CN100395933C - A Distinguishing Method of Positive and Negative Sequence Fault Component Direction and Zero Sequence Power Direction - Google Patents

Abstract

The present invention relates to a method for judging a positive-negative sequence fault component direction and a zero sequence power direction, which comprises the following steps that fault component voltage and current which are protected and measured in real time are input into a computer through a D/A converter and the impedance of a fault component is obtained; On the plane of the impedance, a perpendicular line of a corresponding line segment of the line impedance is made at the point which has a distance of the 0.4-time line impedance from an origin on the basis of the impedance of a protected line; thereby, a reactance line is obtained on the plane of the impedance offline; a fault type is judged according to the upper position and the lower position of the reactance line of an impedance coordinate, if the impedance coordinate is at the lower part of the reactance line, a positive direction fault is judged; otherwise, a negative direction fault is judged; a relay element is started to work according to the fault type, and then the corresponding protection is carried out. The present invention improves the action reliability of a negative direction element, has the higher sensitivity to various faults, improves the reliability of the protection, and is more easily achieved. The present invention is suitable for protecting directional elements of a zero sequence power and a negative sequence power of a high-voltage transmission line, and the directional elements of the compound quantity reflecting the positive sequence fault component and the negative sequence component.

Description

A Distinguishing Method of Positive and Negative Sequence Fault Component Direction and Zero Sequence Power Direction

technical field

The invention relates to the technical field of power system automation, in particular to a method for discriminating the direction of positive and negative sequence fault components and the direction of zero sequence power, which improves the reliability of the operation of the components in the reverse direction on the premise of ensuring the sensitivity of the components in the forward and reverse directions.

Background technique

The directional element, that is, the relay, plays an important role in modern relay protection devices. It has been widely used from simple directional overcurrent protection to fast main protection of complex ultra-high voltage lines. There are three traditional directional elements: 90° wiring directional relays for voltage and current protection, zero-sequence power directional relays for grounding protection, and negative-sequence power directional relays for high-frequency protection. The characteristics of the first type of directional element are affected by the transition resistance of the fault point, and the sensitivity is reduced when a short circuit occurs through the transition resistance, and there is a voltage dead zone when the three-phase outlet is short-circuited; it is used in the longitudinal direction protection and directional zero-sequence protection. Negative-sequence and zero-sequence power directional elements essentially respond to fault components, and have obvious advantages over traditional directional elements. However, the negative-sequence component of the system appears only when a three-phase asymmetrical short circuit occurs, and the zero-sequence component appears only when a grounding short circuit occurs, that is to say, none of them can respond to a three-phase symmetrical short circuit; It is not affected by the system load and the transition resistance of the fault point, and the action sensitivity is high. "Positive Sequence Fault Components and Its Application in Relay Protection" published by An Yanqiu and Gao Houlei in the 8th issue of "Journal of Electric Power System and Its Automation" in 2003 disclosed a direction suitable for various fault components Discrimination method. Wang Kai published "Application of Positive Sequence Fault Component Elements in Relay Protection of EHV Transmission Lines" published in "Electrotechnical Technology" 2003 (4), using the analytical method to analyze in detail the short circuit of positive sequence fault component elements in measuring high voltage transmission lines inside and outside the area. The theoretical basis of the failure, because the component is not affected by disturbance factors such as system oscillation during measurement, it has a strong anti-interference ability. Therefore, the principle of direction comparison of positive sequence fault components or the combination of positive sequence fault components and negative sequence components is widely used to form the main protection of the line. However, the hidden danger of the positive sequence fault component directional element is that for the positive direction fault, if there is a large system behind the protection installation, when the line fails, the sudden change of the positive sequence voltage is small, which cannot be used for phase comparison. It will affect the reliability of the direction determination of the directional element, and may cause the positive sequence fault component directional element to misjudge the direction and cause the directional high-frequency protection to reject the action.

Contents of the invention

In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for judging the direction of positive and negative sequence fault components and the direction of zero sequence power, so as to improve the operation reliability of the directional element in the opposite direction.

