Types of Lightning Arresters-Horn Gap, Rod Gap, Valve Type
There are different types of lightning arresters like Rod Gap Arrester, Horn Gap Arrester, Valve type, and expulsion type and they differ from each other only in construction details. but they operate on the same principle which is to provide a low resistance path for surges to the ground.
Table of Contents
Types of lightning Arresters
- Rod Gap Arrester
- Horn Gap Arrester
- Valve Type lightning arrester
- Expulsion Type lightning arrester
- Multi Gap arrester
Rod Gap Lightning Arrester
Rod Gap Arrester is a very simple type of lightning arrester, which consists of two 15mm rods that are bent at an angle 90° with a gap in between them as depicted in the diagram. One end of the lightning arrester is connected to the line and another end of the rod is connected to the earth.
The distance between the rod and the insulator must not be less than 1/3 of the gap length so the arc may not reach the insulator and damage it.
At a healthy operating condition gap between the rod is non conducting but during the surge, the gap sparks over and conducts excessive current to the earth. in this way, surge energy dissipated into the earth.
Horn Gap Lightning Arrester
Horn gap type lightning arrester consists of two horn-shaped metal rods separated by a small gap as shown in the diagram.
The horns are constructed so that the distance between horns increases gradually toward the top. this horn assembly is mounted on the porcelain insulator and one end of the horn is connected to the line through a choke and resistor. While the other end is connected to the ground.
The choke coil used provides low reactance at normal frequency but high reactance to surge frequency/ voltage. due to this surge not reaching the transformer or the equipment which to be protected.
The gap length between horns is kept such that normal voltage is not enough to cause a spark over the gap.
Valve Type Lightning Arrester
An improved but more expensive surge arrester is the valve type arrester which is extensively used in the system operation on higher voltages.
The diagram shows that the valve type of lightning arrester contains a number of series-connected gaps, coils units, and the valve elements of nonlinear resistance material usually made of silicon carbide discs.
the nonlinear resistors are connected in series with the spark gap and all this assembly is fitted in the tight porcelain container.
Spark gap consists of a number of similar gaps in series. each gap consists of two electrodes with gap spacing. The voltage distribution across the gaps is linearised by using additional resistors called grading resistors.
The gap between two electrodes does not spark during normal voltage but on the occurrence of a high surge, the air between the gaps breaks down forming an arc between electrodes.
this arc carries surge current to the ground through nonlinear resistors. Nonlinear resistors offer high resistance to current at the normal operating voltage and very low resistance to surge current.
Expulsion Type Lightning Arrester
Expulsion type arresters are also called protector tubes and are normally used on a voltage up to 33Kv. this type of arrester consists of a rod gap in series with an additional gap that is enclosed in a fiber tube.
A fiber tube is made of two electrodes. the upper electrode connected to the rod gap and the lower electrode connected to the ground.
When a surge voltage is an incident on an expulsion tube, the series gap is spanned and an arc is formed between the electrodes within the tube. in this way surge current is conducted into the ground.
