CN110601153A - Relay protection method for single-end quantity of direct-current power distribution network - Google Patents

Abstract

The invention discloses a single-ended relay protection method for a DC distribution network. The method includes the following steps: collecting the positive and negative voltages and currents of the rectification side M and the inverter side N of the DC distribution network, and based on the The voltage and current are used to obtain the mode current, the starting current is obtained based on the 1-mode current, the high-frequency current and the low-frequency current are obtained through a band-pass filter based on the starting current; the high-frequency current and the low-frequency current are obtained based on the high-frequency current and the low-frequency current; The amplitude of high-frequency current and low-frequency current; calculate the ratio of high-frequency current amplitude and low-frequency current amplitude, the amplitude ratio is greater than the setting value of relay protection, and determine the fault in the DC distribution network, the amplitude ratio is smaller than the relay protection If the setting value of the electrical protection is used to determine the external fault of the DC distribution network.

Description

Relay Protection Method for Single-Ended Quantity of DC Distribution Network

technical field

The invention belongs to the technical field of direct current distribution networks, in particular to a single-ended relay protection method for direct current distribution networks.

Background technique

Relay protection is the first line of defense for the safe operation of the power grid. The goal of traditional AC power relay protection is to identify faults under the constraints of quick action, selectivity, sensitivity, and reliability, and finally issue fault isolation instructions to circuit breakers. The action of relay protection and mechanical circuit breaker is a typical sequential process control, and the identification and isolation of faults can be completed within 20-30ms at the fastest.

However, the system architecture, working mode, and fault characteristics of the flexible DC distribution network are different from the AC distribution network, and the protection technology of the AC system cannot be copied to the DC distribution network. Moreover, the power electronic equipment contained in the DC distribution network has a very limited ability to withstand overcurrent, and it is required that the protection system can identify and isolate the fault at high speed when a DC fault occurs. Since economical and practical medium-voltage DC circuit breakers have not yet been commercially applied on a large scale, the development of DC distribution network protection technology is also limited. At present, there is no system protection scheme that has been verified in practice and is widely accepted. The improvement of the structure, the formulation of protection standards and the practical feedback of the corresponding protection theory.

Since the medium-voltage DC distribution network is a new type of distribution network, the number of research literature in the field of relay protection is very small, and the literature on relay protection using DC circuit breakers to isolate faults is rarely reported. Similar protection schemes for traditional HVDC transmission lines are generally provided by ABB or SIEMENS. Its main protection is equipped with traveling wave protection (or Wavefront Protection), differential undervoltage protection, and backup protection is equipped with current differential protection. This protection scheme has the problems of single main protection principle, low sensitivity, poor backup protection reliability, and slow action speed, and lacks a protection principle that can reflect the existence of the fault for a long period of time after the fault. At the same time, the medium-voltage DC distribution network is different from the traditional high-voltage DC grid in terms of topology and control characteristics. Therefore, the existing high-voltage DC line protection principles are not suitable for direct application to the medium-voltage DC distribution network, and it is of great significance to study new protection principles and schemes.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention proposes a single-ended relay protection method for a DC distribution network. Starting from the frequency response characteristics of a converter station in a flexible DC distribution network, the present invention proposes a converter station The DC distribution network single-ended protection method with frequency response characteristics has high sensitivity, high backup protection reliability and fast action speed.

The object of the present invention is to be realized by the following technical scheme, a kind of relay protection method of DC distribution network single-ended quantity comprises the following steps:

In the first step, the voltage and current of the positive pole and the negative pole of the rectification side M and the inverter side N of the DC power distribution network are collected, and the modular current is obtained based on the voltage and current, wherein,

i _p and i _n represent the positive and negative currents respectively, and i ₁ and i ₀ represent the 1-mode and 0-mode currents respectively;

In the second step, the starting current is obtained based on the 1-mode current, wherein,

N is the number of sampling points, k represents the kth sampling point, i ₁ (k) is the sampling value of the 1-mode current at the installation position of the relay protection, and I _set1 is the starting current value;

In the third step, the high-frequency current and the low-frequency current are obtained through a band-pass filter based on the starting current;

