Direct current arc fault detector and circuit interrupter, and method of detecting an arc in a direct current power circuit

A direct current arc fault circuit interrupter for a direct current power circuit having a current flowing therein, said direct current arc fault circuit interrupter comprising:

• separable contacts electrically connectable in series with said direct current power circuit;
• an operating mechanism structured to open and close said separable contacts;
• a first current sensor structured to sense an alternating current component of the current flowing in said direct current power circuit;
• a second current sensor structured to sense a direct current component of the current flowing in said direct current power circuit;
• a bandpass filter structured to filter the sensed alternating current component of the current flowing in said direct current power circuit;
• a demodulating logarithmic amplifier including an input of the filtered alternating current component of the current flowing in said direct current power circuit, and an output;
• an integrator or minimum detector circuit including an input electrically connected to the output of said demodulating logarithmic amplifier, and an output;
• and
• a processor structured to repetitively input and then reset the output of said integrator or minimum detector circuit, and:
• (a) to increment a first arc fault accumulator when the sensed direct current component of the current flowing in said direct current power circuit is greater than a first predetermined value and a present value of the output of said integrator or minimum detector circuit is different from a previous value of the output of said integrator or minimum detector circuit by more than a second predetermined value with a first predetermined time being between the present value of the output of said integrator or minimum detector circuit and the previous value of the output of said integrator or minimum detector circuit, or otherwise to decrement the first arc fault accumulator, and to determine an arc in said direct current power circuit when the first arc fault accumulator is greater than a third predetermined value;
• and
• (b) to increment a second arc fault accumulator when the sensed direct current component of the current flowing in said direct current power circuit is greater than the first predetermined value and the present value of the output of said integrator or minimum detector circuit is greater than another previous value of the output of said integrator or minimum detector circuit by more than a fourth predetermined value with a second predetermined time, which is longer than the first predetermined time, being between the present value of the output of said integrator or minimum detector circuit and said another previous value of the output of said integrator or minimum detector circuit, or otherwise to decrement the second arc fault accumulator, and to determine the arc in said direct current power circuit when the second arc fault accumulator is greater than a fifth predetermined value, and
• wherein the processor is structured to output a signal to cause said operating mechanism to trip open said separable contacts in response to determining the arc fault in said direct current power circuit.

A method of detecting an arc in a direct current power circuit having a current flowing therein, said method comprising:

• sensing an alternating current component of the current flowing in said direct current power circuit;
• sensing a direct current component of the current flowing in said direct current power circuit;
• bandpass filtering the sensed alternating current component of the current flowing in said direct current power circuit;
• providing a value proportional to a logarithm of an envelope of the bandpass filtered alternating current component of the current flowing in said direct current power circuit;
• integrating said value to provide an integrated value;
• and
• repetitively inputting and then resetting the integrated value;
• performing an arc determination function including:
• (a) incrementing a first arc fault accumulator when the sensed direct current component of the current flowing in said direct current power circuit is greater than a first predetermined value and a present value of the output of said integrator or minimum detector circuit is different from a previous value of the output of said integrator or minimum detector circuit by more than a second predetermined value with a first predetermined time being between the present value of the output of said integrator or minimum detector circuit and the previous value of the output of said integrator or minimum detector circuit, or otherwise decrementing the first arc fault accumulator, and determining the arc in said direct current power circuit when the first arc fault accumulator is greater than a third predetermined value;
• and
• (b) incrementing a second arc fault accumulator when the sensed direct current component of the current flowing in said direct current power circuit is greater than the first predetermined value and the present value of the output of said integrator or minimum detector circuit is greater than another previous value of the output of said integrator or minimum detector circuit by more than a fourth predetermined value with a second predetermined time, which is longer than the first predetermined time, being between the present value of the output of said integrator or minimum detector circuit and said another previous value of the output of said integrator or minimum detector circuit, or otherwise decrementing the second arc fault accumulator, and determining the arc in said direct current power circuit when the second arc fault accumulator is greater than a fifth predetermined value.