1.0 Introduction of Fault
It is not practical to design and build electrical equipment or network so as to completely eliminate the possibility of failure in service.
It is therefore an everyday fact of life that different types of faults occur on electrical systems, however infrequently, and at random location.
Fault can be broadly classified into two main areas which have been designated “Active” and “Passive”.
1.1 Types of Fault
- Active fault
- Passive fault
- Types of faults on a three-phase system
- Transient and permanent fault
1. Active fault:
The “active” fault is when actual current flows from one phase conductor to another (phase-to-phase) or alternatively from one phase conductor to earth (phase —to-earth). This type of fault can further be classified into two areas, namely the “Solid” fault and “Incipient” fault.
The solid fault occurs as a result of an immediate complete breakdown of insulation as would happen if say, a pick struck an underground cable, bridging conductors etc.
The incipient fault on the other hand, is a fault that starts from very small beginnings from say some partial discharge (excessive electronic activity often referred to as Corona) in a void in the insulation, increasing and developing over an extended period, until such time as it burns away adjacent insulation, eventually running away and developing into a “solid” fault.
Other causes can typically be a high-resistance joint or contact, alternatively pollution of insulators causing tracking across their surface. Once tracking occurs, any surrounding air will ionize which then behaves like a solid conductor consequently creating a “solid” fault.
2. Passive fault:
This are not real faults in the true sense of the word but are conditions that are stressing the system beyond its design capacity, so that ultimately active faults will occur.
Typical examples are
Overloading:
leading to overheating of insulation(deteriorating quality, reduced life and ultimate failure)
Overvoltage:
stressing the insulation beyond its limits.
Under Frequency:
causing plant to behave incorrectly
Power Swings:
generators going out—of-step or synchronism with each other.
3. Three-phase system fault
These are types of fault on a 3-? system
Phase —to-earth fault:
This is cause as a result of the breakdown of insulation of one phase and earth. It occurrence is about 70%.
There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)
Phase—to-phase fault:
this is a type of short circuit fault that due to breakdown of insulation between either of the two phases. It occurrence is 15%.
There is a circuit diagram in the complete material that shows an example (scroll down to the end of this project to get the complete material)
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