CN104143817A - Device and method for distance protection in distribution network with distributed power - Google Patents

Abstract

The invention provides a distance protection method in a distribution network containing distributed power sources. When a fault occurs, if the first stage of distance protection does not operate, compare the negative sequence current of the first feeder with distance protection and the next stage For the amplitude of the negative sequence current of the second feeder, the one with the larger amplitude is determined as the fault line. If the fault line is the first feeder, the fault location is determined according to the negative sequence impedance to ground at both ends of the first feeder, or if the fault line is For the second feeder, the fault location is determined according to the negative-sequence impedance to ground at both ends of the second feeder, and when the determined fault location is within the range of the second-stage distance protection, the second-stage distance protection is implemented after a specified time delay.

Description

Device and method for distance protection in distribution network with distributed power

technical field

The invention relates to a distance protection device and method in a distribution network with distributed power sources.

Background technique

Relay protection is included in the general distribution network, which mainly responds to power system failures and abnormal conditions that endanger safe operation, to protect the power system and its components (generators, transformers, transmission lines, etc.) from damage . The function of relay protection is that when a fault or abnormal working condition occurs in the power system, the faulty equipment is automatically removed from the system in the shortest possible time and in the smallest area, so as to reduce or avoid equipment damage and damage to adjacent areas. impact on power supply. As a kind of relay protection, distance protection is widely used in distribution network.

As a new way of energy supply, so-called distributed energy has emerged. Distributed energy is an energy supply method built on the user side, which can be operated independently or connected to the grid. Distributed energy includes solar energy, wind energy, energy storage batteries, etc. (hereinafter referred to as DG). With the access of distributed energy, it is bound to affect the relay protection in the distribution network. That is, when a short-circuit fault occurs in the power grid, distributed energy resources may make the sensitivity of the distance protection of the transmission line unable to meet the requirements, resulting in the failure of the distance protection.

Fig. 7 is a diagram for explaining distance protection currently used in a power distribution network. The core device of the distance protection is the impedance relay 10 . In Fig. 5, M, N, P are the busbars connected to the feeder of the distribution network respectively, and 1 is the input energy of the grid. 11 is a transformer for measuring the voltage on the bus M, Um is the measured voltage, 12 is a current sensor for measuring the feeder current between the bus M and the bus N, and Im is the measured current. K is where the line fault occurs.

As shown in Figure 7, the measured voltage Um and current Im are added to the impedance relay 10, and the impedance relay 10 obtains their ratio, that is, the impedance Z _M , that is, according to the measured voltage Um and the measured current Im, Calculate the impedance Z _M = Um/Im, which is called the measured impedance Z _M of the impedance relay. The measured impedance of the impedance relay reflects the impedance from the fault point to the protection installation, that is, it reflects the distance from the fault point, that is, the distance from the fault point to Protect the distance of the installation place, so the protection that responds to changes in the electrical quantity of the transmission line composed of impedance relays as the core is called distance protection. The distance protection is installed on each section of the feeder, that is, the same distance protection is also installed between the feeder NPs (illustration omitted).

Usually, the distance protection is divided into three sections, the ranges of section I protection, section II protection and section III protection are shown in Figure 7.

When a fault occurs in the end of the distance protection installation line, that is, the end of the feeder MN and the adjacent next section of the line, that is, the feeder NP, the protection of the second section of the distance protection should act to disconnect the corresponding line through a circuit breaker (not shown).

However, after the DG is connected, since the DG is connected in parallel with the line, the DG also provides a short-circuit current to the faulty line, so the measured current will increase, the measured impedance will decrease, and the measured impedance value of the distance II section protection will decrease, resulting in the protection range decrease. That is, the access of DG affects the measured impedance value Z _M of the distance protection section II. When a fault occurs, the section II protection of the upstream line will refuse to operate, so that the sensitivity of the distance protection cannot meet the requirements.

Aiming at this problem, some studies have also been done in the prior art, and some methods have been proposed.

In the patent document [1], the main method is to improve the current protection method to protect the feeder with distributed power supply. However, there is no mention of improved methods for distance protection on the issue of new energy access.

In the technical literature [2], the influence of the distributed power supply on the distance protection is analyzed, so that the sensitivity of the distance protection is reduced, and when a fault occurs, the distance protection refuses to operate. However, only the impact of distributed power generation on distance protection is analyzed but there is no corresponding solution.

