Page 178 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

Check the mounting of the motor to the base is firm. Check the brake drum is properly keyed to
the shaft.
4 Fix the brake drum’s rope or belt with the spring balances in slack condition.
5 Switch ‘ON’ ICTP switch ‘S’ and start the motor at no- load.
6 Measure the speed and record in Table 1.
Table 1

Sl.No Load Line current(A) Line voltage(volt) Speed(rpm) Slip

1 Full
2 Half

3 Quarter
7 Tighten the belt to apply brake action on the brake drum, until the motor takes 1/4 full load current

8 Read the spring balances (Tension side ST, slack side SS) and record in Table 2.
9 Record the voltmeter, ammeter and wattmeter readings in Table 2.
10 Measure the speed of the motor at this loaded condition and record in Table 2.
11 Repeat the steps 6 to 9 for different load currents, say about 1/2 and full load.
Table 2

Drum radius + Wattmeter Wattmeter
Sl. S1 S1 Torque Power Pf Power
No Load belt thickness (kg) (kg) calculated reading reading (watts) angle factor
(m) 1(watts) 2(watts)
1 Full

2 Half

3 Quarter

TASK 2: Calculate the Torque developed by motor from the readings of the spring balance

1 Measure the diameter of the brake drum and the thickness of the rope/belt.
2 Record Drum radius ‘R’ = m.
3 Record Rope/belt thickness ‘t’= m
4 Calculate the torque, T = (ST - SS) x (R + t) Kg m where (R + t) is in meter, (ST - SS) is in Kg.
5 Measure the speed in rpm

6 Calculate the slip s = Ns-N/Ns where Ns is the synchronous speed calculated from equation= 120f /p (F=50Hz,
P=2/4/6/8 ETC, Ns is next higher to the actual speed measured)
7 Measure “Power” by 2 wattmeter method P=W1+W2

TASK 3: Calculate the power factor of the motor
P P
Calculate Power factor angle F = Φ tan 1 3 P 2 P 1
Calculate power factor cos F 2 1
Tabulate result in Table 2.

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CITS : Power - Electrician & Wireman - Exercise 73