All about Surge Arresters

All about Surge Arresters

Surge arresters are protective devices that limit voltage by bypassing or discharging surge currents. It stops the flow of current to ground continuing and is capable to perform these functions according to ANSI standard C62. An arrester does not absorb lightning or stop lightning. It protects equipment that is connected to it, reduces the voltage, and diverts lightning.

Surge arresters can be used for many purposes, including protecting homes and substations. They can be installed inside residential homes, on pole-mounted transformers or on pad-mounted transformers.

Why use a surge protector?

Different voltage surges will be experienced at the distribution power line. Voltage surges are mainly caused by lightning. Every second, there are around 100 lightning strikes. Lightning strikes are unpredictable and random.

There are also temporary overvoltages and switching surges that can cause voltage surges. Overvoltages caused by changes in operating conditions within a system are called switching surges. They are the main source of voltage surges for station-class arresters. The trapping and subsequent release of energy are known as switching surges. Temporary overvoltages are caused by ground faults in one phase, and the voltage rises in unfaulted stages until the fault is cleared.

What is a surge arrester?

A MOV surge arrester (metal oxide varistor) contains a number of metal oxide varistor blocks. These MOV blocks act as an insulator and switch with line voltage. The MOV blocks are converted to conduction when the voltage that the arrester experiences exceed the reference voltage. Because the MOV blocks have a high non-linearity, conduction ceases once the voltage falls below the reference voltage.

Operation surge arrester

Why do arresters operate?

Surge arresters must be capable of sustaining the constant power-frequency voltage at which they are intended to work. It must be able to discharge any transient energy in the system as current and prevent excessive voltage from being generated. It must work in the same environment that the protected equipment. Temporary Overvoltage (TOV), which shows the maximum overvoltage that an arrester can withstand and how long it can withstand, is an indication of its ability to withstand damage.

There are many reasons why arresters may be called upon:

  • Too long TOV condition
  • Arrester for undersized persons
  • Lightning surges were more than the duty rating
  • Gap degradation in silicon carbide arresters
  • Leakage of silicone oil additive causes damage to oil-based polymer housings
  • Wildlife
  • Disk aging

After an end-of-life event, porcelain arresters can break apart. Polymer arresters might experience a blow to the side or a disconnector that will remove the arrester from the ground.

Different types of surge arresters

Secondary arresters

Secondary arresters are arresters rated under 1000 V. Secondary arresters are used to protect against secondary surges. The failure rate of transformers is between 0.4 and 1%. Low-side surges account for 50-70% of transformer failures. Additional surge duty will be applied to the service transformer by adding secondary surge protection at the home or service entrance. The failure rate of transformers can be significantly reduced by using a secondary arrester.

Distribution arresters

Distribution arresters are 1 to 36 kV rated.

There are three types of arresters within the distribution class: normal duty, light duty, and heavy-duty.

The riser pole arrester is a heavy-duty device.

Distributor arresters can be used in transformers, such as under-oil arresters or cubicle-mounted arresters.

Ordinary duty arresters can be used in low lighting situations, while heavy-duty arresters can be used in high-lighting applications. Riser pole arresters can also be used where the distribution lines run from overhead to underground. The Evolution arrester is suitable for all overhead applications.

An underground cable or equipment can experience a voltage surge if it is not protected by a riser pole. An open point arrester prevents surge reflection and 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 arrester’s cantilever strengths vary for the most challenging applications.

This post was written by Justin Tidd, Director at Swartz Engineering. For nearly half a century, Swartz Engineering has been at the forefront of industry safety. They are a family-owned company specializing in power distribution for the electrical industry. They are the leading manufacturer of Surge Arrestors. The SWARTZ® Current Transducer is a high-performance, a solid-state unit specifically developed to meet requirements for supervisory control and data acquisition (SCA- DA) systems. 

 

Danny White