Transmission-line protection for disturbance-free system operation up to 800 kV
PEXLINK is a concept of Line Surge Arrester (LSA) for minimizing disturbances on overhead lines resulting from unforeseen impulse overvoltages. Based on Hitachi ABB Power Grids' silicone-housed PEXLIM arrester, together with line-hardware and automatic disconnecting device, the PEXLINK concept offers secure and robust performance to improve line availability and security of electricity supply.
The concept of protection using polymer-housed arresters along with additional accessories for fixing the arresters across the insulators and providing automatic disconnection of the arresters in the event of their being overstressed is called the PEXLINK concept. This method is simple and cost- effective.
Hitachi ABB Power Grids' philosophy is to provide protection for line insulation at selected locations. The main item is the gapless silicone polymer-housed arrester, PEXLIM with metal-oxide (MO) active elements. Such arresters have been used for many years for protection of equipment in sub-stations and hence their protective performances well-known. The low weight of the PEXLIM arrester permits installation on existing structures and the polymer housing gives increased safety of the line equipment as well as people and animals which may be in the vicinity of the lines during overstress conditions.
To ensure quick, safe, automatic and controlled disconnection of a failed arrester, Hitachi ABB Power Grids uses a special disconnecting device with a suitable link in the ground circuit of the arresters.
By locating the PEXLINK on sections of lines with high footing impedance towers and one additional low footing-impedance tower at each end of the section, PEXLINK protects existing shielded and non-shielded lines from abnormal lightning surges (frequent or high amplitudes) and reduces the outages.
The reduced outages are beneficial also indirectly in that sensitive equipment is not damaged and the circuit breakers overhaul interval can be increased. Thus, total maintenance costs are also reduced.
This protection may be used for all system voltages where the stated abnormal conditions exist. Arresters with moderate energy capability are often sufficient. However, the high-current capability must be large and distribution-type arresters may not be suitable.
For long EHV lines, surge arresters usually are located at line-ends. In addition, by locating arresters at one or more points along the line e.g. at midpoint or 1/3 and 2/3 line length switching surge overvoltages and thus line insulation requirements could be limited without using pre-insertion resistors. Arresters used for this type of application should be designed for high energy capability. Usually a class 2 or 3 arrester will be sufficient out on the line but higher arrester classes may be necessary at the receiving end of the line.
