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ELECTRICIAN - CITS

EXERCISE 31 : To build up the voltage in DC shunt Generator

Objectives

At the end of this exercise you shall be able to:
• check and identify the terminals of DC shunt Generator
• start & run DC shunt Generator with prime mover
• build up the voltage in DC shunt Generator
• record the field current & induced voltage in the Generator and plot OCC graph.

Requirements

Tools/Equipments/Instruments
• Combination Plier 165mm, • Ammeter MC, 5 A -1 No.
1/2
insulated -1 No. • Multi meter Digital, 3 digit -1 No.
• Screw Driver 150mm, insulated -1 No. • Rheostat 700 Ω, 5A -1 No.
• Neon Tester 75mm, 500 V-1 No. • Tacho meter 3000 RPM -1 No.
• Electrician knife insulated -1 No. Materials/Components
• MG set (AC to DC) with DOL starter, • Test lamp 60 W, 230 V -1 No.
DC shunt Generator 5 KW, 250 V -1 No. • Connecting wire 2.5 sq.mm - as reqd.
• Voltmeter MC, 250 V -1 No. • Cotton waste / cloth - as reqd.

Procedure
TASK 1 : Check the MG set details & terminals

1 Clean the MG set with cotton waste and read its specifications.
2 Draw the circuit diagram of voltage build up of DC shunt generator.
3 Check and identify the terminals of MG set (AC induction motor and DC shunt Generator)

TASK 2 : Connecting & Starting of MG set
1 Make the connection of prime mover AC induction motor with DOL starter.

2 Make the connection of DC shunt Generator with field rheostat and meters.
3 Check all connections and keep the rheostat in cut in position.
4 Switch ON the mains and start the prime mover AC induction motor coupled with DC shunt Generator and
measure the speed with Tacho meter.

TASK 3: Build-up the voltage in DC shunt Generator
1 On starting of MG set observe & record the induced residual voltage in voltmeter.
2 Slowly increase the field current in DC shunt Generator by adjusting field rheostat.
3 Further increase the field current until rated voltage (230 V) is build up in DC shunt Generator.
4 Record the field current and full rated voltage build up in DC shunt Generator.
5 Reduce the voltage to zero by adjusting field rheostat and stop the prime mover motor.

6 . Plot the graph to indicate the field current (IF) & induced voltage (E ).
G
Safety precautions:
1 Ensure proper foundation and perfect coupling of MG set, else it may cause severe injury.
2 Ensure proper direction of rotation of DC generator to avoid demagnetizing of field poles and fails to build up
voltage.

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