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

Extracts from this document...

Introduction

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.

Middle

110.0

0.1

23.0

47.4

4

2.05

6.2

1.9

2.2

6.0

18.3

115.0

0.1

24.6

53.0

5

2.03

7.2

3.0

3.0

7.0

17.5

110.0

0.1

24.4

51.8

6

2.34

8.5

3.5

3.6

7.8

18.3

115.0

0.1

28.1

52.7

7

2.77

9.5

4.2

4.5

9.8

18.3

115.0

0.1

33.2

51.3

8

2.97

11.5

4.0

3.0

12.8

17.5

110.0

0.2

35.6

74.7

9

3.02

13.0

5.0

3.7

13.8

20.0

125.7

0.3

36.2

87.9

10

2.80

13.3

5.1

4.0

15.0

18.3

110.0

0.3

33.6

92.0

11

2.99

15.1

5.2

5.1

17.0

11.7

73.5

0.3

35.9

62.5

Here are the results for my repeat readings:

 F0/N I/A F1/N F2/N F3/N F4/N f/Hz Angular Velocity/ rad/s

Conclusion

There are three main reasons why my results are not very accurate, and the repeat results are quite different to the original results (see Graphs). Firstly, the actual method itself is not very reliable – which means there is a wide margin of error. Secondly, I carried out my first results and my repeat results on separate days, which could have had an effect on the results – especially as the apparatus was set up in a fairly busy laboratory for a period of several days. Thirdly, at the end of my first set of results, the apparatus was becoming very hot and the leather strap melted slightly onto the motor. This changed the shape of the inner strap and could have had a marked effect on the repeat results. This may also explain the large numbers of anomalies in my data.

However, although the results are not as accurate as I would have hoped them to be, the graphs still follow a similar shape as I expected them to, and there is still sufficient evidence to support my conclusion.

Conclusion

I conclude that there is a linear relationship between torque and angular velocity. There is also a linear relationship with positive correlation between the power input and the torque. Thirdly, there is a clear relationship between torque and efficiency up to about 0.25 Nm where it reaches a peak and begins to decrease.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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