Disturbances In LV Networks Due To Surges

Introduction

There are two types of surge: those generated by a lightning impact and those resulting from electrical switchgear switching operations.

Surges resulting from lightning strokes

Surges resulting from lightning strokes (see figure below) can affect all electrical installations. Consequently, they are without doubt the main source of nuisance tripping of electrical protection devices.

In most cases an earth leakage protection device will trip. The incomer circuit-breaker, if it is of the residual current kind, is the first concerned as it affects the entire electrical installation. Should lightning fall on a line or an electrical installation, it will cause a potential build-up that will lead to arcing to the earth resulting in tripping of earth leakage and/or thermal magnetic protection devices.

Operating Overvoltage

Operating overvoltage (see figure below) result from opening or closing of switchgear on the electrical network (current switching on a high power network).

The phenomenon that creates most disturbance is that generated by surges occurring on the network when a protection device cuts an electric current. The electrical power transmitted by this second surge category is markedly less energetic than that transmitted by a lightning stroke occurring close-by.

Surges resulting from breaking of the neutral conductor

In three-phase systems, breaking of the earthed neutral conductor connection results in a potential rise of the neutral (according to load unbalance).

Phase-to-neutral voltage is also affected and can increase by 70% (U₀√3).

Home Surge Protection (VIDEO)

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Resource: Schneider Electric – Increasing availability of LV electrical networks