Literature Review

Hall and Dorf (1993) states that insulation plays an important role in maintaining the performance and the safety of the electrical power apparatus. Electrical power supply should ensure reliability and continuity to the utility concerned; hence the power lines and sub-stations are to be operated and protected against over-voltages such that the numbers of failures are as few as possible. At the same time, the cost involved in the design, installation and operation of the protective devices should not be too high.

Also, that insulator must have sufficient mechanical strength to support the physical loads, but must be so designed to withstand severe electrical and environmental stresses without mechanically failing. [3]

Bello (2004) in his manual, states that faults on power system have been increasing as result of insulation failure. More so, the failure causes various hazards among which are:

Fire outbreak on power system.

Back feeding on transmission and distribution systems.

Damage to equipment and properties.

Personal injury, fatal accident and loss of life

And Unplanned expenses due to replacement. [6]

Bello (2004) in his manual and Mohamed (2004) in his publication observed that the deterioration of insulation is one of the primary causes of electrical equipment failure. The breakdown of insulation occurs when there is a breakdown of dielectric. Few among major causes of insulation failures are cracks on solid insulators, contamination, moisture, humidity, corrosive vapour on liquid and gas insulators, excessive load, excessive voltage, stress due to over-loading, vibration etc. [6],[5]

Herald and Wilism (1992) in their book states that dielectric strength of an insulator is the minimum voltage at which electrical failure or breakdown occurs under prescribed conditions, or it is the voltage at which breakdown occurs when applied between standardized electrodes at a specific temperature. The relationship between dielectric strength and breakdown voltage is given by Herald and Wilism as

Ds = Vbk/d

Where Ds = Dielectric Strength measured in Volts per millimeter.

Vbk = Breakdown voltage of Insulator.

d = Distance between the test electrodes which is usually in millimeter. [4]

From the above, it can be concluded that:

Insulators are meant for a specific voltage.

When that voltage is exceeded, the insulator will breakdown and may or may not behave ass insulator again.

The breakdown may result to fire outbreak, personal injury, loss of life, expenses due to replacement.