FIELD OF THE INVENTION
This invention relates to an improved silencer for A.C. motors with closed air
circuit air cooled (CACA) enclosure for reducing high level of noise produced by
the motors.
BACKGROUND OF THE INVENTION
2 pole large AC motors with CACA (Closed Air circuit air cooled) enclosure
produce noise of the order of 98dB. With a prior art silencer, noise level can be
reduced upto 90dB. In view of stringent environmental norms with regard to
noise pollution, there is requirement of low noise producing machineries across
all industries. The industries for example power plants, refineries, cement
industries, where large A.C motors find application, also require lower noise level
machines. It is imperative to reduce this high level of noise within the acceptable
limit of 85dB.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved silencer
for effectively reducing noise produced by AC motors with CACA enclosure while
in operation.

Another object of the present invention is to propose an improved silencer for
effectively reducing noise produced by AC motors with CACA enclosure while in
operation which reduces the noise level within 85dB to match international
standards.
A still another object of the present invention is to propose an improved silencer
for effectively reducing noise produced by AC motors with CACA enclosure while
in operation which is disposed at non-driving end (NDE) of the motor to
acoustically insulate sound waves of all frequencies including frequencies higher
than 8 KHz generated by a rotating electric or mechanical machine.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved silencer for effectively reducing noise
produced by AC motors with CACA enclosure while in operation. The silencer is
fitted at motor NDE i.e. the location of air inlet to CACA cooler. The technical
modification is based on the idea to extend the path of air travel through the
silencer thereby reducing noise level at air inlet point. The construction of the
improved silencer is such that it does not allow a direct air flow upto an external
fan of the motor, rather it makes air flow path more indirect and longer. Better
noise absorbing material has been used in the new silencer which effectively

absorbs the noise emanating from the motor. The improved silencer reduces
average noise level upto 85dB. The local noise level even upto 81dB at locations
near the silencer has been achieved. With the prior art silencer, minimum noise
level achieved was 89dB and average value was 90dB. Average noise level with
the improved silencer is 85dB as opposed to 90dB.
The silencer is designed such as to keep noise generation point not in the line of
sight which also results in reduction of noise level.
The silencer is formed of at least four numbers 90 degree bends of air along its
path of travel from air entry point of the silencer upto the fan suction i.e. noise
generation source of the motor and with lining of glass wool along the entire
internal wall of the silencer.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows a 3D model of an improved silencer according to the invention.
Figure 2: shows a wire frame model of the improved silencer.
Figure 3: sectional views of the improved silencer.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
A 3D view of the improved silencer is shown in Figure 01. The silencer is
mounted on the external fan suction point by bolting a front plate (02) of the
silencer to a fan ducting flange through or plurality of bolts. A wrapper plate (01)
is formed in final required shape as shown. The wrapper plate (01) is then
welded with the front plate (02) and a back flange (07) (06). A top cover (05) is
made by bending a plate in a shape as shown and is welded to the wrapper plate
(01) and the back flange (06). A back cover (03) is bolted to a flange (06) with a
plurality of bolts. A middle plate (04) which guides air flow to the external fan
suction resulting in longer and indirect air flow path. Glass wool slab (noise
absorbing material) is applied on all internal walls to arrest the noise generated
and it is securely held in position by using a galvanized perforated sheet as
shown in figure 64 03. The application of glass wool is continuous on the entire
internal wall and no portion of the internal wall remains without glass wool. The
galvanized perforated sheet in front of the glass wool has been designed with at
least 70% open surface. The glass wool has been selected to have a required
minimum density so that it considerably absorbs noise waves generated and
reduces the noise level to a large extent. Sectional view of the improved silencer
is shown in figure 03. Wire mesh has been put at entry of air to filter the inlet
air. Air flow duct sizing calculation has been done so as to ensure the availability
of required quantity of cooling air flow at required pressure at the external fan
suction which in turn delivers this cooling air to CAGA cooler mounted on top of
the motor. The complete structure has been made stiff and robust by using
stiffeners as required.

WE CLAIM :
1. An improved silencer for effectively reducing noise produced by AC motors
with CACA enclosure while in operation, comprising:
- a front plate (02) detachably attachable to a fan ducting flange (07) of the
motor structure;
- a shaped wrapper plate (01) welded at one end to the front plate (02), a
second end of the wrapper plate (01) is rigidly joined to a back flange
(06)
- a shaped top cover (05) welded with wrapper plate (01) and back flange
(06);
- a back cover (03) and a flange (06) assembly;
- a middle plate (04) for guiding air flow to the external suction fan;
- a glass wool slab applied on the entire internal walls of the silencer; and
- a perforated sheet disposed cover the glass wool slab, the perforated
sheet having at least 70% open space, and the glass wool slab is selected
to have minimum required density.

2. The silencer as claimed in claim 1, wherein a plurality of stiffeners are
welded along the silencer external surface.

ABSTRACT

The invention relates to an improved silencer for effectively reducing noise produced by AC motors with CACA enclosure while in operation, comprising a front plate (02) detachably attachable to a fan ducting flange of the motor
structure; a shaped wrapper plate (01) welded at one end to the front plate (02), a second end of the wrapper plate (01) is rigidly joined to a back flange (06); a shaped top cover (05) welded with wrapper plate (01) and back flange (06); a
back cover (03) and a flange (06) assembly; a middle plate (04) for guiding air flow to the external suction fan; a glass wool slab applied on the entire internal walls of the silencer; and a perforated sheet disposed cover the glass wool slab, the perforated sheet having at least 70% open space, and the glass wool slab is
selected to have minimum required density.