Page 323 - Electronic Mechanic - TP - Volume - 2

ELECTRONICS MECHANIC - CITS

EXERCISE 217: Run and change the direction of dc shunt
motor using 3 point starter

Objectives

At the end of this exercise you shall be able to:
• to connect dc shunt motor using 3 point starter
• to run and change the direction of rotation of dc shunt motor using 3 point starter.

Requirements

Tools/Equipments/Instruments Materials/Components
• Combination Plier 250mm - 1 No. • Voltmeter 500V - 1 No.
• Screwdriver Set 150mm - 1 No. • Ammeter (10-5) - 2 Nos.
• Wire Stripper - 1 No. • Tester - 1 No.
• Test lamp - 1 No.
• 3 Point starter - 1 No.
• Connecting Wire - as reqd.

Procedure

Working of 3 point stater
For starting the motor, handle is in the OFF position when the supply to the DC motor is switched on. Then handle
is slowly moved against the spring force to make contact with stud No. 1. At this point, field winding of the shunt or
the compound motor gets supply through the parallel path provided to starting the resistance, through No Voltage
Coil. The high starting armature current thus gets limited because at starting entire resistance of the starter comes
in series with the armature.

As the handle is moved further, it goes on making contact with studs 2, 3, 4, etc., thus gradually cutting off the
series resistance from the armature circuit as the motor gathers speed. Finally, when the starter handle is in ‘RUN’
position, the entire starting resistance is eliminated, and the motor runs with normal speed.
This is because as the speed increases, back emf is developed consequently to counter the supply voltage and
reduces the armature current.
3 point starter consists of a resistance which is divided into several sections and includes three terminals namely
L, A and F.
Here, L( line terminal) is connected to the positive supply, A (armature terminal) is connected to the armature
winding, and F (field terminal) is connected to the field winding.
Apart from these, OLR (Overload release) and NVC (No Volt Coil) are also provided in the motor. These two acts
as a protecting device for the motor.
• Draw the circuit diagram and check it.
• Indentify the terminals of motor and starter.
• Connect the A1 of motor to A point of starter.
• Connect the F1 of motor to F point of starter.
• Connect A2*F2 with negative terminal to supply.

• ‘ON’ the supply and gradually move the handle motor starters running.
• Continue the process of motor attain full speed.
• Check the RPM by tachometer.
• Check current and voltage.

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