ELECTRICAL MACHINES-II

The pitch factor, in rotating electrical machinery, is defined as the ratio of resultant emf of a

For a 3 phase uniformly distributed narrow-spread winding, and the distribution factor is

MMF is related to

When a single-phase winding is excited by an alternating current, then which of the following statements is correct?

Three-phase voltages are applied to the three windings of an electrical machine. If any two supply terminals are interchanged, then the rotating MMF wave

An induction motor can be said analogous to

No-load current in induction motor is 10%-20% of full-load current and the no-load current of transformer is 2%-6%.

Mechanically air gaps in induction motor are kept very low to avoid

A shaded pole motor is one of the types of

Which of the following special motors has rotor movement in discrete step?

Compare full pitch coil and chorded coil in a rotating machine. Discuss MMF of a coil along with its distribution in the winding. Explain with the help of suitable neat and labelled diagram.

Discuss the following terms: (i) MMF, flux per pole (ii) Pole pitch (iii) Cylindrical and salient rotor (iv) Winding distribution factor

Differentiate concentrated winding and distributed winding, with neat and labelled diagram. Discuss, why the windings are distributed sinusoidally.

Explain, how pulsating magnetic field is produced in 1-phase induction motor. Whether it supports self-starting or not? If supports, how? If not, what measures do we take to make it start?

Discuss the following with suitable diagrams: (i) 1-Phase windings shifted by $ 90^\circ $ (ii) 3-Phase windings shifted by $ 120^\circ $

Provide a basic constructional detail of 3 phase induction motor. Explain the role of wound rotor and squirrel cage type rotor in an induction motor.

What are the three different modes of operation of an induction motor? Draw typical torque-slip characteristic, along with fan load characteristic, explaining the steady-state operating point.

Why is blocked rotor test performed on an induction motor? What is the information perceived from this test?

Draw and explain the equivalent circuit diagram of an induction motor.

Mathematically and graphically explain how rotor resistance affects starting torque of an induction motor.

A 3-phase, 50 Hz induction motor has a full-load speed of 1440 r.p.m. For this motor, calculate (i) number of poles; (ii) full load slip and rotor frequency. (iii) speed of stator field with respect to 1. stator structure and 2. rotor structure; (iv) speed of rotor field with respect to 1. rotor structure, 2. stator structure and 3. stator field.

Discuss parallel operation of alternators for synchronization and load division.

Develop the power equation for salient pole synchronous machine with the help of two-reaction theory.

The pitch factor, in rotating electrical machinery, is defined as the ratio of resultant emf of a

For a 3 phase uniformly distributed narrow-spread winding, and the distribution factor is

MMF is related to

When a single-phase winding is excited by an alternating current, then which of the following statements is correct?

Three-phase voltages are applied to the three windings of an electrical machine. If any two supply terminals are interchanged, then the rotating MMF wave

An induction motor can be said analogous to

No-load current in induction motor is 10%-20% of full-load current and the no-load current of transformer is 2%-6%.

Mechanically air gaps in induction motor are kept very low to avoid

A shaded pole motor is one of the types of

Which of the following special motors has rotor movement in discrete step?

Compare full pitch coil and chorded coil in a rotating machine. Discuss MMF of a coil along with its distribution in the winding. Explain with the help of suitable neat and labelled diagram.

Discuss the following terms: (i) MMF, flux per pole (ii) Pole pitch (iii) Cylindrical and salient rotor (iv) Winding distribution factor

Differentiate concentrated winding and distributed winding, with neat and labelled diagram. Discuss, why the windings are distributed sinusoidally.

Explain, how pulsating magnetic field is produced in 1-phase induction motor. Whether it supports self-starting or not? If supports, how? If not, what measures do we take to make it start?

Discuss the following with suitable diagrams: (i) 1-Phase windings shifted by $ 90^\circ $ (ii) 3-Phase windings shifted by $ 120^\circ $

Provide a basic constructional detail of 3 phase induction motor. Explain the role of wound rotor and squirrel cage type rotor in an induction motor.

What are the three different modes of operation of an induction motor? Draw typical torque-slip characteristic, along with fan load characteristic, explaining the steady-state operating point.

