An apparatus for monitoring ground current includes a signal generation module that generates a plurality of AC components of different frequencies. An injection module injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load. The set
An apparatus for monitoring ground current includes a signal generation module that generates a plurality of AC components of different frequencies. An injection module injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load. The set of power cables includes an equipment grounding conductor. The AC components are injected in the equipment grounding conductor. An AC detection module that determines an AC current corresponding to each frequency of the AC components present in current in the equipment grounding conductor, an AC threshold module determines if one or more of the AC currents is below an AC threshold, and a trip module opens a contact if the AC threshold module determines that at least one of the AC currents is below an AC threshold. The contact disconnects the power source from the power cables.
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1. An apparatus comprising: a signal generation module that generates a plurality of alternating current (“AC”) components, each of the plurality of AC components comprising a different frequency;an injection module that injects the plurality of AC components on one or more phases of a set of power
1. An apparatus comprising: a signal generation module that generates a plurality of alternating current (“AC”) components, each of the plurality of AC components comprising a different frequency;an injection module that injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load, the set of power cables comprising an equipment grounding conductor, wherein the AC components present in the one or more phases at the load are injected in the equipment grounding conductor at the load;an AC detection module that determines an AC current corresponding to each frequency of the one or more AC components present in current in the equipment grounding conductor;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; anda trip module that opens a contact in response to the AC threshold module determining that at least one of the AC currents is below an AC threshold, the contact disconnecting the power source from the set of power cables. 2. The apparatus of claim 1, further comprising a ground injection module that filters the AC components present in the one or more phases of the set of power cables and injects the AC components in the equipment grounding conductor. 3. The apparatus of claim 2, wherein the ground injection module is located in the load. 4. The apparatus of claim 1, wherein the injection module comprises one or more band pass filters, each band pass filter of the one or more band pass filters tuned to pass one or more of the AC components. 5. The apparatus of claim 1, wherein a frequency of each of the AC components differs from a fundamental frequency of power transmitted on the set of power cables. 6. The apparatus of claim 1, wherein the AC detection module further comprises a fundamental frequency filter that filters out a fundamental frequency of power transmitted on the set of power cables. 7. The apparatus of claim 6, wherein the fundamental frequency filter comprises a comb filter tuned to filter out the fundamental frequency and harmonic frequencies of the power transmitted on the set of power cables. 8. The apparatus of claim 1, wherein the AC detection module further comprises one or more filters for each AC component, the one or more filters of an AC component attenuating frequencies other than a frequency of the AC component. 9. The apparatus of claim 8, wherein the one or more filters for each AC component comprise digital signal processing (“DSP”) filters. 10. The apparatus of claim 8, wherein the one or more filters for each AC component comprise one or more of a band pass filter and a parametric filter. 11. The apparatus of claim 1, wherein the trip module compares each AC component to an AC threshold. 12. The apparatus of claim 1, further comprising: a change module that periodically changes an AC component characteristic of one or more of the plurality of AC components; andan update module that changes an AC component characteristic sensed for one or more of the plurality of AC components to match the changed AC component characteristics of the AC components changed by change module in response to the change module changing the AC component characteristic of one or more of the plurality of AC components. 13. The apparatus of claim 12, wherein the change module changes an AC component characteristic of one or more of the plurality of AC components by changing a frequency of one or more of the plurality of AC components and the update module changes the AC component characteristic sensed for one or more of the plurality of AC components by changing a sensed frequency to match the frequencies of the plurality of AC components changed by the change module. 14. The apparatus of claim 12, wherein the change module changes an AC component characteristic of one or more of the plurality of AC components by changing a phase of one or more of the plurality of AC components and the update module changes the AC component characteristic sensed for one or more of the plurality of the AC components by changing a sensed phase to match the phases of the plurality of AC components changed by the change module. 15. The apparatus of claim 12, further comprising a sync module that synchronizes changes in sensing by the update module with changes to the AC component characteristic of each of the plurality of AC components by the change module. 16. The apparatus of claim 12, wherein the change module changes the AC component characteristic of one or more of the plurality of AC components by one or more of: ramping from a current frequency to a new frequency over a period of time; andramping from a current phase to a new phase over a period of time. 17. The apparatus of claim 12, wherein the change module changes the AC component characteristic of one or more of the plurality of AC components randomly. 18. The apparatus of claim 17, wherein the change module calculates coefficients for an oscillator corresponding to each AC component to generate the random frequency for each of the AC components changed by the change module and the AC detection module calculates coefficients for a filter to match the random frequency for each of the one or more AC components changed by the update module. 19. The apparatus of claim 12, further comprising a frequency test module that determines if a frequency is present on the equipment grounding conductor prior to selecting the frequency for an AC component. 20. The apparatus of claim 1, further comprising a calibration module that determines a baseline amplitude for each of the plurality of AC components and sets, for each AC component, an AC threshold based on the determined baseline amplitude of the AC component. 21. A system comprising: a power source; anda ground monitor in the power source, the ground monitor comprising a signal generation module that generates a plurality of alternating current (“AC”) components, each of the plurality of AC components comprising a different frequency;an injection module that injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load, the set of power cables comprising an equipment grounding conductor, wherein the AC components present in the one or more phases at the load are injected in the equipment grounding conductor at the load;an AC detection module that determines an AC current corresponding to each frequency of the one or more AC components present in current in the equipment grounding conductor;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; anda trip module that opens a contact in response to the AC threshold module determining that at least one of the AC currents is below an AC threshold, the contact disconnecting the power source from the set of power cables. 22. The system of claim 21, further comprising a ground injection module that filters the AC components present in the one or more phases of the set of power cables and injects the AC components in the equipment grounding conductor. 23. A method comprising: generating a plurality of alternating current (“AC”) components, each of the plurality of AC components comprising a different frequency;injecting the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load, the set of power cables comprising an equipment grounding conductor, wherein the AC components present in the one or more phases at the load are injected in the equipment grounding conductor at the load;determining an AC current corresponding to each frequency of the one or more AC components present in current in the equipment grounding conductor;determining if one or more of the determined AC currents is below an AC threshold; andopening a contact in response to determining that at least one of the AC currents is below an AC threshold, the contact disconnecting the power source from the set of power cables. 24. The method of claim 23, further comprising filtering the AC components present in the one or more phases of the set of power cables and injecting the AC components in the equipment grounding conductor.
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