TITLE: FRP - Brush Gear Casing for Hydrogenerators.
FIELD OF THE INVENTION
The invention relates to brush gear casings for generators in general and to
brush gear casings for hydrogenerartors in particular.
BACKGROUND AND PRIOR ART
The applicant is a renowned manufacturer of hydrogenerators. These generators
are mounted vertically in operation in a hydroelectric (hydel) power plant. The
brush gear casing is the topmost part of the generator assembly. Such
generartors are fixed on a generator floor in a hydel station. Hence the brush
gear casing becomes the only part of the generator that is visible, being
positioned above the generator floor. As such, it is this part of the generator that
gives a first impression about the quality of the hydrogenerator.
In the prior art, brush gear casings have been traditionally fabricated out of mild
steel (MS) plates, finished with paint. The fabrication process involved joining by
welding or through fasteners, which gave rise to uneven surface finish.More
importantly, when in operation, most of such joints become sources of additional
noise due to vibration. The painted surface is difficult to maintain, as it calls for
regular painting and leads to shabby look when paint peels off. A brush gear
casing of the prior art has many drawbacks, such as
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- it has to be fabricated from many parts due to its complicated
shape; these parts will then have to be joined.
- an MS casing fabricated from numerous pieces takes a long time to
be manufactured, making it costly.
- joints tend to part due to prolonged exposure to continuous
vibration in operation.
- MS casing is prone to corrosion.
- Imparts shabby looks to the generator.
- MS casing poses threat of electrical short circuit or earthing of DC
collector leads in the event of mechanical or electrical failure of
insulation blocks.
- Due to space constraint inside brush gear casing, it becomes
difficult to install mounting arrangement for auxiliary and control
devices like over speed device, rotor jacking limit switch, stand for
brush gear assembly, speed sensing gear, lighting etc.
OBJECTS OF THE INVENTION
An object of the invention is to provide a brush gear casing which does not have
joints.
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Another object of the invention is to provide a brush gear casing that is easier
and cheaper to manufacture.
Yet another object of the invention is to provide a brush gear casing that does
not need painting, but is still attractive and pleasing to the eye.
A further object of the invention is to provide a brush gear casing that is free
from corrosion.
Another object of the invention is to provide a brush gear casing which has built-
in mounting arrangements from auxiliary and control devices.
DESCRIPTION OF THE INVENTION
The need to overcome above drawbacks of the brush gear casing of the prior art
was long felt by the applicant. After numerous technical discussions and trials, it
was found that the technical quality of FRP (Fibreglass Reinforced Plastic) would
meet the technical and aesthetic requirements of the brush gear assembly in
actual operating conditions. Engineering items produced from FRP were found
to have smooth finish, were aesthetically appealing as well as light in weight,
and possessed the requisite strength for their operational requirements. Brush
gear casings were also developed, using FRP as the material.
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The invention discloses a brush gear casing, hereinafter referred to as "casing",
which is meant for a hydrogenerator. The specification discloses and describes a
preferred embodiment of the invention. However, there can be several other
embodiments of the same invention, all of which are deemed to be covered by
this specification. The invention will be described in detail with the help of the
accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 shows the plan view of the casing without top cover.
Fig.2 shows sectional view BB of Fig.1.
Fig.3 shows sectional view CC of Fig.2.
Fig.4 shows elevation as arrow D of Fig.1.
Fig.5 shows elevation as arrow E of Fig.1.
Fig.6 shows sectional view PP of Fig.2.
Fig.7 shows the plan view of the casing with top cover.
Fig.8 shows the plan and elevation of the PERSPEX cover.
Fig.9 shows the assembly of the door.
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FRP brush gear casing (10) in accordance with the invention, as depicted in the
accompanying drawings, has a hexagonal base (60) and six vertical sides (11-
16). This, however, is a non-limiting exemplary embodiment of the invention.
Other embodiments can have bases in other polygonal shapes consistent with
the shape of the upper bracket of the hydrogenerator.
In the present embodiment, the base (60) is shown in Fig.6.The base has a
bottom flange which has between 20 and 40, preferably 36 inserts for fixing it
with the upper bracket assembly of the hydrogenerator. The shape and the
dimensions of the base of the casing is therefore determined by the shape and
dimensions of the upper bracket assembly of the hydrogenerator on which the
casing is to be fixed.