In the technical literature [3], the protection solution along with the DG access distance is mentioned, but the setting value of the protection needs to be modified every time the DG protection is connected. The existing problem is that every time a DG is connected, it is necessary to re-adjust and modify the fixed value of the distance protection protection, which brings trouble to the setting work of the given value.

Patent literature [1][CN101515715A]

Technical literature [2] Impact of distributed power generation on distance protection and reclosing of substations [Power System Protection and Control, Volume 38, Issue 20, 217-219];

Technical literature [3] Application of distance protection in distribution network system with distributed power generation [Electrical Application, Volume 25, Issue 12, 2006, 56-60]

However, according to the analysis conclusions drawn from the known technologies, such as the technical literature [2] "Influence of Distributed Power Generation on Distance Protection and Reclosing of Substations", the access of DG has no effect on the distance protection section I and section III, so it is necessary to carry out What is improved is the second section protection in the distance protection.

Contents of the invention

The present invention is proposed in response to these problems, and provides a distance protection device and method in a distribution network containing distributed power sources. Considering the impact of distributed energy access on the distance protection in the distribution network, the distance protection, In particular, the protection of stage II is not affected by DG and can operate correctly.

One aspect of the present invention provides a distance protection device in a distribution network containing distributed power sources, which is arranged on the feeder between the busbars of the distribution network, for the feeder and the lower feeder adjacent to the feeder The primary feeder implements the first stage distance protection and the second stage distance protection whose range is larger than the first stage distance protection, wherein,

Assume that the feeder equipped with the distance protection device is the first feeder, the next-level feeder adjacent to the first feeder is the second feeder, the end of each feeder near the upper-level feeder is the first end, and the end of each feeder near the One end of the next level feeder is the second end,

The distance protection device includes:

The first impedance relay obtains the negative-sequence impedance to ground of the first end of the first feeder according to the negative-sequence voltage and negative-sequence current at the first end of the first feeder;

The second impedance relay obtains the negative-sequence impedance of the second end of the first feeder to ground based on the negative-sequence voltage and negative-sequence current at the second end of the first feeder; and,

The distance protection judging device compares the magnitude of the negative sequence current at the first end of the first feeder with the negative sequence current at the first end of the second feeder if the first distance protection does not operate when a fault occurs , the side with the larger amplitude is judged as the faulty line, and,

If the fault line is the first feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the first feeder to ground, and implement the second distance protection after a predetermined time delay,

If the fault line is the second feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the second feeder to ground, and the determined fault location is within the range of the second distance protection In the case of delaying the specified time, implement the second stage of distance protection.

Another aspect of the present invention provides a distance protection method in a distribution network containing distributed power sources. A distance protection device is arranged on the feeder between the busbars of the distribution network to protect the feeder and the The next-level feeder adjacent to the feeder implements the first stage distance protection and the second stage distance protection whose range is larger than the first stage distance protection, wherein,

Assume that the feeder equipped with the distance protection device is the first feeder, the next-level feeder adjacent to the first feeder is the second feeder, the end of each feeder near the upper-level feeder is the first end, and the end of each feeder near the One end of the next level feeder is the second end,

The distance protection methods include:

The step of obtaining the negative-sequence impedance of the first end of the first feeder to ground according to the negative-sequence voltage and negative-sequence current at the first end of the first feeder;

The step of obtaining the negative-sequence impedance of the second end of the first feeder to ground according to the negative-sequence voltage and negative-sequence current at the second end of the first feeder;

When a fault occurs, if the first distance protection does not operate, compare the magnitude of the negative-sequence current at the first end of the first feeder with the negative-sequence current at the first end of the second feeder. Steps for determining a faulty line by one of the parties; and,

If the fault line is the first feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the first feeder to ground, and implement the second distance protection after a predetermined time delay,

If the fault line is the second feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the second feeder to ground, and the determined fault location is within the range of the second distance protection In the case of delaying the specified time, implement the second step of distance protection.

According to the present invention, due to the application of the negative sequence network for analysis, due to the use of negative sequence current fault line selection and the use of negative sequence impedance at both ends of the feeder to measure the fault location, it is possible to accurately determine the specific distance between the fault line and the occurrence of the fault without Affected by DG access, it can especially ensure the normal operation of the distance protection of section II.

