## Question Set 2

#### 16) In which of the following control methods, the no-load speed of a shunt DC motor can be increased beyond rated value?

a. Armature resistance control

b. Armature voltage control

c. Field resistance control

d. Controlling resistance in parallel with armature

#### 17) What is the ideal no-load speed for a series DC motor?

a. $V/(K\phi)$

b. $V/(K\phi)^2$

c. Zero

d. In finite

a. 1115 rpm

b. 1222 rpm

c. 1328 rpm

d. 1404 rpm

#### 19) A full controlled converter is feeding an R-L load with R = 10 $\Omega$ , L=31.83 mH. If the input frequency is 50 Hz, the impedance angle ($\theta$) of the load is

a. $30^o$

b. $45^o$

c. $60^o$

d. $75^o$

a. 149V

b. 169V

c. 179V

d. 189V

#### 22) Discontinuous current operation for a SP-FC-FWR fed separately excited DC motor occurs for speeds

a. Higher than the critical speed

b. Lower than the critical speed

c. Higher than 50% of the critical speed

d. Lower than 50% of the critical speed

#### 23) Extinction angle($\beta$) for a SP-FC-FWR can be calculated by

a. A closed form solution of the relevant equation

b. An iterative solution of the relevant equation

c. Computation of no load speed of the motor

d. Computation of converter output voltage

#### 24) During coasting period in a SP-FC-FWR, the armature voltage is

a. The same as input ac voltage

b. The same as the drop across the armature inductance

c. The same as the armature back-EMF

d. The same as the drop across the armature resistance

#### 25) In which of the following methods, the supply voltage to the armature of a separately excited DC motor is reversed?

a. Forward motoring

b. Forward regenerative braking

c. Forward dynamic braking

d. Forward plugging

#### 26) For a semi-controlled converter fed DC motor, what is the region for $\pi \lt \omega t \lt \beta$ called?

a. Duty interval

b. Coasting interval

c. Freewheeling interval

d. Zero-current interval

#### 27) A 200 V , 900 rpm, 100 A separately excited DC motor has an armature resistance of 0.05 $\Omega$. It is fed by SP-FC-FWR supplied by an ac voltage of 230 V, 50 $H_Z$. Assuming continuous conduction, calculate the firing angle for rated motor torque and 900 rpm speed.

a. $75^o$

b. $65^o$

$30^o$

d. $15^o$

a. 861.2 rpm

b. 746.5 rpm

c. 505.9 rpm

d. 454.7 rpm