Page 105 - Practical Power System and Protective Relays Commissioning

Chapter 9

Surge Arresters Theory Testing

and Commissioning

9.1 INTRODUCTION
A surge arrester protects system equipment such as transformers and trans-
mission lines from excessive voltage and/or overvoltage caused by lightning
or switching surges. The old design was a gap in series with a nonlinear
resistor all enclosed in porcelain cover for protection. The resistance is very
low at high voltage and high for low voltages; during high voltages the gap
sparks over to protect the equipment, as shown in Fig. 9.1.
A new design uses zinc oxide for surge arresters, that have a nonlinear
voltage current characteristic as shown in Fig. 9.2.
In normal voltage the arrester is open circuited, however when surges in
voltage occur, the arrester is short circuited to pass the current and protect
the equipment. Arresters are applied both at the transformer side(s) and also
the circuit breaker side(s) to protect the circuit breakers when it is in the
open position and during its opening.

FIGURE 9.1 A simple surge arrester.

Practical Power System and Protective Relays Commissioning.
DOI: https://doi.org/10.1016/B978-0-12-816858-5.00009-5 103
© 2019 Elsevier Inc. All rights reserved.