Capacitive Coupling from Transmission Lines

Transmission & Distribution

Over the last 5 years or so, a number of micro-shock incidents have occurred under 220 kV and 110 kV transmission lines in New Zealand. Each micro-shock incident had differing circumstances. Investigation into these micro-shock incidents showed these were all caused by capacitive coupling (also known as electrostatic induction), from the nearby high-voltage lines. In some instances, modelling, using specialist software, CDEGS, was conducted to calculate the capacitive coupling issues. The initial aim of this modelling was to model the various scenarios experienced, and to ensure future micro-shock incidents are minimised as far as practically possible. Examples of the micro-shock incidents include:

  • A helicopter winching Search and Rescue personnel.
  • A construction worker handling a tilt slab suspended from a crane. A vineyard worker wearing a heated vest.
  • A dog shocked while in torrential rain.
  • A house owner working on a corrugated iron roof.

In this paper:

  • The concept of electric fields (EF), capacitive coupling, and EF sources are explained. The effects of capacitive coupling are explained.
  • Typical perception and discomfort limits are given in context with New Zealand and Internationally.
  • The capacitively coupled voltages, currents, and energy for each of the micro-shock incidents are discussed.