In the fourth step, the amplitudes of the high-frequency current and the low-frequency current are obtained based on the high-frequency current and the low-frequency current, wherein,

i _H (k), i _L (k) are the filtered results of the 1-mode current at the installation position of the relay protection, and the amplitudes of the high-frequency current and low-frequency current of I _H and _IL ;

In the fifth step, the ratio of the high-frequency current amplitude to the low-frequency current amplitude is calculated, the amplitude ratio is greater than the setting value of the relay protection, and the fault in the DC distribution network is determined, and the amplitude ratio is smaller than the setting value of the relay protection value, it is to determine the fault outside the DC distribution network.

In the method, in the first step, the DC distribution network is a flexible DC distribution network.

In the described method, the zero-mode equivalent network of the flexible DC distribution network is modeled based on the Berelon line model, and the voltages of the positive and negative poles of the rectifier side M and the inverter side N of the zero-mode equivalent network of the flexible DC distribution network are collected and current.

In the method, in the second step, N is the number of sampling points in the 5ms data window, and the starting current value I _set1 is 0.1 times the rated current.

In the described method, in the third step, the band-pass filter includes a high-frequency current band-pass filter and a low-frequency current band-pass filter, the center frequency f _H of the high-frequency current band-pass filter=3500Hz, and the low-frequency current band-pass filter The center frequency f _L of the filter = 100 Hz.

In the above method, in the fifth step, the setting value R _HLset is the ratio of the high and low frequency current amplitudes when the metallic inter-electrode fault is 10m away from the zone.

Description of drawings

Various other advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings in the description are for the purpose of illustrating preferred embodiments only and are not to be considered as limiting the invention. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to these drawings without creative efforts. Also throughout the drawings, the same reference numerals are used to denote the same parts.

In the attached picture:

1 is a schematic diagram of steps of a relay protection method for single-ended quantities of a DC distribution network according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of a double-ended flexible DC system of a relay protection method for a single-ended DC distribution network according to an embodiment of the present invention;

Fig. 3 (a), Fig. 3 (b) are the schematic diagrams of the simulation results of the positive ground fault in the area of the relay protection method of the single-ended quantity of the DC distribution network according to an embodiment of the present invention;

Fig. 4 (a), Fig. 4 (b) are the schematic diagrams of the simulation results of negative pole grounding faults in the area of the relay protection method of single-ended quantity of DC distribution network according to an embodiment of the present invention;

Fig. 5 (a), Fig. 5 (b) are the schematic diagrams of the simulation results of inter-pole faults in the area of the relay protection method of single-ended quantity of DC distribution network according to an embodiment of the present invention;

Fig. 6(a) and Fig. 6(b) are schematic diagrams of out-of-area fault simulation results of a single-ended relay protection method for a DC distribution network according to an embodiment of the present invention.

The present invention will be further explained below in conjunction with the accompanying drawings and embodiments.

Detailed ways

Specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be embodied in various forms and is not limited to the embodiments set forth herein. Rather, these embodiments are provided for more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art should understand that they may use different terms to refer to the same component. The specification and claims do not use differences in nouns as a way of distinguishing components, but use differences in functions of components as a criterion for distinguishing. "Includes" or "comprises" mentioned throughout the specification and claims is an open term, so it should be interpreted as "including but not limited to". The subsequent description in the specification is a preferred implementation mode for implementing the present invention, but the description is for the purpose of the general principles of the specification, and is not intended to limit the scope of the present invention. The scope of protection of the present invention should be defined by the appended claims.

In order to facilitate the understanding of the embodiments of the present invention, further explanations will be given below in conjunction with the accompanying drawings by taking specific embodiments as examples, and each drawing does not constitute a limitation to the embodiments of the present invention.

