UNIT V OVER VOLATGE PROTECTION-TWO MARKS.

1. What are the types of Over voltages?

  • External Over voltages
  • Internal Over voltages

2. Howis the External Over voltages caused?

External Over voltages are caused due to:

  • Direct lightning strokes
  • Electro magnetically induced over voltages due to lightning discharges taking place near the line called as side stroke

3. How are the Internal Over voltages caused?

Internal Over voltages are caused due to:

  • Switching operation or fault condition
  • Sudden release of load in the network.

4. What is lightning phenomenon?

The discharge of the charge cloud to ground is called lightning phenomenon.

5. What is Klydonograph?

It is an instrument for the measurement of surge voltage on transmission lines caused by lightning.

6. What is Magnetic link?

It is an instrument for the measurement of surge currents due to lightning.

7. How the transmission lines are protected against Direct Lightning Strokes?

Ground wires, running parallel to the power conductors of the transmission line, supported on the same towers, above the conductors are used as protection against direct strokes of lightning.

8. What is Surge Absorber?

Surge absorber or surge modifier is a device which absorbs energy contained in a travelling wave and reduces the amplitude of the surge and steepness of its wave front. Ferranti surge absorber is an example.

9. On what factor, does the effectiveness of overhead ground wires depend upon?

The tower footing resistance is the factor on which the effectiveness of the overhead ground wires depend upon.

10. What is an arcing ground?

During a line to ground fault on an ungrounded system, till the fault is cleared, there will be intermittent discharges to ground through the capacitance between the healthy phases and ground. Thisphenomenon is called arcing ground.

11. What is a Peterson Coil?

It is a ground fault neutralizer or arc suppression coil, used to nullify the effect of arcing ground in an ungrounded neutral system. It is basically an inductor with suitable taps to match to the capacitance of the line of various lengths.

12. What is meant by Insulation Coordination?

It is the correlation of the insulation of electrical equipments and lines with the characteristics of protective devices, such that the insulation of the whole power system is protected from excessive voltages.

13. What is Basic Insulation Level(BIL)?

Basic Insulation Level is the reference level expressed in impulse crest voltage with a standard wave not longer than 1.2/50 micro second wave according to ISO. In order to protect the equipments of the power system from over voltages of very high magnitude, it is necessary to fix an insulation level for the system to see that any insulation level for the system to see that any insulation in the system does not break down or flash over this level.

14. What is the use of protective device?

Protective devices are used to protect the power system components against the traveling waves caused by lightning.

12 MARK QUESTIONS:

1. Explain the various causes of over voltages.

2. Explain about lightning arrester.

3. Explain in detail about Insulation Coordination.

4. Explain the methods of protection against over voltages.