EE1402(GENERATION OF HIGH VOLTAGES AND CURRENTS)

UNIT-III

GENERATION OF HIGH VOLTAGES AND CURRENTS

1.What are the methods that are available to generate high DC voltages?

• Rectifiers
• Voltage doubler circuit
• Cascaded Voltage doubler circuit
• Voltage multiplier circuit

2.State some applications of vande Graff generator.

• It is useful for very high voltage and low current applications.
• The output voltage is easily controlled by controlling the corona source voltage and the rate of charging.
• The voltage can be stabilized to 0.01%.
• It is flexible and precise machine for voltage control.

3.What are the drawbacks of cascaded voltage doubler circuit that led to the development of voltage multiplier circuits?

• It requires suitable isolating transformers.
• The filament transformers have to be suitably designed and insulated.
• All the cathodes will not be at the same potential from ground.

o The arrangement becomes cumbersome if more than 4V is needed with cascaded steps.

4.How are capacitances connected in an impulse current generator?

A bank of capacitors connected in parallel are charged to a specified value and are discharged through a series R-L circuits.

5.What are the general methods available for generation of A.C. voltages?

· Cascaded transformer

· Tesla coil

· Resonant transformer

6.What are the uses of high frequency high voltages?

They are required for rectifier dc power supplies. Also for testing electrical

apparatus for switching surges it is used.

7. Mention the advantages of high frequency transformers.

Saving in cost and size, pure sine wave output , uniform distribution of

voltage across

the winding coils due to subdivision of coil stack into number of units.

8. How are impulse waves specified?

By defining the rise of front time, fall time to 50% peak value and the

value of the peak voltage.

9. State the advantages of resonant transformer and high frequency Transformer.

· It gives an output of pure sine wave.

· Power requirements are less.

· No high power arcing and heavy current surges occur if the test object fails, as resonance ceases at the failure of the test object.

· Cascading is possible for very high voltages.

· Simple and compact.

· No repeated flashovers occur in case of partial failures of the test object and insulation recovery.

10. State the principle of operation of Marx circuit for impulse voltage generation.

For producing very high voltages a bank of capacitors are charged in parallel and then

discharged in series.

11. What are the components of impulse generators?

· Capacitance of the generator

· Charging resistor

· Spark gap

· Wave shaping resistors

· Test object

12.What is a tesla coil?

The high frequency resonant transformer is called as a tesla coil, which is doubly tuned resonant winding.

13. What are the advantages of using Tesla coil for high AC voltage generation?

· The absence of iron core in transformers and hence saving in cost and size.

· Pure sine wave output.

· Slow build-up of voltage over a few cycles and hence no damage due to switching surges.

· Uniform distribution of voltage across the winding coils due to subdivision of coil stack into a number of units.

14. What are the advantages of parallel resonance test system over series

resonance test System?

The advantage of parallel resonant circuit is

· More stable output voltage can be obtained along with a high rate of rise of test voltage

· Independent of the degree of tuning and the Q factor.

· Single unit resonant test systems are built for output voltages up to 500KV.

· Cascaded units for outputs up to 3000KV 50/60 Hz are available.

15. What are the drawbacks of RLC type impulse generator?

· The circuit occupies considerable space.

· The effect of inductance is to cause oscillations in the wave front and in the wave tail portions.

16. State the principle of operation of Marx circuit for impulse voltage generation.

For producing very high voltages a bank of capacitors are charged in parallel and then Discharged in series.

17. What are the components of a multistage impulse generator?

Dc charging unit, charging resistors, generator capacitors and spark gaps , wave

shaping resistors and capacitors , triggering system , voltage dividers and gasinsulated impulse generators.

18. Define the duration of the wave.

It is defined as the total time of the wave during which the current is at least 10% of its

peak value.

19. How are impulse currents of large value produced?

A bank of capacitors connected in parallel are charged to a specified value and are

discharged through a series R-L circuit.

20. How will you generate rectangular current pulses with high magnitudes?

They are generated by discharging a pulse network.

21. Mention the advantage of trigatron gap?

It requires much smaller voltage for operation compared to the three electrode gap.

22. What are the components of a trigatron gap?

It consists of a high voltage spherical electrode of suitable size, an earthed

main electrode of spherical shape and a trigger electrode through the main electrode.

PART-B

1. Explain about : - (16)

a) Voltage doubler circuit .

b) Voltage multiplier circuit (Cock-Craft Walton)

2. Explain about :

a) Deltetron circuit. –(8)

b) Van-de-Graft generator. –(8)

c) Electrostatic generator. –(8)

3. Explain the generation of High alternating voltages using Cascaded transformers?
4. Explain the generation of High frequency AC high voltages?- (8)
5. Explain the Multistage impulse generator (Marx-circuit) ? - (8)
6. Explain the impulse current generator? –(8)

7. An impulse generator has 12 capacitors of 0.12 uj% and 200 kV rating. The wave front

and wave tail resistances are 1.25 IcQ and 4 kQ respectively. If the load capacitance

including that of the test object is 10 000 pF, find the wave from and wave tail times

and the peak voltage of impulse wave produced

8. 8-stage impulse generator has 0.12 \iF capacitors rated for 167 kV. What is its

maximum discharge energy ? If it has to produce a 1/50 |is waveform across a load

capacitor of 15,000 pF, find the values of the wave front and wave tail resistances.

9. Calculate the peak current and waveshape of the output current of the following

generator. Total capacitance of the generator is 53 M-F. The charging voltage is 200

kV. The circuit inductance is 1.47 mH, and the dynamic resistance of the test object

is 0.051 ohms.