Electrical Machine - II

Increasing the air gap in an induction motor generally leads to:

In V/f control (voltage-to-frequency control), if both voltage and frequency are reduced while keeping the ratio constant, the maximum torque of the motor:

Hysteresis motors are particularly suited for applications requiring:

One disadvantage often encountered with reluctance motors is:

The term "step angle" in a stepper motor refers to:

In a brushless DC motor, electronic commutation is performed by:

Short-pitch (or chorded) windings are used in AC machines primarily to:

Compared to a distributed winding, a concentrated winding:

At the minimum point on the V-curve of a synchronous machine, the armature current is minimum because:

When two alternators are paralleled. if one is over-excited and the other under-excited. then:

Draw the torque-slip characteristic of three phase induction motor and show the suitable derivations that maximum torque is independent of rotor resistance.

A 6-pole 50Hz induction motor has a rotor resistance of 0.03 $ \Omega $ per phase and standstill reactance of 0.4 $ \Omega $ per phase. Determine the speed at which the maximum torque is developed.

Explain the working of single-phase induction motor using double revolving field theory.

Explain construction and working of any type of capacitor split phase induction motor. What type of capacitor are used.

What are the similarities between brushless DC motor and conventional DC motor. Give the advantage of brushless DC motor over conventional DC motor.

Explain the construction, working and application of stepper motor.

The field excitation of three phase synchronous motor operating on fixed load is increased from a very low value with the help of a V curve.

Explain the two-reaction theory applicable to salient pole synchronous machine.

Explain how the desirable feature of high starting torque and low operating slip are obtained in a double cage polyphase induction motor.

Why is starter necessary for starting of induction motors? Name different starting methods for 3-phase induction motor.

Draw the physical arrangement of winding in stator and cylindrical rotor.

Describe pulsating magnetic field of ac in winding with spatial displacement.

Draw and explain the phasor diagram of loaded synchronous generator under lagging, leading and unity power factor condition.

Calculate the rms value of induced EMF per phase of a 10 pole three phase 50 Hz alternator with 2 slots per pole per phase and 4 conductors per slots in two layers. The coil span is 150 degrees. The flux per pole has a fundamental component of 0.12 Wb and a 20% third harmonic component.

Increasing the air gap in an induction motor generally leads to:

In V/f control (voltage-to-frequency control), if both voltage and frequency are reduced while keeping the ratio constant, the maximum torque of the motor:

Hysteresis motors are particularly suited for applications requiring:

One disadvantage often encountered with reluctance motors is:

The term "step angle" in a stepper motor refers to:

In a brushless DC motor, electronic commutation is performed by:

Short-pitch (or chorded) windings are used in AC machines primarily to:

Compared to a distributed winding, a concentrated winding:

At the minimum point on the V-curve of a synchronous machine, the armature current is minimum because:

When two alternators are paralleled. if one is over-excited and the other under-excited. then:

Draw the torque-slip characteristic of three phase induction motor and show the suitable derivations that maximum torque is independent of rotor resistance.

A 6-pole 50Hz induction motor has a rotor resistance of 0.03 $\Omega$ per phase and standstill reactance of 0.4 $\Omega$ per phase. Determine the speed at which the maximum torque is developed.

Explain the working of single-phase induction motor using double revolving field theory.

Explain construction and working of any type of capacitor split phase induction motor. What type of capacitor are used.

What are the similarities between brushless DC motor and conventional DC motor. Give the advantage of brushless DC motor over conventional DC motor.

Explain the construction, working and application of stepper motor.

The field excitation of three phase synchronous motor operating on fixed load is increased from a very low value with the help of a V curve.

Explain the two-reaction theory applicable to salient pole synchronous machine.

Explain how the desirable feature of high starting torque and low operating slip are obtained in a double cage polyphase induction motor.

Why is starter necessary for starting of induction motors? Name different starting methods for 3-phase induction motor.

Draw the physical arrangement of winding in stator and cylindrical rotor.

