Download High Voltage Engineering - 2 Marks PDF

TitleHigh Voltage Engineering - 2 Marks
TagsElectrical Breakdown Capacitor Insulator (Electricity) Electric Current Transformer
File Size316.1 KB
Total Pages45
Document Text Contents
Page 2

PREPARED BY S.SARAVANAN AND M.SURESH, KONGU ENGINEERING COLLEGE, PERUNDURAI Page 2



2 MARKS QUESTION AND ANSWERS

OVER VOLTAGES IN ELECTRICAL POWER SYSTEMS

1. What are the chief causes of over voltages in electric power system?

1) Lightning over voltages (Natural causes)

2) Switching over voltages (system oriented causes)

2. How are switching over voltages originated in a power system?

Switching over voltages originate in the system itself by the connection and

disconnection of circuit breaker contacts or due to initiation or interruption of faults.

3. What are switching over voltages?

Switching over voltages are highly damped short duration over voltages. They are

temporary over voltages of power frequency or its harmonic frequencies.

Ø They are sustained or weakly damped

Ø They originate in switching and fault clearing process.

4. For ultra high voltages, perhaps, switching surges may be the chief condition for design

considerations. Why?

The magnitudes of lighting voltages appearing on a transmission line do not depend on

line design hence lightning performance does not improve with increasing insulation level, that

is, the system voltage. On the other hand switching over voltages is proportional to operating

voltage. Hence for ultra high voltages switching surges may he the chief condition for

consideration.

5. State the parameters and characteristics of the lightning strokes.

1. Amplitude of currents

2. The rate of rise.

Page 44

PREPARED BY S.SARAVANAN AND M.SURESH, KONGU ENGINEERING COLLEGE, PERUNDURAI Page 44



18. What is the necessity for measurement of RIV?

Sometimes electrical equipment like power Transformer, conductors, rotating machines

etc. produce unwanted electrical signals in the radio frequency range of 150k Hz to 30 M Hz,

where as the power frequency being 50 Hz. These signals affect the communication systems &

should be prevented. Hence RIV measurement is necessary.

19. What is meant by insulation co-ordination in EHV power system?

Insulation co-ordination is the grading of the insulation level of

(1) Various equipments in a power system

(2) Various parts of the equipments

(3) Protection devices in such a way that, in the event of a serious over voltage, less vital,

less important, less costlier, easy to repair equipment/part of equipment breaks down first

and thereby avoiding major breakdown & interruption to consumers, cost of replacement

etc.

For e.g.

1. In the event of an over voltage, a string insulator on Transmission line should

breakdown before the bushing of a power Transformer.

2. The bushing of the power Tr. should breakdown first before the Breakdown of the

winding of the Power Transformer.

20. What is system protection level and its selection depend on what factors?

In the power system, system protection level is established considering the,

1. Location of the station

2. Protection level of arrester

3. Line shielding

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