CN103346541B - Convertor station direct current filter differential protection method and device - Google Patents

Abstract

The invention relates to a DC filter differential protection method and device in a converter station. The protection device first collects high and low voltage side currents of the DC filter, calculates the difference between them, and then performs logical judgment and processing according to the protection logic. The method proposed by the invention can quickly and accurately judge faults, and avoid the risk of protection malfunction or refusal to operate due to measurement distortion caused by current transformer saturation during faults.

Description

Method and device for differential protection of DC filter in converter station

technical field

The invention relates to a DC filter differential protection method and setting value setting in a high-voltage direct current transmission project, which is suitable for a high-voltage direct current transmission DC filter protection system.

Background technique

The DC filter is an important device in the HVDC transmission system. In the converter station, it is located between the busbars on the DC side. As shown in Figure 1, the two ends of the DC filter are respectively connected by the high-voltage side spacer and the low-voltage side spacer. to the high voltage bus and the neutral bus.

The DC filter differential protection is the main protection in the DC filter protection, which realizes the protection function when the DC filter internal ground fault occurs. The DC filter differential protection collects the current signal of the high-voltage side and the low-voltage side of the DC filter to protect the area between the two measuring points. The two measuring points are the current transformers T1 and T4 in Figure 1. When a ground fault occurs in the protection area, there is a large difference between the currents on both sides. When the difference is greater than the action setting value, the protection action signal will be output after a certain delay, and the DC filter high voltage side spacer will be opened. Or shut down the HVDC transmission system.

The existing DC filter differential protection method adopts: the current difference is greater than a fixed value, and the protection action signal is output after a long delay; but when a fault occurs, a large number of currents often flow through the fault point DC current, the magnetic saturation phenomenon of the current transformer will occur, resulting in measurement distortion, and the differential protection of the DC filter has the risk of protection malfunction and refusal.

Contents of the invention

The purpose of the present invention is to provide a DC filter differential protection method, which is used to solve the problems of potential malfunction and refusal in existing protection methods.

To achieve the above object, the solution of the present invention includes:

The method for differential protection of a DC filter in a converter station is characterized in that the steps are as follows:

1) Collect the high voltage side current signal IT1 and the low voltage side current signal IT4 of the DC filter, and calculate the current difference DIF according to the collected current signals;

2) To judge the differential protection, the criterion is DIF>Δ+K*IT1 _rms , Δ is a constant value, K is the ratio braking coefficient, and IT1 _rms is the effective value of the high-voltage side current;

3) When the criterion is met, the protection will act.

The DC filter differential protection is divided into three sections, and each section has its own protection setting, delay and action strategy. The corresponding criteria, delay and action strategy of the three sections are:

(1) DIF>Δ1+K1*IT1 _rms &IT1 _rms <Δ0; time delay T1; action strategy: pull open the spacer on the high-voltage side of the DC filter; Δ0 is the setting value of the arc-drawing capacity of the spacer on the high-voltage side; Δ1 is the first The first and second section protection settings, K1 is the ratio braking coefficient of the first section and the second section, and T1 is the action delay of the first section and the second section;

(2) DIF>Δ1+K1*IT1 _rms &IT1 _rms >Δ0; delay T1; action strategy: send phase-shift locking command to the extreme control system, shut down the HVDC transmission system, and simultaneously trip the AC circuit breaker and start the circuit breaker failure protection;

(3) DIF>Δ2+K2*IT1 _rms ; delay T2; action strategy: send phase-shift locking command to the extreme control system, shut down the high-voltage direct current transmission system, trip the AC circuit breaker at the same time, and start the circuit breaker failure protection; Δ2 It is the fixed value of the third section of protection, K2 is the ratio braking coefficient of the third section, and T2 is the action time of the third section.

The set value Δ0 of the arc-drawing capacity of the spacer knife on the high-voltage side is determined by the arc-drawing capacity of the high-voltage side knife of the primary equipment DC filter; the third section protection setting Δ2, the third section ratio braking coefficient K2 and the third section action delay T2 is determined according to the short-circuit fault point (F1) between the DC filter and the spacer on the high-voltage side; the protection setting Δ1 between the first section and the second section, the ratio braking coefficient K1 between the first section and the second section, and the first section and the second section. The second stage of action delay T1 is determined according to the short-circuit fault points inside the DC filter and the short-circuit fault points (F2, F3, F4) between the low-voltage side spacers.

