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Surge Arresters: fundamentals of surge arresters

What is a surge arrester?

Evolution surge arrester

A surge arrester is a protective device for limiting voltage on equipment by discharging or bypassing surge current. It prevents continued flow to follow current to ground and it is capable of repeating these functions as specified per ANSI standard C62.11. An arrester does not absorb lightning or stop lightning. It diverts the lightning, limits the voltage and protects the equipment installed in parallel.

Surge arresters have many applications, anywhere from protecting a home to a utility substation. They are installed on circuit breakers inside a residential home, inside padmounted transformers, on pole mounted transformers, on pole-mounted riser poles and substations.

Standards for surge arresters are defined by IEEE standard C62.11 and IEC standard 60099-4.

Quick links to surge arrester fundamentals: Use | Operation | Types | Learn more
 

Why use a surge arrester?

The distribution power line will see various voltage surges. Lightning is the main source of voltage surges. There are approximately 100 lightning strikes on the Earth’s surface every second. Lightning is a random and unpredictable event.

Other sources of voltage surges include switching surges and temporary overvoltages. Switching surges are overvoltages produced by changes in operating conditions within the system and are the main voltage surge for station-class arresters. Switching surges is the trapping of energy and the subsequent release of the energy. Temporary overvoltages result from ground faults on one phase and voltage rises on unfaulted phases until the fault can be cleared.

power-lines-during-storm-with-lightning
 

Surge arrester operation

Birds on power line

How does a surge arrester work?

A metal oxide varistor (MOV) surge arrester contains a series of metal oxide varistor blocks. These MOV blocks are like a voltage-controlled switch, which acts as an insulator with line voltage. Once the voltage the arrester experiences rises above the reference voltage of the arrester, the MOV blocks go into conduction. Since the MOV blocks are highly non-linear, once the voltage drops below the reference voltage, the conduction ends.

Why do arresters operate?

A surge arrester must be able to withstand the continuous power-frequency voltage for which it is intended to operate. It must discharge any transient energy from the system in the form of current, while preventing the voltage across the equipment from becoming excessive. It must operate in the same environment as the protected equipment. Temporary overvoltage (TOV) capability shows the allowable overvoltage and duration that an arrester can withstand without damage.

Arresters can operate due to a variety of reasons:

  • TOV condition lasted too long
  • Undersized arrester
  • Lightning surges experienced were greater than the duty rating
  • Gap degradation in silicone carbide arresters
  • Deterioration of oil-based polymer housing due to the leaking of the silicone oil additive
  • Wildlife
  • Disk aging

Porcelain arresters may break apart after experiencing an end-of-life event, whereas polymer arresters may experience a blow out the side or the disconnector will operate which will separate the arrester from ground.

 

Types of surge arresters

Secondary arresters

Secondary arresters are arresters rated under 1000 V. Secondary arresters are used to protect against secondary surges. Transformer failure rates range from 0.4-1%. 50-70% of all transformer failures are due to low-side surges. Secondary surge protection in the home or at the service entrance will cause additional surge duty to the service transformer. When using a secondary arrester, transformer failure rates can be reduced significantly by an order of magnitude. 

VariSTAR Storm Trapper secondaary-class MOV surge arrester
UltraSIL polymer VariSTAR surge arrester

Distribution arresters

Distribution arresters are 1 to 36 kV rated.

Within the distribution class, there are light duty, normal duty and heavy duty arresters.

Heavy duty arresters include the riser pole arrester.

Distribution arresters can also be used in transformers as under-oil arresters, cubicle-mounted arresters and elbow arresters. 

Normal duty arresters are used in low lightning applications, heavy duty arresters are used in high lightning applications, riser pole arresters are used where the distribution line goes from overhead to underground and the Evolution arrester can be used for all overhead applications.

A riser-pole arrester is used to limit the voltage surge seen by the underground cable and equipment. An open point arrester will prevent surge reflection or voltage doubling.

Intermediate arresters

Intermediate arresters offer better discharge voltages, have a high fault current withstand capability and are available in ratings from 3 to 120 kV.

Station class arresters

Station class arresters offer the best discharge voltages of all arresters, provide high energy handling capabilities, have the highest fault current withstand capability and are available in ratings from 3 to 684 kV. Station class arresters have varying cantilever strengths for the most demanding applications.

Hollow core arrester

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