Method and protection device for line protection

Abstract

The invention relates to a method and a protective device for line protection. In the method for line protection, a choke device (7, 8, 27-30) for reactive power compensation is provided on an electrical line (2, L1, L2, L3), and a resonant current (ICT) is measured on the line side of the choke device (7, 8, 27-30) after opening a circuit breaker (5) by means of a first measuring device (9, 24-26), characterized in that a voltage is measured after opening the circuit breaker (5) by means of a second measuring device (10, 31-33), and a current (ISH) in the choke device is calculated from the measured voltage by means of an evaluation device, and the calculated current (ISH) is subtracted from the measured resonant current (ICT) by means of the evaluation device to obtain a corrected current (ICB).

Description

Technical Field

[0001] The present invention relates to a method for line protection and a protection device. Background Art

[0002] On long overhead lines and cables, choke devices are generally installed to compensate for the capacitive reactive current on the line. If a current transformer is installed on the line side of the choke, a gradually decreasing resonant current is measured after the circuit breaker is disconnected. This resonant current has an adverse effect on the functions of the protective equipment that evaluates the cut-off current. These functions are, for example, the closing (Absteuerung) of the disconnect command (Auskommando) and the switch fault protection (Schalterversagerschutz). To date, this problem has been solved by setting the setting value of the minimum current when the circuit breaker is disconnected to a correspondingly large value for the protective equipment. As a result, the current threshold in the switch fault protection is also set to a correspondingly large value. However, as a result, both functions of the protective equipment are significantly limited in terms of their sensitivity.

[0003] From the manual "SIPROTEC 7SD87 Leitungsdifferentialschutz (SIPROTEC 7SD87 Line Differential Protection)", Siemens AG 2018, an expansion module for line protection is known. This expansion module can be used in conjunction with the manual "SIPROTEC 5Schutz, Automatisierung und (SIPROTEC 5 Protection, Automation and Monitoring)", Siemens AG 2016, Article No.: EMDG-B10022-00. Summary of the Invention

[0004] The object of the present invention is to specify a method for line protection which offers a relatively high level of safety for line protection.

[0005] The present invention solves the above technical problems through the method according to the present invention.

[0006] For example, the choke arrangement can be a choke coil, which can optionally be configured for multiple phases. Below, the terms "choke," "choke coil," and "choke arrangement" are used synonymously. Such an inductance is correspondingly used for capacitive reactive power compensation.

[0007] For example, the line can be designed for a three-phase AC voltage, so that the choke arrangement and the measuring device are also designed for three phases. The line can be, for example, a high-voltage line, such as an overhead line with a nominal voltage of more than 52 kV.

[0008] The present invention uses the measured voltage to calculate the current in the choke, and then determines the calculated current at the circuit breaker by subtraction. After the circuit breaker is opened, the compensation current in the choke does not add to the calculated current. This allows the protective equipment to achieve lower triggering sensitivity in its functions, such as disconnection of network sections and switch fault protection, thereby improving the safety of line or network operation.

[0009] The calculated current allows the current threshold for determining the tripping state of the circuit breaker to be set as sensitively as usual. The restrictions caused by installing a current transformer on the line side of the choke coil are eliminated.

[0010] The first measuring device can have, for example, a current transformer, and the second measuring device can have, for example, a voltage transformer.

[0011] The first and second measuring devices can, for example, be separate measuring devices. Alternatively, however, a single measuring device can be used that combines both current and voltage measurement functions. This has the advantage that voltage and current values ​​are present at the same point in time, for example, with the same timestamp, without requiring synchronization between the first and second measuring devices.

[0012] For example, the output value of the measuring device can be transmitted to the evaluation device and / or the protection device via a process bus. Alternatively, other digital data transmission methods can be used.

[0013] A computer with a processor device and a data storage device can be used as the analysis device. However, the analysis device can also be implemented as software and can be configured as a function in a protection device with its own processor device and data storage device.

[0014] In one variant, the first measuring device and the second measuring device can be part of the protective device. In one extension, the evaluation device can also be part of the protective device.

[0015] A resonant current in the sense of the present invention is a current which is measurable for a short time when a line is switched off and which decreases gradually over time.