In step 1), Among them, N is the number of sampling in a power frequency cycle, K is the ratio braking coefficient, It is the average value of the difference between IT1 and IT4 within a power frequency cycle.

${\mathrm{<span\; class="notranslate">\; IT</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; rms</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; IT</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; .</span>$

The DC filter differential protection device of the converter station is characterized in that it includes:

1) Acquisition component: collect the current signal IT1 on the high-voltage side of the DC filter and the current signal IT4 on the low-voltage side, and calculate the current difference DIF according to the collected current signals;

2) Judgment element: to judge the differential protection, the criterion is DIF>Δ+K*IT1 _rms , Δ is a constant value, K is the ratio braking coefficient, IT1 _rms is the effective value of the high-voltage side current;

3) Executing element: when the criterion is met, the protection will act.

The DC filter differential protection is divided into three sections, each section has its own protection setting, delay and action strategy, and the corresponding criteria, delay and action strategy of the three sections are:

(1) DIF>Δ1+K1*IT1 _rms &IT1 _rms <Δ0; time delay T1; action strategy: pull open the spacer on the high-voltage side of the DC filter; Δ0 is the set value of the arc-drawing capacity of the spacer on the high-voltage side; Δ1 is the first The first and second section protection settings, K1 is the ratio braking coefficient of the first section and the second section, and T1 is the action delay of the first section and the second section;

(2) DIF>Δ1+K1*IT1 _rms &IT1 _rms >Δ0; delay T1; action strategy: send phase-shift locking command to the extreme control system, shut down the HVDC transmission system, and simultaneously trip the AC circuit breaker and start the circuit breaker failure protection;

(3) DIF>Δ2+K2*IT1 _rms ; delay T2; action strategy: send phase-shift locking command to the extreme control system, shut down the high-voltage direct current transmission system, trip the AC circuit breaker at the same time, and start the circuit breaker failure protection; Δ2 It is the fixed value of the third section of protection, K2 is the ratio braking coefficient of the third section, and T2 is the action time of the third section.

The set value Δ0 of the arc-drawing capacity of the spacer knife on the high-voltage side is determined by the arc-drawing capacity of the high-voltage side knife of the primary equipment DC filter; the third section protection setting Δ2, the third section ratio braking coefficient K2 and the third section action delay T2 is determined according to the short-circuit fault point (F1) between the DC filter and the high-voltage side spacer; the protection setting Δ1 between the first section and the second section, the ratio braking coefficient K1 between the first section and the second section, and the first section and the second section. The second stage of action delay T1 is determined according to the short-circuit fault points inside the DC filter and the short-circuit fault points (F2, F3, F4) between the low-voltage side spacers.

In step 1), Among them, N is the number of sampling in a power frequency cycle, K is the ratio braking coefficient, It is the average value of the difference between IT1 and IT4 within a power frequency cycle.

${\mathrm{<span\; class="notranslate">\; IT</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}_{\mathrm{<span\; class="notranslate">\; rms</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; IT</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; .</span>$

In the DC filter differential protection method of the present invention, the operating current of the differential protection is no longer a fixed value, but a new criterion of constant plus ratio braking is adopted, and the ratio braking is related to the high-voltage side current, which weakens the magnetic saturation The resulting measurement influence, thereby reducing the risk of misoperation and refusal of differential protection.

Further, the method of the present invention also adopts the protection segmentation strategy, and divides the DC filter differential protection into three sections, each section has a different protection setting value and corresponding delay and action measurement, making the protection more accurate and reliable .

Finally, the method of the present invention also provides a setting measure for a fixed value. By applying the method of the invention, faults can be quickly and accurately judged, and the risk of protection malfunction or refusal to operate due to measurement distortion caused by current transformer saturation during faults can be avoided.

Description of drawings

Figure 1 is a DC filter wiring diagram;

Fig. 2 is the logic block diagram of the differential protection method of embodiment 2;

Fig. 3 is a schematic diagram of key fault points in setting value setting of DC filter differential protection.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

The DC filter differential protection device of the converter station claimed in the present invention should be understood as a functional module component based on the differential protection method of the present invention, not a physical device, so the device embodiment is omitted below. The present invention can be realized by an embedded industrial control platform or a PC device, and these two devices are commonly used devices in the field of high-voltage direct current transmission.

