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In transmission line faults, roughly 5% - 10% are asymmetric line-to-line faults. [2] line-to-ground fault - a short circuit between one line and ground, very often caused by physical contact, for example due to lightning or other storm damage. In transmission line faults, roughly 65% - 70% are asymmetric line-to-ground faults. [2]
In polyphase electrical systems, generally phase-to-phase, phase-to-ground (earth), and phase-to-neutral faults are examined, as well as a case where all three phases are short-circuited. Because impedances of cables or devices varies between phases, the prospective short-circuit current varies depending on the type of fault.
A line-to-ground fault will cause a voltage sag until the protective switchgear (fuse or circuit breaker) operates. [2] [11] Some accidents in power lines such as lightning or a falling object can cause a line-to-ground fault. [11] Sudden load changes or excessive loads [11] Depending on the transformer connections, transformers energizing [6]
By expanding a one-line diagram to show the positive sequence, negative sequence, and zero sequence impedances of generators, transformers and other devices including overhead lines and cables, analysis of such unbalanced conditions as a single line to ground short-circuit fault is greatly simplified. The technique can also be extended to ...
Using network topology, transmission line parameters, transformer parameters, generator location and limits, and load location and compensation, the load-flow calculation can provide voltage magnitudes and angles for all nodes and loading of network components, such as cables and transformers.
Any conducting object connected to the substation earth ground, such as telephone wires, rails, fences, or metallic piping, may also be energized at the ground potential in the substation. This transferred potential is a hazard to people and equipment outside the substation. A computer calculation of the voltage gradient around a small substation.
Failing insulation is essentially a high impedance fault which will allow current to flow through any available path to ground, a condition which can cause shocks or fires if left unmitigated. This leakage can occur when there is damage caused by physical, thermal, or chemical stresses to insulation on power lines, especially but not limited to ...
Although usually the result of a fault, there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors. In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an 'ideal' short circuit, this means ...