Why is blocked rotor test performed on an induction motor? What is the information perceived from this test?

Draw and explain the equivalent circuit diagram of an induction motor.

Mathematically and graphically explain how rotor resistance affects starting torque of an induction motor.

A 3-phase, 50 Hz induction motor has a full-load speed of 1440 r.p.m. For this motor, calculate (i) number of poles; (ii) full load slip and rotor frequency. (iii) speed of stator field with respect to 1. stator structure and 2. rotor structure; (iv) speed of rotor field with respect to 1. rotor structure, 2. stator structure and 3. stator field.

Discuss parallel operation of alternators for synchronization and load division.

Develop the power equation for salient pole synchronous machine with the help of two-reaction theory.

The pitch factor for a two-thirds short-pitch coil is

The speed regulation of a synchronous motor is

The armature flux helps the main field flux when the load power factor is

In alternators, damper windings are used to

In a split-phase motor, the running winding should have

In a capacitor start and run motors, the function of the running capacitor in series with the auxiliary winding is to

In case the field of a synchronous motor is under excited, the power factor will be

When the excitation of an unloaded salient pole synchronous motor gets disconnected

The back e.m.f. setup in the stator of a synchronous motor will depend on

If two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively, then the highest speed of alternators will be

Explain the armature reaction phenomenon in a cylindrical rotor synchronous generator by drawing the space and time phasor diagram when operating at an internal power factor of (i) zero-lagging and (ii) zero-leading.

For a salient pole, machine $ P_1 $ and $ P_2 $ are the maximum values of electromagnetic power and reluctance power respectively. Show that the load angle $ \delta $, at which the resultant power is maximum can be obtained from the relation $ \cos \delta = \frac{-P_1 \pm \sqrt{P_1^2 + 32 P_2^2}}{8P_2} $

A 6-pole, 3-phase, 50 Hz alternator has 12 slots per pole and 4 conductors per slot. The winding is five-sixth pitch and the flux per pole is 1.5 Wb. The armature coils are all connected in series with star connection. Calculate the induced e.m.f. per phase.

Define the various modes of excitation of synchronous generator. Also draw the V curve and inverted V curve for such system.

Discuss Blondel's two-reaction theory of salient pole synchronous machine.

The speed regulations of two 800 kW alternators A and B running in parallel are 100% to 104% and 100% to 105% from full-load to no-load respectively. How will the two alternators share a load of 1000 kW?

State the need for parallel operation of alternators. What are the conditions for parallel operation of three-phase alternators?

A 500-kVA, 1.1-kV, 50 Hz, three-phase star-connected alternator has an effective armature resistance of 0.2 ohm per phase. The synchronous reactance per phase is 1.5 ohm. Find the full-load voltage regulation at (i) 0.8 lagging power factor and (ii) 0.8 leading power factor. Draw phasor diagram in each case.

Explain why a synchronous motor does not have starting torque. Explain one method of starting a synchronous motor.

An industrial plant has a load of 800 kW at a power factor of 0.8 lagging. It is desired to install a synchronous motor to deliver a load of 200 kW and also serve as a synchronous condenser to improve the overall power factor of the plant to 0.92. Determine the kVA rating of the synchronous motor and its power factor. Assume that the motor has an efficiency of 90 percent.

Explain how the stationary, pulsating m.m.f. wave of a single-phase induction motor can be considered as equivalent to two equal but oppositely rotating m.m.f. waves. Also explain why the forward flux wave is several times greater than the backward flux wave at normal rotor speed.

A 230-V, 4-pole, 50 Hz capacitor start a single-phase induction motor has the following constants and losses: $ r_1 = 2.10 \Omega $, $ r_2 = 4 \Omega $, $ X_m = 70 \Omega $, $ x_1 = 3 \Omega $, $ x_2 = 3 \Omega $. Core loss = 48 watts, Friction and windage loss = 20 watts. For a slip of 0.05, compute the stator current, pf, power output, torque and efficiency when this motor is running at rated voltage and frequency with its auxiliary winding open.

Draw the complete torque-speed characteristics of a single-phase induction motor when no auxiliary winding is provided on the stator. Show how the torque speed characteristics is modified when an auxiliary winding is provided.

