Overvoltage protection

[Cerkit]

Hi,

If the surge diverters on incoming 33kV lines to a substation limit the overvoltage at the substation below the impulse insulation of a transformer at the site will additional overvoltage be required for the transformer? I am thinking that it shouldn't be required since the surge diverters on the line are adequate.

Thanks

 

[dpc]

Transient impulses can be high frequency traveling waves so if your goal is protect the transformer, the surge arresters should be as close to the transformer as physically possible (primary and secondary). Standard practice is to mount arresters directly on the transformers just ahead of the bushings. Ground arresters to the tank and also to the ground grid. Not the place to try to save a few dollars.

 

[bacon4life]

Checking whether surge diverters the same thing as MOV surge arrestors? Other kinds of devices such as spark gaps might be used on distribution lines, but would not provide adequate protection for substation transformers.

Typically substation class surge arrestors will be much heavier duty than the surge suppression devices out on distribution lines. The consequences of a distribution line flashing over is a short outage; the consequences of the substation transformer failing from a surge is a very expensive emergency replacement project along with the potential for catastrophic collateral damage to other substation equipment.

It also depends on how much lightning your area receives. There are a few areas of the world with flash densities below 0.5 flashes/sq km/year where it might make economic sense to forgo the second set of arrestors.

 

[RRaghunath]

Lightning or switching surge protection should not be confused with Over voltage protection.
The latter is for sustained overvoltages that could cause transformer overfluxing and consequent damage if prolonged. This is not required unless there is a possibility of sustained overvoltages in the said distribution systems.
In transmission networks some people do provide overfluxing protection for grid transformers.
Flux is proportional to V/f and the Overfluxing protection is more appropriate for transformers than simple overvoltage protection.