Differential protection method, differential protection device, and differential protection system

Patent metadata

Field	Value
Publication number	US-11588319-B2
Application number	US-202117189531-A
Country	US
Kind code	B2
Filing date	Mar 2, 2021
Priority date	Mar 2, 2020
Publication date	Feb 21, 2023
Grant date	Feb 21, 2023

Abstract

A differential protection method for monitoring a line of a power grid. Current phasor measured values are captured at the ends of the line and transmitted to an evaluation device which is used to form a differential current value with current phasor measured values temporally allocated to one another. Time delay information indicating the time delay between local timers of the measuring devices is used for the temporal allocation of the current phasor measured values captured at different ends, and a fault signal indicating a fault affecting the line is generated if the differential current value exceeds a predefined threshold value. The reliability of the time synchronization is further increased by forming a quotient of the current phasor measured values to form an asymmetry variable, that is used to check a transit time difference of messages transmitted via the communication connection in different directions.

First claim

The invention claimed is:

1. A differential protection method for monitoring a line of a power grid, the method comprising:
capturing current phasor measured values with measuring devices at respective ends of the line, the measured values indicating an amplitude and a phase angle of a phase current flowing at a respective end of the line, wherein the measuring devices include local timers and allocate a timestamp to the current phasor measured values indicating a time of a capture of the current phasor measure values;
transmitting at least the current phasor measured values captured at one end via a communication connection to an evaluation device;
forming a differential current value through vectorial addition by the evaluation device with current phasor measured values temporally allocated to one another;
determining time delay information indicating a time delay between the local timers of the measuring devices with a transit-time-based time synchronization method and using the time delay information for temporally allocating the current phasor measured values captured at different ends of the line;
forming a quotient of the current phasor measured values temporally allocated to one another to form an asymmetry variable, and using the asymmetry variable to check a transit time difference of messages transmitted via the communication connection, the transit time difference arising on account of transmission times that are different depending on the direction; and
generating a fault signal indicating a fault affecting the line if the differential current value exceeds a predefined threshold value.

2. The differential protection method according to claim 1 , which comprises forming the quotient by dividing the current phasor measured value with a smaller absolute value by a current phasor measured value with a larger absolute value.

3. The differential protection method according to claim 2 , which comprises forming the asymmetry variable only when the quotient of the current phasor measured values exceeds a predefined minimum value.

4. The differential protection method according to claim 2 , which comprises: analyzing a position of the asymmetry variable in a complex number plane; and inferring a presence of a transit time difference based on the position.

5. The differential protection method according to claim 4 , which comprises generating a fault message on a basis of a distance between the position of the asymmetry variable and a reference operating point.

6. The differential protection method according to claim 5 , which comprises blocking the generation of the fault message indicating a fault affecting the line when the distance between the position of the asymmetry variable and the reference operating point exceeds a maximum distance.

7. The differential protection method according to claim 5 , which comprises determining the position of the reference operating point based on a capacitive charging current of the line.

8. The differential protection method according to claim 4 , which comprises:
defining a region, within which the position of the symmetry variable is allowed, in the complex number plane; and
suspending the checking of the transit time difference if the asymmetry variable lies outside the defined region.

9. The differential protection method according to claim 1 , which comprises forming the asymmetry variable only when the absolute value of at least one of the current phasor measured values exceeds a capacitive charging current of the line by a predefined factor.

10. The differential protection method according to claim 1 , which comprises forming the asymmetry variable only when the absolute values of the current phasor measured values are below a threshold dependent on a nominal current of the power grid.

11. A differential protection device for monitoring a line of a power grid, the device comprising:
a measuring device having a local timer and being configured to capture current phasor measured values at one end of the line, the values indicating an amplitude and a phase angle of a phase current flowing at the one end of the line, and to allocate a timestamp to the current phasor measured values indicating a time of a capture thereof;
a communication device configured to exchange current phasor measured values via a communication connection with another differential protection device; and
an evaluation device configured to form a differential current value with its own current phasor measured values temporally allocated to one another on the one hand, and current phasor measured values received from the other differential protection device on the other hand, through vectorial addition, wherein time delay information indicating a time delay between the local timers of the measuring devices of the differential protection devices is used for temporally allocating the current phasor measured values captured at different ends, wherein the time delay information is determined using a transit-time-based time synchronization method, and to generate a fault signal indicating a fault affecting the line if the differential current value exceeds a predefined threshold value;
wherein a quotient is formed of the current phasor measured values temporally allocated to one another, forming an asymmetry variable, and wherein the asymmetry variable is used to check a transit time difference of messages transmitted via the communication connection, the transit time difference arising on account of transmission times that are different depending on a direction.

12. A differential protection system for monitoring a line of a power grid, the system comprising:
at least two differential protection devices each disposed at a respective end of the line;
a communication connection connecting the individual said differential protection devices for a transmission of current phasor measured values;
each of said at least two differential protection devices including:
a measuring device having a local timer and being configured to capture current phasor measured values at a respective end of the line, the measured values indicating an amplitude and a phase angle of a phase current flowing at the respective end of the line, and to allocate a timestamp to the current measured values indicating the time of a capture thereof;
a communication device configured to exchange current phasor measured values via said communication connection with a respective other differential protection device;

at least one of said at least two differential protection devices including:
an evaluation device configured to form a differential current value with its own current phasor measured values temporally allocated to one another and current phasor measured values received from the respectively other differential protection device, through vectorial addition, wherein time delay information indicating the time delay between the local timers of said measuring devices of said differential protection devices is used for the temporal allocation of the current phasor measured values captured at different ends, wherein the time delay information is determined using a transit-time-based time synchronization method, and to generate a fault signal indicating a fault affecting the line if the differential current value exceeds a predefined threshold value; and

wherein said at least one of said at least two differential protection devices is configured to form a quotient of the current phasor measured values temporally allocated to one another to form an asymmetry variable, the asymmetry variable being used to check a transit time difference of messages transmitted via the communication connection, whi

Assignees

• Siemens Ag

Inventors

• Kerger Torsten
• Matussek Robert
• Gross Matthias

Classifications

• G01R19/10

  Measuring sum, difference or ratio · CPC title

• H02H1/0007

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

• H02H3/265 Primary

  responsive to phase angle between voltages or between currents · CPC title

• G01R31/085

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

• H02H3/283

  and taking into account saturation of current transformers · CPC title