ABB Excount II User Manual page 57

6. Surge arrester monitoring theory
Another source of harmonics in the total leakage current is the har-
monic content in the system voltage. The voltage harmonics produce
capacitive harmonic currents in the arrester. This is clearly illustrated in
figure 6.3.3, showing results from total leakage current measurements
on two different arresters in service conditions that are significantly
different in terms of system voltage harmonics.
Figure 6.3.3
Total leakage currents of metal-oxide
surge arresters in different service conditions
The capacitive harmonic currents produced by the voltage harmonics
may be of the same order of magnitude as the harmonic currents
generated by the non-linear resistive leakage current. This means
that the third harmonic content originating from the system voltage
interferes with the third harmonic content associated with the resistive
leakage current of the arrester. In order to perform accurate measure-
ments of the resistive leakage current by means of third order harmo-
nic analysis, it is therefore necessary to compensate for the third order
harmonic content in the system voltage.
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1HSA 801 080-15en EXCOUNT-II Users Manual