131 135

131. Advantages of vvvf drives over non vvvf drives for EOT cranes? 

1. Smooth start and stop. 

2. No jerking of load. 

3. Exact positioning 

4. Better protection for motor. 

5. high/low speed selection. 

6. Reliability of break shoe. 

7. Programmable break control. 

8. Easy circuitry 

9. Reduction in controls 

10. Increases motor life 

132. What is the significance of vector grouping in Power Transformers? 

Every power transformer has a vector group listed by its manufacturer. 

Fundamentally it  tells you the information about how the windings are connected (delta or wye) and the phase difference between the current and voltage. EG. 

DYN11 means Delta primary, Wye Secondary and the current is at 11 o clock referred to the voltage. 

133. Type of A.C motor is used in the fan (ceiling fan, exhaust fan, pedestal fan, bracket fan  etc) which are find in the houses? 

Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start 

capacitor run. 

134. Why, when birds sit on transmission lines or current wires doesn’t get shock? 

It’s true that if birds touch the single one line (phase or neutral) they don’t get electrical shocked. 

If birds touch 2 lines than the circuit is closed and they get electrical shock. 

So if a human  touch single one line (phase) then he doesn’t get shock if he is in the air (not touching – standing 

on the ground if he is standing on the ground then touching the line (phase) he will get a shock.

Because the ground on what we standing is like line (ground bed – like neutral) । and in the most  of electric lines the neutral is grounded. 

So that means that human who touch the line closes the  circuit between phase and neutral. 

135. What happens if we give 220 volts dc supply to tube light? 

Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC  supply. 

Normally they have low resistance. When DC supply is applied, due to low resistance,  the current through lamp would be so high that it may damage the bulb element.