## AIMS

To provide the student with an opportunity to acquire knowledge, skills and attitude in the area of alternating current machines with special emphasis on :

- power transformer.
- auto transformer.
- 3-phase induction motor.

## SHORT DESCRIPTION

Transformer : principle of operation & construction, emf equation, transformation ratio, losses, equivalent resistance, leakage reactance, tests, regulation, efficiency, three phase connection, auto transformer, parallel operation, Three-phase induction motor: working principle, construction, magnetic field, torque, power stage, tests, starting and speed control.

## DETAIL DESCRIPTION

__Theory__**:**

# TRANSFORMER

**Understand working principle and construction of transformer.**- Define transformer.
- Explain the working principle of transformer.
- Describe the construction of a transformer.
- Identify the materials used in transformer construction.
- List different types of transformers.
- Describe core type, shell type and spiral core type transformer.
- Compare the core type and shell type transformer.

**Understand the emf equation.**- Define emf equation.
- Express the derivation of emf equation.
- Solve problems on emf equation.

**Understand the transformation ratio.**- Explain voltage ratio and current ratio.
- Explain turns ratio.
- Solve problems on transformation ratio.

**Understand different losses of transformer.**- List the losses in transformer.
- Explain hysteresis loss, eddy current loss and core loss.
- Explain copper loss.

**Understand the principle of operation of transformer on no-load condition.**- Explain no-load operation of transformer.
- Define no-load voltage, current, mutual flux, no load power factor.
- Draw the vector diagram of transformer on no load.
- Solve problems related to no load test.

**Understand the principle of operation of transformer on load condition.**- Explain operation of transformer on load.
- Draw the vector diagram of transformer on lagging, leading and unity power factor load condition.
- Solve problems related to transformer on load.

**Understand the open circuit test and short circuit test of transformer**- Describe open circuit test.
- Describe short circuit test.
- Draw vector diagram.
- Solve problems related to short circuit test.

**Understand the equivalent resistance, magnetic leakage and leakage reactance of transformer.**- Deduce the equivalent resistance of transformer as referred to primary.
- Deduce the equivalent resistance of transformer as referred to secondary.
- Explain magnetic leakage of transformer.
- List the disadvantages of magnetic leakage.
- Deduce equivalent resistance & leakage reactance of transformer in terms of primary and in terms of secondary.
- Solve problems on equivalent resistance, leakage reactance and impedance of transformer.

**Understand equivalent circuit of transformer.**- Draw the equivalent circuit of transformer.
- Explain the equivalent circuit of transformer.
- Draw the equivalent vector diagram of transformer.

**Understand the voltage regulation of transformer.**- Define voltage regulation.
- Express the deduction of the equation for voltage regulation at unity, lagging and leading power factor load.
- Solve problems related to regulation.

**Understand the percentage resistance, reactance & impedance.**- Define percentage resistance, reactance and impedance.
- Express the deduction of the equation for percentage resistance, reactance and impedance.

**Understand the efficiency of transformer.**- Express the deduction of the formula for calculation of efficiency of transformer.
- Explain the factors affecting core loss and copper loss of the transformer.
- Express the deduction of the equation for maximum efficiency.
- Evaluate the variation of efficiency with power factor.
- Explain all day efficiency.
- Solve problems on efficiency and maximum efficiency.
- Solve problems on all day efficiency.

**Understand the cooling of transformer.**- Explain the necessity of cooling of transformer.
- Describe the methods of cooling the transformer.
- Describe the transformer oil and its properties.

**Understand the construction and principle operation of three phase transformer.**- Describe the construction of three phase transformer.
- Describe the different parts of a three phase transformer.
- List various methods of connection of 3-phase transformer.
- Describe the methods of star – star, delta – delta, star – delta and delta – star connection.
- Describe the application of the above methods.
- Describe open delta connection or V-V connection.
- Describe scott or T-T connection.
- Explain the application of V-V and T-T connection.
- Draw the connection of 3-phase to 2-phase
- Draw the connection of 2-phase to 3-phase.

**Understand the principle of auto-transformer.**- Describe auto-transformer.
- Explain the terms transformed power and conducted power.
- List the advantages and disadvantages of auto-transformer.
- Convert a 2-winding transformer to auto-transformer.
- Mention the uses of auto-transformer.
- Solve problems on auto-transformer.

**Understand the principle of parallel operation of transformer.**- Explain the purpose of parallel operation.
- List the conditions for parallel operation.
- Explain the purpose of polarity test.
- Describe the subtractive and additive polarity.
- Describe the test to determine the polarity of a transformer.
- Describe the parallel operation of transformers with equal voltage ratio.
- Solve problems related to parallel operation.
- List the conditions for parallel operation of 3-phase transformer.
- List the standard ratings of transformer.
- Explain the specification on the name plate of a transformer.

# THREE PHASE INDUCTION MOTORS.

**Understand the principle and construction of 3-phase induction motor.**- Explain the general principle of induction motor.
- Distinguish between induction motor and conduction motor.
- List various types of induction motor.
- List different parts of a 3-phase induction motor.
- Describe the construction of stator of an induction motor.
- Describe the construction of squirrel cage rotor, double squirrel cage rotor and wound rotor of induction motor.
- Explain the purpose of skewing the rotor bars in a squirrel cage rotor.
- Define slip and slip speed.
- Express the derivation the equation = sf and
- Explain rotor voltage, rotor current and rotor power.
- Mention the uses of induction motor.
- Solve problems related to slip. .

