# Electrical Machines

OBJECTIVES
• To develop understanding and skill on DC generator.
• To develop understanding and skill on DC motor.
• To familiarize with the construction and operation of transformer.
• To develop understanding on the principles of operation on 3-phase and 1-phase induction motor.
• To develop understanding on the principle of synchronous motor and alternator.

SHORT DESCRIPTION
DC generator; DC motor; Transformer; Induction motor; 3-phase induction motor; 1-phase induction motor; Synchronous motor; Alternator.

DETAIL DESCRIPTION

Theory :

DC GENERATOR
1 Understand the principles of operation of DC generator.
1.1 Explain the working principle of DC generator.
1.2 Describe the constructional features of DC generator.
1.3 Explain the function of commutator.
1.4 Describe the factors determining induced emf.
1.5 Develop the emf equation of a DC generator.
1.6 Describe different types of excitation.
1.7 Identify different types of DC generator.
1.8 Explain losses and efficiency of DC generator.

2 Understand the principle of operation of DC motor.
2.1 Explain the working principle of DC motor.
2.2 Explain the factors determining torque of a DC motor.
2.3 Identify different types of DC motor.
2.4 Describe starting process and speed control of DC motor.
2.5 Explain losses and efficiency of DC motor.
TRANSFORMER
3 Understand the working principle and construction of transformer.
3.1 Define transformer.
3.2 Explain the working principle of transformer.
3.3 List of uses of transformer.
3.4 Describe the constructional details of transformer.
3.5 List different types of transformer.
3.6 Distinguish between core type and shell type transformer.

4 Understand emf equation and transformation ratio of transformer.
4.1 Explain the emf equation of a transformer.
4.2 Solve problems on emf equation of transformer.
4.3 Explain transformation ratio (voltage, current and turns).
4.4 Solve problems on transformation ratio.

5 Understand losses, efficiency and voltage regulation of transformer.
5.1 Explain different losses in transformer.
5.2 Explain the factors affecting core loss and copper loss.
5.3 Explain the equation for maximum efficiency.
5.4 Solve problems on efficiency and maximum efficiency.
5.5 Explain the equation for voltage regulation of transformer.
5.6 Solve problems on voltage regulation of transformer.

6 Apply the principle of impedance transformation and equivalent circuit of transformer.
6.1 Explain equivalent resistance of transformer in terms of primary and in terms of secondary.
6.2 Explain equivalent reactance of transformer in terms of primary and in terms of secondary.
6.3 Solve problems on impedance transformation.
6.4 Explain the equivalent circuit of transformer.

INDUCTION MOTOR
7 Understand the principle of induction motor.
7.1 Explain the general principle of induction motor.
7.2 Distinguish between the principles of induction motor and conduction motor.
7.3 Define slip and slip speed.
7.4 List the types of induction motor.
7.5 List the uses of induction motor.

THREE-PHASE INDUCTION MOTOR
8 Understand the working principle of 3-phase induction motor.
8.1 Describe the construction of 3-phase induction motor.
8.2 Explain the construction of squirrel cage induction motor.
8.3 Explain the construction of wound rotor induction motor.
8.4 Explain the production of rotating magnetic field in a 3-phase induction motor.
8.5 Describe double squirrel cage induction motor.
8.6 Explain the methods of starting of 3-phase induction motor.
8.7 Explain the principles of speed control of 3-phase induction motor.

SINGLE-PHASE INDUCTION MOTOR
9 Understand the working principle of 1-phase induction motor.
9.1 Explain single phase motor is not self starting.
9.2 List the methods of making single phase motor self starting.
9.3 Describe standard split phase motor.
9.4 Describe capacitor motor.
9.5 Describe shaded pole motor and repulsion motor.
9.6 Describe hysteresis motor, universal motor, reluctance motor and AC series motor.
9.7 Describe the methods of speed control of single phase induction motor.

SYNCHRONOUS MOTOR
10 Understand synchronous motor.
10.1 Explain the principle of operation of synchronous motor.
10.2 Describe the constructional features of synchronous motor.
10.3 Describe the starting methods of synchronous motor.
10.4 Explain the characteristics of synchronous motor.
10.5 Describe the application of synchronous motor.
10.6 Explain V-Curves.

ALTERNATOR
11 Understand the concept of alternator.
11.1 Explain the principle of alternator.
11.2 List the parts of an alternator.
11.3 Explain the emf equation of an alternator.
11.4 Discuss the effect of load on alternator.
11.5 Explain the losses and efficiency of an alternator.
11.6 Describe voltage regulation of an alternator.
11.7 Define the term synchronizing.
11.8 Describe the process of synchronizing alternators.
11.9 List the conditions for synchronizing.

