Field ground fault detector and field ground fault relay for detecting ground fault corresponding to DC component extracted from ground fault current

A field ground fault detector for detecting an occurrence of a ground fault in a field circuit, comprising:

• a resistor having first and second terminals, the first terminal connected to ground;
• a DC voltage source connected to a negative electrode of the field circuit and the second terminal of the resistor;
• a first filter circuit for receiving a voltage between the first and second terminals of the resistor and for attenuating an AC component of the received voltage to extract a DC voltage;
• a second filter circuit for receiving a voltage between the negative electrode of the field circuit and ground and for attenuating an AC component of the received voltage to extract a DC voltage;
• and
• a determining circuit for determining the occurrence of a ground fault from a ratio of the extracted DC voltage from the first filter circuit and the extracted DC voltage from the second filter circuit.

A field ground fault detector for detecting an occurrence of a ground fault in a field circuit, comprising:

• a resistor having first and second terminals, the first terminal connected to ground;
• a DC voltage source connected to a negative electrode of the field circuit and the second terminal of the resistor for providing a DC voltage output;
• a DC voltage extracting circuit connected to the first and second terminals of the resistor for extracting a DC voltage between the first and second terminals of the resistor;
• and
• a ground fault position determining circuit connected to the DC voltage extracting circuit for comparing the extracted DC voltage from said DC voltage extracting circuit with a predetermined value corresponding to the DC voltage output of the DC voltage source and for determining that a ground fault has occurred at the negative electrode of the field circuit based upon the comparison.

A field ground fault detector for detecting an occurrence of a ground fault in a field circuit, comprising:

• a resistor having first and second terminals, the first terminal connected to ground;
• a DC voltage source connected to a negative electrode of the field circuit and the second terminal of the resistor;
• a DC voltage extracting circuit connected to the negative electrode of the field circuit and ground for extracting a DC voltage between the negative electrode of the field circuit and ground;
• and
• a ground fault position determining circuit connected to the DC voltage extracting circuit first comparing the extracted DC voltage from the DC voltage extracting circuit with a predetermined value and for determining that a ground fault has occurred on the negative electrode side of the field circuit based upon the comparison.

A field ground fault detector for detecting an occurrence of a ground fault in a field circuit, comprising:

• a resistor having first and second terminals, the first terminal connected to ground;
• a DC voltage source connected to a negative electrode of the field circuit and the second terminal of the resistor;
• a first DC voltage extracting circuit connected to the first and second terminals of the resistor for extracting a DC voltage between the first and second terminals of the resistor;
• a second DC voltage extracting circuit connected to the negative electrode of the field circuit and ground for extracting a DC voltage between the negative electrode of the field circuit and ground;
• and
• a measuring circuit connected to the first DC voltage extracting circuit and the second DC voltage extracting circuit for measuring a ground fault resistance based on a ratio of the extracted DC voltage from said first DC voltage extracting circuit and the extracted DC voltage from said second DC voltage extracting circuit.

A field ground fault detector for detecting an occurrence of a ground fault in a field circuit, comprising:

• a resistor having first and second terminals, the first terminal connected to ground;
• a DC voltage source connected to a negative electrode of the field circuit and round through the second terminal of the resistor;
• and
• a determining circuit connected to the first and second terminals of the resistor, the negative electrode of the field circuit, and ground for receiving a voltage between the first and second terminals of the resistor, for receiving a voltage between the negative electrode of the field circuit and ground, and for determining that a ground fault has occurred based upon a ratio of the received voltage between the first and second terminals of the resistor and the received voltage between the negative electrode of said field circuit and ground.