# US 10,768,242 B1 · Ground-fault protection for direct current circuits > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,768,242 B1 - Document ID: US10768242B1 - Status: Granted - Kind: B1 - Application number: 15/993,145 - Filed: 2018-05-30 - Granted: 2020-09-08 - Earliest claimed: 2017-05-31 - Assignees: Cottonwood Creek Technologies, Inc. - Applicants: Cottonwood Creek Technologies, Inc. - Inventors: Dwight W. Kitchin; Alan K. Schott - Web page: https://patentgrep.com/patent/US10768242B1 ## CPC - G01R 31/50: Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) - G01R 27/08: Measuring resistance by measuring both voltage and current - G01R 31/52: Testing for short-circuits, leakage current or ground faults - H02J 1/06: Two-wire DC power distribution systems - H02J 4/00: Circuit arrangements for mains or distribution networks not specified as AC or DC; Circuit arrangements for mains or distribution networks combining AC and DC sections or sub-networks (arrangements using intermediate DC-AC-DC conversion H02J1/002; arrangements using high-voltage DC [HVDC] links H02J3/36) - H04B 3/46: Monitoring; Testing - H04B 3/54: Systems for transmission via power distribution lines - H04M 19/001: {Current supply source at the exchanger providing current to substations} - G01R 19/2513: {Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - H04B: TRANSMISSION - H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08) ## Abstract Systems and methods for detecting ground faults in a power transmission circuit powering a load. The system includes a common mode union that is connected to a positive terminal of a power supply and a negative terminal of the power supply. The power supply may be a bifurcated symmetrical power source. A power supply symmetry circuit is connected to the common mode union and a offset threshold comparator circuit is connected to the power supply symmetry circuit. The offset threshold comparator circuit is configured to compare a signal from the power supply symmetry circuit to a threshold voltage value and generate a ground-fault signal indicating a ground fault when the signal from the power supply symmetry circuit exceeds a threshold voltage value. A local load control circuit is connected to the offset threshold comparator circuit and configured to receive a signal from the offset threshold comparator circuit. ## Claims ### Claim 1 A ground fault detection system for detecting ground faults, the system comprising: a common mode union, wherein a first portion of the common mode union is connected to a positive source of a power supply and a second portion of the common mode union is connected to a negative source of the power supply, wherein: the positive source has a more positive terminal and a more negative terminal, and the negative source has a more negative terminal and a more positive terminal; and the first portion of the common mode union is attached to the more negative terminal of the positive source and the second portion of the common mode union is attached to the more positive terminal of the negative source; a power supply symmetry circuit connected to the common mode union, wherein the power supply symmetry circuit is configured to generate a symmetry signal indicative of the symmetry of voltages of the positive terminal of the power supply and the negative terminal of the power supply; an offset threshold comparator circuit configured to generate a ground-fault signal indicating a ground fault based on the symmetry signal indicative; and a local load control circuit configured to remove power to a load in response to the ground-fault signal. ### Claim 2 (depends on 1) The system of claim 1, wherein the power supply symmetry circuit is further configured to receive the symmetry signal from the power supply symmetry circuit and compare the symmetry signal to a threshold voltage value. ### Claim 3 (depends on 1) The system of claim 1, wherein the local load control circuit is connected to the offset threshold comparator circuit and configured to receive the ground-fault signal from the offset threshold comparator circuit. ### Claim 4 (depends on 1) The system of claim 1, wherein the ground fault detection system detects ground faults in a power transmission circuit powering a load. ### Claim 5 (depends on 4) The system of claim 4, wherein the load is a local communications device and the power transmission circuit includes plain old telephone system (POTS) communication lines. ### Claim 6 (depends on 4) The system of claim 4, wherein the power supply provides direct-current power to the power transmission circuit. ### Claim 7 (depends on 1) The system of claim 1, wherein the power supply symmetry circuit includes at least one voltage divider and the offset threshold comparator circuit includes at least one comparator. ### Claim 8 A ground fault detection system for detecting ground faults in a power transmission circuit for powering a load with direct-current power, the system comprising: a common mode union, wherein a first portion of the common mode union is connected to a positive source of a power supply and a second portion of the common mode union is connected to a negative source of the power supply, wherein: the positive source has a more positive terminal and a more negative terminal, and the negative source has a more negative terminal and a more positive terminal; and the first portion of the common mode union is attached to the more negative terminal of the positive source and the second portion of the common mode union is attached to the more positive terminal of the negative source; a power supply symmetry