Line surge arresters

Non-Gapped Line Arrester (NGLA) – Directly connected to the overhead line

Non-gapped line surge arresters (NGLA) offer a high degree of mounting flexibility and operational reliability. Depending on the tower design and the arrangement of insulators and lines, these arresters can either be installed directly on the insulators or on the tower. NGLAs limit overvoltages to value levels below the insulator withstand voltage.

Benefits:

• Most flexible solution (installation at conductor, tower, insulator etc.)
• Offer a very high level of protection against lightning and switching overvoltages thanks to their high energy absorption capacity
• A disconnector is installed in series that disconnects the arrester in case of thermal overload
  This ensures further operation of the overhead line until a replacement can be scheduled
• Designed and tested to comply with the latest IEC 60099-4 standard

Externally Gapped Line Arrester (EGLA)– Insulated from the high-voltage line by series gap

Siemens Energy EGLA line surge arresters have an external spark gap placed in series that galvanically isolates the active part of the line surge arrester from the line voltage under normal conditions.

In case of lightning, the spark gap flashes over and the arrester limits the ground fault current from several kA to a few amperes, and extinguishes the arc within 10 ms such that no circuit breaker operation at both line ends is needed, i.e. no reclosing operation.

Benefits:

• No leakage current, since the series gap disconnects the arrester part of the EGLA - metal-oxide varistor (MOV) blocks - from the system voltage under normal service conditions
• Lower arrester rated voltage required (arrester is not energized all the time, i.e. it's insulated by the series GAP)
• --> less material and fewer MOVs are needed
• No disconnector and no ground lead are needed
• Suitable for multiple-circuit towers with short clearances - the highly compact design of the EGLA and the absence of a ground lead allow installation and lightning protection even on towers with very small cross-arm clearances
• Better suited for live installation
• Complete EGLA solutions with polymer insulators also available
• Designed and tested to comply with the latest IEC 60099-8 standard

Siemens Energy optionally offers software analysis (simulation) based on Cigré studies to examine and conduct preliminary tests of customer-specific applications as a way of determining the optimal, cost-effective solution. With this approach, the customer only needs to equip particular phases or individual line segments with line surge arresters, and can still ensure sufficient lightning protection of the overhead line.

In the first phase of an analysis, all important parameters of the transmission line under study are entered into the simulation software, and the installations to be examined are selected. This approach takes the following factors into consideration:

• Line parameters: operating voltage, number of three-phase circuits, ground wire data, length, span length and sag on line, conductor type, diameter, and clearances
• Tower data: tower surge impedances and footing resistance, tower geometry (position and distances of the individual phases and any existing ground wires)
• Insulator data: arcing distance, connection length, rated lightning impulse withstand voltage
• Lightning activity: keraunic level (lightning strokes per year and km²), network topology (elevation profile)
• Customer priorities: fewer short interruptions, prevention of phase and multisystem short-circuits, elimination of ground wires