**Understand the concept of development of rotating magnetic field.**- Explain the development of rotating magnetic field for three phase induction motor in 3-phase supply.
- Express the deduction of the formula .
- Explain the principle of rotation of a 3-phase motor.

**Understand the principle of torque developed in rotor.**- Explain starting torque, running torque and maximum torque.
- Express the deduction of the equation of starting torque, running torque and maximum torque.
- Describe the condition for maximum torque for running and starting condition.
- Mention the relation between torque and rotor power factor.
- Explain the relation between torque and speed.
- Draw the torque speed curve.
- Explain the effect of changing the voltage on torque and speed.

**Understand the concept of power stages of induction motor.**- List the losess in 3-phase induction motor.
- Indicate different stages of power developed in an induction motor in a diagram.
- Solve problems on power distribution.

**Understand the equivalent circuit and maximum power output of an induction motor.**- Draw the equivalent circuit of an induction motor.
- Explain the circuit diagram.
- Explain maximum power output of an induction motor.
- Express the deduction of the maximum power output

**Understand the principle of starting of a 3-phase induction motor.**- Explain the purpose of starter.
- List the starters used for starting 3-phase induction motor.
- Describe the direct online starter method, start-delta starter method (manual and automatic), auto transformer starter method of starting squirrel cage induction motor.
- Describe the rheostat method of starting slip ring induction motor. .

**Understand the principle of speed control of induction motor.**- List the methods of speed control of 3-phase induction motor.
- Describe speed control by changing applied voltage, changing applied frequency and changing stator poles.
- Describe rheostat control method, concatenation method & injecting emf in rotor circuit.

__Practical__:

**Determine the transformation ratio of a single phase transformer.**- Sketch the required circuit diagram.
- List the tools, equipments & materials for the experiment.
- Connect the equipment according to the circuit diagram.
- Apply the voltage to the high side and connect the load to the low side.
- Tabulate the readings from the instruments and calculate the transformation ratio from the formula:

**Determine the voltage regulation of single phase transformer by direct loading.**- Sketch the necessary circuit diagram.
- List the tools, equipment & materials required.
- Connect the meters according to the diagram.
- Connect the source to the primary keeping the secondary open and record no load voltage (V
_{o}). - Connect full load on the secondary & record the load voltage.
- Calculate the voltage regulation from the formula:

% Voltage Reg. =

**Perform the open circuit test of single phase transformer.**- Draw the circuit diagram.
- List the tools, equipment & materials required.
- Connect the equipment according to the diagram.
- Connect the low side of its rated supply voltage keeping high side open.
- Record the readings of the instruments.
- Calculate Io, Im, Iw, Ro and Xo.
- Draw no load vector diagram with data obtained.

**Perform the short circuit test of a single phase transformer.**- Sketch the required circuit diagram.
- List tools, equipment & materials required.
- Connect the equipment according to the circuit diagram keeping high side to the source.
- Short circuit the low side by a low resistance wire.
- Energize the circuit by applying reduced voltage and increase the voltage until it takes full load of current.
- Record the instrument readings.
- Observe copper loss and calculate and find Re¢, Xe¢ & Ze¢.

**Perform the polarity test of a single phase transformer.**- Draw the required circuit diagram.
- Collect tools, equipment & materials required.
- Connect the equipment according to the diagram.
- Connect the circuit to the source.
- Record the voltmeter readings.
- Determine whether it is additive or subtractive polarity.

**Perform parallel operation of two single phase transformers.**- Draw the circuit diagram.
- Collect tools, equipment & materials required.
- Connect the equipment according to the circuit diagram with proper polarity.
- Energize the circuit and connect the load to the secondary.
- Record the power shared by each transformer.

**Identify and rectify the troubles of a single phase transformer.**- Select a single phase transformer.
- Collect the tools and equipment required.
- Take a test lamp or an AVO meter.
- Perform continuity test, earth test and insulation test employing test lamp and AVO meter.
- Identify the troubles and suggest remedial measures.

**Perform transformer banking.**- Collect the tools, equipment and materials required.
- Draw the circuit diagram of Y-Y, Y-D, D-D and D-Y banking respectively.
- Connect the equipment according to the diagram separately.
- Record the meter readings for each case separately.
- Calculate the voltage ratio in each case.

**Perform the operation of auto-transformer and determining its transformation ratio.**- Sketch the circuit diagram.
- Collect tools, equipment & materials required.
- Connect the equipment according to the circuit diagram.
- Energize the circuit and tabulate the meter readings.
- Calculate transformation ratio, conducted power & transformed power.

**Perform the identification of the parts of a three phase induction motor.**- Select a 3-phase induction motor.
- Collect different tools required for the experiment.
- List different parts of a 3-phase induction motor.
- Dismantle the parts of the motor.
- Identify different parts and make sketch of each part. .
- Assemble the dismantled parts.

**Start a 3-phase induction motor by manual star-delta starter.**- Take a 3-phase squirrel cage induction motor.
- Collect the equipment & tools required.
- Draw the working diagram to perform the experiment.
- Connect the starter with the motor as per diagram.
- Start the motor with the starter: first in star and then in delta position.
- Measure the speed of the motor with tachometer.
- Calculate slip of the motor.

**Start a 3-phase induction motor by automatic star-delta starter.**- Take a 3-phase squirrel cage induction motor.
- Collect the equipment & tools required.
- Draw the working diagram to perform the experiment.
- Connect the starter with the motor as per diagram.
- Push the start button to start the motor automatically first in star and then in delta position.
- Measure the speed of the motor with tachometer.
- Calculate slip of the motor.