GENERAL ELECTRICAL REPAIR SHOP

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.

RGULATOR/RECTIFIFRUNIT:

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