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.