Describe pulsating magnetic field of ac in winding with spatial displacement.

Draw and explain the phasor diagram of loaded synchronous generator under lagging, leading and unity power factor condition.

Calculate the rms value of induced EMF per phase of a 10 pole three phase 50 Hz alternator with 2 slots per pole per phase and 4 conductors per slots in two layers. The coil span is 150 degrees. The flux per pole has a fundamental component of 0.12 Wb and a 20% third harmonic component.

• Cogging and crawling
• Parallel operation of alternators
• Pitch factor and Distribution factor

Cylindrical-rotor synchronous m/c has ______ field winding.

In a synchronous m/c the rotor field axis and the resultant field have an angle between them called ______.

Prime mover for a salient pole synchronous machine is ______.

Emf induced in SM under loaded conditions is known as ______.

Short circuit test on SM is conducted at ______ excitated condition with armature current at 1-50% of the rated value.

Saliency in a synchronous causes the production of ______ torque which is proportional to ______.

In a 1-Phase IM auxiliary winding located at ______ to main winding causes development of ______ torque.

A two-phase servomotor at any control phase voltage has almost ______ torque speed characteristic with torque ______ with increase in speed.

A steeper motor does not require an output ______ sensor.

Universal motors have ______ power factor of ______.

What is "Synchronous" in a synchronous m/c? Why does such a m/c produce no torque at any other speed.

A 50 Hz, 6-pole synchronous generator has 36 slots. It has a two-layer winding with full pitch coil of eight turns each. The flux per pole is 0.015 wb. Determine the induced emf (line-to-line) if the coils are connected to form (a) 2-phase winding. (b) star-connected 3-phase winding.

Explain the meaning and significance of SCR. (Short circuit ratio).

A 3-phase 2.5 MVA, 6.6 kV synchronous generator gave the following data for occ at synchronous speed.
If (A): 20, 25, 32, 45
Voc (line) (V): 4400, 5500, 6600, 7700, 8800
With the armature short-circuited and full load current flowing, the field current is 18 A. When the m/c is applying full-load current at zero pf at rated voltage, the field current is 45 A. Determine the leakage reactance in per phase and the full-load armature reaction in terms of equivalent field amperes. Find also the field current and voltage regulation when the m/c is supplying full load at 0.8 p.f lagging at rated voltage neglect armature resistance.

For a salient-pole synchronous m/c neglecting the effect of armature resistance, derive an expression for power developed as a function of load angle.

Two identical, 3-$ \phi $, star-connected generators, operating in parallel, share equally a total load of 750 kW at 6000 V and p.f 0.8. The synchronous reactance and resistance of each machine are respectively 50 $ \Omega $ and 2.5 $ \Omega $ per phase. The field of first generator is excited so that armature current is 40 A (lagging). Find (a) the armature current of the second alternator; (b) the p.f of each machine (c) the electromotive force of each machine (d) the load angle of each machine.

What are V-curves of a synchronous motor? What are the main characteristic of a synchronous motor.

A 3-$ \phi $, 11 kV star connected synch. motor takes 50 A input current. The effective resistance and synchronous reactance per phase are 1 $ \Omega $ and 30 $ \Omega $ respectively. Calculate the induced emf for a power factor of (a) 0.8 lagging (b) 0.8 leading and (c) the power supplied to the motor.

A 230V, 50 Hz, 4-pole single-phase Induction motor has the following equivalent circuit parameters: $ R_{1m} = R_2 = 8 \Omega $, $ X_{1m} = X_2 = 12 \Omega $, $ X_M = 200 \Omega $. At a slip of 4% calculate (a) input current (b) input power (c) developed power, and developed torque at rated voltage. The motor speed is 140 rpm.

Draw and explain the phasor diagram of an ac series motor.

A universal series motor, when operating on 220 V d.c draws 10A and runs at 1400 rpm. Find the new speed and p.f. when connected to 220 V, 25Hz supply, the motor current remains the same. The motor has total resistance of 1 $ \Omega $ and total inductance of 0.1 H.