The casing has 6 vertical sides (11-16), of which 4 sides (12,13,15,16) are
provided with doors (90) and the remaining two sides (11,14) have provision for
exhaust fan (50).
Fig.1 shows the plan view of the casing without the top cover (80), which is
made of transparent fibre glass material known in the trade as "PERSPEX". This
cover is fixed on to the top of the casing with suitable fastners.
Fig.4 shows one of the four sides (12,13,15,16) which has a door.
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Fig.5 shows one of the two sides (11,14) with provision for exhaust fan (50)
Fig. 7 is the plan view of the casing with the top cover (80) installed.
Fig. 8 shows details of the top cover (80) made of fibre glass (PERSPEX).
Fig. 9 shows the details of the door (90) that is provided on each of the four
vertical sides (12,13,15,16) shown in Fig. 4.
The material (FRP) of the casing consists of chopped strand mat woven roving
polyester resin, hardener, catalyst and accelerator. The FRP used has high
strength, is fire retardant and can be coloured as desired during manufacture.
The FRP brush gear casing in accordance with the invention is manufactured by
contact moulding process. Such a casing manufactured by moulding offers a
unique advantage over the prior art. The fixing provisions for control devices like
speed sensing gear (SSG), over-speed devices (OSD), rotor jacking limit switch
as well as auxiliary devices like light fitting, terminal clamps, cables, DC
connections and brush gear assembly are provided during the moulding itself.
This saves very valuable time during commissioning of the hydrogenerator at
site. Moreover, the mounting and fixing hardware required during assembly is
also reduced appreciably.
The FRP-casing is much lighter when compared to the MS-casing of the prior art.
This saves cost of transportation to installation sites, which are usually difficult to
access in case of hydel power plants, where hydrogenerators are installed.
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The moulded construction of the FRP casing in accordance with the invention
eliminates all joints, both welded and fastened. The joints in a casing of the
prior art have raised visible marks on the casing, lending it inferior aesthetics.
Moreover, as such casings are painted, the paint tends to peel off primarily at
the joints, again leading to inferior looks and need for frequent repainting.
The FRP casing according to the present invention overcomes these problems.
As it is without joints, it offers a smooth surface. FRP can be coloured during
manufacture, hence it does not require painting throughout its life. It also
overcomes problems of added noise emanating from the fastened joints due to
exposure to sustained vibrations during operation.
The MS casing of the prior art poses another serious threat, which the FRP
casing overcomes. The DC leads from collector to excitation equipment carry
high currents in the range of 1000-3000 Amperes. These leads are supported
inside the brush gear casing on insulator blocks.In case of failure of these
insulator blocks, the MS casing of the prior art may provide a short circuit path,
leading to earthing and hazardous accidents which may turn fatal. The FRP
casing provides no such short circuit path, the material FRP being non-
conducting. The FRP casing is therefore safer to use.
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Another disadvantage of the MS casing is that it is prone to corrosion due to
rusting.This calls for frequent repairing and even replacement. The FRP casing is
free from rusting, hence has much longer life and is less expensive to maintain.
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We claim:
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1. FRP brush gear casing (10) comprising a hexagonal base (60), six
vertical sides (11,12,13,14,15,16) and a cover (80) detachably fixed on
top of the casing, characterized in that the casing is manufactured by
contact moulding process from FRP material.
2. The casing (10) as claimed in claim 1, wherein four vertical
sides(12,13,15,16) are each provided with a door (90).
3. The casing (10) as claimed in claim 1, wherein two vertical sides
(11,14) are provided with provision for exhaust fan (50).
4. The casing (10) as claimed in claim 1, wherein the material of the
casing is high strength FRP which is fire resistant and corrosion free.
5. The casing (10) as claimed in claim 1, wherein the said casing has a
smooth surface and is free from joints.
6. The casing (10) as claimed in claim 1, wherein the FRP is coloured
during its manufacture and does not need any painting subsequently.

FRP brush gear casing (10) comprising a hexagonal base (60), six
vertical sides (11,12,13,14,15,16) and a cover (80) detachably fixed on
top of the casing, characterized in that the casing is manufactured by
contact moulding process from FRP material.