Mention the conditions necessary for the production of rotating magnet field with the help of stationary windings.

What is a universal motor? How is it different from a d.c. series motor? Mention its applications.

Explain the construction and working principles of a repulsion motor. How is a repulsion-induction motor different from a repulsion motor?

The pitch factor for a two-thirds short-pitch coil is

The speed regulation of a synchronous motor is

The armature flux helps the main field flux when the load power factor is

In alternators, damper windings are used to

In a split-phase motor, the running winding should have

In a capacitor start and run motors, the function of the running capacitor in series with the auxiliary winding is to

In case the field of a synchronous motor is under excited, the power factor will be

When the excitation of an unloaded salient pole synchronous motor gets disconnected

The back e.m.f. setup in the stator of a synchronous motor will depend on

If two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively, then the highest speed of alternators will be

Explain the armature reaction phenomenon in a cylindrical rotor synchronous generator by drawing the space and time phasor diagram when operating at an internal power factor of (i) zero-lagging and (ii) zero-leading.

For a salient pole, machine $ P_1 $ and $ P_2 $ are the maximum values of electromagnetic power and reluctance power respectively. Show that the load angle $ \delta $, at which the resultant power is maximum can be obtained from the relation $ \cos \delta = \frac{-P_1 \pm \sqrt{P_1^2 + 32 P_2^2}}{8P_2} $

A 6-pole, 3-phase, 50 Hz alternator has 12 slots per pole and 4 conductors per slot. The winding is five-sixth pitch and the flux per pole is 1.5 Wb. The armature coils are all connected in series with star connection. Calculate the induced e.m.f. per phase.

Define the various modes of excitation of synchronous generator. Also draw the V curve and inverted V curve for such system.

Discuss Blondel's two-reaction theory of salient pole synchronous machine.

The speed regulations of two 800 kW alternators A and B running in parallel are 100% to 104% and 100% to 105% from full-load to no-load respectively. How will the two alternators share a load of 1000 kW?

State the need for parallel operation of alternators. What are the conditions for parallel operation of three-phase alternators?

A 500-kVA, 1.1-kV, 50 Hz, three-phase star-connected alternator has an effective armature resistance of 0.2 ohm per phase. The synchronous reactance per phase is 1.5 ohm. Find the full-load voltage regulation at (i) 0.8 lagging power factor and (ii) 0.8 leading power factor. Draw phasor diagram in each case.

Explain why a synchronous motor does not have starting torque. Explain one method of starting a synchronous motor.

An industrial plant has a load of 800 kW at a power factor of 0.8 lagging. It is desired to install a synchronous motor to deliver a load of 200 kW and also serve as a synchronous condenser to improve the overall power factor of the plant to 0.92. Determine the kVA rating of the synchronous motor and its power factor. Assume that the motor has an efficiency of 90 percent.

Explain how the stationary, pulsating m.m.f. wave of a single-phase induction motor can be considered as equivalent to two equal but oppositely rotating m.m.f. waves. Also explain why the forward flux wave is several times greater than the backward flux wave at normal rotor speed.

A 230-V, 4-pole, 50 Hz capacitor start a single-phase induction motor has the following constants and losses: $ r_1 = 2.10 \Omega $, $ r_2 = 4 \Omega $, $ X_m = 70 \Omega $, $ x_1 = 3 \Omega $, $ x_2 = 3 \Omega $. Core loss = 48 watts, Friction and windage loss = 20 watts. For a slip of 0.05, compute the stator current, pf, power output, torque and efficiency when this motor is running at rated voltage and frequency with its auxiliary winding open.

Draw the complete torque-speed characteristics of a single-phase induction motor when no auxiliary winding is provided on the stator. Show how the torque speed characteristics is modified when an auxiliary winding is provided.

Mention the conditions necessary for the production of rotating magnet field with the help of stationary windings.

What is a universal motor? How is it different from a d.c. series motor? Mention its applications.

Explain the construction and working principles of a repulsion motor. How is a repulsion-induction motor different from a repulsion motor?

Why is high-voltage winding of alternator placed on stator?

Write the expression of distribution factor of synchronous machine.

What do you mean by hunting in synchronous motor?

