Voltage spike
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Voltage spikes are fast, short duration electrical transients (overvoltages) in the electric potential of a circuit. These are typically caused by lightning strikes, although power outages, tripped circuit breakers, short circuits, power transitions in other large equipment on the same power line, and malfunctions caused by the power company can also cause them. Other transients can be created by an electromagnetic pulse (EMP) with electromagnetic energy distributed typically up to the 100 Khz and 1 Mhz frequency range. Pulse produced by a nuclear explosion detonation are called nuclear electromagnetic pulse (NEMP) with energy distributed in frequencies from 1 Khz into the Gigahertz range.
The effect of a voltage spike is to produce a corresponding increase in current. However some voltage spikes may be created by current sources. Voltage would increase as necessary so that a constant current will flow. Current from a discharging inductor is one example.
For sensitive electronics, excessive current can flow if this voltage spike exceeds a material's breakdown voltage, or if it causes avalanche breakdown. In semiconductor junctions, excessive electrical current may destroy or severely weaken that device. An avalanche diode, transient voltage suppression diode, transil, varistor, overvoltage crowbar, or a range of other overvoltage protective devices can divert (shunt) this transient current thereby minimizing voltage.
While generally referred to as a voltage spike, the phenomenon in question is actually an energy spike, in that it is measured not in volts but in joules; a transient response defined by a mathematical product of voltage, current, and time.
Voltage spike may be created by a rapid buildup or decay of a magnetic field, which may induce energy into the associated circuit. However voltage spikes can also have more mundane causes such as a fault in a transformer or higher-voltage (primary circuit) power wires falling onto lower-voltage (secondary circuit) power wires as a result of accident or storm damage.
Voltage spikes may be longitudinal (common) mode or metallic (normal or differential) mode. Some equipment damage from surges and spikes can be prevented by use of surge protection equipment. Each type of spike requires selective use of protective equipment. For example a longitudinal mode voltage spike may not even be detected by a protector installed for normal mode transients.
