Multi-frequency ground monitor current sensing without a DC component

A system comprising:

• a power source;
• a ground monitor in the power source, the ground monitor comprising
• a signal generation module that injects a signal in a pilot conductor, the signal comprising one or more alternating current (“AC”) components, each AC component of the one or more AC components comprising a frequency different from other AC components of the one or more AC components, wherein current in the pilot conductor is injected in a grounding conductor of a set of power cables connecting a power source to a load, the grounding conductor connected to a ground return, wherein the set of power cables, the grounding conductor and the pilot conductor are combined from the power source to the load;
• a current monitor module that monitors current in at least one of the pilot conductor and the ground return, wherein the current is affected by a rectification circuit positioned between the pilot conductor and the grounding conductor;
• a DC detection module that determines a direct current (“DC”) current present in the current monitored by the current monitor module;
• a DC minimum threshold module that determines if the DC current is below a DC current minimum threshold;
• an AC detection module that determines an AC current corresponding to each frequency of the one or more AC components present in the current monitored by the current monitor module;
• an AC threshold module that determines if one or more of the AC currents determined by the AC detection module is below an AC threshold;
• and
• a trip module that opens a contact in response to one or more of the DC threshold module determining that the DC current is below the DC current minimum threshold longer than a DC current minimum time threshold and the AC threshold module determining that at least one of the AC currents is below an AC threshold for longer than an AC current time threshold, the contact disconnecting the power source from the set of power cables.

A method comprising:

• injecting a signal in a pilot conductor, the signal comprising one or more alternating current (“AC”) components, each AC component of the one or more AC components comprising a frequency different from other AC components of the one or more AC components, wherein current in the pilot conductor is injected in a grounding conductor of a set of power cables connecting a power source to a load, the grounding conductor connected to a ground return, wherein the set of power cables, the grounding conductor and the pilot conductor are combined from the power source to the load;
• monitoring current in at least one of the pilot conductor and the ground return, wherein the current is affected by a rectification circuit positioned between the pilot conductor and the grounding conductor;
• determining a direct current (“DC”) current present in the monitored current;
• determining if the DC current is below a DC current minimum threshold;
• determining an AC current corresponding to each frequency of the one or more AC components present in the monitored current;
• determining if one or more of the AC currents determined by the AC detection module is below an AC threshold;
• and
• opening a contact in response to one or more of determining that the DC current is below the DC current minimum threshold longer than a DC current minimum time threshold and determining that at least one of the AC currents is below an AC threshold for longer than an AC current time threshold, the contact disconnecting the power source from the set of power cables.