The typical structure diagram of the DC filter and the measuring points of the differential protection current are shown in Figure 1. It is installed between the DC high-voltage bus and the DC neutral bus, and its structure is composed of high-end capacitors, low-end resistors, inductors and other components; the main measuring points are high-voltage measuring current IT1 and low-voltage measuring current IT4.

Example 1

According to the method of the present invention, first collect the current signal IT1 on the high-voltage side of the DC filter and the current signal IT4 on the low-voltage side, and calculate the current difference DIF according to the collected current signals; then judge the differential protection, and the criterion is DIF>Δ+K *IT1 _rms , Δ is a constant value, K is the ratio braking coefficient, IT1 _rms is the effective value of the high-voltage side current; when the above criteria are met, the protection operates.

As a calculation method of DIF and IT1 _rms , Among them, N is the number of sampling in a power frequency cycle, K is the ratio braking coefficient, is the average value of the difference between IT1 and IT4 within a power frequency cycle, ${\mathrm{IT}1}_{\mathrm{rms}}=\frac{\sqrt{\underset{1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{IT}1}^2}}{N}.$

Example 2

In order to implement protection better, carry out protection segmentation: DC filter differential protection is divided into three sections, and each section has different protection settings and corresponding delay and action strategies. The corresponding criteria, delay and action strategy are:

(1) DIF>Δ1+K1*IT1 _rms &IT1 _rms <Δ0; time delay T1; action strategy: pull open the spacer on the high-voltage side of the DC filter; Δ0 is the setting value of the arc-drawing capacity of the spacer on the high-voltage side; Δ1 is the first K1 is the ratio braking coefficient of the first and second segment, T1 is the action delay of the first and second segment; & is logic and.

(2) DIF>Δ1+K1*IT1 _rms &IT1 _rms >Δ0; delay T1; action strategy: send phase-shift locking command to the extreme control system, shut down the HVDC transmission system, and simultaneously trip the AC circuit breaker and start the circuit breaker failure protection;

(3) DIF>Δ2+K2*IT1 _rms ; delay T2; action strategy: send phase-shift locking command to the extreme control system, shut down the high-voltage direct current transmission system, trip the AC circuit breaker at the same time, and start the circuit breaker failure protection; Δ2 It is the fixed value of the third section of protection, K2 is the ratio braking coefficient of the third section, and T2 is the action time of the third section.

The setting of the protection setting is based on the results of the dynamic performance test. During the test, it is especially necessary to consider that the DC component increases during the fault. At this time, the measurement results of the current transformer will be distorted. Detailed testing of each fault point further ensures that the protection function can operate correctly under various operating conditions. The key fault points F1, F2, F3, and F4 of the DC filter differential protection setting are shown in Figure 3. In the present invention, the fixed value and ratio coefficient of each section of protection are determined by the dynamic performance test results. The setting principle is based on the fact that the protection can operate reliably when the ground fault occurs in the zone, and prevent the protection from malfunctioning caused by the through-type current when the fault occurs outside the zone, so as to determine the protection action. Fixed value, ratio brake coefficient, and action delay.

Claims (8)