[0016] In a preferred embodiment of the method according to the invention, the protection device uses the corrected current as the input variable of the line protection function. This is advantageous because false ( )Influence.

[0017] In a preferred embodiment of the method according to the invention, a threshold value is used for the protective device to determine the tripped state of the circuit breaker, wherein this threshold value is lower than when using the measured resonant current as the input variable. This is advantageous because it allows for a higher triggering sensitivity of the protective device, thereby achieving increased safety.

[0018] In a preferred embodiment of the method according to the invention, a main reactor shunt and a neutral reactor shunt are used for the choke arrangement.

[0019] In a preferred embodiment of the method according to the invention, the current in the inductor arrangement is determined for each phase by analyzing the symmetrical components. This is advantageous because it is a simple and proven method.

[0020] Furthermore, the object of the present invention is to specify a protection device which offers a relatively high degree of safety for line protection.

[0021] The present invention solves the above technical problem by the protection device according to the present invention. Preferred embodiments are obtained from the following description. Here, the same advantages as those described at the beginning for the method according to the present invention are obtained similarly.

[0022] Furthermore, the present invention is directed to the technical problem of specifying a method with which the safety in the power grid can be further increased.

[0023] The present invention solves the above technical problems through a method for line protection, in which a choke device for reactive power compensation is arranged on an electrical line, and on the line side of the choke device, a first current is measured in the closed state of the circuit breaker by means of a first measuring device, characterized in that a voltage is measured in the closed state of the circuit breaker by means of a second measuring device, and a current in the choke device is calculated based on the measured voltage by means of an analysis device, and the calculated current is subtracted from the measured first current by means of the analysis device to obtain a corrected current.

[0024] In this alternative embodiment of the invention, the (first) current (in this case, that is, not the resonant current) and the voltage can also be measured for each phase before opening the circuit breaker, ie in the closed state, in order to calculate the corrected current.

[0025] In a preferred embodiment, the protection device uses the corrected current as an input variable for other protection functions.

[0026] In a preferred embodiment, the protection device uses a threshold value for triggering further protection functions that is lower than when the first current is used as the input variable. Further protection functions may be, for example, fault location and / or distance protection. This is advantageous because the more accurate current acquisition according to the present invention allows for improved results for the aforementioned further protection functions, thereby achieving increased safety in the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To further illustrate the present invention,

[0028] Figure 1 A first electrical network is schematically shown, and

[0029] Figure 2 A second electrical network is schematically shown, and

[0030] Figure 3 The equivalent circuit diagram of the symmetrical components is shown schematically, and

[0031] Figure 4 The simulation of the three-phase current flow is shown schematically. DETAILED DESCRIPTION

[0032] Figure 1 A so-called single-line diagram (single-phase diagram) 1 of an electrical line 2 with a length of 360 km is shown. An electrical energy feed 3, for example a photovoltaic system, is provided on a busbar 4. Along the line 2, chokes 7 and 8 are arranged downstream of a circuit breaker 5. The chokes have a so-called "main reactor shunt" 7 and a so-called "neutral reactor shunt" 8. A current transformer, as a first measuring device, is arranged on the line side downstream of the chokes 7 and 8. The current transformer measures the resonant current, which, in such long lines, can assume relatively large values ​​for a short period of time due to the resonance effects when the circuit breaker 5 is opened. This current value can be above the triggering threshold of a protective device (not shown), so that the protective device cannot perform certain protective functions, such as switch failure protection.

[0033] According to the present invention, on line 2 (on the line side relative to the circuit breaker, Figure 2 In the example shown on the right in the figure, a capacitively operating voltage transformer 10 or a second measuring device is arranged to measure the voltage applied to the choke coil. From this voltage, the current in the choke coil can be inferred accordingly and used to correct the measured resonant current.

[0034] For example, the following values ​​are obtained:

[0035]

[0036] When the circuit breaker is opened, the current measured in the first measuring device corresponds to the current flowing through the choke coil. Therefore, if this measured current is greater than a threshold value (e.g., 50 mA) for determining that the line 2 is disconnected by the protective device, the triggering ("tripping") of the protective device can be deactivated with a delay.