In order to accomplish the above object, the overall technical solution adopted by the present invention is: a method for discriminating the direction of positive and negative sequence fault components and the direction of zero sequence power, comprising the following steps:

Step 1. Input the voltage and current measured by the protection device in real time to the data processing unit of the protection device through the digital-to-analog converter, and detect whether the power line is faulty in real time. If a fault occurs in the line, the protection device enters the fault processing program;

从而求得故障分量的阻抗；Step 2: Obtain the positive sequence voltage and current variation from the current positive sequence voltage and current and the positive sequence voltage and current before the fault

In order to obtain the impedance of the fault component;

Step 3. On the impedance plane, according to the impedance of the protected line, draw a vertical line corresponding to the line segment of the line impedance at a distance of 0.3-0.6 times the line impedance from the origin, so as to obtain the reactance line on the impedance plane;

Step 4. According to the impedance obtained in step 2, calculate the relationship between its coordinates and the upper and lower positions of the reactance line. If it is in the lower part of the coordinate reactance line, it will be judged as a fault in the forward direction; otherwise, it will be judged as a fault in the reverse direction;

Step 5: Start the directional relay element to work according to the determined fault direction, and perform corresponding protection logic judgment.

The vertical line made in step 3 is located at the line impedance 0.3-0.6 times (generally 0.4 times) from the origin.

The present invention has the following advantages: the present invention provides a fault discrimination method for positive and negative sequence fault component directional elements and zero-sequence power directional elements in relay protection of high voltage power grid. Measure the impedance of the fault component after the fault, determine the direction of the fault according to the magnitude of the fault component impedance, and use the reactance line on the impedance plane to replace the original phase comparison criterion, which is equivalent to adding the amplitude comparison on the basis of the phase judgment Components to make up for the defect that misjudgment of the direction will be caused when ΔU ₁ and U ₀ are small, and improve the reliability of the operation of the opposite direction element. It has high sensitivity to various faults, and there is no dead zone; it has clear directionality to various faults, and is not affected by the initial angle and fault distance. The invention effectively improves the reliability of the protection without reducing the sensitivity in the forward and reverse directions, and is easier to realize. The invention preferably solves the problems of sensitivity and misjudgment of the direction of the positive sequence fault component directional element when the end of a long line of a large system fails.

Description of drawings

Fig. 1 is main flowchart of the present invention;

Fig. 2 a is the forward fault schematic diagram of the positive sequence fault component equivalent network of the embodiment of the present invention;

Fig. 2b is a reverse fault schematic diagram of the positive sequence fault component equivalent network of the embodiment of the present invention;

Fig. 3 is impedance plan view;

Fig. 4 is a schematic diagram of the direction judgment action area.

Detailed ways

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

For the analysis of power system faults, the symmetrical component theory and superposition principle can be used for analysis. The three-phase electrical quantity in the system is decomposed into three rotating symmetrical components of positive sequence, negative sequence and zero sequence, and the positive sequence component can be decomposed into the superposition of normal component and fault component when fault occurs.

Please refer to Fig. 1 main flowchart of the present invention, the method for discriminating the positive and negative sequence fault component direction and the zero sequence power direction in the transmission line is as follows:

从而求得故障分量的阻抗；First, the protection device inputs the voltage and current measured in real time to the data processing unit of the protection device through an analog-to-digital converter, and detects whether a fault occurs in the power line in real time. If a fault occurs in the line, the protection device enters a fault processing program; and The positive sequence voltage and current variation is obtained from the current positive sequence voltage and current and the positive sequence voltage and current before the fault

In order to obtain the impedance of the fault component;

Then, on the impedance plane, according to the impedance of the protected line, the line impedance is 0.3-0.6 times (generally 0.4 times) away from the origin as a vertical line corresponding to the line segment, so as to obtain the reactance line on the impedance plane;

Afterwards, according to the obtained impedance, calculate the relationship between its coordinates and the upper and lower positions of the reactance line. If it is below the coordinate reactance line, it will be judged as a fault in the positive direction; otherwise, it will be judged as a fault in the reverse direction;

Finally, according to the direction of the determined fault, the directional relay element is started to work, and the corresponding protection logic is judged.