circuit connected to the common mode union, wherein the power supply symmetry circuit is configured to generate a symmetry signal indicative of a symmetry of voltages in the power transmission circuit; an offset threshold comparator circuit configured to receive the symmetry signal, wherein the offset threshold comparator circuit is further configured to compare the symmetry signal from the power supply symmetry circuit to a threshold voltage value and generate a ground-fault signal indicating a ground fault when the symmetry signal exceeds the threshold voltage value; and a local load control circuit configured to receive the ground fault signal, wherein the local load control circuit is further configured to remove power from the load based on the received ground-fault signal. ### Claim 9 (depends on 8) The ground fault detection system of claim 8, wherein removing power from the load includes opening the power transmission circuit. ### Claim 10 (depends on 8) The ground fault detection system of claim 8, wherein the symmetry of voltages in the power transmission circuit is a symmetry of voltages around at least one of an earth ground or a virtual ground. ### Claim 11 (depends on 8) The ground fault detection system of claim 8, wherein the load is a local communications device and the power transmission circuit includes plain old telephone system (POTS) communication lines. ### Claim 12 (depends on 8) The ground fault detection system of claim 8, wherein the power supply symmetry circuit comprises: a first resistor having a first end connected to the first portion of the common mode union; a second resistor connected to a second end of the first resistor and one of an earth ground or a virtual ground, wherein the first resistor and the second resistor operate as a first voltage divider; a third resistor having a first end connected to the second portion of the common mode union; and a fourth resistor connected to a second end of the third resistor and one of an earth ground or a virtual ground, wherein the third resistor and the fourth resistor operate as a second voltage divider. ### Claim 13 (depends on 12) The ground fault detection system of claim 12, wherein the power supply symmetry circuit comprises: a first buffer amplifier, wherein an input of the first buffer amplifier is connected to the second end of the first resistor; and a second buffer amplifier, wherein an input of the second buffer amplifier is connected to the second end of the third resistor. ### Claim 14 (depends on 12) The ground fault detection system of claim 12, wherein the offset threshold comparator circuit comprises: a first comparator, wherein a first input of the first comparator is connected to the first voltage divider and a second input of the first comparator is connected to a reference signal representative of the threshold voltage value; and a second comparator, wherein a first input of the first comparator is connected to the second voltage divider and a second input of the second comparator is connected to a reference signal representative of the threshold voltage value. ### Claim 15 (depends on 8) The ground fault detection system of claim 8, wherein the local load control circuit comprises a relay. ### Claim 16 (depends on 8) The ground fault detection system of claim 8, further comprising an over-current detection circuit connected to the common mode union. ### Claim 17 (depends on 8) The ground fault detection system of claim 8, further comprising an over-voltage detection circuit connected to the power transmission circuit. ### Claim 18 A ground fault detection system for detecting ground faults in a power transmission circuit powering a load, the system comprising: a common mode union, wherein a first portion of the common mode union is connected to a positive source of a power supply and a second portion of the common mode union is connected to a negative source of the power supply, wherein: the positive source has a more positive terminal and a more negative terminal, and the negative source has a more negative terminal and a more positive terminal; and the first portion of the common mode union is attached to the more negative terminal of the positive source and the second portion of the common mode union is attached to the more positive terminal of the negative source; a power supply symmetry circuit connected to the common mode union, wherein the power supply symmetry circuit is configured to detect symmetry of voltages in a power transmission circuit; an offset threshold comparator circuit connected to the power supply symmetry circuit and configured to receive a signal from the power supply symmetry circuit, wherein the offset threshold comparator circuit is further configured to compare the signal from the power supply symmetry circuit to a threshold voltage value and generate a ground-fault signal indicating a ground fault when the signal from the power supply symmetry circuit exceeds the threshold voltage value; an over-current detection circuit connected to the common mode union, the over-current detection circuit configured to detect an over-current event; an over-voltage detection circuit connected to the power transmission circuit, the over-voltage detection circuit configured to detect an over-voltage event; and a local load control circuit configured to receive a signal from the offset threshold comparator circuit, a signal from the over-current detection circuit, and a signal from the over-voltage detection circuit, wherein the local load control circuit is further configured to open the power transmission circuit based on the received signals.