Q4.a) Explain what is meant by the terms wave form, frequency, and average value. (6)
b) A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across 110 V sinusoidal a.c. supply. The circuit has a resistance of 50Ω to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate
(i) The reading on the ammeters
(ii) The form and peak factors of the current wave (10)
Q5. a) What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer? (6)
b) The following results were obtained on a 50 kVA transformer: open circuit test-primary voltage, 3300 V; Second voltage, 415 V: primary power, 430 W. Short circuit test-primary voltage, 124 V: primary current, 15.3 A; primary power, 525 W; secondary current, to be assumed at full load value. Calculate:
(i) The efficiencies at full load and at half load for 0.7 power factor.
(ii) The voltage regulations for power factor 0.7 (i) lagging, (ii) leading
(iii) The secondary terminal voltages corresponding to (i) and (ii) (10)
Q6. a) What is a silicon-controlled rectifier (SCR)? How is the breakover voltage of the SCR defined?
b) A d.c. motor takes an armature current of 110 A at 480 V. the resistance of the armature circuits is 0.2Ω. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate
a) The speed:
b) The gross torque developed by the armature. (10)
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