Arc fault identification unit

An arc fault identification unit for an electrical three-phase alternating current circuit having three phase conductors and a neutral conductor, comprising:

• voltage sensors, each of the respective voltage sensors being assigned to each of a respective phase conductor of the three phase conductors, to periodically determine phase-neutral conductor voltage values and phase-phase voltage values;
• current sensors, each of the respective current sensors being assigned to each of a respective phase conductor of the three phase conductors, to periodically determine phase conductor current variables usable to determine phase conductor current values and a value for a change in electrical current with respect to time;
• and,
• an evaluation unit, connected to the voltage and connected to the current sensors, and configured to, from the phase conductor current values periodically determined from periodically determined phase conductor current variables, determine current differences of two phase conductors as concatenated currents and configured to, from values for a change in the electrical current with respect to time per phase, determine change differences of two phase conductors as concatenated change current values,
• the evaluation unit being further configured to:
• to determine a ground current from the phase conductor current values,
• to determine a respective current root-mean-square value for each of the phase conductor current values and for a ground current,
• to compare the respective current root-mean-square value, for each of the phase conductor current values and for a ground current, with a first, second, third and fourth current threshold value,
• to respectively output a first, second, third or fourth overcurrent signal upon the comparing indicating that a respective first, second, third or fourth current threshold value is exceeded,
• calculate a first arc voltage from the phase-neutral conductor voltage values,
• to calculate a second arc voltage from the phase-phase voltage values,
• to calculate a third arc voltage from the phase current values,
• to calculate a fourth arc voltage from the concatenated currents,
• to calculate a fifth arc voltage from values for a change in electrical current with respect to time,
• to calculate a sixth arc voltage from the concatenated change current values per phase-neutral conductor and per phase-phase
• to respectively compare the first arc voltage, second arc voltage, third arc voltage, fourth arc voltage, fifth arc voltage and sixth arc voltage to a sixth threshold values, and to respectively output a first to sixth arc fault identification signal based upon the respective comparisons,
• to respectively calculate a seventh arc voltage, an eighth arc voltage, a ninth arc voltage, a tenth arc voltage, an eleventh arc voltage, and a twelfth arc voltage from the phase-neutral conductor voltage values,
• to respectively compare the seventh to twelfth arc voltages to seventh to twelfth threshold values, such that a respective seventh to twelfth arc fault identification signal is output upon a respective one of the seventh to twelfth arc voltages exceeding a respective one of the seventh to twelfth threshold values, and
• to output an output-side arc fault identification signal upon at least one overcurrent signal and one arc fault identification signal being present.