Single Phase Induction Motors Emec – GATE EE Electrical MachinesPractice Questions & PYQs

The operating region of the developed torque $\left(\mathrm{T}_{\mathrm{em}}\right)$ and speed $(\omega)$ of an induction motor drive is given by the shaded region OQRE in the figure. The load torque $\left(\mathrm{T}_{\mathrm{L}}\right)$ characteristic is also shown. The motor drive moves from the initial operating point O to the final operating point S. Which one of the following trajectories will take the shortest time?

A 10-pole, $50 \mathrm{~Hz}, 240 \mathrm{~V}$ , single phase induction motor runs at 540 RPM while driving rated load. The frequency of induced rotor currents due to backward field is

The following columns present various modes of induction machine operation and the ranges of slip

The correct matching between the elements in column A with those of column B is

The four stator conductor $\left(A, A^{\prime}, B\right.$ and $\left.B^{\prime}\right)$ of a rotating machine are carrying DC currents of the same value, the directions of which are shown in figure (i). The rotor coils $a-a^{\prime}$ and $b-b^{\prime}$ are formed by connecting the back ends of conductor ' $a$ ' and ' $a^{\prime}$ ' and ' $b$ ' and ' $b^{\prime}$ ', respectively, as shown in figure (ii). The e.m.f. induced in coil $a-a^{\prime}$ and coil $b-b^{\prime}$ are denoted by $E_{a-a^{\prime}}$ and $E_{b-b^{\prime}}$ ; respectively. If the rotor is rotated at uniform angular speed $\omega \mathrm{rad} / \mathrm{s}$ in the clockwise direction then which of the following correctly describes the $\mathrm{E}_{\mathrm{a}-\mathrm{a}^{\prime}}$ and $\mathrm{E}_{\mathrm{b}-\mathrm{b}^{\prime}}$ ?

A 4-pole induction motor with inertia of 0.1 $kg-m^2$ drives a constant load torque of 2 Nm. The speed of the motor is increased linearly from 1000 rpm to 1500 rpm in 4 seconds as shown in the figure below. Neglect losses in the motor. The energy, in joules, consumed by the motor during the speed change is ____________. (round off to nearest integer)

The type of single-phase induction motor, expected to have the maximum power factor during steady state running condition, is

A three-phase, 50 Hz, 4-pole induction motor runs at no-load with a slip of 1%. With full load, the slip increases to 5 %. The % speed regulation of the motor (rounded off to 2 decimal places) is _________ .

The magnetic circuit shown below has uniform cross-sectional area and air gap of 0.2 cm. The mean path length of the core is 40 cm. Assume that leakage and fringing fluxes are negligible. When the core relative permeability is assumed to be infinite, the magnetic flux density computed in the air gap is 1 tesla. With same Ampere-turns, if the core relative permeability is assumed to be 1000 (linear), the flux density in tesla(round off to three decimal places) calculated in the air gap is __________

The equivalent circuit of a single phase induction motor is shown in the figure, where the parameters are $R_{1}=R'_{2}=X_{i1}=X'_{i2}=12\Omega$ , $X_{M}=240\Omega$ and s is the slip. At no-load, the motor speed can be approximated to be the synchronous speed. The no-load lagging power factor of the motor is___________ (up to 3 decimal places).

A transformer with toroidal core of permeability $\mu$ is shown in the figure. Assuming uniform flux density across the circular core cross-section of radius $r\lt \lt R$ , and neglecting any leakage flux, the best estimate for the mean radius R is

A 375W, 230 V, 50 Hz capacitor start single-phase induction motor has the following constants for the main and auxiliary windings (at starting): $Z_{m}=(24.50+j12.75)\Omega$ (main winding), $Z_{n}=(24.50+j12.75)\Omega$ (auxiliary winding). Neglecting the magnetizing branch the value of the capacitance (in $\mu$ F ) to be added in series with the auxiliary winding to obtain maximum torque at starting is _______.

The flux linkage ( $\lambda$ ) and current (i) relation for an electromagnetic system is $\lambda = (\sqrt{i})/g$ . When i=2A and g (air-gap length)=10cm, the magnitude of mechanical force on the moving part, in N, is ________.

The direction of rotation of a single-phase capacitor run induction motor is reversed by

A 220 V, 3-phase, 4-pole, 50 Hz inductor motor of wound rotor type is supplied at rated voltage and frequency. The stator resistance, magnetizing reactance, and core loss are negligible. The maximum torque produced by the rotor is 225 % of full load torque and it occurs at 15% slip. The actual rotor resistance is 0.03 $\Omega$ /phase. The value of external resistance (in Ohm) which must be inserted in a rotor phase if the maximum torque is to occur at start is ______.

A 200 V, 50 Hz, single-phase induction motor has the following connection diagram and winding orientations as shown. MM' is the axis of the main stator winding( $M_1M_2$ ) and AA' is that of the auxiliary winding( $A_1A_2$ ). Directions of the winding axis indicate direction of flux when currents in the windings are in the directions shown. Parameters of each winding are indicated. When switch S is closed, the motor

In a stepper motor, the detent torque means

A 230 V, 50 Hz, 4-pole, single-phase induction motor is rotating in the clockwise (forward) direction at a speed of 1425 rpm. If the rotor resistance at standstill is 7.8 $\Omega$ , then the effective rotor resistance in the backward branch of the equivalent circuit will be

A three-phase, three-stack, variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is

For a single phase capacitor start induction motor, which of the following statements is valid ?

In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve