CN104134976B - Fault identification method in power transmission line distance protection - Google Patents

Abstract

The invention provides a fault identification method in power transmission line distance protection, which comprises the following steps: acquiring three-phase voltage and three-phase current at a protection installation position; is determined byPositive sequence voltage, positive sequence current, negative sequence current and zero sequence current with phases as references; determining a current asymmetry at the protective installation; determining an included angle between the positive sequence voltage and the positive sequence current; and identifying the fault according to the plane of the current asymmetry. The comprehensive utilization of current asymmetry andthe characteristics realize fault identification in distance protection and improve the action performance of the existing power transmission line distance protection in the process of fault and overload in oscillation.

Description

A Fault Identification Method in Transmission Line Distance Protection

technical field

The invention relates to a method in the field of distance protection, in particular to a fault identification method in the distance protection of transmission lines.

Background technique

The distance protection is divided into three sections. Among them, distance I and II section, after 150ms after the fault is opened, enter the oscillation lock. The increase of the load and the transfer of the load after the line fault will cause the line overload. Area without power.

In the prior art, the re-opening condition of oscillation blocking fault is to use m (open asymmetric fault) and (open symmetrical faults), for asymmetrical faults, when the transition resistance of a single-phase ground fault is large, it cannot be opened. It is to set the load limit line on the impedance plane to avoid the load, and this method will sacrifice the sensitivity of the distance protection. As the load continues to increase, the action area of the distance protection will be greatly reduced. The range of resistance change is large. When the transition resistance is large, due to the influence of the load limit line, the distance protection will refuse to operate, and the ability of the distance protection to withstand transition resistance will be greatly weakened.

Therefore, it is necessary to provide a fault identification method in distance protection of transmission lines that can quickly open distance protection, improve the ability of distance protection to withstand transition resistance, and overcome the shortcomings of traditional methods that only use a single feature.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a fault identification method in distance protection of transmission lines, which uses the current asymmetry m-positive sequence voltage cosine component plane, using both m and The two kinds of features identify line faults, and can quickly open the distance protection when a line fault occurs during the oscillation blocking period, which improves the sensitivity of asymmetric fault opening and the rapidity of symmetrical fault opening.

The solution adopted to achieve the above purpose is:

A method for identifying faults in distance protection of transmission lines, the improvement of which is that the method includes the following steps:

I. Obtain the three-phase voltage and three-phase current at the place where the protection is installed;

II. Determine to Phase-based positive sequence voltage, positive sequence current, negative sequence current and zero sequence current;

III. Determine the current asymmetry at the protective installation;

IV, determining the angle between the positive sequence voltage and the positive sequence current;

V. Carry out fault identification according to the plane of current asymmetry.

Further, in the step II, according to the three-phase voltage and the three-phase current respectively determined by the following formula Phase-based positive sequence current negative sequence current Zero sequence current and positive sequence voltage

In the formula, for phase current; are the currents of the other two phases respectively; for phase voltage; for phase lagging phase voltage, for The leading phase voltage of the phase. , is the lagging phase voltage of φ phase, is the leading phase voltage of φ phase.

Further, in the step III, the current asymmetry m is determined according to the following formula:

In the formula, respectively Phase-based positive sequence current, negative sequence current, zero sequence current.

Further, in the step IV, the angle between the positive sequence voltage and the positive sequence current is determined as follows:

In the formula, is the positive sequence voltage based on φ phase, is the positive sequence current based on φ phase; φ ₁ is the positive sequence voltage and positive sequence current the angle between, is the positive sequence voltage amplitude, It is the value per unit, and the benchmark is the φ-phase voltage at the place where the protection is installed.

Further, in the step V, fault identification is performed according to the current asymmetry degree and the current asymmetry degree plane at the protection installation site.

Further, said step V includes the following steps:

S501. Judgment If it is established, if it is established, it will be judged as an asymmetric fault, and the distance protection will be enabled, otherwise, go to step S502;

S502. Judgment If it is established, if it is established, the current asymmetry plane of the previous cycle will be added Otherwise, block the distance protection;

S503. Comparing the current asymmetry plane of the previous cycle and 0.3pu, if If it is judged as a symmetrical fault, open distance protection;

like Then delay open distance protection section I and II, and open distance protection section III, the unit of pu is per unit value.

Compared with the prior art, the present invention has the following beneficial effects:

1. The method of the present invention comprehensively utilizes the current asymmetry and U1cosφ characteristics to improve the action performance of the existing transmission line distance protection in the event of a fault or overload during oscillation;

2. The method of the present invention can accurately identify asymmetrical faults and symmetrical faults, and at the same time improve the resistance to transition resistance of grounding distance protection;

3. In the method of the present invention, there is no need for manual adjustment, which avoids false adjustment;

4. The method of the present invention is of great significance to the safe and stable operation of the power grid and the expansion of the scope of limiting accidents;

5, a kind of based on that the present invention provides Two-dimensional plane, comprehensive use of current asymmetry and Two kinds of characteristics identify symmetrical faults and asymmetrical faults, and the method of quickly opening distance protection overcomes the shortcomings of traditional methods that only use a single characteristic, and at the same time improves the ability of distance protection to withstand transition resistance, which is of great significance to the safe and stable operation of the power grid and the expansion of the scope of limited accidents. of great importance;

6. The present invention is designed for the re-opening of the transmission line distance protection during the oscillation blocking period, and utilizes The plane characterizes line faults. Compared with traditional open conditions, for asymmetric faults, using m and combined can improve ground faults via larger transition resistances, utilizing Variations can increase the opening speed of symmetric faults.

