Substation Surge Arrestors

Substation surge arrestors are installed on systems from 3kv-330kv.

Why install high voltage surge arrestors on Sub-transmission lines?

Sub-transmission surge arrestors are installed on overhead lines from 66kv-132kv to prevent tripping of equipment at the Sub-station.

Sub station installations

Station class surge arrestors are usually installed in substations. It often happens however, that nuisance breaker trips occurr with faults higher up on the line and thus need remedy (eg lightning flashover). This requires additional surge arrestors on the overhead line at the closest points of incidence.

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Email : sales@liveline.co.za

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Steps taken when Installing HV surge arrestors on sub transmission lines

Step 1

Analysis into the possible cause of the line fault.

Are the clearances of the overhead line according to the correct specification ?
Are there broken insulators causing the faults in wet weather ?
Are the insulators dirty or are the flashovers due to Birds or Bird faeces ?
Check Poor Earthing -Places where flashovers occur between the structure to the phase
Lightning (use fault location)

Step 2

Get a good Earth.

Use as many short conductors with large surface areas in the ground (thick conductors) rather than one long conductor in the crowfoot.
Resistance needs to be improved to less than 50? at low current values to ensure that the effective earth resistance is at least 16 ? at a 16kA impulse (average measured) that will result in a volt drop of 256 kV.
Welding cables are used between the GLD and the tower structure.
Use agricultural gypsum to improve conductivity with soil.
Get soil resistivity as low as possible.
Use a crowfoot method, using a three foot crowfoot system , 500mm below the system and not further than 5m in length from the structure.

Step 3

Install the surge arrestor.

The conductor size needs to be measured for the arrestor connection fittings
Line arrestors are fitted on all three phases.
A welding cable is connected from the bottom of the surge arrestor, to the steel structure.
The crowfoot method is used to earth the structure.
Surge arrestors need to be installed as close to the point of incidence as possible, and may be installed on three or four spans before and after the point of incidence.