Lighting arresters
https://www.slideshare.net/younistanzeela/lightning-power-system-presentation
The typical lightning arrester has a high-voltage terminal and a ground terminal. When
a lightning surge (or switching surge, which is very similar) travels along the power line to
the arrester, the current from the surge is diverted through the arrester, in most cases to
earth.
TYPES OF LA
https://circuitglobe.com/types-of-lightning-arresters.html
12 types
1.
2.
3.
4.
5.
6.
Road Gap Arrester
Sphere Gap Arrester
Horn Gap Arrester
Multiple-Gap Arrester
Impulse Protective Gap
Electrolytic Arrester
7. Expulsion Type Lightning Arrester
8. Valve Type Lightning Arresters
9. Thyrite Lightning Arrester
10. Auto valve Arrester
11. Oxide Film Arrester
12. Metal Oxide Lightning Arresters
LOCATION OF LA
Lightning arrester should be located close to the equipment that it is expected to protect.
In large substations, arrestors should be installed at take-off points of the lines and of the
terminal apparatus.
RANGE OF LA
On structures less than 30 metres (about 100 feet) in height, a lightning rod provides a
cone of protection whose ground radius approximately equals its height above the ground.
On taller structures, the area of protection extends only about 30 metres from the base of
the structure.
Lightning Arrester Ratings
https://studyelectrical.com/2014/06/lightning-arrester-location-rating-and.html
The rating of a lightning arrester is given below,
Normal or rated voltage:
It is designated by the maximum permissible value of power frequency voltage
which it can support across its line and earth terminal while still carrying
effectively and without the automatic extinction of the follow-up current.
The voltage rating of the arresters should be greater than the maximum sound
phase to ground voltage.
Normal Discharge current:
It is the surge current that flows through the LA after the spark over, expressed in
crest value (peak value) for a specified wave shape. Example 10, 5, 2.5, 1.5, 1 kA
rating.
Power frequency spark over voltage:
It is the RMS value of the power frequency voltage applied between the line and
earth terminals of the arrester and earth which causes spark over of the series gap.
As per IS 3070, the recommended spark overvoltage is 1.5 times the rated voltage.
There are also other ratings like maximum impulse spark over-voltage, residual or
discharge voltage, maximum discharge current, etc.
Selection of LA
Here we are selecting an appropriate rating of lightning arresters for the substation.
For the protection of substation above 66kV, an arrester of 10kA rating is used.
Voltage rating of LA = Line to line voltage × 1.1 × coefficient of earthing.
Power frequency spark over voltage = 1.5 ×Voltage rating of LA (Assuming
the coefficient of earthing equals 0.8 for the effectively earthed system)
For 220KV side:
 Voltage rating = 1.1 × 220 × 0.8 = 193.6KV
 Power frequency spark over voltage = 1.5 ×193.6 = 290.4KV
 Rated discharge current = 10 kA
For 110KV side:
 Voltage rating = 1.1 × 110×0.8 = 96.8KV
 Power frequency spark over voltage = 1.5 × 96.8 = 145.2KV
 Rated discharge current = 10kA
For 66kV Side
 Voltage rating = 1.1 × 66×0.8 = 58.08kV
 Power frequency spark over voltage = 1.5 × 58.08 = 87.12kV
 Rated discharge current = 10kA
For 11 KV side:
 Voltage rating = 1.1× 11×0.8 = 9.68KV
 Power frequency spark over voltage = 1.5×9.68 = 14.52KV
 Nominal discharge current = 5kA
https://www.nemaarresters.org/understanding-arrester-datasheet/