UNIT – I
PROTECTION
AGAINST OVER VOLTAGES
PART – A (2
MARKS)
1. What are the causes over
voltages on power system?
2. What is meant by voltage
surge?
3. State the attenuation and
distortion of traveling waves.
4. What are the causes of power
frequency and its harmonic over voltage?
5. What is ground wire?
6. What is use of ground wire?
7. What is a protector tube?
8. Define basic impulse level.
9. Mention the various insulation
levels in substations?
10. What is a surge absorber?
PART - B
1. (a) What are the causes of
over voltage on a power system? (8)
(b) Why is it necessary to
protect the lines and other equipment of the power system against over
voltages? (8)
2. Describe the phenomenon of
lightning. (16)
3. What protective measures are
taken against lightning over voltages? (16)
4. (a) What is tower-footing
resistance? (4)
(b) Why is it required to have
this resistance as low as economically possible? (4)
(c) What are the methods to
reduce this resistance? (8)
5. (a) What is necessity of
protecting electrical equipment against traveling waves?(6)
(b)Describe in brief the
protective devices used for protection of equipment against such waves? (10)
6. Describe the protection of
stations and sub-stations against direct lightning stroke. (16)
7. Describe the construction and
principle of operation of
(i) expulsion type lightning
arrester, (8)
(ii) Value type lightning
arrester. (8)
8. What is Peterson coil? What
protective functions are performed by this device? (16)
9. Write short notes on the
following.
(i) klydonograph and magnetic
link (4)
(ii) Rod gap (4)
(iii) Arcing horns (4)
(iv) Basic impulse insulation
level (4)
10. What are the requirements of
a ground wire for protecting power conductors against direct lightning stroke?
Explain how they are achieved in practice. (16)
11. Determine the inductance of
Peterson coil to be connected between the neutral and ground to neutralize the
charging current of overhead line having the line to ground capacitive of 0.15μf.
If the supply frequency is 50Hz and the operating voltage is 132 KV, find the
KVA rating of the coil. (16)
12. (a) Explain the term
insulation coordination. (8)
(b) Describe the construction of
volt-time curve and the terminology associated with impulse-testing. (8)
13. Explain the operation of
various types of surge absorbers (16)