Practical Project (2863/02): The Characteristics of a Shunt Wound Motor

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A2 COURSEWORK (UNIT 2864): RESEARCH PROJECT

The Characteristics of a Shunt Wound Motor

Introduction

In my coursework I am going to look at different characteristics of a shunt wound motor, and analyse the change in the variables involved as I alter the torque on the motor. I expect to find that as the torque on a shunt wound motor increases, the angular velocity will decrease, the power input will increase, and the efficiency will start small, rise to a peak, and then decrease again.

Variables

The variables that are involved in my coursework are:

  • The angular velocity of the motor
  • The power input
  • The efficiency

Method 1

For method 1, you would need to place a motor at the top of a very high building, and have a long weighted string attached to it, starting from rest on the ground. Then, after starting the motor, the weight would move upwards towards the motor.

It would begin accelerating but would at a point reach a steady speed. The time when a steady speed is reach can be determined by marking equally spaced marks on the wall, and timing how long it takes for the weight to travel between the marks. Once this time is the same for more than one mark in a row, the weight has reached a steady speed. This then allows you to work out the angular velocity of the motor at different tensions.

The torque can be calculated by multiplying the weight at the end of the string (which equals the tension of the string) by the radius of the motor.

The experiment would then be repeated with a variety of different weights.

The apparatus and how it is set out can be seen in the diagram above.

Method 2

Method 2 is on a smaller scale, and involves a motor being held in place on a bench with a leather strap being wrapped around it and attached on either end to a Newton meter. The Newton meters are then attached to a bar on a retort stand to allow the tension to be altered.

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A similar leather strap would be placed on the opposite side of the motor, as shown in the diagram on the right, which shares the tension across the straps and avoids too much damage of the bearings in the motor (which would be more of a risk if there was only one strap involved in the experiment).

The torque would be measured by taking the tension of the straps and multiplying that by the radius of the motor.

The angular velocity can be measured by using a stroboscope, which determines how many turns the motor makes per ...

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