# US 2019/0170801 A1 · Apparatus and method for dc-component-based fault classification of three-phase distribution power cables with magnetic sensing

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- Number: US 2019/0170801 A1
- Document ID: US20190170801A1
- Status: Published application
- Kind: A1
- Application number: 15/831,558
- Filed: 2017-12-05
- Published: 2019-06-06
- Earliest claimed: 2017-12-05
- Assignees: The University of Hong Kong
- Applicants: The University of Hong Kong
- Inventors: Wing Tat PONG; Ke ZHU
- Web page: https://patentgrep.com/patent/US20190170801A1

## CPC

- G01R 31/085: {in power transmission or distribution lines, e.g. overhead}
- G01R 15/20: using galvano-magnetic devices, e.g. Hall-effect devices {, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices}
- G01R 31/083: {in cables, e.g. underground}
- G01R 31/52: Testing for short-circuits, leakage current or ground faults
- H02H 1/0007: {concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445)}
- H02H 3/332: {with means responsive to DC component in the fault current}
- G01R 19/16571: {comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current (G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533, G01R19/1659 take precedence; measuring currents by using elements sensitive to the magnetic field generated G01R15/14; measuring earth resistance G01R27/18; testing for leakage or short circuits in electrical apparatus G01R31/52)}
- G01R 31/001: {Measuring interference from external sources to, or emission from, the device under test, e.g. EMC, EMI, EMP or ESD testing (measuring electromagnetic fields G01R29/08; circuits for generating HV pulses in dielectric strength testing G01R31/14)}
- G01R 31/086: {in power transmission or distribution networks, i.e. with interconnected conductors}
- H02H 1/04: Arrangements for preventing response to transient abnormal conditions, e.g. to lightning {or to short duration over voltage or oscillations; Damping the influence of DC component by short circuits in AC networks}
- H02H 3/50: responsive to the appearance of abnormal wave forms, e.g. AC in DC installations
- Y04S 10/52: Outage or fault management, e.g. fault detection or location
- 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)
- Y04S: SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS

## Abstract

A DC-component-based fault classification apparatus and method for a three-phase power distribution cable utilizes the reconstructed three-phase currents by measuring the magnetic field around the cable with an array of magnetic sensors arranged around the cable surface. A magnetic shield houses the magnetic sensors and blocks background magnetic fields. A data acquisition system acquires analog signals from the sensors and a processing system extracts DC components in the analog signals for the phases during the transient period after a fault. The potential DC components are extracted by mathematical morphology. These DC components arise in the faulted phases when a fault occurs since there is a large current change in the inductive power network.

## Claims

### Claim 1

An apparatus for fault classification of a three-phase power distribution cable, comprising:
at least three magnetic sensors, wherein the sensors are arranged in a circular way to form an array about the cable;
a magnetic shield to house the magnetic sensors and to block external magnetic fields;
a data acquisition system for acquiring analog signals from the sensors; and
a processing & display system to extract DC components in the analog signals for phases during the transient period after a fault and to display those components.

### Claim 2 (depends on 1)

The apparatus according to claim 1, wherein the sensors can be Hall-effect sensors, anisotropic magneto-resistance (AMR) sensors, tunnel magneto-resistance (TMR) sensors, giant magneto-resistance (GMR) sensors, or other compact magnetic sensors.

### Claim 3 (depends on 1)

The apparatus according to claim 1, wherein the magnetic shielding is multi-layered and made of high-permeability material.

### Claim 4

A method of classifying faults in three-phase distribution power cable of a power system, comprising the steps of:
sensing the magnetic field around the cable surface with a plurality of magnetic sensors and producing signals related thereto;
applying three-phase current extraction (TCE) to reconstruct the three-phase currents from the magnetic signals by a stochastic optimization method;
extracting a DC component from the reconstructed three-phase current using mathematical morphology (MM); and
classifying the fault based on the extracted DC component.

### Claim 5 (depends on 4)

The method according to claim 4, wherein the stochastic optimization method is comprised of inverse current program (ICP), magnetic field evaluation (MFE) and source position optimization (SPO).

### Claim 6 (depends on 4)

The method according to claim 4 wherein the stochastic optimization method terminates when the Euclidean distance between the measured and calculated magnetic fields is smaller than a pre-set threshold.

### Claim 7 (depends on 5)

The method according to claim 5, wherein the ICP optimizes the three-phase current through the least square method based on preset three-phase conductor positions and measured magnetic fields.

### Claim 8 (depends on 5)

The algorithm according to claim 5, wherein the MFE calculates the magnetic fields at sensing points of the sensors with preset three-phase conductor positions and optimized current.

### Claim 9 (depends on 5)

The algorithm according to claim 5, wherein the SPO optimizes the three-phase conductor position by the genetic algorithm.

### Claim 10 (depends on 4)

The algorithm according to claim 4, wherein the step of classifying the short-circuit fault involves referencing a logic table of the possibilities of the existence of DC components in the sensed currents of the phases, and using the logic table to identify phase-to-ground short-circuit fault, phase-phase-to-ground short-circuit fault, phase-to-ground short-circuit fault, and three-phase short-circuit fault.