Hao Jie Experiment 8-AC Single Phase Induction Motors | Chan's Kingdom
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Tuesday, March 29, 2016


Experiment 8-AC Single Phase Induction Motors

I started to take photos of my Power Laboratory experiment for no reasons since my first lab work. Since many do not have the chance to actually operate an AC machine( even my electronics engineering course mates hahaha), ceiling fan and machine machine excluded, I think it’s a good idea I share the photos out.
My theory might not be perfect, so please correct me if you spot any mistake of any kind, I thank you in advance. ( But I wouldn’t go into too much theory though…)
My experiment is divided into Split-Phase motor, Capacitor-Start motor and Capacitor-Run motor. These are all induction motor, operating with a single phase supply. Thus we need to create another phase of supply to provide a rotating magnetic field to turn the rotor.
Capacitor-start motor
We used the capacitor-start motor without the capacitor, functioning as a split-phase motor. The auxiliary or the start winding has a high resistance and inductive reactance, while the main winding or the run winding has low resistance and high inductive reactance. Because of the different ratio of winding resistance to the inductive reactance, the run winding current  lags the start winding current, creating a phase difference between them. This creates fields that are out of phase, which in turn produces a rotating magnetic field in the stator. This develops torque in the rotor, starting the motor. ( And almost all of these are copied from my lab manual. Credits to whoever produced these sheets. )

The starting current of split-phase induction motor is 4 to 5 times of their full-load current, thus the starting period has to be short to prevent over heating. ( And I felt the heat after applying power for just 3 seconds!) A centrifugal switch will switch out the start winding ( which has high resistance and will overheat and burn out easily ) once the rotor reaches certain rpm.
Capacitor of capacitor-start motor
A big ass capacitor of the capacitor start motor.
The construction of the motor
Showing the auxiliary winding ( the thinner wire) and the main winding ( the thicker wire).
Closer shot of the windings and also observe the clearance of the stator and the rotor.

The operation of a capacitor-start motor is pretty similar to a split-phase motor. Now we connect the capacitor in series with the auxiliary winding. This provides a rotating magnetic field as well. The cap and winding are disconnected with a centrifugal switch as well.
This is the full setup, including ammeter, voltmeter, wattmeter and electrodynamometer.
Another type of capacitor, mounted for capacitor-run motor.

The capacitor in capacitor-run motor is always connected to the auxiliary winding and power. It doesn’t get disconnected with centrifugal switch. The manual states that it’ll be more quiet at full load, but honestly I didn’t feel the difference. Still vibrating like no body’s business!

Determining the starting torque
Posted by Chan Hao Jie on Monday, March 28, 2016

This video was taken to find out the starting torque. The scale was too fast for my slow eyes! :(

Measuring the starting current.

Posted by Chan Hao Jie on Monday, March 28, 2016

Another one for measuring starting current.
I would slowly update this blog with my previous and next experiment. Other than Power Lab, I have Advanced Power Electronics Lab as well, dealing with thyristors! Stay tuned. :D


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Author: Chan HJ
An enthusiast in papercraft. Paper model designing sounds fun too! More about me at my Blog Bio or