Device for measuring an electrical quantity of one phase of an AC electric current of an overhead electrical network

Patent metadata

Field	Value
Publication number	US-10690706-B2
Application number	US-201716077300-A
Country	US
Kind code	B2
Filing date	Feb 10, 2017
Priority date	Feb 12, 2016
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

The invention relates to a device for measuring an electrical quantity of one phase of an AC electric current in an overhead electrical network, comprising: a sensor designed to be attached to an electric line of the network, the sensor including: an electrically conductive plate; an electrical conductor, designed to electrically connect the plate to the line, in order to circulate a first current from the line through the conductor; a processing unit, designed to determine the electrical quantity from value values of the first electric current and a value of a capacitance between the plate and ground. The device also comprises a generator, electrically connected to the conductor and designed to inject a second current through the conductor, the second current having a frequency other than the frequency of the first current, the processing unit also being designed to calculate the capacitance between the plate and ground as a function of the second current.

First claim

The invention claimed is:

1. A device for measuring an electrical quantity of one phase of an AC electric current of an overhead electrical network, comprising:
a sensor, configured to be attached to an electric line of the overhead electrical network, this sensor comprising:
an electrically conductive plate, and
an electrical conductor, configured to electrically connect the plate to the electric line, for the circulation of a first electric current from the electric line through the electrical conductor,

a computation unit, configured to determine the electrical quantity from a value of the first electric current and a value of an electrical capacity between the plate and the ground,

wherein the device further includes:
a generator, electrically connected to the electrical conductor and configured to inject a second electric current through the electrical conductor, this second electric current having a frequency different from the frequency of the first electric current,
the computation unit further being configured to compute the value of the electrical capacity between the plate and the ground as a function of a value of the second electric current.

2. The device according to claim 1 , wherein it further includes:
a second electrically conductive plate, and
a second electrical conductor, configured to electrically connect the second plate to the electric line for the circulation of at least part of the first electric current from the electric line to the second plate through the second electrical conductor, the second electrical conductor being electrically connected to the output of the generator for the circulation of at least part of the second current injected through the second conductor.

3. The device according to claim 2 , wherein the device further includes a second measuring apparatus configured to measure the first electric current and the second electric current circulating through the second electrical conductor.

4. The device according to claim 3 , wherein the second electrical conductor has a second resistance, the second measuring apparatus including a second voltage sensor to measure the electric voltage across the terminals of the second resistance.

5. The device according to claim 1 , wherein the device further includes a first measuring apparatus configured to measure the first electric current and the second electric current circulating through the electrical conductor.

6. The device according to claim 5 , wherein the first electrical conductor has a first resistance, the first measuring apparatus including a first voltage sensor to measure the electric voltage across the terminals of the first resistance.

7. The device according to claim 6 , wherein the electrical capacity C pt is computed by the computation unit according to the equation:

C

p
⁢

⁢
t

=

U

m
⁢

⁢
1

-

U

m
⁢

⁢
2

ω
×

R
m

⁡

(

1
-

K
′

)

×

(

U
p

-

U

m
⁢

⁢
1

)

where U m1 and U m2 are respectively the electric voltages measured by the first and second measuring apparatuses, ω is the pulse of the AC current circulating in the overhead electrical network, U p is the electric voltage across the terminals of the generator injecting the second electric current, R m is equal to the value of the first resistance and K′ is a numerical value that depends on the ratio between the distance d′ and the distance d, d being the distance between the first plate and the electric line and d′ being the distance between the second plate and the electric line.

8. The device according to claim 7 , wherein:
when the first and second sensors are attached to the electric line, the device includes first and second stray electrical capacities that respectively connect the first and second plates to the electric line and allow the circulation, from the electric line, of first and second electric leak currents, and
the value K′ is equal to the ratio between the second and first electric leak currents.

9. The device according to claim 1 , wherein the frequency of the second injected electric current is comprised between 1 kHz and 1 MHz, preferably between 10 kHz and 100 kHz.

10. The device according to claim 1 , wherein the electrical quantity is the voltage of the phase of the AC current.

11. A method for measuring an electrical quantity of one phase of an AC electric current of an overhead electrical network, comprising:
a) attaching a sensor to an overhead electric line of the electrical network, this sensor comprising:
an electrically conductive plate, and
an electrical conductor, configured to electrically connect the plate to the electric line, such that a first electric current circulates from the electric line through the electrical conductor,

b) measuring the first electric current circulating through the electrical conductor, using a measuring apparatus, and
c) computing an electrical quantity, using a computation unit, from the measured first electric current and the value of the electrical capacity between the plate and the ground,
wherein the method includes, before the attachment, a calibration sequence to determine a value of the electrical capacity, this calibration sequence comprising:
i) injecting, using a generator, a second electric current through the electrical conductor, this second electric current having a frequency different from the frequency of the first electric current,
ii) measuring, using the measuring apparatus, the second electric current circulating in the electrical conductor, and
iii) determining, via the computation unit and based on the measured second electric current, the value of the electrical capacity.

Assignees

• Schneider Electric Ind Sas

Inventors

• Clemence Michel
• Houbre Pascal
• Contini Erick

Classifications

• G01R15/16 Primary

  using capacitive devices · CPC title

• G01R19/2513 Primary

  Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging · 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

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• G01R15/165

  measuring electrostatic potential, e.g. with electrostatic voltmeters or electrometers, when the design of the sensor is essential (electrometers with passively moving electrodes G01R5/28; measuring electrostatic fields G01R29/12; measuring charge G01R29/24; measuring in circuits with high internal resistance G01R19/0023) · CPC title