Description of drawings

Fig. 1 shows a schematic diagram of the principle of distance protection in a distribution network containing distributed power sources according to the present invention.

Figure 2 shows the grid structure diagram when the distributed power generation is connected to the distribution network.

FIG. 3 shows a diagram in which the power grid structure in FIG. 1 connected to the distributed power supply DG is equivalent to a negative-sequence network.

FIG. 4 is a block diagram showing the structure of the distance protection device 100 of the present invention.

FIG. 5 is a flow chart showing a control flow performed by the distance protection judging device 103 in the distance protection device 100 of the present invention installed on the line MN which is the first feeder.

Fig. 6 shows a schematic diagram of a topological grid connected by multiple DGs.

Fig. 7 is a diagram for explaining distance protection currently used in a power distribution network.

Detailed ways

First, the technical idea and principle of the present invention will be described.

In the present invention, considering the impact of distributed energy access on the distance protection in the distribution network, in order to make the distance protection, especially the II-segment protection not affected by DG, and to operate correctly, the distance protection is mainly implemented through the following steps Protect.

(1) When the line fails, first compare the I-section protection of the first feeder, if it is within the I-section protection range, the I-section will act. The action criterion of the distance protection in section I is consistent with the existing distance protection criterion, that is, Z _M <K _rel *Z _MN . If it is not within the protection scope of paragraph I, then go to judge whether it is within the protection scope of paragraph II.

Wherein Z _M is the measurement impedance, as background technology explains, obtains by the ratio U _m /I _m of measurement voltage and measurement current; Z _MN is the line total impedance of the feeder (hereinafter referred to as the 1st feeder) between busbar MN; K _rel is the compensation coefficient. According to the practice of distance protection, it can be 0.8-0.85, and the specific value can be matched with other protection.

(2) Section II protection protects two parts, the end part of the first feeder and a part of the feeder between the busbar NP (hereinafter referred to as the second feeder). Firstly, use the known negative-sequence current fault line selection method to judge whether the fault is at the end of the first feeder or on the second feeder. Since the amplitude of the negative-sequence current on the faulty line of the first feeder and the second feeder is the largest, the amplitude of the negative-sequence current is used first to select the fault line and find out the fault line. As a method of using the amplitude of the negative sequence current to select the fault line, for example, the known amplitude scalar product method can be used.

(3) If the result of the fault line selection is that the faulty line is on the line (the first feeder) installed by the distance protection, according to the cooperation of the I-section protection and the II-section protection of the distance protection, since the fault is not within the scope of the I-section protection, Then stage I protection will not operate, so after a delay of 0.5S, let stage II protection act. Furthermore, the location of the fault point can be determined by calculating the double-terminal negative-sequence impedance of the first feeder.

(4) If the result of fault line selection is that the fault line is on the second feeder, which is the adjacent line of the protection installation line at this distance, further calculate the double-ended negative sequence impedance of the second feeder to determine the location of the fault point. If the location of the fault point Within the protection range of the second stage of the distance protection, let the second stage protection act, otherwise it will not act.

As we all know, in the power distribution system, the appearance of positive sequence, negative sequence and zero sequence is to analyze the asymmetry of the system voltage and current, and decompose the asymmetrical components of the three phases into symmetrical components, that is, positive, negative sequence and Zero sequence components. For an ideal power system, due to the three-phase symmetry, that is, there are only positive-sequence components in the normal state, so the values of the negative-sequence and zero-sequence components are both zero. And when the system fails, the three phases become asymmetrical. At this time, at least one of the negative sequence and zero sequence components with amplitude can be decomposed from the measured current through calculation. Therefore, by detecting these two If there is a component that should not normally appear, you can know that the system has failed. In addition, the negative sequence current and negative sequence voltage can also be directly measured through a dedicated negative sequence current/voltage sensor.

As the reason for using the magnitude of the negative sequence current for fault line selection, the following three aspects should be considered.

A. When an asymmetrical short circuit occurs, the negative sequence voltage is the highest at the fault point, and the farther away from the fault point, the lower the voltage. For a certain fault point, the flow direction of the negative sequence current is determined, and it flows from the fault point to the lowest point of the negative sequence voltage, which has the advantages of single power supply and radial shape.

B. The negative sequence network has the same network structure and similar component parameters as the positive sequence network. When a fault occurs, the negative sequence component analysis method is used to analyze the fault without changing the network structure.

