The present invention relates generally to trip units. More specifically, the present invention relates a method of instantaneous protection in an electronic trip unit.
Electronic trip units are well known. Electronic trip units typically comprise voltage and current sensors which provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals which are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality firmware, including initializing parameters, and boot code. The EEPROM includes operational parameters for the application code.
These trip units are required to meet certain standards, e.g., UL/ANSI/IEC, which define trip time curves specifying under what conditions a trip must occur, i.e., short time, long time, instantaneous, or ground fault, all of which are well known. These standards also specify a short time delay from the instant power is applied to when a trip unit must be ready to trip.
The present invention is being directed to the instantaneous trip condition. Various electronic circuits (analog electronics) and customized integrated circuits (application specific integrated circuit (ASIC)) have been employed to perform instantaneous protection. The microcontroller of the present trip units has also been programmed to execute algorithms which implement a protection curve, such curves are typically specified by the aforementioned standards.