Different type of
electric motors, electric generators, welding transformers are repaired
overhauled in general Electrical Repairing Shop.
Ø Electrical
motors such as Compressor motors , Blower motors, Single phase series motors,
Three
phase induction motors.
Ø Electric
generator such as Alternator (4.5 KW, 18 KW, 25KW) and D.G. set.
Ø Welding
plant transformers are repaired and overhauled.
There are separate
section in this shop to perform different tasks:
1. Alternator
overhauling and rewinding section.
2. Alternator
testing section.
3. Electric
POH and testing lab section.
4. Electric
motor and rewinding section.
5. Vacuum
impregnation plant and furnace section.
6. Welding
plant over hauling section.
7. DG
set repair section.
8. Electro
planting section.
4.5
KV ALTERNATOR:
Technical Description
Voltage : 120 V DC
Current : 37.5 Amp
Cut in
speed : 358 rpm (211.5 km/hour)
Min speed for
full output : 550 to 600 rpm
Maximum
speed : 2500 rpm (30km/hour)
Setting on
regulator : Voltage setting 124 V DC
Current
setting 37.5 Amp
Principal
of operation:
The alternator
consist of two sets of winding namely AC winding and field winding, both
accommodated in the stator. The AC windings are distributed in small slots and
field windings are concentrated in two slots. Each field coil spans half the
total no. of slots. AC coils are connected in star and field coils are connected ion series.
The rotator consisting
of stacked stamping reassembles a cogged wheel having eight sets of teeth and
slots, uniformly distributed on the rotor surface skewing the rotor axis.
The core the stator
which is completely embraced by the field coil will retain a residual magnetism
if excited by a battery once. The fluxed produced by field coils find its path
through the rotor. When the rotor is rotated the passage of the rotor teeth and
slots alternatively under the field offers a varying reluctance path for the
flux produced by the field coils. This flux which varies periodically links
with the AC coil and induced alternating voltage in the AC coil. The frequency
of the induction voltage depends on the speed of the rotor. The magnitude
depends on the speed of rotor and level of excitation. The field is
strengthened by a positive feedback system in the regulator to attain the
desired output voltage.
The regulator/rectifier
unit has following main function:
Ø Rectifying
the 3 phase AC output of the alternator to DC using full wave Rectifier Bridge.
Ø Regulating
the voltage generated by the alternator at se value.
Ø Regulating
the output current at set value.
The regulator rectifier
unit consists of following basic parts.
Ø Power
Rectifier
Ø Voltage
Regulator
Ø Excitation
Transformer
Ø Voltage
Detector
Ø Magnetic
Amplifier
Ø Field
Rectifier Unit
Ø Free-
Wheeling Diode
Ø Rectifier
Bridge
Ø Current
Regulation Circuit
Ø Over
Voltage protection Circuit
Testing
of Alternator:
The alternator is
testing by direct loading. The shaft of the alternator is rotated through a
prime mover (Synchronous Motor) and following specifications which are given at
half load are tested:
|
Specification
|
ALT-1
|
ALT-2
|
ALT-3
|
|
Rating
|
4.5KW
|
1800 KW
|
25 KW
|
|
Speed
(rpm)
|
1500
|
1500
|
1500
|
|
Current
(Amp)
|
19
|
70
|
97
|
|
Voltage
(volts)
|
127
|
127
|
127
|
Data for 4.5 KW Alternator
at full load:
Current : 37.5 Amp
Voltage : 122Volts
Speed : 600 to 700 rpm
