TimeCurrentKurven

TimeCurrentKurven are graphical representations that relate the magnitude of electrical current through a protective device to the time it takes for the device to operate, i.e., to trip or interrupt the circuit. They are used in electrical power systems to characterize and compare protective devices such as fuses and circuit breakers, and to support protection coordination and selectivity.

In a typical TimeCurrentKurven, the horizontal axis shows current as a multiple of the device’s rated current (In), while the vertical axis shows operating time in seconds. The curves illustrate how longer operating times occur at currents only slightly above In, and how the time decreases as the current increases. Different characteristic families exist, including inverse-time, very-inverse-time, extremely-inverse-time, definite-time, and instantaneous trip regions. Each family describes a distinct relationship between current and trip time, reflecting the device’s design and intended application.

TimeCurrentKurven are provided by manufacturers and referenced in standards such as IEC 60269 for fuses and IEC 60898/60947 for circuit breakers. They are essential tools for protection coordination, allowing engineers to overlay curves from upstream and downstream devices to ensure selective tripping and adequate fault clearance.

Practical use involves selecting devices whose curves provide the desired coordination under prescribed operating conditions, while accounting for real-world factors. Limitations include variations due to ambient temperature, aging, manufacturing tolerances, and installation conditions, which can cause actual operation times to deviate from the published curves. Nevertheless, TimeCurrentKurven remain a fundamental concept in the design and analysis of electrical protection schemes.