[0037] For this reason, the present invention proposes to mathematically correct the measured current by subtracting the calculated current flowing through the choke coil from the measured current. This current flowing through the coil is calculated based on the voltage measured using a voltage transformer as a second measuring device. The voltage transformer is arranged on the line side relative to the circuit breaker. Furthermore, the calculated impedance of the choke coil is used for the calculation.

[0038] exist Figure 2 The three phases are shown in Figure 1 The circuit diagram 20 is equivalent to the single-line diagram in FIG. Each phase L1, L2, L3 has a circuit breaker 21, 22, 23, wherein for each phase, the actual current I sought is applied to the circuit breaker. CB (For phase L3, this is indicated by an arrow.) Furthermore, each phase has a current measuring device 24, 25, 26, at which the measured current I can be determined accordingly. CT The voltage is measured at the voltage measuring device 31, 32, 33 for each phase. The choke coils 27 to 30 have a first part of a so-called "main reactor" for each phase, which has a coil 27, 28, 29, wherein here the current to be calculated I flows. SH Furthermore, a so-called “neutral reactor” 30 is provided.

[0039] The current I on the circuit breaker can be calculated (for one of the phases) as follows CB :

[0040] I CB =I CT -I Sh

[0041] To calculate ISH, use the phase voltage:

[0042] V Ph =I Sh_N ·ZN Sh +I Sh ·ZL Sh

[0043] In order to determine the current split into ZNSh and ZLSh, the so-called symmetrical components are analyzed for the choke coil. The symmetrical component analysis is a common method in electrical engineering and is known, for example, from Wikipedia (permanent link:

[0044] https: / / de.wikipedia.org / w / index.php?title=Symmetrische_Komponenten&oldid=198714718).

[0045] I SH_A =I1+I2+I0

[0046] For phase A, we get:

[0047]

[0048]

[0049] Correspondingly, for the other two phases B and C, the current on the circuit breaker can also be calculated based on the analysis based on symmetrical components.

[0050] Figure 3 Equivalent circuit diagrams 41 to 43 are shown as examples for the symmetrical components positive sequence system, negative sequence system and zero sequence system, wherein the positive sequence system and the negative sequence system have the same impedance Z SH , and the zero sequence system passes Z SH +3*ZN SH Circuit diagram 41 shows a so-called positive sequence system (Mitsystem), circuit diagram 42 shows a negative sequence system (Gegensystem), and circuit diagram 43 shows a zero sequence system (Nullsystem) (see the Wikipedia article mentioned above).

[0051] Figure 4 The curves of the measured resonant currents 80, 81, and 82 are shown for the three phases L1, L2, and L3, respectively. In this simulation, a long-distance short circuit occurred on a 350 km long line at t = 0 ms. The resulting amplitude of the short-circuit current I (A) (on the secondary side, i.e., at the current transformer) is between 1 A and -1 A. For example, with a current transformer transformation ratio of 1000, an amplitude of between 1000 A and -1000 A is obtained on the primary side of the line.

[0052] In the simulation, the circuit breaker is opened at the time 460 ms, which is indicated by the vertical line 90 .

[0053] For the first "measurement" after 450 ms, ie before the opening of the circuit breaker at approximately 460 ms, the following values ​​are obtained (vector measurement variables respectively given in magnitude (length) and angle):

[0054] Measurements Quantity Angle (°) Current phase A 417mA 135 Current phase B 629mA 89 Current phase C 519mA -108 Voltage phase A 60.75V -49 Voltage Phase C 48.41V -169 Voltage Phase C 58.07V 80

[0055] Since the switch is still closed at this point in time, the measured current is not called the resonant current. In the following example, the current measured after the switch is opened is called the resonant current.

[0056] The following calculated values ​​are derived from the measured values:

[0057] Calculated parameters Quantity Angle (°) Positive sequence system 55.61V -46 Negative sequence system 6.37V -86 Zero-sequence system 1.36V 36 Corrected current phase A 424mA 147 Corrected current phase B 696mA 91 Corrected current phase C 505mA -99

[0058] It can be clearly seen that the corrected current (before opening the circuit breaker) deviates only slightly from the measured current in terms of magnitude and angle, respectively.