Embodiment 1: A method for determining the direction of positive sequence fault components. Please refer to Figure 2a and Figure 2b. Figure 2a and Figure 2b show the equivalent network of positive sequence fault components when a simple two-terminal power supply system fails. If the protection of M side is considered, then Figure 2a and Figure 2b are positive Equivalent networks for faults and reverse faults. in the picture is the voltage at point F under normal operating conditions, and ΔZ is the additional fault impedance, which changes with the type of short circuit and the location of the fault point.

According to the above two figures, the following conclusions can be drawn: when the fault occurs in the forward direction:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; sm</span>}}$

In case of failure in the reverse direction:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; sn</span>}}$

是-Z_sm还是Z_L+Z_sn可以判断出是正方向还是反方向故障。From the above two formulas, it can be seen that according to the real-time measured

Whether it is -Z _sm or Z _L +Z _sn can determine whether it is a fault in the forward or reverse direction.

求得的阻抗，在图中阻抗平面上确定是P点还是Q点。P点对应正方向，Q点对应反方向。Please refer to the impedance plane diagram in Figure 3, the key to determine the direction is how to judge the direction according to

The obtained impedance is determined to be point P or point Q on the impedance plane in the figure. Point P corresponds to the positive direction, and point Q corresponds to the reverse direction.

For the protection device, the system impedance Z _sm and Z _sn change with the system operation mode and are unknown parameters. But the impedance of the line to be protected is known, that is, only the line segment 0R in Fig. 3 is known. In order to distinguish the positive and negative directions, a vertical line of the line segment 0R in Figure 3 can be drawn at a certain point to distinguish the positive and negative directions. From this, the direction-judging action area diagram in Figure 4 can be obtained. The vertical line in the figure is 1, and the vertical line Setting it at 0.4ZL can ensure that the sensitivity of the reverse direction element is slightly higher than that of the forward direction element.

make $\mathrm{\&Delta;}{\stackrel{\&CenterDot;}{u}}_1/\mathrm{\&Delta;}{\stackrel{\&CenterDot;}{I}}_1=\mathrm{\&Delta;R}+j\&CenterDot;\mathrm{\&Delta;X},$ ΔR and ΔX can be measured in real time. If the coordinate point (ΔR, ΔX) is on the upper side of straight line 1, it is judged as the reverse direction; if it is on the lower side of 1, it is judged as the positive direction.

Since the impedance of the protected line is known, the vertical foot of the line 1 and the line segment 0R and the slope of the line 1 can be obtained offline, that is, 1 is a known line, and its equation is: aR+bX=c.

Wherein, a, b, and c are known constants, and a>0, R is the abscissa, and X is the ordinate.

The action criterion of the final direction element is as follows

The action criterion of the positive direction element is a·ΔR+b·Δ<c;

The action criterion of the opposite direction element is a·ΔR+b·ΔX>c.

It can be seen from Figure 4 that for long transmission lines, the sensitivity of the positive direction element of the criterion is greatly improved, and the longer the line, the higher the sensitivity. At the same time, the reverse direction element also has a direction judgment margin space corresponding to 0.6Z _L. Under the premise that the impedance of the power system on both sides is the same, the sensitivity of the reverse direction element is still significantly higher than that of the forward direction element.

参考图2a、图2b。Embodiment: a method for discriminating the direction of zero-sequence power components. The fault component used is

Refer to Figure 2a, Figure 2b.

When the positive direction is faulty: ${\stackrel{\&CenterDot;}{u}}_0/{\stackrel{\&CenterDot;}{I}}_0=-Z_{0\mathrm{sm}}$

In case of failure in the reverse direction: ${\stackrel{\&Center\; Dot;}{u}}_0/{\stackrel{\&Center\; Dot;}{I}}_0=Z_{0L}+Z_{0\mathrm{sn}}$

是-Z_0sm还是Z_0L+Z_0sn可以判断出是正方向还是反方向故障。余下的判别方法和正序故障分量方向元件的判别方法完全一样。In the formula, Z _0sm and Z _0sn are the zero-sequence impedance of the systems on both sides of m and n respectively, and Z _0L is the zero-sequence impedance of the line. From the above two formulas, it can be seen that according to the real-time measured

Whether it is -Z _0sm or Z _0L +Z _0sn can determine whether it is a fault in the forward or reverse direction. The rest of the discrimination method is exactly the same as that of the positive sequence fault component directional element.

