Electric and Magnetic Fields from Overhead Lines:
Biological effects of Electric and Magnetic Fields from Overhead Lines and even cables in close proximity of buildings have recently attracted attention and have also caused some concern. Power frequency (50 or 60 Hz) and even their harmonics are not considered harmful. Investigations carried out in certain advanced countries have so far proved inconclusive.
The electrical and electronics engineers, while being aware of this controversy, must know that many other environmental agents are moving around that can cause far greater harm to human health than does electromagnetic radiation.
As a piece of information it may be quoted that directly under an Electric and Magnetic Fields from Overhead Lines of 400 kV, the electric field strength is 11000 V/m and magnetic flux density (depending on current) may be as much as 40 μT. Electric field strength in the range of 10000-15000 V/m is considered safe.
Visual and Audible Impacts:
These environmental problems are caused by the following factors.
- Right of way acquires land underneath. Not a serious problem in India at present. Could be a problem in future.
- Lines converging at a large substation mar the beauty of the landscape Underground cables as alternative are too expensive a proposition except in congested city areas.
- Radio interference (RI) has to be taken into account and countered by various means.
- Phenomenon of corona (a sort of electric discharge around the high tension line) produces a hissing noise which is audible when habitation is in close proximity At the towers great attention must be paid to tightness of joints, avoidance of sharp edges and use of earth screen shielding to limit audible noise to acceptable levels.
- Workers inside a power plant are subjected to various kinds of noise (particularly near the turbines) and vibration of floor. To reduce this noise to tolerable level foundations and vibration filters have to be designed properly and simulation studies carried out. The worker must be given regular medical examinations and sound medical advice.