Page 299 - Electronic Mechanic - TP - Volume - 2

ELECTRONICS MECHANIC - CITS

MODULE 21: Electrical control of AC/ DC machines &
AC Drives

EXERCISE 205: Demonstrate unmarked Terminals of 3

phase induction motor

Objectives

At the end of this exercise you shall be able to:
• to known the unmarked 3 phase induction motor.
Requirements

Tools/Equipments/Instruments

• Combination Plier 250mm - 1 No. • Single phase A.C supply
• Screwdriver Set 150mm - 1 No. • A.C Voltmeter
• Wire Stripper - 1 No. • Center – zero galvanometer or
milli voltmeter or milli ammeter
Materials/Components
• Switch and wires
• Six terminal Induction motor • Battery (1.5V or 3V)
• Multimeter or Continuity Tester

Note:
Conducting Polarity test of new three phase Induction motor is necessary before running into
operation. If the wrong polarity motor is supplied with three phase supply, the magnetic field
distribution within the motor windings become uneven and the output torque becomes pulsating.
The motor draws excessive currents leads to damage of the windings.
Suppose we have a new Induction motor without any marking of the leads, then we need to identify
its polarity before using it. Usually six terminals from the three phases of an induction motor are
available. If their polarity markings (A1, A2; B1, B2; C1, C2) are not known, then these can be found
out by a polarity test on the induction motor.

Procedure

Polarity test induction motor
There are two methods to identify the Polarity of three phase Induction motor
1 finding polarity of AC supply.
2 finding polarity of DC supply
Finding polarity of induction motor-Method I (by A.C)

Step 1:
Continuity test to identify each of the winding terminals [AA BB CC]
We can do this test with the help of Multimeter by checking continuity between any two terminals. If the two
terminals belong to same winding a beep will come.

Do this procedure for all and identify terminals, then mark the terminals as AA, BB and CC.
Step 2:
Test to identify polarities [A1A2 B1B2 C1C2]
Take any two windings randomly and mark the terminals as A1 A2, B1 B2 (this is the assumption) as shown in
figure.

282