参考图2a、图2b。Embodiment 2: A method for determining the direction of a negative sequence power component. The fault component used is

Refer to Figure 2a, Figure 2b.

When the positive direction is faulty: ${\stackrel{\&Center\; Dot;}{u}}_2/{\stackrel{\&Center\; Dot;}{I}}_2=-Z_{2\mathrm{sm}}$

In case of failure in the reverse direction: ${\stackrel{\&Center\; Dot;}{u}}_2/{\stackrel{\&Center\; Dot;}{I}}_2=Z_{2L}+Z_{2\mathrm{sn}}$

是-Z_2sm还是Z_2L+Z_2sn可以判断出是正方向还是反方向故障。余下的判别方法和正序故障分量方向元件的判别方法完全一样。In the formula, Z _2sm and Z _2sn are the negative-sequence impedances of the systems on both sides of m and n respectively, and Z _2L is the negative-sequence impedance of the line. From the above two formulas, it can be seen that according to the real-time measured

Whether it is -Z _2sm or Z _2L +Z _2sn can determine whether it is a fault in the forward or reverse direction. The rest of the discrimination method is exactly the same as that of the positive sequence fault component directional element.

For zero-sequence and negative-sequence power directional elements, as well as directional elements that respond to the composite quantity of positive and negative sequence fault components, similar criteria to the above can be used to improve the reliability of the operation of the opposite direction element. Especially for the zero-sequence power directional element, the protection refusal to operate due to the small zero-sequence voltage or current has occurred several times in the field, and the invention can accurately and effectively determine the fault direction.

Finally, it should be noted that the above embodiments are only used to illustrate and not limit the technical solutions of the present invention, although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified Or an equivalent replacement, any modification or partial replacement without departing from the spirit and scope of the present invention shall fall within the scope of the claims of the present invention.

Claims (4)

1. positive-negative sequence fault component direction and zero sequence power direction method of discrimination is characterized in that this method may further comprise the steps:

Step 1, the fault component voltage and current that protective device is measured in real time are input to the data processing unit of protective device through digital to analog converter, and try to achieve the impedance of fault component;

Step 2, on impedance plane, according to the impedance of protected circuit, do the vertical line of the corresponding line segment of line impedance apart from 0.3～0.6 times of line impedance place of initial point, thereby off-line obtains the reactance line on impedance plane;

Step 3, according to the upper-lower position failure judgement type of impedance coordinates at the reactance line, if impedance coordinates in the bottom of its reactance line, then is judged to the positive direction fault, otherwise be judged to reverse direction failure;

Step 4, according to fault type starting relay element work, carry out corresponding protection.

2. positive-negative sequence fault component direction according to claim 1 and zero sequence power direction method of discrimination is characterized in that, following formula is adopted in the impedance of trying to achieve fault component in the step 1:

$\mathrm{\&Delta;}{\stackrel{\&CenterDot;}{U}}_1/\mathrm{\&Delta;}{\stackrel{\&CenterDot;}{I}}_1=\mathrm{\&Delta;R}+j\&CenterDot;\mathrm{\&Delta;X}$

Wherein

Be respectively the positive sequence voltage current change quantity, (Δ R, Δ X) is the coordinate points of impedance on impedance plane, represents resistance and reactance respectively.

3. positive-negative sequence fault component direction according to claim 1 and zero sequence power direction method of discrimination is characterized in that, the vertical line in the described step 2 is positioned at 0.4 times of line impedance place of impedance plane map range initial point.

4. positive-negative sequence fault component direction according to claim 3 and zero sequence power direction method of discrimination, it is characterized in that described step 3 further comprises: with the coordinate of positive sequence fault component impedance correspondence on impedance plane the declaring that measures as positive and negative direction component to actuating quantity.

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