Surge arresters protect power lines

Edited by the Engineeringtalk editorial team Sep 5, 2007

The Pexlim surge arrester is a sacrificial device, designed to fail safely to limit overvoltages to an acceptable level.

ABB's Pexlink TLA (transmission line arrester) is designed to ensure disturbance-free operation and maximum availability for overhead power lines by providing lightning protection and switching overvoltage control.

The system consists of a Pexlim surge arrester fitted with a line connector clamp and a disconnecting device.

Pexlink is easy to install as well as being mechanically robust and secure.

There are a number of approaches to improving the reliability and availability of overhead lines.

Duplication of the system is a very expensive and often impractical option.

A compromise is to install two lines on one tower.

Increasing insulation can be expensive and can create other problems, such as the need for increased insulation of substation equipment.

Improving footing impedance is often difficult and expensive, especially in hilly terrain.

If provision was not made in the original tower design it can be expensive to retrofit shielding.

It helps to eliminate a large number of interruptions but this is not enough to obtain the necessary degree of reliability.

An alternative is line insulation by surge arresters connected in parallel with line insulators at selected towers.

ABB's Pexlink TLA concept is based on the use of Pexlim arresters together with accessories for fixing them across the insulators and providing automatic disconnection in the event of them being overstressed.

The Pexlim surge arrester uses gapless ZnO technology.

It is a sacrificial device, designed to fail safely to limit overvoltages to an acceptable level.

Pexlim is enclosed in a lightweight silicone housing dimensioned to withstand the electrical, mechanical and environmental conditions found in transmission line applications.

The low weight of the Pexlink concept, compared with porcelain-housed arresters, permits installation on existing structures, while the polymer housing offers increased safety for the line equipment as well as for people or animals who may be near the lines during overstress conditions.

A computer program is used to determine the optimum number of locations for Pexlink devices along the line (generally where the footing impedance is high) and to calculate the arrester stresses at each of the selected locations.

The design permits installation using standard transmission line hardware and it can be mounted at different angles based on tower geometry and conductor spacing.

Pexlink has been installed in many applications worldwide to provide lightning protection and switching overvoltage control for system voltages from 52kV up to 800kV.

The reduction in outages ensures that sensitive equipment is not damaged and the circuit breaker overhaul interval can be increased, resulting in a reduction of total maintenance costs.

Eskom, the South African utility, has nearly 200 Pexlink units installed on seven key 275kV lines, with a total length of over 400km.

In the cases where Pexlink has been installed on existing lines, the average number of faults per 100km per year has been reduced from nine to under three.

Pexlink has also been installed on the Russian side of the 400kV link between Russia and Finland in order to reduce the annual number of lightning-related outages from two per 100km to a target of one every two years.

In fact, during the two lightning seasons since Pexlink was installed no double circuit line trips have been reported on the Russian side of the link, while they have continued on the unprotected Finnish side.