Which parameters are used to draw inverted V curve of synchronous machine?

What are the methods available for making a 1-$ \phi $ induction motor self-starting?

Differentiate between 'capacitor-start' and 'capacitor-start capacitor-run' for a 1-$ \phi $ induction motor.

Suggest one domestic application of universal motor.

Write any one application of stepper motor.

List two applications of synchronous motor.

State any two uses of single-phase synchronous motor.

A 3-phase, Y-connected synchronous generator rated at 10 kVA and 230 V has a synchronous reactance of 1.2 ohm per phase and an armature resistance of 0.5 ohm per phase. Calculate the % voltage regulation at full load with 0.8 lagging power factor.

Derive the e.m.f. equation of an alternator.

Discuss the effects of field current on synchronous motor power factor with the help of phasor diagram.

Show that for alternators running in parallel, the division load between them is governed mainly by the speed-load characteristics of their prime movers.

A 4-pole alternator has an armature with 25 slots and 8 conductors per slot and rotates at 1500 r.p.m. and the flux per pole is 0.05 Wb. Find the e.m.f. generated, if winding factor is 0.96 and all the conductors are in series.

A universal series motor has a resistance of 20 ohms and an inductance of 0.2 H. When connected to a 200-V d.c. supply and loaded to take 0.5 A, it runs at 1500 r.p.m. Determine the speed, torque, p.f. and regulation, when connected to a 200-V, 50 Hz a.c. supply and loaded to take the same current.

Define armature reaction and explain the effect of armature reaction on the different power system loads of synchronous generator.

Explain two-reaction theory of salient pole synchronous machine.

Explain the principle of operation of the two-phase servomotor with the help of neat illustration. Also mention its advantages.

Explain the e.m.f. method of determining the regulation of an alternator.

State and explain the conditions for parallel operation of alternators.

Describe in detail about the effect of load change on load angle and power factor of a 3-phase synchronous motor operating on infinite bus bar and constant excitation.

Why is high-voltage winding of alternator placed on stator?

Write the expression of distribution factor of synchronous machine.

What do you mean by hunting in synchronous motor?

Which parameters are used to draw inverted V curve of synchronous machine?

What are the methods available for making a 1-$ \phi $ induction motor self-starting?

Differentiate between 'capacitor-start' and 'capacitor-start capacitor-run' for a 1-$ \phi $ induction motor.

Suggest one domestic application of universal motor.

Write any one application of stepper motor.

List two applications of synchronous motor.

State any two uses of single-phase synchronous motor.

A 3-phase, Y-connected synchronous generator rated at 10 kVA and 230 V has a synchronous reactance of 1.2 ohm per phase and an armature resistance of 0.5 ohm per phase. Calculate the % voltage regulation at full load with 0.8 lagging power factor.

Derive the e.m.f. equation of an alternator.

Discuss the effects of field current on synchronous motor power factor with the help of phasor diagram.

Show that for alternators running in parallel, the division load between them is governed mainly by the speed-load characteristics of their prime movers.

A 4-pole alternator has an armature with 25 slots and 8 conductors per slot and rotates at 1500 r.p.m. and the flux per pole is 0.05 Wb. Find the e.m.f. generated, if winding factor is 0.96 and all the conductors are in series.

A universal series motor has a resistance of 20 ohms and an inductance of 0.2 H. When connected to a 200-V d.c. supply and loaded to take 0.5 A, it runs at 1500 r.p.m. Determine the speed, torque, p.f. and regulation, when connected to a 200-V, 50 Hz a.c. supply and loaded to take the same current.

Define armature reaction and explain the effect of armature reaction on the different power system loads of synchronous generator.

Explain two-reaction theory of salient pole synchronous machine.

Explain the principle of operation of the two-phase servomotor with the help of neat illustration. Also mention its advantages.

Explain the e.m.f. method of determining the regulation of an alternator.

State and explain the conditions for parallel operation of alternators.

Describe in detail about the effect of load change on load angle and power factor of a 3-phase synchronous motor operating on infinite bus bar and constant excitation.

• Shaded pole induction motor
• Hysteresis motor
• Universal motor
• Reluctance motor
• Stepper motor