For a better understanding, FIG. 1 is a schematic diagram of the steps of a method according to an embodiment of the present invention. As shown in FIG. 1 , the relay protection method for single-ended quantities of a DC power distribution network includes the following steps:

In the first step S1, the voltage and current of the positive pole and the negative pole of the rectification side M and the inverter side N of the DC power distribution network are collected, and the modular current is calculated based on the voltage and current, wherein,

i _p and i _n represent the positive and negative currents respectively, and i ₁ and i ₀ represent the 1-mode and 0-mode currents respectively;

In the second step S2, the starting current is obtained based on the 1-mode current, wherein,

N is the number of sampling points, k represents the kth sampling point, i ₁ (k) is the sampling value of the 1-mode current at the installation position of the relay protection, and I _set1 is the starting current value;

In the third step S3, the high-frequency current and the low-frequency current are obtained through a band-pass filter based on the starting current;

In the fourth step S4, the amplitudes of the high-frequency current and the low-frequency current are obtained based on the high-frequency current and the low-frequency current, wherein,

i _H (k), i _L (k) are the filtered results of the 1-mode current at the installation position of the relay protection, and the amplitudes of the high-frequency current and low-frequency current of I _H and _IL ;

In the fifth step S5, the ratio between the high-frequency current amplitude and the low-frequency current amplitude is calculated, the amplitude ratio is greater than the setting value of the relay protection, and the fault in the DC distribution network is determined, and the amplitude ratio is smaller than the setting value of the relay protection The setting value is used to determine the fault outside the DC distribution network.

In order to further understand the present invention, in order to simplify the analysis, a double-ended flexible direct current system is used for analysis, as shown in FIG. 2 . When a fault occurs outside the zone, the capacitor exhibits low impedance characteristics for high-frequency currents, but high-impedance characteristics for low-frequency currents, so the high-frequency current measured at the protection installation should be selected to be smaller than the high-frequency current measured when the fault occurs in the zone. However, the low-frequency current when the fault is outside the zone is not much different from the low-frequency current when the fault is inside the zone. Specifically, the difference between the inside and outside the zone can be realized through the amplitude ratio of the high-frequency current and the low-frequency current. The specific implementation steps of the DC distribution network single-ended quantity protection method based on the frequency response characteristics of the converter station are as follows:

Step 1: collect the positive and negative currents on both sides, and calculate the 1-mode current according to formula 1.

Among them, i _p and i _n represent the positive and negative currents respectively, and i ₁ and i ₀ represent the 1-mode and 0-mode currents, respectively.

Step 2: Calculate the starting current through formula 2 and compare it with the setting value.

Where N is the number of sampling points in the 5ms data window, i ₁ (k) is the sampled value of the 1-mode current at the protection installation, and I _set1 is the start-up value, which can be set to 0.1 times the rated current.

Step 3: Calculate the high-frequency current and the low-frequency current through the band-pass filter, wherein the center frequency of the high-frequency current band-pass filter is set to f _H =3500 Hz, and the center frequency of the low-frequency current band-pass filter is set to f _L =100 Hz .

Step 4: Obtain the amplitudes of the high-frequency current and the low-frequency current. The specific calculation formula is shown in formula 3.

Among them, i _H (k) and i _L (k) are the filtered results of the 1-mode current at the protection installation, and the amplitudes of high-frequency current and low-frequency current of I _H and _IL .

Step 5: Calculate the ratio of the high-frequency current amplitude to the low-frequency current amplitude and compare it with the set value, as shown in formula 4. If it is greater than the set value, it is an internal fault, and if it is set by the cell, it is an external fault.

Among them, R _HLset is the ratio of high and low frequency current amplitudes when there is a fault between metallic poles 10m away from the zone.

In order to further understand the technical effect of the present invention, simulation verification is carried out, based on the simulation model shown in Figure 2, R _HLset = 1.5×10 ^-3 , respectively simulate the positive pole in the zone, the negative pole in the zone, the bipolar fault in the zone and the fault outside the zone , the simulation results are shown in Figure 3(a)-Figure 6(b). Comparing the simulation results, it can be seen that when there is a fault in the zone, the ratio of the high and low frequency currents of the DC line is greater than the protection action threshold, and the full-line quick action protection quickly and correctly judges the fault in the zone; when the fault is outside the zone, the ratio of the high and low frequency currents of the DC line Action threshold, full-line quick action protection to ensure reliable and no false action.

In a preferred implementation of the method, in the first step S1, the DC distribution network is a flexible DC distribution network.

