Question 1: AC Test transformers
(a) Briefly explain the need for reactive power compensation when testing large capacitive loads.
(b) Explain the primary function of a feed transformer used in resonant transformer circuits with the help of an illustration.
(c) How one can assure a uniform flux distribution in the core of a high voltage testing transformer with its mid-point potential at core?
(d) A 100 kVA, 400V/250kV testing transformer has 8% leakage reactance and 2% resistance on 100 kVA base. A cable has to be tested at 500 kV using the above transformer as a resonant transformer at 50 Hz. If the charging current of the cable at 500 kV is 0.4 A, find the series inductance required. Assume 2% resistance for the inductor to be used including the connecting leads. Neglect any dielectric losses in the cable. What will be the input voltage to the transformer?
Question 2: DC Generators:
(a) With the help of a circuit, describe the charge transfer mechanisms in a voltage doubler, and show that the output terminal voltage is twice the peak of the input AC source voltage. How would you reverse the polarity of the output voltage in such a circuit?
(b) Define the output voltage drop, ΔVo, and the ripple, δV with the help of voltage waveforms, for a two-stage Cockcroft-Walton voltage multiplier.
(c) In the case of voltage multiplier circuits, what are the design parameters that can be adjusted to minimize the ripple and voltage drop? Explain briefly.
(d) A ten-stage Cockcroft-Walton type voltage multiplier has all capacitances equal to 0.06μF. The supply transformer secondary voltage is 100kV at a frequency of 150Hz. If the load current is 1mA,find (i) the voltage regulation, (ii) the ripple, (iii) the optimum number of stages and (iv) the maximum output voltage.