DieselShip's Online Content Library

Q3. A relay coil has resistance 24 W and inductance 2 H. It operates on 12 V d.c.

(a) Calculate the time after switching on the supply for the relay to close if it requires a current of 0.25 A to operate.

(b) Calculate the energy stored in the coil at the time of operation.

(C) Calculate the time delay before operation if a resistor of 6 o is connected in series with the relay coil and it is operated from 15 V supply.

Q2. Fig Q3 shows a basic voltage stabilizer circuit intended to give a regulated output of 8 V d.c. from an unregulated input which can vary between 12 V and 20V. The Zener diode has a breakdown voltage of 8 V, a forward resistance after breakdown of 2 () and requires a minimum forward current of 2 mA. The Zener Diode has a maximum power rating of 1 W. Calculate EACH of the following:

(a) The minimum value of the sense resistance ‘R’;

(b) The regulated output voltage when the input is 15 V and the toad output current is 40 mA;

(a) The maximum permissible output current for satisfactory regulation if the input voltage is 12 V.

Q5. A star connected three phase Load has a coil of resistance 50 Ω and inductance 0.1 H in each phase. It is connected to a three-phase, three-wire supply of 415V, 50Hz.

Calculate EACH of the following:

(a) The Line current;

(b) The power factor of the Load;

(c) The value of EACH of three identical delta connected capacitors, which if connected in parallel with this Load, will raise the overall power factor to unity.