In the preferred implementation of the method, the zero-mode equivalent network of the flexible DC distribution network is modeled based on the Berillon line model, and the positive poles of the rectifier side M and the inverter side N of the flexible DC distribution network are collected. and negative voltage and current.

In a preferred implementation of the method, in the second step S2, N is the number of sampling points in the 5ms data window, and the starting current value I _set1 is 0.1 times the rated current.

In a preferred embodiment of the method, in the third step S3, the bandpass filter includes a high-frequency current bandpass filter and a low-frequency current bandpass filter, and the center frequency f _H of the high-frequency current bandpass filter=3500Hz , the center frequency f _L of the low-frequency current band-pass filter = 100 Hz.

In a preferred implementation of the method, in the fifth step S5, the setting value R _HLset is the ratio of high and low frequency current amplitudes when a metallic inter-electrode fault occurs 10 m away from the area.

In the DC distribution network single-ended protection method for the frequency response characteristics of the converter station of the present invention, when a fault occurs outside the area, the capacitor exhibits low impedance characteristics for high-frequency currents, but high impedance characteristics for low-frequency currents, so the protection installation The high-frequency current measured at the site should be selected to be smaller than the high-frequency current measured at the time of the fault in the area, and the low-frequency current at the time of the fault outside the area is not much different from the low-frequency current at the time of the fault in the area. The amplitude ratio realizes the discrimination between inside and outside the zone.

Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields, and the above-mentioned specific embodiments are only illustrative, instructive, and not restrictive . Under the enlightenment of this description and without departing from the protection scope of the claims of the present invention, those skilled in the art can also make many forms, which all belong to the protection of the present invention.

Claims (6)

1. A method for relay protection of DC distribution network single-ended quantity, said method comprising the following steps: In the first step (S1), the voltage and current of the positive pole and the negative pole of the rectification side M and the inverter side N of the DC distribution network are collected, and the modular current is obtained based on the voltage and current, wherein, i _p and i _n represent the positive and negative currents respectively, and i ₁ and i ₀ represent the 1-mode and 0-mode currents respectively; In the second step (S2), the starting current is obtained based on the 1-mode current, wherein, N is the number of sampling points, k represents the kth sampling point, i ₁ (k) is the sampling value of the 1-mode current at the installation position of the relay protection, and I _set1 is the starting current value; In the third step (S3), the high-frequency current and the low-frequency current are obtained through a band-pass filter based on the starting current; In the fourth step (S4), the amplitudes of the high-frequency current and the low-frequency current are obtained based on the high-frequency current and the low-frequency current, wherein, i _H (k), i _L (k) are the filtered results of the 1-mode current at the installation position of the relay protection, and the amplitudes of the high-frequency current and low-frequency current of I _H and _IL ; In the fifth step (S5), the ratio between the high-frequency current amplitude and the low-frequency current amplitude is calculated, the amplitude ratio is greater than the setting value of the relay protection, and the fault in the DC distribution network is determined, and the amplitude ratio is smaller than the relay protection The setting value of the protection is used to determine the fault outside the DC distribution network. 2. The method according to claim 1, wherein, preferably, in the first step (S1), the DC distribution network is a flexible DC distribution network. 3. The method according to claim 2, wherein, modeling the zero-mode equivalent network of the flexible DC distribution network based on the Berillon line model, collecting the rectification side M and the inverter side of the zero-mode equivalent network of the flexible DC distribution network The voltage and current of the positive and negative poles of N. 4. The method according to claim 1, wherein, in the second step (S2), N is the number of sampling points in the 5ms data window, and the starting current value I _set1 is 0.1 times the rated current. 5. The method according to claim 1, wherein, in the third step (S3), the bandpass filter comprises a high-frequency current bandpass filter and a low-frequency current bandpass filter, and the center of the high-frequency current bandpass filter The frequency f _H =3500 Hz, and the center frequency f _L of the low-frequency current band-pass filter = 100 Hz. 6. The method according to claim 1, wherein, in the fifth step (S5), the setting value R _HLset is the ratio of high and low frequency current amplitudes when there is a metallic inter-electrode fault 10m away from the zone.