## Question Set 1

#### 1) Which is the most efficient way of controlling a DC shunt motor below rated speed?

a. Armature resistance control

b. Armature voltage control

c. Field resistance control

d. Diverter resistance control in field circuit

#### 2) Which of the following is an interface between Electric Power Supply and the motor?

b. Sensing Unit

c. Power Modulator

d. Mechanical Gear

#### 3) Fixed voltage Fixed Frequency AC can be converted to Variable Voltage Variable Frequency AC by:

a. AC voltage regulator

b. Cycloconverter

c. Fully controlled converter

d. Half controlled converter

#### 4) Which of the following is called the inertial torque?

where $J$ is moment of inertia in $kg\cdot m^2$, B is the coefficient of viscous friction in $N\cdot m$/(rad/s) and $\omega_m$ is the rotor speed in rad/sec.

a. $J\cdot \dfrac{d\omega_m}{dt}$

b. $J\cdot \dfrac{d^2\omega_m}{dt^2}$

c. $B\cdot \omega_m$

d. $B\cdot \omega_m^2$

#### 5) A motor drives two loads. One has rotational motion. It is coupled to the motor through a reduction gear with a=0.2 and efficiency of 95% . The load has moment of inertia of 5 $kg\cdot m^2$ and load torque of 20 $N\cdot m$. The other load has translational motion and has a weight of 500 kg which has to be lifted at a constant speed of 1 $\frac{m}{s}$. The coupling between the translational load and the motor has an efficiency of 90%. The motor inertia can be taken as 0.5 $kg\cdot m^2$ and the motor runs at a speed of 960 rpm. The equivalent inertia referred to the motor shaft is:

a. 0.54 $kg\cdot m^2$

b. 0.64 $kg\cdot m^2$

c. 0.74 $kg\cdot m^2$

d. 0.84 $kg\cdot m^2$

a. 3873 Watt

b. 4873 Watt

c. 5873 Watt

d. 6873 Watt

#### 8) Which of the following types of friction is independent of speed?

a. Coulomb friction

b. Static friction

c. Viscous friction

d. Windage friction

#### 9) Which of the following load offers a constant load torque?

b. Low speed hoist

d. High speed hoist

#### 10) A motor-load combination has the following speed torque characteristics:

$T = 100 - 0.1 \omega_m$ ($N\cdot m$)

$T_L = 0.05\cdot \omega_m$ ($N\cdot m$)

where T = motor torque in $N\cdot m$, $T_L$ = load torque in $N\cdot m$ and $\omega_m$ = speed of the motor-load combination in rpm. The steady state speed of the drive is:

a. 333.33 rpm

b. 455.55 rpm

c. 666.66 rpm

d. 721.66 rpm

#### 11) A drive has the following motor and load speed-torque equation

Motor: $T=1+2\cdot \omega_m$

Load: $T_L=3\cdot \sqrt{\omega_m}$

The steady state equilibrium speeds are:

a. $1$ & $1/4$

b. $1$ & $1/2$

c. $2$ & $1/4$

d. $2$ & $1/2$

#### 12) The drive in Q11 will operate in the steady state at a speed of:

a. $2$

b. $3/2$

c. $1$

d. $1/4$

#### 13) What is the most appropriate way to smoothen the motor torque for a pulsating type load torque?

a. By connecting an inductance in series with the motor.

b. By connecting a flywheel with the motor-load combination.

c. By controlling the triggering angle of the converter feeding the motor.

d. By introducing a gear with appropriate gear ratio.

#### 14) The motor torque speed characteristic is given by the equation $\omega_m= 100 - T$ where $\omega_m$ is in rad/sec and T is in $N\cdot m$. The initial motor torque is $10~N\cdot m$. A step load torque of $50~N\cdot m$ is applied at $t = 0$. If the total inertia of the motor load combination is $5~kg\cdot m^2$, the value of the motor torque after 5 sec is:

a. 50.0 $N\cdot m$

b. 45.2 $N\cdot m$

c. 35.2 $N\cdot m$

d. 25.2 $N\cdot m$