| Rotating Electrical Machines : : : : : : Construction Details |
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| Enclosure |
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| Jyoti motors are made with enclosures
TEFC (Totally Enclosed Fan Cooled),
CACA (Closed Air Circuit Air Cooled),
CACW (Closed Air Circuit Water Cooled),
SPDP (Screen Protected Drip Proof).
For CACA motors, top mounted air to
air heat exchanger is used for horizontal
motors and side mounted air to air heat
exchanger is used for vertical motors.
Suitable material for tube is selected
depending upon environmental condition.
For TEFC motors finned body is used
for proper heat transfer. For some application,
Neema type weather enclosure is provided. |
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| Body and End Shields |
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| Motor body and end shields are made
from either cast iron or fabricated
from St. 42 steel. |
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| Stator Stack |
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| Stator stack is built from high permeability,
low loss silicon steel laminations,
accurately notched in our stamping unit.
Laminations are insulated on both sides
to minimize eddy current losses. Special
standing fixture, which accurately locate
stator bore, is used for building stator
stack. Build up stack is hydraulically
pressed to required dimension and welded
with stacking bars and rings. |
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| Rotor Stack |
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| Using high permeability silicon steel
stampings, rotor stack is built on spider
and hydraulically pressed and held by
end plates. |
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| Stator Windings |
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| Stator Windings for LT motors are
made using modified polyester enamel
covered copper wires confirming to IS
: 13730 Part - 3. For special application
dual coated copper wires as per IS :
13730 part - 13 is used. Standard motors
are insulated using class F materials.
Motor with class H insulation can be
given on request. |
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| For HT motors Resin rich insulation
system is used for stator winding insulation
stress grading conducting and semi conducting
tapes are used for coils having rated
voltage 6.6 KV and above for corona
protection. Sealing tape is applied
on overhang portion to provide protection
against moisture and contamination in
atmosphere. The overhang portions of
windings are braced rigidly to stator
body. |
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| Stator stack with winding is impregnated
in varnish. Special treatment is given
to wound stator to protect against atmospheric
contamination. |
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| Squirrel Cage Rotor |
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| Aluminum die-cast squirrel cage rotors
are used up to 315 frame size. Rotor
of higher frames are fabricated using
copper / copper alloy cage bars and
rings. Depending upon starting torque
requirements, different types of rotor
cage bar sections are used. Rotor cage
bars are brazed to short circuiting
rings using high silver content brazing
alloys. Complete rotor is impregnated
in class F varnish and baked in oven.
Rotor is balanced dynamically to grade
G2.5 and tested for over speed as per
IS:325. |
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| Wound Rotor |
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| Insulation system having high dielectric
and mechanical strength is used for
rotor winding. Rotor winding overhang
portions are braced adequately, using
Res-i-glass banding tapes to prevent
fanning of rotor winding overhangs due
to centrifugal forces. Rotor winding
with its stack is impregnated using
class F varnish / resin and baked in
oven. Rotor is balanced dynamically
to grade G2.5 and tested for over speed
as per IS : 325. Wound rotors are provided
with slip rings and brush gear arrangements.
Slip rings used, have excellent stability
at high temperature and have good tracking
property. |
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| Shaft |
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| Shafts are liberally designed to have
critical speed more than 130% of operating
speed. The shaft is made using C40 steel.
Shaft made using special steel can also
be given on request to suit the application
requirements. For 2-Pole Motors EN-8
shafts are used. |
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| Bearings |
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| Horizontal Motors - Generally,
roller bearing is used on DE side and
either ball bearing or combination of
ball and roller bearings are used on
NDE side. The size of bearings and arrangement
are determined to ensure long operational
life. The bearings are lubricated using
lithium base high temperature grease.
On line greasing arrangement is provided
to DE and NDE side bearings. In order
to protect bearings from shaft currents
NDE side bearing is insulated from motor
body for High Voltage Motors. |
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| Vertical Motors - Motors
are provided with 6 terminals. Clearances
and creep age distances in the terminal
box are as per IS : 6381. The terminal
box provided for standard LT motors
is of fabricated steel or cast iron.
The LT Terminal box is suitable for
with standing fault level of 35 MVA
(i.e. 50 KA at 415 volt for 0.25 sec)
are provided on request. As a standard
practice, 3.3 KV motors are provided
with phase segregated terminal box.
Our phase segregated terminal box (PSTB)
is type tested for 500 MVA, at 6.6 KV
for 0.25 sec. at CPRI Banglore. For
star point and rotor terminal box bushing
and stud type arrangement is used. Separate
terminal boxes are provided for winding
RTDs, bearing RTDs, space heaters etc. |
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Terminal Boxes
Motors are provided with 6 terminals. Clearances and creep age distances in the terminal box are as per IS : 6381. The terminal box
provided for standard LT motors is of fabricated steel or cast
iron. The LT Terminal box is suitable for with
standing fault level of 35 MVA (i.e. 50 KA at 415 volt for 0.25 sec)
are provided on request. As a standard practice, 3.3 KV motors are
provided with phase segregated terminal box. Our phase segregated
terminal box (PSTB) is type tested for 500 MVA, at 6.6 KV for 0.25
sec. at CPRI Banglore. For star point and rotor terminal box bushing
and stud type arrangement is used. Separate terminal boxes are
provided for winding RTDs, bearing RTDs, space heaters etc. |
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| Accessories |
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| For proper monitoring and control,
following accessories are provided on
each motor on request. |
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3/6 Nos. PTC Thermisters. |
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6 Nos. Pt.-100, Simplex / Duplex
winding RTDs |
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2 Nos. Pt.-100 Simplex/Duplex
bearing RTDs |
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2 Nos. Mercury in steel type
dial thermometers for local indication
of bearing temperature. |
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Suitable number of space heaters,
of adequate capacity (Watts),
240 Volts, 1-phase. |
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If required, Cts for differential
protection(above 1000kV). |
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Flow-switch for CACW motor (on
request). |
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| Following type test is conducted
on each motor : |
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All tests mentioned
in routine test |
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Load test to determine performance |
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Temperature rise test |
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Vibration measurement |
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Noise level measurement |
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Shaft voltage measurement |
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| Special Features for HT Motors |
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Type tested PSTB
(Phase segregated terminal box) |
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Design ambient temperature of
50 deg. C |
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Stator coil type tested for
impulse levels as per IEC 34-15 |
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Winding bracing and shaft design
suitable for out of phase re closing. |
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Low vibration and noise level |
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Optimised performance |
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Special cage construction for
high starting torque and low starting
current. |
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Bearing life more than 100000
hours |
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Jyoti make tilting pad type
T & J bearings if required. |
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