C. And the negative sequence current and voltage exist only in the negative sequence network, and the negative sequence network has nothing to do with the fault type. Various asymmetrical faults can be analyzed by applying the negative sequence component analysis method, such as: single-phase ground fault, two-phase ground fault, two-phase short-circuit fault, etc. The calculation method is not restricted by the type of fault.

Generally speaking, the I-stage protection in the distance protection can only protect 80% to 85% of the total length of the line; the protection range of the II-stage protection is the entire length of the line and extends to a part of the next line, as a backup for the I-stage protection Protection, II protection has a time delay compared with I protection, generally 0.5 seconds. The so-called cooperation between the I-stage protection and the II-stage protection of the distance protection means that if there is a fault within the I-stage protection range, the I-stage protection will be activated; if the I-stage protection refuses to operate, the second-stage protection will be activated after a delay of 0.5 seconds; if If the fault is outside the protection range of section I and within the protection scope of section II, then section I will not act and section II will act.

In the present invention, a double-terminal impedance relay is also used to determine the fault distance. The so-called double-terminal impedance relay is to install impedance relays at both ends of the feeder of the transmission line, measure the current and voltage values at both ends, and then calculate the impedance value to obtain the fault distance.

Fig. 1 shows a schematic diagram of the principle of distance protection in a distribution network containing distributed power sources according to the present invention. For the convenience of illustration, the same distribution network model as in Fig. 7 is used. M, N, and P are the busbars connected to the line, 1 is the input energy of the power grid, and K is the line fault location. The ranges of section I protection, section II protection and section III protection are shown in Figure 1.

111 is a transformer used to measure the voltage on the bus M, U _m2 is the negative sequence component in the measured voltage, 112 is a current sensor used to measure the feeder current at the end of the bus M, and I _m2 is the negative sequence component in the measured current. ordinal component.

Add the measured negative-sequence voltage _Um2 and negative-sequence current _Im2 to the impedance relay 101, and the impedance relay 101 obtains their ratio, that is, according to the obtained negative-sequence voltage Um2 and negative-sequence current _Im2 , calculate the bus The negative-sequence impedance Z _T12 of terminal M to ground =U _m2 /I _m2 .

113 is a transformer used to measure the voltage on the bus N, U _n2 is the negative sequence component in the measured voltage, 114 is a current sensor used to measure the feeder current at the N end of the bus N, and I _n2 is the negative sequence component in the measured current. ordinal component.

Add the measured negative-sequence voltage U _n2 and negative-sequence current I _n2 to the impedance relay 102, and the impedance relay 102 obtains their ratio, that is, according to the obtained negative-sequence voltage U _n2 and negative-sequence current I _n2 , find Negative-sequence impedance Z _T22 to ground at the N terminal of the bus bar =U _n2 /I _n2 .

In addition, although not shown in the figure, the NP section of the feeder is also provided with the same distance protection as the MN section in the figure.

Figure 2 shows the grid structure diagram when the distributed power generation is connected to the distribution network. Here, it is assumed that the distributed power supply DG204 is connected to the bus M and provides a current _IDG to M. 201 and 202 are circuit breakers, which operate according to the control signal sent by the distance protection, so as to cut off the faulty line.

FIG. 3 shows a diagram in which the power grid structure in FIG. 1 connected to the distributed power supply DG is equivalent to a negative-sequence network. The negative sequence impedance of DG is included in Z _T12 and Z _T22 . By measuring Z _T12 and Z _T22 , DG has been taken into account. Therefore, no matter how many DGs are connected, the correct fault distance can be calculated through the negative sequence impedance at both ends. In the transmission line, the negative sequence impedance is equal to the positive sequence impedance, so the distance protection can operate normally without modifying the setting value of the distance protection. In the present invention, this method of measuring the fault distance is called double-terminal fault distance measurement.

