding. This closing sheet (4) facilitates prevention of secondary grouting (liquid
grout). The tapper pin hole (6) is drilled on to the foundation frame (1) through
transfer from bearing pedestal (2).
The strands (9) are bent by lifting the pipe (8) and pushing them against the
bottom closing sheet (4). The bent strands (9) are rotated inside the pipe (8) to
loosen the chips (7) from position.
Compressed air supply (11) is given to the straight end to remove out the
loosened chips (7) lying in the groove.
In accordance with another preferred embodiment, the inventive device
addresses the problem in fixed number of steps rather than trial and error
method.
WE CLAIM
1. A method for removal of trapped chips between the bearing pedestal and
foundation frame to achieve desired insulation resistance of the bearing in
a turbo generator, the method comprising the steps of:
- drilling a tapper pin hole in the foundation frame and driving an insulation
plug into the holes;
- transferring the dowel pin hole from the bearing housing to the
foundation frame;
- closing all the recesses below each dowel pin hole and tapper pin hole in
the foundation frame by welding closing sheels;
- deploying a first component having a pipe and a plurality of steel wires of
a removal device into the tapper pin hole, pushing the pipe and forcing
the steel wires against the closing sheet to produce bend strands, and
rotating the bent strands inside the pipe to loosen the entrapped chips;
- proving a second component of the device having a bent configuration at
a distal end, and inserting into the gap accommodating the loosened
ships; and
- allowing injection of compressed air through the second component to
remove the chips.
2. A method for removal of trapped chips between the bearing pedestal and
foundation frame to achieve desired insulation resistance of the bearing in
a turbo generator as substantially described and illustrated herein with
reference to the accompanying drawings.

A method for removal of trapped chips between the bearing pedestal and
foundation frame to achieve desired insulation resistance of the bearing in a
turbo generator, the method comprising the steps of drilling a tapper pin hole in
the foundation frame and driving an insulation plug into the holes; transferring
the dowel pin hole from the bearing housing to the foundation frame; closing all
the recesses below each dowel pin hole and tapper pin hole in the foundation
frame by welding closing sheels; deploying a first component having a pipe and
a plurality of steel wires of a removal device into the tapper pin hole, pushing the
pipe and forcing the steel wires against the closing sheet to produce bend
strands, and rotating the bent strands inside the pipe to loosen the entrapped
chips; proving a second component of the device having a bent configuration at
a distal end, and inserting into the gap accommodating the loosened ships; and
allowing injection of compressed air through the second component to remove
the chips.
The invention further relates to a device for removal of entrapped steel chips
between the bearing pedestal and foundation frame to achieve desired insulation
resistance of the bearings in turbo generators.