1. A method for differential protection of a DC filter in a converter station, characterized in that the steps are as follows: 1) Collect the high voltage side current signal IT1 and the low voltage side current signal IT4 of the DC filter, and calculate the current difference DIF according to the collected current signals; 2) To judge the differential protection, the criterion is DIF>Δ+K*IT1 _rms , Δ is a constant value, K is the ratio braking coefficient, and IT1 _rms is the effective value of the high-voltage side current; 3) When the criterion is satisfied, the protection action; The DC filter differential protection is divided into three sections, each section has its own protection setting, delay and action strategy, and the corresponding criteria, delay and action strategy of the three sections are: (1) DIF>Δ1+K1*IT1 _rms &IT1 _rms <Δ0; time delay T1; action strategy: pull open the spacer on the high-voltage side of the DC filter; Δ0 is the setting value of the arc-drawing capacity of the spacer on the high-voltage side; Δ1 is the first The first and second section protection settings, K1 is the ratio braking coefficient of the first section and the second section, and T1 is the action delay of the first section and the second section; (2) DIF>Δ1+K1*IT1 _rms &IT1 _rms >Δ0; delay T1; action strategy: send phase-shift locking command to the extreme control system, shut down the HVDC transmission system, and simultaneously trip the AC circuit breaker and start the circuit breaker failure protection; (3) DIF>Δ2+K2*IT1 _rms ; delay T2; action strategy: send phase-shift locking command to the extreme control system, shut down the high-voltage direct current transmission system, trip the AC circuit breaker at the same time, and start the circuit breaker failure protection; Δ2 It is the fixed value of the third section of protection, K2 is the ratio braking coefficient of the third section, and T2 is the action time of the third section. 2. The differential protection method for a DC filter in a converter station according to claim 1, wherein the setting value Δ0 of the arc-drawing capacity of the high-voltage side knife is determined by the arc-drawing capacity of the high-voltage side knife of the primary equipment DC filter ; The third section protection setting value Δ2, the third section ratio brake coefficient K2 and the third section action delay T2 are determined according to the short-circuit fault point (F1) between the DC filter and the high voltage side spacer; the first section and the second section The second-stage protection setting value Δ1, the ratio brake coefficient K1 of the first stage and the second stage, and the action delay T1 of the first stage and the second stage are based on the internal short-circuit fault point of the DC filter and the short-circuit fault between the low-voltage side barrier Click (F2, F3, F4) to confirm. 3. The method for differential protection of DC filter of converter station according to claim 1, characterized in that, in step 1), Among them, N is the number of sampling in a power frequency cycle, K is the ratio braking coefficient, It is the average value of the difference between IT1 and IT4 within a power frequency cycle. 4. The method for differential protection of DC filter of converter station according to claim 3, characterized in that, ${\mathrm{IT}1}_{\mathrm{rms}}=\frac{\sqrt{\underset{1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{IT}1}^2}}{N}.$ 5. The DC filter differential protection device of the converter station, characterized in that it includes: 1) Acquisition component: collect the current signal IT1 on the high-voltage side of the DC filter and the current signal IT4 on the low-voltage side, and calculate the current difference DIF according to the collected current signals; 2) Judgment element: to judge the differential protection, the criterion is DIF>Δ+K*IT1 _rms , Δ is a constant value, K is the ratio braking coefficient, IT1 _rms is the effective value of the high-voltage side current; 3) Executing element: when the above criteria are met, the protection will act; The DC filter differential protection is divided into three sections, each section has its own protection setting, delay and action strategy, and the corresponding criteria, delay and action strategy of the three sections are: (1) DIF>Δ1+K1*IT1 _rms &IT1 _rms <Δ0; time delay T1; action strategy: pull open the spacer on the high-voltage side of the DC filter; Δ0 is the set value of the arc-drawing capacity of the spacer on the high-voltage side; Δ1 is the first The first and second section protection settings, K1 is the ratio braking coefficient of the first section and the second section, and T1 is the action delay of the first section and the second section; (2) DIF>Δ1+K1*IT1 _rms &IT1 _rms >Δ0; delay T1; action strategy: send phase-shift locking command to the extreme control system, shut down the HVDC transmission system, and simultaneously trip the AC circuit breaker and start the circuit breaker failure protection; (3) DIF>Δ2+K2*IT1 _rms ; delay T2; action strategy: send phase-shift locking command to the extreme control system, shut down the high-voltage direct current transmission system, trip the AC circuit breaker at the same time, and start the circuit breaker failure protection; Δ2 It is the fixed value of the third section of protection, K2 is the ratio braking coefficient of the third section, and T2 is the action time of the third section. 6. The DC filter differential protection device of the converter station according to claim 5, wherein the setting value Δ0 of the arc-drawing capacity of the high-voltage side knife is determined by the arc-drawing capacity of the high-voltage side knife of the DC filter of the primary equipment ; The third section protection setting value Δ2, the third section ratio brake coefficient K2 and the third section action delay T2 are determined according to the short-circuit fault point (F1) between the DC filter and the high voltage side spacer; the first section and the second section The second-stage protection setting value Δ1, the ratio brake coefficient K1 of the first stage and the second stage, and the action delay T1 of the first stage and the second stage are based on the internal short-circuit fault point of the DC filter and the short-circuit fault between the low-voltage side barrier Click (F2, F3, F4) to confirm. 7. The DC filter differential protection device of the converter station according to claim 5, characterized in that, in step 1), Among them, N is the number of sampling in a power frequency cycle, K is the ratio braking coefficient, It is the average value of the difference between IT1 and IT4 within a power frequency cycle. 8. The DC filter differential protection device of the converter station according to claim 7, characterized in that, ${\mathrm{IT}1}_{\mathrm{rms}}=\frac{\sqrt{\underset{1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{IT}1}^2}}{N}.$