Describe the construction of permanent-magnet d.c. motor. What are the advantage and disadvantage of permanent magnet d.c. motor compared with conventional shunt d.c. motors?

Cylindrical-rotor synchronous m/c has ______ field winding.

In a synchronous m/c the rotor field axis and the resultant field have an angle between them called ______.

Prime mover for a salient pole synchronous machine is ______.

Emf induced in SM under loaded conditions is known as ______.

Short circuit test on SM is conducted at ______ excitated condition with armature current at 1-50% of the rated value.

Saliency in a synchronous causes the production of ______ torque which is proportional to ______.

In a 1-Phase IM auxiliary winding located at ______ to main winding causes development of ______ torque.

A two-phase servomotor at any control phase voltage has almost ______ torque speed characteristic with torque ______ with increase in speed.

A steeper motor does not require an output ______ sensor.

Universal motors have ______ power factor of ______.

What is "Synchronous" in a synchronous m/c? Why does such a m/c produce no torque at any other speed.

A 50 Hz, 6-pole synchronous generator has 36 slots. It has a two-layer winding with full pitch coil of eight turns each. The flux per pole is 0.015 wb. Determine the induced emf (line-to-line) if the coils are connected to form (a) 2-phase winding. (b) star-connected 3-phase winding.

Explain the meaning and significance of SCR. (Short circuit ratio).

A 3-phase 2.5 MVA, 6.6 kV synchronous generator gave the following data for occ at synchronous speed.
If (A): 20, 25, 32, 45
Voc (line) (V): 4400, 5500, 6600, 7700, 8800
With the armature short-circuited and full load current flowing, the field current is 18 A. When the m/c is applying full-load current at zero pf at rated voltage, the field current is 45 A. Determine the leakage reactance in per phase and the full-load armature reaction in terms of equivalent field amperes. Find also the field current and voltage regulation when the m/c is supplying full load at 0.8 p.f lagging at rated voltage neglect armature resistance.

For a salient-pole synchronous m/c neglecting the effect of armature resistance, derive an expression for power developed as a function of load angle.

Two identical, 3-$ \phi $, star-connected generators, operating in parallel, share equally a total load of 750 kW at 6000 V and p.f 0.8. The synchronous reactance and resistance of each machine are respectively 50 $ \Omega $ and 2.5 $ \Omega $ per phase. The field of first generator is excited so that armature current is 40 A (lagging). Find (a) the armature current of the second alternator; (b) the p.f of each machine (c) the electromotive force of each machine (d) the load angle of each machine.

What are V-curves of a synchronous motor? What are the main characteristic of a synchronous motor.

A 3-$ \phi $, 11 kV star connected synch. motor takes 50 A input current. The effective resistance and synchronous reactance per phase are 1 $ \Omega $ and 30 $ \Omega $ respectively. Calculate the induced emf for a power factor of (a) 0.8 lagging (b) 0.8 leading and (c) the power supplied to the motor.

A 230V, 50 Hz, 4-pole single-phase Induction motor has the following equivalent circuit parameters: $ R_{1m} = R_2 = 8 \Omega $, $ X_{1m} = X_2 = 12 \Omega $, $ X_M = 200 \Omega $. At a slip of 4% calculate (a) input current (b) input power (c) developed power, and developed torque at rated voltage. The motor speed is 140 rpm.

Draw and explain the phasor diagram of an ac series motor.

A universal series motor, when operating on 220 V d.c draws 10A and runs at 1400 rpm. Find the new speed and p.f. when connected to 220 V, 25Hz supply, the motor current remains the same. The motor has total resistance of 1 $ \Omega $ and total inductance of 0.1 H.

Describe the construction of permanent-magnet d.c. motor. What are the advantage and disadvantage of permanent magnet d.c. motor compared with conventional shunt d.c. motors?