Simple Idea:
Protection against Direct lightening strokes is provided by using the earthing screen and ground wires. But these two apparatuses fail to provide protection against travelling waves; which may reach the terminal apparatus.
·
The
lightening arresters or surge diverters provide protection against such surges.
·
A
lighting arrester or surge diverter is protection device, which diverts high current and voltage surges on the power system to the ground.
·
Fig
shows the basic construction of lighting arrester. It mainly consists of spark
gap and non linear resister in series with it.
·
One end
of the surge diverter is connected to the terminal of the equipment to be protected
and the other end us effectively grounded.
·
The air
gap between the spheres is so adjusted such that under normal line voltage this
gap does not produces any arc. But a dangerously high voltage will break down
the air insulation and form an arc.
·
The nonlinear
resistances are the resistance which having the nonlinear characteristic i.e.
the magnitude of resistance decreases as the voltage or current increases and
vice versa.
Working:
The action of the spark
gap lightening arrester or surge diverter is explained as follows.
· Since the spark gap and nonlinear resistances provides
very high resistance to normal operating voltage, the lightening arrester
conducts no current to earth or the gap is non conducting.
· When the over voltage occurs on the system the air insulation
across the gap breaks down and an arc is formed.
· Now the nonlinear resistance provides a low resistance
path for the surge to the ground. In this way, the excess charge is diverted
towards the earth and hence equipment is protected against failure.
· It should be noted that designing a lightening arrester
that when the surge is over the arc in gap should cease. Otherwise if the arc
does not go out , the current would continue to flow through the resister and
both resister and gap may be destroyed.
Types of lightening
arrester:
1 .Rod gap arrester
2.Horn gap arrester
3.Multigap arrester
4.Expulsion type lightening arrester
5 .Valve type lightening arrester.
MCQ on Lightening
arrester:
1. Following which is
type of lightening arrester ?
(A) Rod gap arrester
(B) Horn gap arrester
(C) Multigap arrester
(D) All of Above
Answer: (D) All of Above
2. Which is used to
provide protection against direct lightening strokes?
(A) Transformers
(B) Earthing screen and
ground wires
(C) Current Transformer
(D) None of above
Answer: (B) Earthing
screen and Ground wire
3. Which is used to provide
protection against traveling waves?
(A) Ground wire
(B) Earth wire
(C) lighting arrester or
surge diverter
(D) All of above
Answer: (C) lighting arrester
or surge diverter
4. Lightening arrester or
surge diverter divert which types of surges to ground?
(A) Low voltage surges
(B) High Voltage Surges
(C) Both (A) & (B)
(D) None of above
Answer: (B) High
Voltage Surges
5. Which of following lightening
arrester consists?
(A) Spark gap
(B) Non linear resister
(C) Bothe (A) & (B)
(D) None of above
Answer: (C) Bothe (A)
& (B)
6. Non linear resister
are connected in ….. in lightening arrester?
(A) Series & parallel
(B) Parallel
(C) Series
(D) None of above
Answer: (C) Series