Introduction; Surge Counting - ABB Excount II User Manual

6. Surge arrester monitoring theory
52

6.1 Introduction

The rising demands for improved reliability of power supply and
reduced maintenance costs have increased the attention on condi-
tion monitoring of equipment in HV substations. As far as metal-oxide
surge arresters are concerned, there are two important aspects which
are related to the reliability of the arresters:
• The stress on the arrester in terms of the intensity
and frequency of impulse currents
• The condition of the arrester in terms of its insulating
properties in normal service
The first aspect is addressed by performing continuous surge coun-
ting and the second by leakage current measurements on regular
basis.
The EXCOUNT-II is designed to handle both surge counting and
leakage current measurements in a single monitoring system. The
EXCOUNT-II system comprises a sensor, permanently mounted at the
base of the arrester, a transceiver for wireless communication with the
sensor, and proprietary software installed on a personal computer.
In the following, the bases for surge counting and leakage current
measurements are described, and the corresponding functions of the
EXCOUNT-II are presented. For general information on various diag-
nostic methods for metal-oxide arresters, please refer to IEC 60099-5.

6.2 Surge counting

General
The primary aim of a surge counter is to give an indication of the
stress on the arrester from impulse currents caused by overvoltages.
In addition, surge counters may be helpful in analysing the occur-
rences of overvoltages on the system, provided the surge counting
information is sufficiently detailed.
Surge counting with EXCOUNT-II
Surge counters operate at impulse currents above a certain ampli-
tude. The EXCOUNT-II sensor is equipped with an impulse current
1HSA 801 080-15en EXCOUNT-II Users Manual