Defective wiring
Introduction
A fault or fault current, in an electrical power system, is an abnormal electrical current. For example, a short circuit is a fault in which a live wire is in contact with a neutral or ground wire. An open circuit fault occurs if a circuit is interrupted due to a defect in a current-carrying wire (hot or neutral), a blown fuse, or a circuit breaker. In three-phase systems, a fault may involve one phase, more than one phase with ground, or may occur only between phases. In a "ground fault" current flows toward the ground. The presumed short-circuit current of a predictable fault can be calculated in most cases. In electrical power systems, protective devices can detect fault conditions and intervene on circuit breakers and other devices to limit loss of service due to a fault.
In a polyphase system, a fault can affect all phases equally, which is called a "symmetric fault." If it only affects some of the phases, the resulting "asymmetric system" becomes a little more complicated to analyze. The analysis of this type of failure is often simplified if methods such as the symmetric components theorem are used.
The design of systems to detect and interrupt faults in an electrical energy supply system is the main objective of power system protections.
Transient failure
A transient fault is a fault that ceases to exist if power is removed for a short period and then restored. It can also be an insulation fault that only temporarily affects the dielectric properties of a device and is restored shortly thereafter. Many faults on overhead power lines are transient in nature. When a fault occurs, the equipment used to protect the electrical system works to isolate the fault zone. The transient fault will then be cleared and the power line can be returned to service. Among the typical examples of transient failures we find:.
• - Momentary contact with a tree.
• - Contact with a bird or other animal.
• - A lightning bolt.
• - The crash of a vehicle.
Transmission and distribution systems utilize an automatic shutdown function typically used on overhead lines to attempt to restore power should a transient fault occur. This functionality is not as common in underground systems, as faults are usually persistent in nature. Transient faults can still cause damage either at the site of the original fault or, as the fault is generated, elsewhere in the power grid.