Page 85 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 35 : Manual voltage control in DC Generator

Objectives

At the end of this exercise you shall be able to:
• make the connections of DC Generator
• start & run the Generator, and build up the voltage
• connect the load on DC Generator, and measure the load current & terminal voltage
• control the terminal voltage by varying the field current.

Requirements

Tools/Equipments/Instruments
• Combination Plier 165mm, • Multi meter Digital, 3 digit -1 No.
1/2
insulated -1 No. • Rheostat 700 Ω, 5A -1 No.
• Screw Driver 150mm, insulated -1 No. • Tacho meter 3000 RPM -1 No.
• Neon Tester 75mm, 500 V -1 No. • Lamp load 5 KW -1 No.
• Electrician knife insulated -1 No. Materials/Components
• MG set (AC to DC) with DOL
starter,DC shunt Generator • Test lamp 60 W, 230 V -1 No.
5 KW, 250 V -1 No. • DPST switch 250 V, 32 A -1 No.
• Voltmeter MC, 250 V -1 No. • Connecting wire 2.5 sq.mm - as reqd.
• Ammeter MC, 5 A -1 No. • Cotton waste / cloth - as reqd.
• Ammeter MC, 20 A -1 No.

Procedure

TASK 1 : Check the MG set details & terminals
1 Read and note down the specifications of MG set.

2 Draw the circuit diagram of voltage build up and loading of DC shunt generator.
3 Select the required meters and equipments for the experiment.

TASK 2 : Starting the Generator and building up voltage
1 Make the connection of prime mover AC induction motor with DOL starter.
2 Make the connection of DC shunt Generator as per circuit diagram.

3 Check all connections and switch ON the prime mover motor.
4 Now build up the voltage in generator by increasing field current.
5 Record the rated induced voltage, field current and speed of generator.

TASK 3 : Loading of Generator and manual control the terminal voltage by field rheostat
1 Connect the lamp load on generator terminals through DPST switch.
2 Close the DPST / load switch, increase the load gradually on the generator and record the load current &
terminal voltage.
3 As load current increases on generator, the terminal voltage tends to decrease.
4 Control & maintain the terminal voltage to approx. 250 V by increasing the field current by manually adjusting
field rheostat.
5 Now decrease load gradually, and observe the decrease of load current & increase of terminal voltage more
than rated voltage.

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