Q2. In the network shown in Fig Q1 the 15 Ω resistor dissipates 60 W.
Calculate EACH of the following:
(a) The current taken from the supply;
(b) The value of the applied voltage V;
(c) The value to which the 60 Ω resistor must be changed to increase the current taken from the supply to 4 A.
Q4. A silicon power transistor with the characteristics given in Worksheet Q3 is operated from a 12 V supply and has a maximum power rating of 18 mW.
(a) Plot the 18 W power dissipation curve on the characteristics.
(b) Determine the minimum safe collector load resistor for the transistor.
(c) If the transistor is biased with 80 mA and a sinusoidal signal of 40 mA is applied to the base, determine EACH of the following:
(i) The variation in collector current;
(ii) The corresponding variation in collector voltage;
(iii) The a.c. power output of the transistor.
Q2. Two impedances Z1 and Z2 are connected in parallel to a 240 V single phase a.c. supply. The total current drawn is 10 A at unity power factor. Impedance Z1 takes a current of 5A at p.f 0.6 lag.
(a) The current in impedance Z2;
(b) The resistance and reactance of each impedance;
(c) The power dissipated by each impedance.
Q1. A 3ph 440 V a.c. generator supplies the following loads:
A. a star connected load of 33 kVA at p.f. 0.9 leading
B. a delta connected load of 40 kW at p.f. 0.85 lagging
C. Miscellaneous loads of 23 kVA at p.f. 0.8 lagging
(a) The kVA supplied by the generator;
(b) The current supplied by the generator;
(c) The phase currents for the star and delta connected loads.
Q1. An unbalanced star connected three phase load is supplied from a 440 V 50 Hz four wire supply.
The current in the red line is 6 A lagging by 30º, the current in the yellow line is 5A in phase and the current in the blue line is 7A lagging by 15º. Determine EACH of the following:
(a) The value of the current in the neutral line;
(b) Its phase relationship to the voltage between the red line and the neutral;
(c) The total power dissipated in the circuit.
Q5. (a) Describe the FOUR conditions which have to be met before an alternator can be connected to live busbars.
(b) Explain the process by which kW load can be taken up by a newly synchronized alternator.
(c) Describe the effect of increasing the excitation of an alternator which is sharing a load without increasing the power input to the machine.
Username or email address *Required
Password *Required
Note: Entering wrong username in the login form will ban your IP address immediately. Entering wrong password multiple times will also ban your IP address temporarily.
Log in
Lost your password? Remember me
No account yet?
