Contribution in edited book
Proceedings of the 21st International Symposium on High Voltage Engineering

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Jörres, S.; Claudi, A.; Finis, G.
The International Symposium on High Voltage Engineering
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Book title:
Proceedings of the 21st International Symposium on High Voltage Engineering
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Lecture Notes in Electrical Engineering
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Nowadays, varistors are widely used because of their energy absorption
capability (EAC) with concomitant economy and efficiency. Surges and
overvoltage transients unnoticeably degrade Metal Oxide Varistors (MOV)
over time. A newly developed condition monitoring system is based on a
time-resolved measurement of the discharge current. In order to be able
to compare and interpret acquired data sets from the monitoring system
with relevant aging models, extensive investigations of the measurable
influences are required. Therefore, an experimental setup has been
developed for determining different aging characteristics and process
influences. A precise continuous curve recording over nine current
decades from the ohmic leakage current area to the limiting resistance
region up to several thousand Amperes allows studying aging
characteristics of differently stressed MOVs. This method combines
common spot-measurements from the curves like mA-Point, leakage current
and the nonlinearity exponent alpha. In this paper, a fully automated
test bench is presented. The performance of the system and its
advantages are compared to manually operated tests and different test
equipment. First experimental results show that single point
measurements, depending on the type of stress, are insufficient to
detect degradation characteristics. Especially in the transition area
from the ohmic linear range to the non-linear range, irregularities
terms of degradation are ascertained. These studies are the basis for
building up relevant aging models depending on the process measurement
variables. This results in more accurate predictions for the state of
health of varistor ceramics by using recorded data sets as the
time-resolved measurement of the discharge current. Finally, it helps to
understand the change of characterization by different impacts. In
addition, the system is scalable for the study of layered surge
arresters and thus applicable to all network levels.

Last updated on 2019-03-12 at 11:07