Differential protective method

• US 20030058594A1
• Filed: 10/15/2002
• Published: 03/27/2003
• Est. Priority Date: 12/07/1999
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Kerger, Torsten, Ngambo, Yves Ngounou, Philippot, Luc
• Granted Patent: US 6,867,577 B2
• Time in Patent Office: Days
• US Class Current: 361/80
• CPC Class Codes: H02H 7/263 involving transmissions of measured values comparison of currents or voltages using pilot wires H02H3/30

Abstract

The invention relates to a method for generating an error signal which characterizes a fault current in an electrical conductor (130) provided with two conductor ends (120, 123, 126, 129) and comprising charge measuring devices (100, 103, 106, 109) which are connected to each other by data lines (112). At least one device is attached to each end of the conductor. In the inventive method, charge measuring values are determined using charge measuring devices. The measured charge values take into account the direction of the charge flow a total measured charge value is formed by addition. Said error signal is generated when the total measured charge value exceeds a certain threshold value. According to the invention, the measured charge values are determined synchronously and determined repeatedly at regular intervals in such a way that the time interval between each sequential determination is smaller than the predefined measuring period.

Claims

1. A method for generating an error signal that characterizes a fault current in an electric conductor (130) having at least two conductor ends (120, 123, 126, 129), and conducting an alternating current and having charge measuring devices (100, 103, 106, 109) that are connected to one another via data lines (112), and of which respectively one is fitted at each end of the conductor, in which method

the charge measuring devices are used to measure measured charge values that in each case specify the charge quantity flowing through the respective conductor end during a prescribed measuring period,

a total measured charge value is formed by addition with the aid of the measured charge values taking account of the direction of the flow of charge, and

the error signal is generated when the total measured charge value exceeds in absolute terms a threshold value set as a function of the respective magnitude of the alternating current,

characterized in that

the measurement of the measured charge values is carried out in a time-synchronized fashion and is repeated regularly in such a way that the time interval between two sequential measurements is smaller in each case than the prescribed measuring period.

2. The method as claimed in one of claims 1, characterized in that

the prescribed measuring period is dimensioned in such a way that it is shorter than half the cycle length of the current.

3. The method as claimed in one of claims 2, characterized in that

the prescribed measuring period corresponds approximately to a quarter of the cycle length of the current.

4. The method as claimed in one of claims 1 to 3, characterized in that the time interval between in each case two sequential measurements is approximately half as long as the prescribed measuring period.

5. The method as claimed in one of the preceding claims, characterized in that

in the case of a conductor (130) having at least three conductor ends (120, 123, 126, 129) there is transmitted to a selected charge measuring device (109) an intermediate value (QA+QB+QC) that is formed by addition in advance from the measured charge values of the remaining charge measuring devices,

and the total measured charge value (QA+QB+QC+QD) is formed by addition with the aid of the measured charge value (QD) of the selected charge measuring device (109) and with the aid of the intermediate value (QA+QB+QC).

6. The method as claimed in one of claims 1 to 4, characterized in that in the case of a conductor (6) with at least three conductor ends (9, 12, 15, 18, 21),

two intermediate values are transmitted to the selected charge measuring device (30), specifically

a first intermediate value, which is formed by addition from the measured charge values (QB+QC) of a first group of the remaining charge measuring devices, and

a second intermediate value (QD+QE), which is formed by addition from the measured charge values of a second group of the remaining charge measuring devices, the second group including all charge measuring devices apart from the selected charge measuring device and the charge measuring devices of the first group,

the total measured charge value (QA+QB+QC+QD) is formed by addition with the aid of the measured charge value (ID) of the selected charge measuring device (30) and two intermediate values (QA+QB+QC).

7. The method as claimed in one of the preceding claims, characterized in that

the current in the respective conductor end is measured with the aid of each of the charge measuring devices by forming measured current values, and

the measured charge values are formed in each case by integrating the measured current values.

8. The method as claimed in claim 7, characterized in that the measured current values are formed by sampling and A/D conversion, and the integration is performed in a digital computer by digital summation.