Next, how to calculate the impedance from the fault point to the corresponding bus by applying the double-terminal fault location is described. In Figure 3, U _d2 is the negative sequence voltage, I _m2 is the negative sequence current at the M terminal, U _m2 is the negative sequence voltage at the M terminal to ground, I _n2 is the negative sequence current at the N terminal, and U _n2 is the negative sequence current at the N terminal to ground. sequence voltage. Z _T12 is the negative sequence impedance of the M terminal to the ground, and Z _T22 is the negative sequence impedance of the N terminal to the ground. If it is assumed that the negative-sequence impedance value Z _MN2 of the feeder line from bus M to bus N = R+jX, where R is the negative-sequence resistance value per unit length of the line, and X is the negative-sequence reactance value per unit length of the line, then Z _m2 is the fault point Negative sequence impedance to terminal M (Z _MN2 m). Here, let m be the percentage of the distance from the fault point K to the M-end bus in the total distance from the bus M to the bus N, that is, 0<m<1, then n=(1-m) is the distance from the fault point to the N-end bus Percentage of the total distance from bus M to bus N. Z _n2 is the negative sequence impedance from the fault point to the N terminal (Z _MN2 (1-m)). In this case, the following formulas (1) and (2) hold

U _d2 ＝I _m2 (Z _m2 +Z _T12 ) (1)

U _d2 ＝I _n2 (Z _n2 +Z _T22 ) (2)

Through the transformer and current sensors 111-114 in Fig. 1, I _m2 , U _m2 , I _n2 , U _n2 are measured respectively, and according to the above four variables, the following equations (3) and (4) can be used to calculate the M terminal to ground The negative sequence impedance Z _T12 of the N terminal and the negative sequence impedance Z _T22 of the N terminal to the ground.

Z _T12 ＝U _m2 /I _m2 ＝R _T12 +JX _T12 (3)

Z _T22 ＝U _n2 /I _n2 ＝R _T22 +JX _T22 (4)

Like this, only m is unknown number in above formula (1), (2), other each parameter is all known through measuring, makes formula (1) and formula (2) get the square of modulus value:

|I _m2 | ² |Z _MN2 m+R _T12 +jX _T12 | ² ＝|I _n2 | ² |Z _MN2 (1-m)+R _T22 +jX _T22 | ²

After simplification:

Am ² +Bm+C=0

in:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; RR</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; XX</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; RR</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; XX</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; XX</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; RR</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

Solving the equation gives: $m=(-B\&PlusMinus;\sqrt{B^2-4\mathrm{AC}})/\left(2A\right)$

By substituting the relevant parameters that have been measured, it can be obtained that m has one and only one value between (0, 1). Then, through the following formula (5), the negative-sequence impedance measurement impedance Z _M2 from the fault point to the M terminal can be obtained.

Z _M2 = Z _MN m = (R+jX)m (5)

According to the obtained Z _M2 , pass the action criterion Z _M2 <K _rel (Z _MN2 +K _b *Z _setI ) of stage II protection,

Wherein Z _setI =K _rel Z _NP2 can judge whether the stage II protection should be activated at this time.

Among them, Z _NP2 is the negative-sequence impedance of the feeder between NPs, that is, the second feeder; K _b is the branch coefficient. In order to ensure the selectivity in any case, K _b should choose the minimum value in any case. K _rel is the compensation coefficient, which can be 0.8-0.85, and the specific value can be matched with other protections.

Based on this criterion, according to the distance protection of the first feeder, the stage II protection of the distance protection of the first feeder cooperates with the stage I protection of the second feeder, that is, if the second feeder fails, the stage I of the distance protection of the second feeder is judged first, and if it does not act, the stage I protection of the second feeder 1. Section II of the distance protection of the feeder operates with a delay of 0.5s. Here, 0.5s is just an example, and it can also be set to other values according to the coordination of distance protection.

FIG. 4 is a block diagram showing the structure of the distance protection device 100 of the present invention. The distance protection device 100 includes: an impedance relay 101 , an impedance relay 102 and a distance protection judging device 103 .

The impedance relay 101 obtains the ground negative sequence voltage U _m2 and negative sequence current I _m2 of the M bus terminal of the first feeder from the transformer 111 and the current sensor 112, and calculates the ground negative sequence impedance Z _T12 of the M bus terminal of the first feeder .

The impedance relay 102 obtains the ground negative sequence voltage U _n2 and negative sequence current I _n2 of the N bus terminal of the first feeder line from the transformer 113 and the current sensor 114, and calculates the ground negative sequence impedance Z _T22 of the N bus terminal of the first feeder line .

The distance protection judging device 103, in addition to obtaining the negative-sequence impedance Z _T12 and Z _T12 to ground calculated by the impedance relays 101 and 102, also obtains the double-terminal impedance relay of the feeder NP from the distance protection device set on the feeder NP of the next stage. Measure the impedance and the negative sequence current at the bus N terminal of the feeder NP.

