High-Voltage Surge Arresters

High-Voltage Surge Arresters

In safe and reliable

protection of electrical equipments, surge arresters are the primary protection against atmospheric and switching over voltages. The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrester, in most cases to earth. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices.
Different relevant standards exists for design and type tests like IEC 60099-4 , ANSI/IEEEC62.11 and other specific standards.

Applications.

1). Protection of AIS and GIS substation equipment
2). HVDC protection
3). Protection of series capacitor banks
4). Protection of cables
5). Protection of transmission lines
6). Polluted areas and areas with high seismic activities.

Types.

1). Silicone-housed surge arrester :-

A flexible type of arrester for line discharge class 2 to 5 and system voltage up to 550 kV.

2). Composite-housed surge arrester :-

A high strength arrester for line discharge class 3 to 5 and system voltage up to 800 kV.

3). Porcelain-housed surge arrester :-

A high strength arrester family for line discharge class 2 to 5 and system voltage up to 800 kV.

Other Types

Horn Gap Arresters

Horn gap arresters are named for their two horn-shaped metal rods. These rods are arranged around a small air gap, and the distance between the two rods increases as they rise 

o two different wires: One attaches to the electrical line. Between it and the horn is a resistance and a choke coil. The resistance regulates the level of current allowed into the arrester at once, and the choke coil increases the reactivity of the arrester when transient frequency occurs. The other wire is connected to a ground, which siphons the excess electricity to the ground.

Multi-Gap Arresters

Multi-gap arresters are made from a series of metal cylinders. These cylinders are all insulated from one another as well as separated by air gaps. The first cylinder gets connected to the electrical line, while all of the other cylinders are attached to the ground through a series resistance, which gradually wears down the power of the current. Some of the gaps between the later cylinders have a shunt resistance that catches a surge when there is an excess of voltage.

Valve-Type Arresters

Valve-type arresters are commonly used in more high-powered electrical systems. They consists of two main parts: a series of spark gaps and a series of non-linear resistor discs. Valve-type arresters work when excessive voltage causes the spark gaps to touch, and the non-linear resisters carry the voltage into the ground. Once the surge of excess power ends, the resisters push the spark gaps apart.

Brief performance data of Typical Lightning Arresters

System voltage	kV	72 - 145	24 - 170	52 - 420	52 - 420	300 - 550
Rated voltage	kV	75 - 120	18 - 144	42 - 360	42 - 360	228 - 444
Nominal discharge current	kApeak	10	10	10	20	20
Line discharge class	Class	2	2	3	4	4
Mechanical strength (SSL)	Nm	1 300	1 600	4 000	4 000	9 000

Building Blocks

The most important component for the surge arresters is the ZnO blocks, the varistors. Stacked in the center of the surge arrester, the varistor is the heart of the surge arrester. The varistor consist of a mix of zink oxide and other metallic powders that are blended and pressed into cylindrical blocks.

Typical type tests performed for different size of ZnO varistor.

Tests on ZnO blocks

Energy withstand test on all blocks - The blocks pass three energy test cycles with cooling in-between. In each cycle, the injected energy is far in excess of the single impulse energy capability.

Classification of all blocks

Visual inspection and classification of the blocks at 1 mA (d.c.) and 10 kA (8/20 μs) and the residual voltages are printed on each block together with a batch identification.

Accelerated life tests on samples

Here power losses after 1 000 hours is calculated from a test with shorter duration (approximately 300 hours) at an elevated temperature of 115 °C at 1.05 times Uc shall not exceed the losses at start of the test.

Impulse current tests on samples

Blocks are subjected to high current impulses (4/10 μs) and long duration current impulses (2 500 μs) of amplitudes verifying catalogue data.