# The effect of increasing the length of air gap in an induction motor is to increase the

55 views
The effect of increasing the length of air gap in an induction motor is to increase the (a) power factor (b) speed (c) magnetising current (d) air gap flux

## Related questions

The ratio of rotor output to rotor input in an induction motor is 0.96. The slip of the motor is (a) 0.04% (b) 4% (c) 6% (d) 12%

What happens to the reluctance of a magnetic circuit, when an air gap is introduced to the core cross section ? (A) Decreases (B) Increases (C) Remain same (D) None of the above

An air gap is usually inserted in magnetic circuits to?

Full load current of an Induction motor is 20 Ampere. The no-load current may be expected to be: A) 25 Ampere to 28 Ampere B) 15 Ampere to 18 Ampere C) 11 Ampere to 14 Ampere D) 6 Ampere to 10 Ampere

The frequency (fr) of the rotor current in an induction motor is given by the expression (s = slip, f = supply frequency)

The power factor of an induction motor under no load conditions will be close to (A) 0.2 lagging (B) 0.2 leading (C) 0.5 lagging (D) Unity

Under no load condition, if the applied voltage to an induction motor is reduced from the rated voltage to half the rated value,  (A) the speed decreases and the stator current increases (B) both the speed and the stator current decreases (C) the speed and the stator current remain practically constant (D) there is negligible change in the speed but the stator current decreases

When the supply voltage to an induction motor is reduced by 10%, the maximum torque will decrease by about  A) 5% B) 10% C) 20% D) 40%

The effect of increasing load on a synchronous motor running with normal excitation is (A) Increase both its Ia and power factor. (B) Decrease Ia, but increase power factor. (C) Increase Ia, but decrease power factor (D) Decrease both Ia and power factor.

In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve (A) low starting torque (B) quick acceleration (C) high efficiency (D) reduced size

The maximum torque of an induction motor is 200 kg-m at a slip of 12%. The torque at 6% slip would be (a) 100 kg-m (b) 160 kg-m (c) 50 kg-m (d) 40 kg-m

The actual speed of an induction motor is always • Less than synchronous speed • More than synchronous speed • Equal to synchronous speed • None of the above.

An 8 pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of the rotor current is (a) 30 Hz (b) 60 Hz (c) 120 Hz (d) 180 Hz

Leakage flux in an induction motor is  (A) flux that leaks through the machine (B) flux that links both stator and rotor windings (C) flux that links none of the windings (D) flux that links the stator winding or the rotor winding but not both

Crawling in an Induction motor is caused by (A) Low voltage supply (B) High loads (C) Harmonics developed in the motor (D) Improper design of the machine

In case of four pole, lap wound machine if the air gap under each pole is the same, then what will be the result?  (A) There will be reduced eddy currents (B) There will be reduced hysteresis loss (C) Current in each path will not be the same (D) It will result in higher terminal voltage

Effect of increase in temperature in an overhead transmission line is (a) to increase stress and length both (b) to decrease stress and length both (c) to decrease stress and increase length (d) None of the above

Which statement out of the following is a wrong statement with regard to Induction motor? A) Auto-transformer starter is costlier to “direct on line” (DOL) starter B) DOL starter is used for motors up to 5 horse power only C) Auto transformer starter is used for motors up to 20 horse power only D) Star delta starter connects the motor first in delta at the time of starting then in star for running

in a three-phase induction motor, the rotor field runs at the following speed with respect to the stator structure:

The slip of an induction motor normally does not depend on  (A) rotor speed (B) synchronous speed (C) shaft torque (D) core-loss component

In an induction motor if the flux density is reduced to one-half, of its normal value then the torque will  (1) reduce to one-half (2) reduce to one-fourth (3) remain unchanged (4) increase four times

An induction motor having full load torque of 60 Nm when delta connected develops a starting torque of 120 Nm. For the same supply voltage if the motor is changed to star connection, the starting torque developed will be  A) 40 Nm B) 60 Nm C) 90 Nm D) 120 Nm

An induction motor operating at 0.8 pf lagging is consuming 300 kW. A zero real power consuming synchronous motor is connected across the induction motor to raise the pf to 0.92 lagging. The reactive power drawn by the synchronous motor is a. - 352 kVAR b. - 225 kVAR c. - 127.8 kVAR d. - 97.2 kVAR

The number of poles in a phase induction motor at 50 Hz and running at 1500 rpm will be?

