The document discusses the behavior of zinc oxide surge arresters under pollution conditions. It describes various laboratory and field tests conducted to study the effects of pollution and dry band formation on surge arresters. The laboratory tests included salt fog method, solid layer method, partial wetting method, and slurry method. Field tests were also conducted in marine and industrial pollution areas. The tests showed that salt fog method and slurry method best replicated thermal stresses under natural pollution. Dry band formation led to higher internal currents, discharges, and local temperatures near the varistor column.

1. BEHAVIOUR OF ZINC OXIDE SURGE ARRESTER
UNDER POLLUTION
DEPARTMENT OF ELECTRICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY
BANARAS HINDU UNIVERSITY
VARANASI-221005 INDIA
submitted by:
Mukesh Kumar Tanwar (11104EN067)
Akhilesh Kumar Singh (11104EN064)

2. CONTENTS
1. Introduction
2. Test arrangement and measuring equipment
3. Pollution and dry band formation
4. Results of pollution test with standard test procedure
5. Conclusion
6. References

3. Introduction
Here we presents results of pollution tests with A.C. voltages on a
zinc oxide arrester. Zinc oxide surge arresters are exposed to heavy
thermal and electrical stresses if the porcelain housings of the
arrester units are polluted together with other environmental stresses
such as temporary over voltages or high temperatures this can lead
to thermal runaway of the metal oxide arrester (MOA).

4. What is surge arrester ?
A surge arrester is a device to protect electrical equipment from over-voltage
transients caused by external (lightning) or internal (switching) events. This class
of device is used to protect equipment in power transmission and distribution
systems.
What is varistor ?
A varistor is an electronic component with a nonlinear current–voltage
characteristic, and is therefore also known as a voltage-dependent resistor
(VDR). At low voltage it has a high electrical resistance which decreases as the
voltage is raised.

5. Test arrangement and measuring equipment
The varistor column is mounted
inside of the porcelain housing
and is fixed to the housing using
different constructions depending
on the manufacturer. In most
industrial designs there is an air
insulation between the porcelain
housing and the arrester column.

6. Pollution and dry band formation
To investigate the influence of dry band formation on the
stresses of the zinc oxide material a special test has been
carried out with a single arrester unit. First the arrester housing
was polluted and dried. Afterwards at a certain location on the
porcelain housing a dry zone of about 10 % of the total creep
age length was formed artificially which was just large enough
to prevent arcing across the dry zone.

8. Impulsive Currents Caused by Internal Discharges
In case of only one dry zone at the bottom flange of the arrester
housing there is a high radial electric field strength between the
pollution layer and the varistor elements. This electric field is
caused by the full applied test voltage only reduced by a small
voltage drop along the outside pollution layer and the voltage
drop along a few bottom varistor element.

9. Results of pollution test with standard test procedure
The thermal preformation of a ZnO surge arrester in polluted
condition studied in:
1. Laboratory Test
a. Salt Fog Method
b. Solid Layer Method
c. Partial Wetting Method
d. Slurry Method
2. Field Test

10. a. Salt Fog Method
The test procedure consisted of energizing the arrester at a
voltage of 245/√3 kV for a predetermined time in a salt fog
atmosphere, unless a flash over occurred in this period. The
main characteristics of the salt fog method is the possibility
of high thermal stress on the arrester. The thermal stress on
the one unit is maintained on the same unit during the entire
test period.

11. b. Solid layer method
The solid layer tests were performed with an increased
steam input rate. The solid layer test gives a considerably
lower external charge accumulation compared to the other
test method. This is due to the washing effect of the steam
fog, which limits the duration of the pollution activity.

12. c. Partial wetting method
The partial wetting test differs considerably from the
other test methods. The location of temperature rise in the
upper half of the arrester is predetermined by the wetting
procedure, and a very high temperature rise may appear
in a very short time.

13. d. Slurry Method
In contrast to the partial wetting test, the slurry test implies that
the pollutant (Slurry) is applied to the complete arrester and not
only to the lower half. The main characteristic of slurry test is
that the temperature rise may appear any arrester any unit with
about the same probability. The external charge depends on the
number of test cycles in included in the test. The temperature rise
varies from one cycle to another.

14. 2. Field Test
The pollution test on surge arrester at Martigues (France) and
Lista (Norway) were carried out in areas of marine and
industrial pollution. The results from the field test can be used to
select a laboratory test method which is able to regenerate the
actual thermal stress imposed on ZnO surge arrester in naturally
polluted condition. The field tests show that:

15. Conti…
a. Significant temperature rise may appear in any unit
of a multi-unit arrester.
b. The influence of the specific creep age distance on the
accumulated external charge in negligible within the
range studied.
c. The thermal stress on the arrester is not mainly
caused by larger surface leakage currents during short
periods.

16. Conclusion
A comparison of test results from the field test and the
laboratory test shows that the salt fog method and the slurry
method are both capable of regenerating the thermal stress
imposed on surge arresters in naturally polluted conditions.

17. Conti…
Dry band formation on polluted metal oxide surge arresters at A.C.
voltages may result in:
a. Rise of the internal A.C. current in the arrester column up to
four times higher than under clean condition.
b. Discharges inside of the arrester due to a high radial electric field
strength.
c. High local temperatures at the varistor column near to the dry
band depending on the size and position the dry band

18. Future work
Modelling and Simulation of the Surge Arresters using IES
COULOMB, a dedicated software for 3D-Field Solution of any
3D Model.
 The result obtained by the simulation will be verified by taking
some experimental data if available from the internet or doing
by ourselves.

19. References
1. Behavior of ZnO surge arresters under pollution, IEEE
transactions on power delivery vol. 6, No. 2, April 1991.
2. Thermal stress on ZnO surge arresters in polluted
conditions part-1 and part-2, IEEE.

20. Thank you……!!