When a fault occurs, if the first stage distance protection does not operate, compare the negative sequence current Im2 of the M bus terminal of the feeder MN with the negative sequence current Im2 of the N bus terminal of the feeder NP, and determine the one with the larger amplitude as the fault line. If the fault line is an MN feeder, determine the fault location according to the negative-sequence impedance Z _T12 and Z _T12 of the MN feeder to ground at both ends, and implement the second distance protection after a specified time delay. If the fault line is the feeder NP, determine the fault location according to the negative-sequence impedance of the two ends of the second feeder to the ground. If the determined fault location is within the range of the second distance protection, implement the second distance Protect. That is, the circuit breaker 120 is controlled to cut off the faulty line.

FIG. 5 is a flow chart showing a control flow performed by the distance protection judging device 103 in the distance protection device 100 of the present invention installed on the line MN which is the first feeder.

First of all, after a fault occurs, in step 501, it is confirmed whether the I-section protection of the first feeder should act according to the criterion of the I-section protection, that is, Z _M <K _rel *Z _MN , that is, to determine whether the fault point is in the I-section protection within the range. If the I-segment protection should act, that is, the fault point is within the range of the I-segment protection, go to step 506, and determine the location of the fault point according to the ratio of Z _M to Z _MN . Otherwise, go to step 502.

In step 502, according to the negative-sequence currents of the first feeder and the adjacent second feeder, the side with the larger negative-sequence current is confirmed as the faulty line, and the faulty line selection is completed.

In step 503, it is judged whether the fault point is on the first feeder, which is the feeder where the distance protection is installed. If it is on the first feeder, go to step 504, otherwise go to step 505.

In step 504, the above-mentioned double-ended fault distance measurement is performed on the first feeder. Since the section I protection of the distance protection installed on the first feeder can protect 80% of the lines in the first feeder, in this step, the specific location of the fault point in the 80%-100% part of the first feeder can be determined.

In step 505, the above-mentioned double-ended fault distance measurement is performed on the second feeder, and the specific location of the fault point on the second feeder is determined.

In step 507, it is determined whether the fault point is within the protection range of stage II.

In step 508, delay 0.5s.

In step 509, the circuit breaker is operated to cut off the faulty line.

In step 510, the location of the fault point is reported to the management center of the distribution network or the like.

According to the present invention, considering the impact of distributed energy access on the distance protection of the distribution network, the fault line is found by using the amplitude of the negative sequence current for fault line selection, and the double-terminal fault distance measurement is performed according to the negative sequence impedance, Within the protection range of the second section of the distance protection, let the second section protection operate, so that the distance protection will not be affected by DG and can operate correctly.

In addition, when multiple DGs are connected, since multiple DGs provide short-circuit current to the fault point, the measured current will be affected multiple times, and the measured impedance will be more inaccurate. However, according to the present invention, due to the application of the negative-sequence network for analysis, according to the characteristics of the negative-sequence network, that is, the negative-sequence voltage is the highest at the fault point when an asymmetrical short circuit occurs, and the farther away from the fault point, the lower the voltage, so for the determined At the fault point, the flow direction of the negative sequence current is determined, and it flows from the fault point to the lowest point of the negative sequence voltage. That is to say, the negative sequence impedance of DG is included in Z _T12 and Z _T12 , by calculating Z _T12 and Z _T12 , all DGs have been taken into account, and the fault distance can be calculated accurately. In other words, the present invention is also suitable for the connection of multiple DGs. Due to the use of negative-sequence current fault line selection and double-terminal negative-sequence impedance measurement method, the fault line and the specific distance of the fault can be accurately determined, no matter how many DGs are connected. The average input can ensure the normal operation of the protection of the distance section II.

In addition, the present invention can also be applied in the topological grid structure as shown in FIG. 6 . In the figure, Load1 Load2 Load3 represent loads, 301, 302, 303, 304, 305 are circuit breakers, 306, 307 are short-circuit faults; 308, 309 are distributed power access points.

As mentioned above, since the negative sequence impedance of DG is included in Z _T12 and Z _T22 , by calculating Z _T12 and Z _T22 all DGs have been taken into account, the fault distance can be calculated accurately. Therefore, the present invention is also suitable for the access situation of multiple DGs shown in FIG. 6 .

