Line surge arresters

Line surge arresters (LSA) are designed to prevent ground faults and short circuits in power lines caused by lightning or switching overvoltages. Insulator flashovers, voltage dips and interruptions are prevented by eliminating all lightning and switching overvoltages above the insulator insulation level (the lightning-impulse withstand level, or LIWL for short).

Overvoltage protection by line surge arresters

Installation of line surge arresters at recommended locations along the line in accordance with our line simulation ensures anhanced overvoltage protection. Selecting the optimum line surge arresters, especially in terms of their quantity and installation locations, significantly improves the reliability of the overall line system and the quality of power that it supplies. We offer line surge arresters for system voltages up to 800 kV and an energy discharge capability of 3.6 C.

Beneficial applications of line surge arresters

  • Improve lightning protection performance
  • Reduce outages caused by poor grounding and high lightning activity
  • Reduce double-circuit outage rates / protect underbuild distribution lines
  • Provide switching surge control - structural optimization and lower clearances
  • Improve safety - prevents personal injuries and damage to equipment
  • For line upgrading and compaction - reduced insulation levels
  • For live work on the line -temporarily reduce minimum approach distance
  • Achieve lower installation costs and losses in line system (outages)

Two different LSA designs are available

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.


  • 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.


  • 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

Software analysis for customer-specific applications

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
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Surge arresters and composite insulators portfolio
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