Current measurement

Patent metadata

Field	Value
Publication number	US-9933463-B2
Application number	US-201615229815-A
Country	US
Kind code	B2
Filing date	Aug 5, 2016
Priority date	Nov 23, 2011
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

The present invention relates to current measurement apparatus. The current measurement apparatus comprises first and second measurement devices with each of the first and second measurement devices being operative to measure current in a respective one of a live conductor and a neutral conductor substantially simultaneously. The current measurement apparatus is operative to make plural different determinations in dependence on the substantially simultaneous current measurements.

First claim

The invention claimed is:

1. Current measurement apparatus comprising:
a first current sensor for sensing a current in a first conductor;
a first measurement circuit configured to buffer an output of the first current sensor to provide a first buffered signal having a first dynamic range and to measure the first buffered signal to provide a first measurement signal; and
a second measurement circuit configured to buffer the same output of the first current sensor to provide a second buffered signal having a second dynamic range different from the first dynamic range and to measure the second buffered signal to provide a second measurement signal.

2. The current measurement apparatus of claim 1 ,
wherein the first measurement circuit includes a first gain stage and a first analog to digital converter and the second measurement circuit includes a second gain stage and a second analog to digital converter; and
wherein a signal range of the first analog to digital converter is larger than a signal range of the second analog to digital converter.

3. The current measurement apparatus of claim 2 ,
wherein the first measurement circuit is configured for use in arc fault detection in a power distribution network and the second measurement circuit is configured for use in at least one of ground fault detection and metering of current flow.

4. The current measurement apparatus of claim 2 ,
wherein the first and second measurement circuits are configured for clocking at different frequencies.

5. The current measurement apparatus of claim 1 further including:
a second current sensor for sensing a current in a second conductor and a third measurement circuit responsive to an output of the second current sensor;
where the first and second conductors act as the supply and return wires to a load, such that under no fault conditions the currents in the first and second conductors are the same.

6. The current measurement apparatus of claim 5 further including:
circuitry operative to perform calibration in respect of the current paths associated with the first and second current sensors to align a measurement signal produced by the third measurement circuit and a measurement signal produced by at least one of the first and second measurement circuits.

7. The current measurement apparatus of claim 6 further including:
circuitry to introduce a calibration signal to cause a shared perturbation in currents measured by the first and second current sensors, such that transfer functions associated with the first and second current sensors can be adjusted to have substantially matching responses to the calibration signal or such that corrective factor can be applied.

8. The current measurement apparatus of claim 7 further including:
a correlation and detection circuit that is operative during calibration to extracts parts of a first signal from one of the first and second measurement circuits, the first signal containing a contribution from the calibration signal and a contribution from a current passing along the first conductor; and the correlation and detection circuit being further arranged to extract parts of the a second signal from the third measurement circuit, the second signal containing a contribution from the calibration signal and a contribution from the current passing along the second conductor, the extracted parts relating to the calibration signal being used to adjust the transfer functions; and
at least one processing circuit operative to determine a magnitude of a current flowing in the first conductor and a magnitude of a current flowing in the second conductor.

9. The current measurement apparatus of claim 8 ,
wherein the processing circuit is configured to vary its determination of a fault condition based on a magnitude of the current being drawn by the load.

10. The current measurement apparatus of claim 5 ,
wherein one of the first and second current sensors is a differential current measurement device configured to provide a sum of the of the current in the first and second conductors.

11. The current measurement apparatus of claim 1 further including:
a voltage measurement circuit to measure the voltage of the first conductor with respect to a reference voltage.

12. The current measurement apparatus of claim 3 , wherein the first conductor is a live conductor carrying a first phase of a power distribution network, the apparatus further comprising a voltage measurement circuit for measuring a voltage difference between the first conductor and a second conductor; and
wherein the second conductor is one of a second phase and a neutral of the power distribution network, and wherein a voltage signal representative of the voltage between the first and second conductors is analyzed for arc fault detection.

13. The current measurement apparatus of claim 3 further including:
a second current sensor for sensing a current in a second conductor, a third current sensor for sensing a current in a third conductor and a fourth current sensor for sensing a current is a fourth conductor, where the first to third live conductors and a neutral conductor are conductors of a three phase supply.

14. An apparatus for ground fault detection and/or power metering, comprising:
a first current transducer responsive to a difference in magnitude between currents flowing in live and neutral conductors connecting a device to a supply, wherein the device comprises a load or power source;
a second current transducer configured to measure the magnitude of the current in the neutral conductor; and
a circuit configured to measure power consumption and/or to detect a fault condition based on first information from the first current transducer about the difference in magnitude between currents flowing in the live and neutral conductors and second information from the second current transducer about the magnitude of the current in the neutral conductor.

15. The apparatus for ground fault detection and/or power metering of claim 14 further including:
a second circuit arranged to correlate signals from the first and second current transducers and to determine information about a current in the live conductor by subtracting the acquired neutral current acquired by the second transducer from the differential signal acquired by the first current transducer.

16. The apparatus for ground fault detection and/or power metering of claim 14 further including:
a third current transducer arranged to measure the magnitude of the current flowing in the live conductor, wherein estimates of differences between the currents in live and neutral conductors are provided by forming a difference between the magnitudes of current as determined by the second and third current transducers and also from output of the first current transducer thereby allowing the transducers to be selected to enhance fault detection over different current and frequency ranges.

17. The apparatus for ground fault detection and/or power metering of claim 14 further including:
a calibration circuit for introducing a calibration signal which causes a shared perturbation in the currents measured by the first and second current transducers, such that transfer functions can be adjusted to have substantially matching responses to the calibration signal or such that corrective functions can be applied.

18. The apparatus for ground fault detection and/or power metering of claim 17 further including:
a correlation and detection circuit that is operative during calibration to extracts parts of a first signal f

Assignees

• Analog Devices Global

Inventors

• Danesh Seyed Amir Ali
• Hurwitz Jonathan Ephraim David

Classifications

• H02H3/006

  Calibration or setting of parameters · CPC title

• H02H3/32

  involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors · CPC title

• H02H1/0015

  Using arc detectors · CPC title

• G01R19/2506

  Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values (G01R19/003 takes precedence); Details concerning sampling, digitizing or waveform capturing (displaying waveforms G01R13/00; analog sampling G01R19/0053) · CPC title

• G01R35/005

  Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references (G01R33/0035, G01R35/002 take precedence) · CPC title