Consider the following statements: Star delta starter is used in 3-phase induction motor because it  1. Prevents heating of the motor winding  2. Ensures permissible minimum starting current  3. Is regulated by electricity authority  4. Ensures smooth run up to full load   Of these statements (a) 1, 2 and 3 are correct (b) 2, 3 and 4 are correct (c) 1, 3 and 4 are correct (d) 1 and 2 are correct

A change of 4% in the supply voltage to an induction motor will produce a change of approximately

In air-core cable the surge voltage travels approximately at the speed of light and a cable of 100m length gives a delay of a. 0.666μsec b. 0.333μsec c. 1.555μsec d. 1μsec

A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will?

The stator of a 415V, 50 Hz, 4-pole slip ring Induction Motor is excited by rated frequency with slip rings open circuited. The rotor is made to rotate at a speed of 600 rpm in the opposite direction to the normal direction, The frequency of induced voltage across slip ring is A) 30 Hz B) 70 Hz C) 20 Hz D) 35 Hz

The rotor frequency for a 3-phase 6-pole, 1000 r.p.m. induction motor with a slip of 0.04 is (a) 2 Hz (b) 4 Hz (c) 6 Hz (d) 8 Hz

A 6-pole, 50Hz, 3-φ induction motor is running at 950 r.p.m. and has Cu loss of 5kW. The rotor input is (a) 10 kW (b) 95 kW (c) 100 kW (d) 9.5 kW

If a 3-phase, 400V, 50Hz, 4 pole induction motor is running at a slip of 5% then the relative speed of rotor field with respect to stator filed is:

The direction of rotation of a 3-phase induction motor is clockwise when it is supplied with 3-phase sinusoidal voltage having phase sequence A-B-C. For counter clockwise rotation of the motor, the phase sequence of the power supply should be  (A) B-C-A (B) C-A-B (C) A-C-B (D) B-C-A or C-A-B

The type of single-phase induction motor having the highest power factor at full load is (A) shaded pole type (B) split-phase type (C) capacitor-start type (D) capacitor-run type

The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f ) constant. At rated frequency of 50 Hz and rated voltage of 400 V its speed is 1440 rpm. Find the speed at 30 Hz, if the load torque is constant  (A) 882 rpm (B) 864 rpm (C) 840 rpm (D) 828 rpm

For a single phase capacitor start induction motor, which of the following statements is valid?  A) The capacitor is used for power factor improvement B) The direction of rotation can be changed by reversing the main winding terminals C) The direction of rotation cannot be changed D) The direction of rotation can be changed by interchanging the supply terminals

The ratio of air-gap line voltage from open-circuit characteristic and armature current from short-circuit characteristic for a particular value of the field current in a synchronous generator is (A) synchronous reactance (B) synchronous impedance (C) unsaturated synchronous reactance (D) unsaturated synchronous impedance

In a 3-phase voltage source inverter used for speed control of induction motor, anti-parallel diodes are used across each switching device. The main purpose of diodes is to:

A change of 5% in supply voltage to an induction motor will produce a change of approximately (a) 5% in the rotor torque (b) 7.5% in the rotor torque (c) 10% in the rotor torque (d) 25% in the rotor torque

Slip test is performed to determine :  (A) Slip in an induction motor  (B) Xd and Xq in a salient pole alternator  (C) Synchronous impedance in an alternator  (D) Positive and negative sequence impedances of an alternator