What's a Surge Arrester||Purpose of a surge Arrester||Surge Arrester Components||Failure of Surge Arrester||Methods of monitoring Surge Arrester

1. Sub-Station Equipments-19
SURGE ARRESTER

2. INTRODUCTION
• A surge arrester is a device to protect electrical
equipment from over-voltage transients caused by
external (lightning) or internal (switching) events.
• To protect a unit of equipment from transients
occurring on an attached conductor, a surge arrester is
connected to the conductor just before it enters the
equipment .

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• The purpose of using a surge arrester is to always limit the voltage
across the terminals of the equipment to be protected below its
insulation withstand voltage.
• This is achieved by connecting elements with an extremely
nonlinear voltage current characteristic (varistor) in parallel to the
terminals of the equipment.
• Metal oxide (MO) surge arresters containing ceramic MO elements
mainly made from zinc oxide and bismuth oxide are used.

4. Surge Arrester Components

5. Causes for Failure of Metal Oxide Surge Arresters
• Incorrect arrester specification corresponding to actual
system voltage and overvoltage stress
• Overloading due to:
o Temporary over voltages (cracking, puncturing)
o Switching over voltages (cracking, puncturing and flashover)
o Lightning overvoltage (change of characteristic/ageing,
flashover, puncturing).
• External pollution or moisture penetration
• Consequence of aging: Increase in the continuous resistive
leakage current. This is a good indicator of the arrester
condition.

6. Methods for Monitoring of degradation of MOSA
• Visual inspection
Locating external abnormalities on the arrester and gives practically
no information about the internal of the arrester.
• Surge counters
Frequently installed on MOSA, but has no practical use for diagnosis
of condition of the arresters.
• Temperature measurements–Thermo Vision
Frequently used method. Detects the increased block temperature
on the housing surface of the arrester.
• Leakage current measurements
For in-service testing, the method with indirect determination of
the resistive leakage current with compensation for harmonics in
the voltage provides the best available information quality with
respect to diagnostic efficiency.

7. SUMMARY
• All electrical equipments in an electrical system
need to be protected from voltage surges.
• The rating of the arrester, the class of arrester
and the location of the arrester all play a part in
surge protection.
• Surge arresters protect equipment of
transmission and distribution systems, worth
several magnitudes more than the arresters
themselves, from the effects of lightning and
switching over voltages.

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