[0059] If the measurement is repeated 500 ms after opening the circuit breaker (i.e. after the circuit breaker opens), the following measured values ​​are obtained:

[0060] Measurements Quantity Angle (°) Resonant current phase A 89mA 62 Resonant current phase B 30mA -55 Resonant current phase C 88mA -170 Voltage phase A 77.98V -12 Voltage phase B 4.87V 27 Voltage Phase C 76.72V 81

[0061] This results in the following calculated values:

[0062] Calculated parameters Quantity Angle (°) Positive sequence system 48.44V -25 Negative sequence system 15.85V -85 Zero-sequence system 37.41V 34 Corrected current phase A 7mA -27 Corrected current phase B 3mA -149 Corrected current phase C 7mA 104

[0063] By correcting the measured resonant current, a very small corrected current (less than 10 mA) is obtained, which can be considered essentially zero (the value expected when the circuit breaker is open). The corrected current is below the typical threshold of 50 mA, which is considered by the protection device to be the current flow that still exists when the circuit breaker is closed. Thus, the present invention enables better identification of an open switch for downstream protection devices.

[0064] At 550ms, we get the following:

[0065]

[0066]

[0067] This results in the following calculated values:

[0068] Calculated parameters Quantity Angle (°) Positive sequence system 63.17V -26 Negative sequence system 1.74V -43 Zero-sequence system 2.85V 105 Corrected current phase A 7mA -22 Corrected current phase B 5mA -98 Corrected current phase C 8mA 113

[0069] By correcting the measured resonant current, very small corrected currents (below 10 mA) are again obtained, which enable improved fault detection in the protective equipment.

Claims

1. A method for performing line protection, wherein: On an electrical line (2, L1, L2, L3), a choke arrangement (7, 8, 27-30) for reactive power compensation is provided, and on the line side of the choke arrangement (7, 8, 27-30), a resonant current (I CT ), It is characterized in that Measuring the voltage after opening the circuit breaker (5, 21-23) by means of a second measuring device (10, 31-33) on the line side, and The current (I SH ), and by means of the analysis device, from the measured resonant current (I CT ) minus the calculated current (I SH ) to obtain the corrected current (I CB ).

2. The method according to claim 1, characterized in that The corrected current (I CB ) is used by the protected device as an input parameter for the line protection function.

3. The method according to claim 2, characterized in that For the protection device, a threshold value for determining the disconnection state of the circuit breaker (5) is used, wherein the threshold value is greater than the value obtained by using the measured resonant current (I CT ) is small when used as an input parameter.

4. The method according to any one of claims 1 to 3, characterized in that For the choke arrangement (7, 8, 27-30), a main reactor shunt (7, 27-29) and a neutral reactor shunt (8, 30) are used.

5. The method according to any one of claims 1 to 3, characterized in that Accordingly, the current (I SH ).

6. A protection device for line protection, comprising: An electrical line (2, L1, L2, L3) having a choke arrangement (7, 8, 27-30) for reactive power compensation, and a circuit breaker (5, 21-23), the circuit breaker being used to connect or disconnect the line (2, L1, L2, L3), and A first measuring device (9, 24-26) is arranged on the line side of the choke device (7, 8, 27-30) for measuring the resonant current (I CT ), It is characterized in that A second line-side measuring device (10, 31-33) is designed to measure the voltage after the circuit breaker (5, 21-23) is opened, and The evaluation device is designed to calculate the current (I SH ), and from the measured resonant current (I CT ) minus the calculated current (I SH ) to obtain the corrected current (I CB ).

7. The protection device according to claim 6, characterized in that The protection device is configured to convert the corrected current (I CB ) is used as an input parameter for line protection functions.

8. The protection device according to claim 7, characterized in that The protection device is configured to use a threshold value for determining the disconnected state of the circuit breaker (5, 21-23), wherein the threshold value is greater than the value obtained by using the measured resonant current (I CT ) is small when used as an input parameter.

9. The protection device according to any one of claims 6 to 8, characterized in that The choke arrangement (7, 8, 27-30) has a main reactor shunt (7, 27-29) and a neutral reactor shunt (8, 30).

10. The protection device according to any one of claims 6 to 8, characterized in that The current (I) in the choke arrangement (7, 8, 27-30) is determined for each phase by means of the analysis device, respectively, by means of a symmetrical component analysis. SH ).

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