Important Short Questions and Answers: Generation of High Voltages and High Currents

GENERATION OF HIGH VOLTAGES AND CURRENTS

1. What is the necessity for generating high voltages:

Applications like electric microscope, X rays, particle accelerators, Electro static precipitators etc.

·        Testing power apparatuses.

·        Insulation testing.

2. What are the various methods available for generating High DC voltage?

1.   Half & full wave rectifiers.

2.   Voltage multiplayer circuits.

Cockcraft Walten Circuit

Delta-tran/Engi-tran

3.   Van de graaff generators.

4.   Electro static generators.

3. What is the expression for average ripple in a Cock- craft Walten voltage multipler.

δ v = I 2n(2n+1)

ƒC 2

Where δ v = total ripple

I = the current

n = number stages

f = frequency of input voltage.

4. What is the expression for regulation (drop in voltage) Δv in a cock croft Walten method?

Δv = 2/ ƒc [(2n3 /3) + (n2 /2) – (n/6)

Where Δv = voltage drop

f = frequency c = capacitance

n = number of stages

5. Give the expression for optimum number of stages in a cock croft Walter voltage multiplier.

Where V max = Maximum of voltage

f = frequency c = capacitance I = current

6. State the principle of Van de Graaff generator ?

Mechanical energy is directly converted into electrostatic, electrical energy (without any electromagnetic conversion, as in the case of an electromagnetic machine like synchronous generator).

7. How Impulse voltages are produced in the lab?

Capacitors previously charged to DC voltage is discharged into a wave shaping network (LR, R1 R2, R3 or other combination) by closing a switch. This gives the desired output (double exponential wave).

8. What is the principle of Marx circuit.

A bank of capacitors are charged in parallel and then discharged in series into a wave shaping network to produce a lighting impulse voltage, double exponential fast rising & slow decaying voltage.

9. How switching Impulse voltage can be produced in the lab.

1. Impulse generator circuits can be used by suitably modifying the R₁ & R₂.

2. Power Tr or Testing Tr, excited by dc voltages giving oscillatory wave (Tesla tal)