ELECTROMAGNETISM AND WAY-LEAVE CORRIDOR

Wayleave corridor is the distance from the centre of voltage transmission power lines which varies in value according to the transmission voltage in the electric lines and is supposed to be clear of any activities.

The law prohibits the public to undertake or engage in any activity in the vicinity of any electrical installation in a manner likely to interfere with the installation or cause danger to a person or property. Additionally, the electricity system produces extremely low frequency electromagnetic field which comes under non ionizing radiations which can cause health effects.

The cases of encroachment on the transmission network include buildings, markets, and brick making and planting of tall vegetation which touch the conductors within the corridor.

66kV transmission line passing over houses in Chilobwe, Blantyre

What are Electric and Magnetic fields

Electromagnetism is a fundamental physical force that is responsible for interactions between charged particles which occur because of their charge and for the emission and absorption of photons referred to as electromagnetic force. Electric and magnetic fields, often referred to as electromagnetic fields (emf) occur naturally and as a result of the Power generation, Power Transmission, Power distribution and use of electric power.emf is a field of force and is created by electric voltage and current. It occurs around electrical devices or whenever power lines are energized.Magnetic fields result from the motion of the electric charge or current, such as when there is current flowing through a power line. Magnetic field lines run in circles around the conductor (i.e. produces magnetic induction on objects and induced currents inside them). This phenomenon is also possible in human and animal or any other conducting bodies causing possible health effects and a multitude of interference problems. The higher the current, the greater the strength of the magnetic field.

ELECTRICAL SURGES

A surge is a transient wave of current, voltage or power in an electric circuit. Surges, or transients, are brief overvoltage spikes or disturbances on a power waveform that can damage, degrade, or destroy electronic equipment within any home, commercial building, industrial, or manufacturing facility. 

There are several sources of power surges. They can originate from the electric utility company during power grid switching. Switching transients result from electrical equipment switching operations, fault initiations, and interruptions in a power distribution system.

Other sources of electric surges are within the home or facility and these are termed internal sources for instance; switching of electrical loads, magnetic and inductive coupling and static electricity.

Externally the most recognizable source of surges generated outside the home or facility is lightning. Lightning surges are the result of a direct flash terminating on the power system, structures, or to the soil, and can also be induced on the utility system and distribution circuits by nearby lightning flashes.

Cloud-Ground Lightening Strike

Lightning is a natural phenomenon caused by separation of electrical positive and negative charges by atmospheric processes. Lightening is usually comprehended through damage it causes at the point when a cloud-ground stroke terminates on a tree, structure, or elevated wiring. This is generally called a lightning strike. Unless the struck items are protected from lightning, the results of the strike are often visible and lasting. But the lightning current pulse continues into conductive parts of the structure, cables, and even underground wiring and pipes. Because the initial lightning impulse is so strong, equipment connected to cables a mile or more from the site of the strike can be damaged.

Surge protective devices applied at the service entrance mains of residential AC power circuits will be subjected to normal and abnormal surge conditions as well as abnormal AC voltage conditions. The design of the application must consider these conditions to prevent premature degradation and failure. 

ELECTRIC CHOCK (ELECTROCUTION)

An electric shock occurs when a human or animal body comes into contact with a source of voltage. An electric shock is usually painful and can be lethal. However the voltage level is not directly proportional to the level of injury or danger of death. The factors affecting the severity of the shock are the amount of current flowing through the body, path of the current through the body and length of time the body is in the circuit. Severity of the shock may also be affected by:

• The voltage .
• The presence of moisture in the environment.
• The phase of the heart cycle when the shock occurs.
• The general health of the person prior to the shock.
• Large amounts of electric currents through the heart can cause cardiac arrest.