Apparatus and method for DC-component-based fault classification of three-phase distribution power cables with magnetic sensing

Patent metadata

Field	Value
Publication number	US-10852359-B2
Application number	US-201715831558-A
Country	US
Kind code	B2
Filing date	Dec 5, 2017
Priority date	Dec 5, 2017
Publication date	Dec 1, 2020
Grant date	Dec 1, 2020

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.

First claim

We claim:

1. An apparatus for short-circuit fault classification of a three-phase power distribution cable, comprising:
at least three magnetic sensors, wherein the magnetic 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 magnetic sensors; and
a processing and display system to extract DC components in the analog signals for phases during a transient period after a short-circuit fault and to display those DC components as an indication of the short-circuit fault classification.

2. The apparatus according to claim 1 , wherein the magnetic 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.

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

4. A method of classifying short-circuit faults in a three-phase distribution power cable of a power system, comprising the steps of:
sensing a 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 three-phase currents from the magnetic signals by a stochastic optimization method;
extracting a DC component from the reconstructed three-phase currents using mathematical morphology (MM); and
classifying a short-circuit fault based on the extracted DC component.

5. 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).

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

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

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

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

10. The algorithm according to claim 4 , wherein the step of classifying a 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.

Assignees

• Univ Hong Kong

Inventors

• Pong Wing Tat
• Zhu Ke

Classifications

• G01R31/085 Primary

  in power transmission or distribution lines, e.g. overhead · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• G01R31/083

  in cables, e.g. underground · CPC title

• G01R15/20

  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} · CPC title