Page 79 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 32 : To build up the voltage in DC compound

Generator

Objectives

At the end of this exercise you shall be able to:
• check and identify the terminals of DC compound Generator
• start & run DC compound Generator with prime mover
• build up the voltage in DC compound 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 1/2 -1 No.
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 • Test lamp 60 W, 230 V -1 No.
starter,DC compund Generator • Connecting wire 2.5 sq.mm - as reqd.
5 KW, 250 V -1 No. • Cotton waste / cloth - as reqd.
• Voltmeter MC, 250 V -1 No.

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 compound generator.
3 Check and identify the terminals of MG set (AC induction motor and DC compound 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 compound 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 compound Generator
and measure the speed with Tacho meter.

TASK 3: Build-up the voltage in DC compound Generator
1 On starting of MG set observe & record the induced residual voltage in voltmeter.

2 Slowly increase the field current in DC compound Generator by adjusting field rheostat.
3 Further increase the field current until rated voltage is build up in DC compound Generator.
4 Record the field current and full rated voltage build up in DC compound 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

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