Description of drawings

Fig. 1 is method flowchart of the present invention;

Fig. 2 is current asymmetry m and relation chart.

detailed description

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

As shown in Figure 1, Figure 1 is a flow chart of the method of the present invention, a fault identification method in the distance protection of a transmission line provided by the present invention includes the following steps:

Step 1. Obtain the three-phase voltage and three-phase current at the place where the protection is installed;

Step 2. Determine to Phase-based positive sequence voltage, positive sequence current, negative sequence current and zero sequence current;

Step 3, determining the current asymmetry at the protection installation site;

Step 4. Determine the angle between the positive sequence voltage and the positive sequence current

Step 5: Carry out fault identification according to the current asymmetry plane.

In step 1, the voltage sensor and the current sensor are used to obtain the three-phase voltage and three-phase current at the protection installation site respectively.

In step 2, according to the three-phase voltage and three-phase current, the following formulas are used to determine Phase-based positive sequence current negative sequence current Zero sequence current and positive sequence voltage

The positive sequence current, negative sequence current, zero sequence current and positive sequence voltage based on phase A are as follows:

The positive sequence current, negative sequence current, zero sequence current and positive sequence voltage based on phase B are as follows:

The positive sequence current, negative sequence current, zero sequence current and positive sequence voltage based on phase C are as follows:

In step 3, the current asymmetry degree is determined according to the formula:

In the formula, They are the positive-sequence current, negative-sequence current and zero-sequence current based on any phase, respectively.

In step 4, the angle between the positive sequence voltage and the positive sequence current is determined according to the following formula:

In the formula, for phase-based positive sequence voltage, for Phase-based positive sequence current; is the positive sequence voltage and positive sequence current the angle between, for phase-based positive sequence voltage, for phase-based positive sequence current, The value of is A, B, C three-phase, is the per unit value, and the benchmark is the protection installation place phase voltage.

In step five, fault identification is performed according to the current asymmetry degree and the current asymmetry degree plane at the protection installation site. Specifically include the following steps:

S501. Judgment If it is established, if it is established, it will be judged as an asymmetric fault, and the distance protection will be enabled, otherwise, go to step S502;

S502. Judgment If it is established, if it is established, the current asymmetry plane of the previous cycle will be added Otherwise, block the distance protection;

S503. Comparing the current asymmetry plane of the previous cycle and 0.3pu, if If it is judged as a symmetrical fault, open distance protection;

like Then open the distance protection sections I and II with a delay, and open the distance protection section III directly, and the unit of pu is per unit value.

As shown in Figure 2, Figure 2 is the current asymmetry m and Relationship diagram; the horizontal axis is the current asymmetry degree m, and the vertical axis is the cosine component of the positive sequence voltage Among them, the current asymmetry degree m represents the asymmetric fault, Characterize symmetric faults using both m and Can characterize the high-resistance ground fault, where the mathematical expression of the arc The right side of the curve is An asymmetric fault is represented on the left, a symmetrical case (normal operation or a symmetrical fault) is represented on the left.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than limit the scope of protection thereof. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation of the application, but these changes, modifications or equivalent replacements are all within the protection scope of the pending claims of the application.

Claims (3)

1. in a kind of transmission line distance protecting fault recognition method it is characterised in that：The method comprising the steps of：

I, the three-phase voltage obtaining protection installation place and three-phase current；

II, determine withPositive sequence voltage on the basis of phaseForward-order current, negative-sequence current and zero-sequence current；

III, determine the current asymmetry degree m of described protection installation place：In formula,Point Be not withForward-order current on the basis of phase, negative-sequence current, zero-sequence current,

IV, determine angle between described positive sequence voltage and described forward-order current；

V, the current asymmetry degree according to described protection installation place and current asymmetry degree plane carry out Fault Identification, specifically include Following steps：

S501, judgementWhether set up, set up and be then judged as unbalanced fault, open away from From protection, otherwise enter step S502； For positive sequence voltage and forward-order current angle；

S502, judgementWhether set up, set up and then write afterwards previous cycleOtherwise, locking away from From protection；

S503, comparison electric current unsymmetrical planAnd 0.3pu, if Then it is judged as symmetric fault, open distance is protected；

IfThen time delay open distance protection I, II section, open distance protects III section；For perunit value, benchmark is protection installation placePhase voltage, pu is unit：Perunit value.

2. the method for claim 1 it is characterised in that：In described step II, according to described three-phase voltage and three-phase electricity Stream determine respectively as the following formula withForward-order current on the basis of phaseNegative-sequence currentZero-sequence currentAnd positive sequence voltage

In formula,ForPhase current；It is respectively other biphase electric currents；ForPhase voltage；ForThe delayed phase of phase Voltage,ForThe advanced phase voltage of phase.

3. the method for claim 1 it is characterised in that：In described step IV, determine as the following formula described positive sequence voltage and Angle between described forward-order current

In formula,Be withPositive sequence voltage on the basis of phase,Be withForward-order current on the basis of phase；For positive sequence voltageAnd forward-order currentBetween angle.