Electrical Machine-I (EX-402) - Important Questions

Derive the conditions for zero (and maximum/negative) voltage regulation of a transformer.

Find the voltage regulation of the 20 kVA, 2000/200 V single-phase transformer with given winding resistances and reactances at (i) 0.8 pf lagging, (ii) unity pf, (iii) 0.707 pf leading.

Using the transformer EMF equation $E = 4.44 f N \Phi_m$, solve numerical problems to find number of turns, induced EMF, flux density, or core cross-sectional area.

What is an auto-transformer? Compare auto-transformer with two-winding transformer and state advantages of auto-transformer.

Given hysteresis, eddy current and copper losses at one voltage-frequency, calculate the losses at a new voltage and frequency.

Explain the short-circuit test on a transformer conducted at rated current with circuit diagram.

Discuss the constructional features of transformers. Draw neat diagrams.

Calculate transformer efficiency at full load and half load at unity power factor and determine the load for maximum efficiency and the corresponding copper loss.

Explain the operation of a practical single-phase transformer under no-load condition with relevant phasor diagrams.

Draw the exact equivalent circuit of a transformer and explain the various parameters.

Solve numerical on no-load test of transformer to find core loss, no-load power factor, active (core-loss) component and magnetizing component of no-load current.

Derive the condition for maximum efficiency of a transformer and find the load current at maximum efficiency.

Explain the Scott / T-T connection for 3-phase to 2-phase (and 2-phase to 3-phase) conversion with circuit and phasor diagrams, including balanced/unbalanced operation and teaser winding ratio.

Explain the conservator and breather in transformers.

Write short notes (Any two)

For a Delta-Delta bank with one transformer removed (V-V operation) supplying a given kVA load, calculate the kVA per transformer, percent loading, total bank rating, and V-V to Delta-Delta rating ratio.

Derive the condition for no circulating current at no-load when two transformers are operated in parallel.

Write short notes on any two.

Numerical on Scott-connected transformer supplying two single-phase loads: calculate 3-phase side line currents.

Describe the parallel operation of three-phase transformers with unequal voltage ratios.

Explain the need/advantages and essential conditions for successful parallel operation of single-phase transformers.

Numerically determine no-load circulating current and load sharing (current, kVA and power factor) for two transformers in parallel with different open-circuit voltages and given per-unit impedances.

Numerically calculate kVA loading and operating power factor of each transformer when two transformers with given percentage resistance and reactance share a load in parallel.

Derive the relationship between rotor input power, rotor copper loss, and mechanical power developed (rotor output) in terms of slip $s$ for a three-phase induction motor.

Explain the torque-speed (and torque-slip) characteristics of a 3-phase induction motor.

Explain the construction and working principle of a three-phase induction motor

Explain the operation of a polyphase (three-phase) induction motor and draw and explain its equivalent circuit.

Explain the principle of production of rotating magnetic field in a 3-phase induction motor

Calculate stator core loss from no-load test and rotor losses, rotor copper loss and speed at full load

Compare the construction, characteristics and applications of squirrel cage and slip-ring (wound rotor) three-phase induction motors.

Explain the procedure for conducting no-load and blocked-rotor tests and drawing the circle diagram of a three-phase induction motor to predetermine its performance characteristics.

Calculate synchronous speed, rotor speed/slip and rotor current frequency for a polyphase induction motor given poles, supply frequency and slip/speed

Calculate rotor copper loss, shaft torque and efficiency of a 3-phase induction motor from power flow, slip, stator losses and mechanical losses

Draw the circle diagram from given no-load and blocked-rotor test data and determine full-load current, power factor, maximum power developed and starting torque.

Derive the torque-slip equation for a 3-phase induction motor and the slip for maximum torque.

Explain the construction and torque-speed characteristics of a double-cage rotor induction motor and how it improves starting performance compared to a single squirrel-cage motor.

Find the external rotor resistance to be inserted to obtain maximum torque at starting.

Explain cogging and crawling together with double-cage / deep-bar (deep-cage) induction motor

Explain the phenomena of cogging and crawling in a three-phase induction motor

Explain the working of star-delta starter for a three-phase induction motor with neat sketch.

Explain the various schemes of starting a squirrel cage induction motor.

Explain speed control techniques of an induction motor from the rotor side.

Find the starting current on rated voltage with short-circuited slip rings neglecting stator impedance.

Explain the different speed control methods of a squirrel cage induction motor.

Explain the principle, concept and working of an induction generator, including self-excited and externally excited types with circuit diagram.

Explain the terms braking and induction motor.

Explain speed control of a three-phase induction motor by varying supply frequency and by varying rotor resistance.

Construction and working principle of single-phase A.C. series motor

Explain the construction, working principle, operation and applications of a (single-phase) linear induction motor.

Role of compensating winding in the operation of AC series motor

Explain the constructional features and working principle of single-phase induction motor.

Explain why a single-phase induction motor is not self-starting using double revolving field theory and principle of operation.

Explain types / classification of single phase induction motors with working principle

Explain / derive the equivalent circuit of a single-phase induction motor

Discuss the procedure / tests to determine the parameters of the equivalent circuit of a single-phase induction motor

Explain the types, construction and working principle of servomotors.

Explain double revolving field theory with equivalent circuit of single-phase induction motor and its determination.

A 4-pole, 250 W, 115 V, 60 Hz capacitor-start induction motor takes a full-load line current of 5.3 A while running at 1760 r.p.m. If the full load efficiency of the motor is 64%, find

Write short notes on linear induction motor and servo motor.

Discuss the excitation phenomenon in transformers (including options on breather, induction motor braking and steady-state performance).

Write short notes on: (any Two)

What do you mean by SPP related to electrical machine? What is it significance?