In an
electric power system, overcurrent or excess current is a situation where a larger than intended
electric current exists through a
conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include
short circuits, excessive load, incorrect design, an
arc fault, or a
ground fault.
Fuses,
circuit breakers, and
current limiters are commonly used overcurrent protection (OCP) mechanisms to control the
risks.
Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent.[1]
transients during the large load changes will cause large variations of the grid voltage, causing problems with the loads (e.g., some motors might not be able to start in the
undervoltage condition);
the grid protection devices are designed to be triggered by a sufficient level of overcurrent. In a weak system the short circuit current might be hard to distinguish from a normal transient overcurrent encountered during the load changes;
during a
black start operation after a failure, large
inrush current might be needed to energize the system components. For example, if some loads in a weak system remain connected, and
inverter-based resource might not be able to start.
Related standards
IEC 60364-4-43: Electrical installations of buildings – Part 4-43: Protection for safety – Protection against overcurrent