# US 12,222,371 B2 · Residual current monitoring type B with integrated self-test system and method

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- Number: US 12,222,371 B2
- Document ID: US12222371B2
- Status: Granted
- Kind: B2
- Application number: 18/079,098
- Filed: 2022-12-12
- Published: 2023-06-15
- Granted: 2025-02-11
- Earliest claimed: 2021-12-10
- Assignees: Vertiv Corporation
- Applicants: Vertiv Corporation
- Inventors: Kevin R. Ferguson; Jason Armstrong
- Web page: https://patentgrep.com/patent/US12222371B2

## CPC

- G01R 15/18: using inductive devices, e.g. transformers
- G01R 31/52: Testing for short-circuits, leakage current or ground faults
- G01R 15/185: {with compensation or feedback windings or interacting coils, e.g. 0-flux sensors (using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20)}
- G01R 19/0038: {Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller (comparing pulses or pulse trains according to amplitude)}
- G01R 35/00: Testing or calibrating of apparatus covered by the other groups of this subclass
- H02H 3/335: {the main function being self testing of the device}
- G01R 19/10: Measuring sum, difference or ratio
- 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)
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## Abstract

The present disclosure is a system and method for measuring AC residual current and DC residual current using a singular type-B residual current monitoring device. The system includes a sensor comprising two or more cores that measure residual AC current and residual DC current from two or more current carrying conductors through the cores that carry AC current and DC current. The system includes a controller that sends both an AC excitation current to the cores, as well as a DC nulling current that cancels out the DC residual current, allowing the system to then accurately measure the AC residual current. The system also includes a self-test feature that injects known quantities of both AC current and DC current through the sensor to determine if the sensor is functioning properly.

## Claims

### Claim 1

A system, comprising:
a residual current sensor circuitry comprising a residual current sensor configured to measure residual current from a source of AC power;
a controller electrically coupled to the residual current sensor circuitry comprising:
one or more processors; and
a memory configured to store data and instructions executable by the one or more processors, where the instructions include:
transmitting an excitation voltage to an excitation path of the residual current sensor circuitry;
receiving an unbalanced current signal from a detection path of the residual current sensor circuitry;
determining a DC residual current contribution to the unbalanced current signal;
calculating a DC injection scheme configured to negate the DC residual contribution;
injecting a DC current into a DC nulling path of the residual current sensor circuitry based on the DC injection scheme;
receiving a balanced current signal from the detected path; and
determining an AC residual current; and
a testing module configured to send a test AC current and a test DC current through the residual current sensor.

### Claim 2 (depends on 1)

The system of claim 1, wherein the unbalanced current signal comprises a 2nd order harmonic distortion at a current waveform zero-crossing.

### Claim 3 (depends on 2)

The system of claim 2, wherein the balanced current signal is characterized as sinusoidal at fundamental frequency.

### Claim 4 (depends on 3)

The system of claim 3, wherein the controller further comprises a proportional-integral-derivative controller configured to calculate the DC injection scheme.

### Claim 5 (depends on 1)

The system of claim 1, wherein the residual current sensor comprises:
a first core comprising:
a first excitation coil winding; and
a first secondary coil winding;
a second core comprising:
a second excitation coil winding; and
a second secondary coil winding; and
a DC null winding configured to wind through both the first core and the second core.

### Claim 6 (depends on 1)

The system of claim 1, wherein the testing module is configured to send a test AC
current and a test DC current through the residual current sensor according to a periodic schedule or upon user input.

### Claim 7 (depends on 1)

The system of claim 1, wherein the testing module is configured to provide an alert when a fault is detected.

### Claim 8 (depends on 7)

The system of claim 7, wherein the testing module repeats delivery of the test AC current and the test DC current through the residual current sensor until the fault is no longer detected.

### Claim 9

A system, comprising:
a residual current sensor configured to sense a residual current from a source of AC power, comprising:
a first core comprising:
a first excitation coil winding; and
a first secondary coil winding;
a second core comprising:
a second excitation coil winding; and
a second secondary coil winding; and
a DC null winding configured to wind through both the first core and the second core;
a residual current sensor circuitry electrically coupled to the residual current sensor comprising a controller electrically coupled to the residual current sensor circuitry, the controller comprising:
one or more processors; and
a memory configured to store data and instructions executable by the one or more processors, wherein the instructions include:
transmitting an excitation voltage to an excitation path of the residual current sensor circuitry;
receiving an unbalanced current signal from a detection path of the residual current sensor circuitry;
determining a DC residual current contribution to the unbalanced current;
calculating a DC injection scheme configured to negate the DC residual contribution;
injecting a DC current into a DC nulling path of the residual current sensor circuitry based on the DC injection scheme;
receiving a balanced current signal from the detection path; and
determining an AC residual current.

### Claim 10 (depends on 9)

The system of claim 9, further comprising:
a testing module configured to send a test AC current and a test DC current through the residual current sensor.

### Claim 11 (depends on 9)

The system of claim 9, wherein the unbalanced current signal comprises a 2nd order harmonic distortion at a current waveform zero-crossing.

### Claim 12 (depends on 11)

The system of claim 11, wherein the balanced current signal is characterized as sinusoidal at fundamental frequency.

### Claim 13 (depends on 9)

The system of claim 9, wherein the controller further comprises a proportional-integral-derivative controller configured to calculate the DC injection scheme.

### Claim 14 (depends on 10)

The system of claim 10, wherein the testing module is configured to send a test AC current and a test DC current through the residual current sensor according to a periodic schedule or upon user input.

### Claim 15 (depends on 10)

The system of claim 10, wherein the testing module is configured to provide an alert when a fault is detected.

### Claim 16 (depends on 15)

The system of claim 15, wherein the testing module repeats delivery of the test AC current and the test DC current through the residual current sensor until the fault is no longer detected.

### Claim 17

A method, comprising:
transmitting an excitation voltage to an excitation path of a residual current sensor circuitry;
receiving an unbalanced current signal from a detection path of the residual current sensor circuitry;
determining a DC residual current contribution to the unbalanced current signal;
calculating a DC injection scheme configured to negate the DC residual contribution;
injecting a DC current into a DC nulling path of the residual current sensor circuitry based on the DC injection scheme;
receiving a balanced current signal from the detection path; and
determining an AC residual current.

### Claim 18 (depends on 17)

The method of claim 17, further comprising testing the residual current sensor with a test AC current and a test DC current.

### Claim 19 (depends on 18)

The method of claim 18, wherein testing the residual current sensor with the test AC current and the test DC current comprises:
measuring a baseline AC residual current and a baseline DC residual current;
executing a self-test voltage waveform and generating the self-test current through a self-test wire;
measuring a test AC residual current and a test DC residual current;
calculating an AC test residual current value, a test DC residual current value, and comparing the test residual current value to a reference residual current value; and
reporting a status of the self-test.