So far, the present invention has been described in conjunction with the above-mentioned embodiments and modifications, but the present invention is not limited thereto, and any changes and combinations can be made within the scope not departing from the gist of the present invention, and these should be understood as included in within the scope of the present invention.

Claims (6)

1. A distance protection device in a distribution network containing a distributed power supply, which is configured on the feeder between the busbars of the distribution network, and implements the first step on the feeder and the next-level feeder adjacent to the feeder. 1-stage distance protection and a 2nd-stage distance protection with a range larger than said 1st-stage distance protection, wherein, Assume that the feeder equipped with the distance protection device is the first feeder, the next-level feeder adjacent to the first feeder is the second feeder, the end of each feeder near the upper-level feeder is the first end, and the end of each feeder near the One end of the next level feeder is the second end, The distance protection device includes: The first impedance relay obtains the negative-sequence impedance to ground of the first end of the first feeder according to the negative-sequence voltage and negative-sequence current at the first end of the first feeder; The second impedance relay obtains the negative-sequence impedance of the second end of the first feeder to ground based on the negative-sequence voltage and negative-sequence current at the second end of the first feeder; and, The distance protection judging device compares the magnitude of the negative sequence current at the first end of the first feeder with the negative sequence current at the first end of the second feeder if the first distance protection does not operate when a fault occurs , the side with the larger amplitude is judged as the faulty line, and, If the fault line is the first feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the first feeder to ground, and implement the second distance protection after a predetermined time delay, If the fault line is the second feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the second feeder to ground, and the determined fault location is within the range of the second distance protection In the case of delaying the specified time, implement the second stage of distance protection. 2. The distance protection device according to claim 1, characterized in that, The distance protection judging device obtains the negative sequence current of the first end of the second feeder and the negative sequence current of the first end and the second end of the second feeder from the distance protection device arranged on the second feeder. sequence impedance. 3. The distance protection device according to claim 1, characterized in that, The distance protection device reports the determined fault location to the management center of the distribution network. 4. The distance protection device according to claim 1, characterized in that, The distribution network includes one or more distributed power sources. 5. The distance protection device according to claim 1, characterized in that, If U _d2 is set as the negative sequence voltage, I _m2 is the negative sequence current of the first terminal, I _n2 is the negative sequence current of the second terminal, and Z _m2 is the negative sequence impedance from the fault point to the first terminal (Z _MN2 m), Z _n2 is the negative-sequence impedance (Z _MN2 (1-m)) from the fault point to the second end, Z _T12 is the negative-sequence impedance to ground of the first end, and Z _T22 is the pair of the second end Ground negative sequence impedance, Z _MN2 is the negative sequence impedance value of the feeder, m is the percentage of the distance from the fault point to the first end to the total distance of the feeder, The distance protection device, by solving the equation group composed of formula (1), (2), U _d2 ＝I _m2 (Z _m2 +Z _T12 ) (1) U _d2 ＝I _n2 (Z _n2 +Z _T22 ) (2) To determine the fault location m. 6. A distance protection method in a distribution network containing a distributed power supply. A distance protection device is configured on the feeder between the busbars of the distribution network to protect the feeder and the next feeder adjacent to the feeder. The level feeder implements the first section distance protection and the second section distance protection whose range is larger than the first section distance protection, wherein, Assume that the feeder equipped with the distance protection device is the first feeder, the next-level feeder adjacent to the first feeder is the second feeder, the end of each feeder near the upper-level feeder is the first end, and the end of each feeder near the One end of the next level feeder is the second end, The distance protection methods include: The step of obtaining the negative-sequence impedance of the first end of the first feeder to ground according to the negative-sequence voltage and negative-sequence current at the first end of the first feeder; The step of obtaining the negative-sequence impedance of the second end of the first feeder to ground according to the negative-sequence voltage and negative-sequence current at the second end of the first feeder; When a fault occurs, if the first distance protection does not operate, compare the magnitude of the negative-sequence current at the first end of the first feeder with the negative-sequence current at the first end of the second feeder. Steps for determining a faulty line by one of the parties; and, If the fault line is the first feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the first feeder to ground, and implement the second distance protection after a predetermined time delay, If the fault line is the second feeder, determine the fault location according to the negative-sequence impedance of the first end and the second end of the second feeder to ground, and the determined fault location is within the range of the second distance protection In the case of delaying the specified time, implement the second step of distance protection.