Types of Lightning Arresters:
There are many styles of lightning arresters generally use. They take issue solely in constructional details however treat a similar principle viz. providing a coffee resistance path for the surges to the bottom. we tend to shall discuss the subsequent styles of lightning arresters :
- Rod gap arrester
- Horn gap arrester
- Multigap arrester
- Expulsion type lightning arrester
- Valve type of lightning arrester
Rod gap arrester:
It is an awfully easy style of the diverter and consists of 2 1·5 cm rods that are bent at right angles with a niche in between. One rod is connected to the road circuit and therefore the different rod is connected to the planet. the gap between gap and material (i.e. distance P) should not be but simple fraction of the gap length in order that the arc might not reach the material and harm it. Generally, the gap length is thus adjusted that breakdown ought to occur at eightieth of spark-over voltage so as to avoid cascading of terribly steep wavefronts across the insulators. The string of insulators for AN overhead line on the bushing of the electrical device has oft a rod gap across it.
- Once the surge is over, the arc within the gap is maintained by the traditional provide voltage, resulting in a short-circuit on the system.
- The rods might soften or get broken thanks to excessive heat created by the arc.
- The climate (e.g. rain, humidity, temperature, etc.) have an effect on the performance of rod gap restraint.
- The polarity of the surge additionally affects the performance of this restraint. thanks to the higher than limitations, the rod gap restraint are barely used as a ‘back-up’ protection just in case of main arresters.
Horn gap arrester:
The horns square measure, therefore, created that the gap between them bit by bit will increase towards the highest as shown. The horns square measure mounted on ceramic ware insulators. One finish of the horn is connected to the road through a resistance R and choking coil L whereas the opposite finish is effectively grounded. The resistance R helps in limiting the follow current to a little worth. The choking coil is therefore designed that it offers tiny electrical phenomenon at traditional power frequency however an awfully high electrical phenomenon at transient frequency. so the choke doesn’t permit the transients to enter the equipment to be protected. The gap between the horns is therefore adjusted that ordinarily provides voltage isn’t enough to cause an associated arc across the gap.
At some position of the arc (perhaps position 3), the gap is also too nice for the voltage to keep up the arc. Consequently, the arc is destroyed. the surplus charge on the road is so conducted through the arrester hook to the ground.
- The arc is self-clearing. Therefore, this kind of arrester hook doesn’t cause short-circuiting of the system once the surge is over as within the case of rod gap.
- Series resistance helps in limiting the follow current to a little worth. Limitations
- The bridging of the gap by some external agency (e.g. birds) will render the device useless.
- The setting of the horn gap is probably going to alter thanks to corrosion or indentation. This adversely affects the performance of the arrester hook.
- The time of operation is relatively long, say concerning three seconds. insight of the terribly short operative time of recent protecting gear for feeders now is much longer. thanks to the on top of limitations, this kind of arrester hook isn’t reliable and might solely be used as a second line of defence just like the rod gap arrester hook.
It consists of a series of gilded (generally alloy of zinc) cylinders insulated from each other and separated by tiny intervals of air gaps. the primary cylinder (i.e. A) within the series is connected to the road and therefore the different to the bottom through a series resistance. The series resistance limits the ability arc. By the inclusion of series resistance, the degree of protection against movement waves is reduced. so as to beat this problem, a number of the gaps (B to C) square measure shunted by a resistance.
Under traditional conditions, the purpose B is at earth potential and therefore the traditional offer voltage is unable to interrupt down the series gaps. On the incidence of overvoltage, the breakdown of series gaps A to B happens. The serious current when breakdown can select the straight – through the trail to earth via the shunted gaps B and C, rather than the choice path through the shunt resistance. once the surge is over, the arcs B to Cleave and any power current following the surge is proscribed by the 2 resistances (shunt resistance and series resistance) that square measure currently nonparallel.
Expulsion type lightning arrester:
It basically consists of a rod gap A A′ asynchronous with a second gap closed at intervals the fiber tube. The gap within the fiber tube is made by 2 electrodes. The higher conductor is connected to the rod cap and therefore the lower conductor to the world. One expulsion constraint is placed underneath every line conductor.
On the incidence of AN overvoltage on the road, the series gap A A′ is spanned ANd an arc is affected between the electrodes within the tube. the warmth of the arc vaporizes a number of the fiber of tube walls, leading to the assembly of neutral gas. In an especially short time, the gas builds up high and is expelled through the lower conductor that is hollow. because the gas leaves the tube violently, it carries away ionizing air around the arc.
- They are not very expensive.
- They are improved form of rod gap arresters as they block the flow of power frequency follow currents.
- They can be easily installed.
- AN expulsion sort constraint will perform AN solely a restricted variety of operations as throughout every operation a number of the fiber material is employed up.
- This kind of constraint can’t be mounted in a very piece of closed instrumentality because of the discharge of gases throughout the operation.
- Because of the poor volt/amp characteristic of the constraint, it’s not appropriate for the protection of high-priced instrumentality.
Valve type of lightning arrester:
Valve kind arresters incorporate non-linear resistors and square measure extensively used on systems operating at high voltages. shows the assorted elements of a valve kind arrester hook. It consists of 2 assemblies
(i) series spark gaps and
(ii) non-linear electrical device discs serial.
Series Spark gaps:
The spark gap is multiple assemblies consisting of a variety of identical spark gaps serial. every gap consists of 2 electrodes with a set gap spacing. The voltage distribution across the gaps is linearized by suggests that of further resistance components (called grading resistors) across the gaps. The spacing of the series gaps is specified it’ll face up to the traditional circuit voltage.
Non-linear Electrical device discs serial:
The non-linear electrical device discs square measure fabricated from Associate in Nursing compounds like Thyrite or Metrosil. These discs square measure connected serially. The non-linear resistors have the property of providing high resistance to current flow once the traditional system voltage is applied, however low resistance to the flow of high-surge currents. In different words, the resistance of those non-linear components decreases with the rise in current through them and vice-versa.
Underneath traditional conditions, the traditional system voltage is meagerly to cause the break-down of the air gap assembly. On the incidence of overvoltage, the breakdown of the series spark gap takes place and also the surge current is conducted to earth via the non-linear resistors. Since the magnitude of surge current is extremely massive, the non-linear components can provide terribly low resistance to the passage of surge. The result’s that the surge can speedily visit earth rather than being sent back over the road. once the surge is over, the non-linear resistors assume high resistance to prevent the flow of current.
- They supply terribly effective protection (especially for transformers and cables) against surges.
- They operate terribly speedily taking but a second.
(iii) The impulse quantitative relation is much unity.
(i) they’ll fail to visualize the surges of the terribly steep wavefront from reaching the terminal equipment. This necessitates further steps to visualize steep-fronted waves.
(ii) Their performance is adversely laid low with the entry of wetness into the enclosure. This necessitates effective protection of the enclosure in any respect times.
in step with their application, the valve sort arresters area unit classified as
(i) station sort and
(ii) line sort.
The station sort arresters area unit usually used for the protection of vital instrumentation in power stations operative on voltages up to 220 potential unit or higher. the road sort arresters also are used for stations handling voltages up to sixty-six potential units.