Electrical breakdown
The term electrical breakdown has several similar but distinctly different meanings. The term may apply to a failure of an electric circuit or system with consequent lack of function.
Alternately, it may refer to a rapid reduction in the resistance of an electrical insulator that can lead to a
spark jumping around or through the insulator. This may be a momentary event , or may lead to a continuous
arc discharge if protective devices fail to interrupt the current in a high power circuit.
Encyclopedia
The term
electrical breakdown has several similar but distinctly different meanings. The term may apply to a failure of an electric circuit or system with consequent lack of function.
Alternately, it may refer to a rapid reduction in the resistance of an electrical insulator that can lead to a
spark jumping around or through the insulator. This may be a momentary event , or may lead to a continuous
arc discharge if protective devices fail to interrupt the current in a high power circuit.
Electrical system failure
The most common meaning is related to
automobiles and is the failure of an electric circuit or associated device resulting in a loss of vehicle function . Common problems include battery discharge,
alternator failure, broken wires, blown fuses, and a failed
fuel pump.
Failure of electrical insulation
The second meaning is more specifically a reference to the breakdown of the
insulation of an electrical
wire or other electrical component. Such breakdown usually results in a
short circuit and/or a blown fuse. Actual insulation breakdown is more generally found in
high-voltage applications, where it sometimes causes the opening of a protective
circuit breaker. Electrical breakdown is often associated with the failure of solid or liquid insulating materials used inside high voltage
transformers or
capacitors in the
electricity distribution grid. Electrical breakdown can also occur across the strings of insulators that suspend overhead
power lines, within underground power cables, or lines arcing to nearby branches of trees. Under sufficient electrical stress, electrical breakdown can occur within solids, liquids, or gases. However, the specific breakdown mechanisms are significantly different for each phase of
dielectric.
Electrical breakdown occurs within a gas when the dielectric strength of the gas is exceeded. Regions of high electrical stress can cause nearby gas to partially ionize and begin conducting. This is done deliberately in low pressure discharges such as in
fluorescent lights. ' or in an electrostatic precipitator.
Partial electrical breakdown of the air causes the "fresh air" smell of
ozone during thunderstorms or around high-voltage equipment. Although air is normally an excellent insulator, when stressed by a sufficiently high voltage , air can begin to break down, becoming partially conductive. If the voltage is sufficiently high, complete electrical breakdown of the air will culminate in an electrical
spark or
arc that bridges the entire gap. While the small sparks generated by static electricity may barely be audible, larger sparks are often accompanied by a loud snap or bang.
Lightning is an example of an immense spark that can be many miles long. The color of the spark depends upon the gases that make up the gaseous media.
If a fuse or
circuit breaker fails to interrupt the current flowing through a spark in a power circuit, current may continue to flow, forming a very hot
electric arc. The color of an arc depends primarily upon the conductor materials . Although sparks and arcs are usually undesirable, they can be useful in everyday applications such as
spark plugs for gasoline engines, electrical
welding of metals, or for metal melting in an
electric arc furnace.
Corona breakdown
Partial breakdown of the air occurs as a corona discharge on high voltage conductors at points with the highest electrical stress . Corona is sometimes seen as a bluish glow around high voltage wires and heard as a sizzling sound along high voltage power lines. Corona also generates radio frequency noise that can also be heard as 'static' or buzzing on radio receivers. Corona can also occur naturally at high points during thunderstorms as
St. Elmo's Fire.
Although corona discharge is usually undesirable, until recently it was essential in the operation of photocopiers and
laser printers. Many modern copiers and laser printers now charge the photoconductor drum with an electrically conductive roller, reducing undesirable indoor ozone pollution.
See also
- Breakdown voltage
- Avalanche breakdown