Practical :

1 Show skill in studying of a DC generator.
1.1 Prepare a list of the parts of a DC generator.
1.2 Dismantle the components/parts of the DC generator.
1.3 Develop sketches of each parts.
1.4 Sketch the developed diagram of the winding of the generator.
1.5 Assemble the dismantled parts.
1.6 Start the generator.

2 Show skill in constructing load versus speed characteristic curve of DC shunt motor.
2.1 Sketch the required circuit diagram for the experiment.
2.2 List the instrument and materials required for the experiment.
2.3 Connect all the instruments and equipment according to circuit diagram.
2.4 Take the necessary data from the connected instruments.
2.5 Draw the required curve.

3 Show skill in determining the transformation ratio of a transformer.
3.1 Develop a circuit to perform the experiment.
3.2 Collect required equipment and materials.
3.3 Connect the components according to the circuit diagram.
3.4 Check the connections.
3.5 Record the primary (EP) and secondary (ES) voltages.
3.6 Calculate the transformation ratio using the relation
ESEP = NSNP = K

4 Show skill in performing open circuit test of a single phase transformer.
4.1 Select the circuit diagram for the experiment.
4.2 Collect required tools, equipment and materials.
4.3 Connect all the equipment according to the circuit diagram.
4.4 Connect the low side to its rated voltage to the power supply keeping high side open.
4.5 Record instrument readings.
4.6 Calculate required data.
4.7 Draw no load vector diagram with the data obtained.

5 Show skill in performing short circuit test of a single phase transformer.
5.1 Select the required circuit diagram for the experiment.
5.2 Collect required tools, equipment and materials.
5.3 Connect the equipment according to the circuit diagram.
5.4 Energize the circuit by applying reduced voltage.
5.5 Record copper loss and calculate Re , Xe and Ze.

6 Show skill in determining the equivalent circuit of a transformer.
6.1 Select required tools, equipment and materials.
6.2 Perform open circuit and short circuit tests for the transformer.
6.3 Calculate required data for the equivalent circuit.
6.4 Draw the equivalent circuit.

7 Show skill in winding of a small transformer.
7.1 Develop the design of a small transformer.
7.2 Select the transformer core.
7.3 Select super enamel copper wire for both high voltage winding and low voltage winding.
7.4 Select other necessary materials eg. leatheroid paper, ampere cloth, ampere tube, soldering material, varnish etc.
7.5 Perform the windings.
7.6 Test the windings.
7.7 Connect power supply.

8 Show skill in studying the components/parts of a 3-phase induction motor.
8.1 Prepare a list of the different parts of a 3-phase induction motor.
8.2 Dismantle the components/parts of the motor.
8.3 Develop sketches of each part.
8.4 Sketch the developed diagram of the windings of the motor.
8.5 Assemble the dismantled parts.

9 Show skill in operating a 3-phase induction motor.
9.1 Sketch the circuit diagram.
9.2 List tools, equipment required for the experiment.
9.3 Connect starter with motor.
9.4 Connect power supply to the circuit.
9.5 Observe the operation.
9.6 Measure the speed of the rotor.

10 Show skill in winding of a 3-phase induction motor.
10.1 Develop the winding diagram of a 3-phase induction motor.
10.2 Select the proper size of copper wire.
10.3 Place the required coils in proper space and turns.
10.4 Place the coils in proper ways into slots.
10.5 Connect the coils in proper sequence.
10.6 Test the winding and connections.
10.7 Connect 3-phase supply with the motor stator.

11 Show skill in starting a capacitor type motor/ceiling fan with regulator.
11.1 List the tools and equipment required for the experiment.
11.2 Sketch a working diagram.
11.3 Identify two sets of coils.
11.4 Connect the capacitor with the proper set of coil.
11.5 Connect a regulator with the fan.
11.6 Connect power supply to the fan.
11.7 Test the rotation of fan in opposite direction by changing the capacitor connection.

12 Show skill in winding of a single phase capacitor motor.
12.1 Develop the winding diagram of a single phase capacitor motor.
12.2 Select correct size of super enamel copper wire for starting and running windings.
12.3 Prepare coils in proper space and turns.
12.4 Place the coils in slots.
12.5 Connect the coils.
12.6 Select the correct size of capacitor for motor.
12.7 Test the capacitor.
12.8 Connect the capacitor with the starting winding.
12.9 Connect proper supply and observe operation of motor.

13 Show skill in operating a synchronous motor by changing field excitation.
13.1 Select required tools, equipment, machine and materials.
13.2 Sketch the circuit diagram.
13.3 Connect the instrument according to the diagram.
13.4 Check the circuit.
13.5 Change the field excitation.
13.6 Record armature and field current.
13.7 Draw the ‘V’ curve.

14 Show skill in operation of an alternator.
14.1 List the required tools, equipment and machine for the experiment.
14.2 Sketch the circuit diagram.
14.3 Connect the equipment according to circuit diagram.
14.4 Start the alternator.
14.5 Develop the voltage.
14.6 Record the data.