CN107104420B - I segment protection method of route distance suitable for THE UPFC access - Google Patents

Abstract

The invention belongs to the field of relay protection of power system lines, in particular to a line distance section I protection method suitable for unified power flow controller access. The invention utilizes the geometric characteristics of the voltage and current phasors of the system after a fault to construct a virtual similar triangle, and constructs a new fault distance solution equation based on this to accurately solve the fault distance, and then combines the fault distance measurement volatility auxiliary criterion to correctly distinguish internal and external faults. This method is not affected by the transition resistance, and the fault location can be accurately located only by using the single-end electrical quantity information, and the fault inside and outside the zone can be reliably distinguished in combination with auxiliary criteria. In addition, this method is suitable for distance elements of various fault types and various operating characteristics, has good universality and is not affected by the operation mode of UPFC, and provides a solid theory for the design and development of relay protection with UPFC lines Calculation basis.

Description

Protection method for section Ⅰ of line distance suitable for unified power flow controller access

technical field

The invention belongs to the field of relay protection of power system lines, in particular to a line distance section I protection method suitable for unified power flow controller access.

Background technique

With the rapid development of our country's economy, the modern power system has gradually become the largest, most complex and highly integrated giant-dimensional nonlinear entity system in modern industry. At the same time, modern power systems are also facing issues such as system planning, resource optimization allocation, and safe and stable operation. In order to solve these problems, the Flexible AC Transmission System (FACTS) came into being, which integrates modern power electronics technology, automatic control technology and computer technology to achieve safer, more stable, more efficient and more flexible control of the power system. UPFC (Unified Power Flow Controller), as the third-generation FACTS original, can realize series compensation and parallel compensation at the same time, and has incomparable advantages over traditional FACTS devices. Theoretical analysis and engineering examples show that UPFC can realize rapid and frequent adjustment and control of voltage, phase angle, impedance and system power flow, significantly improve line transmission capacity and system stability level, and damp system oscillation. Therefore, domestic and foreign experts and scholars have conducted a lot of research on it. Research mainly includes: physical model, electromagnetic transient simulation, system oscillation and control strategy, etc. However, while UPFC improves the system performance, it also changes the electrical quantities such as impedance, voltage, and phase angle as relay protection criteria, which threatens the reliable operation of relay protection devices, especially the most serious impact on distance protection: there are literatures The impedance of the transmission line based on UPFC is analyzed in detail, pointing out that different installation positions have a great influence on the protection action boundary, and it is believed that UPFC will complicate the transient process of the system, and the effect of UPFC on distance protection is theoretically analyzed in detail Influenced by the influence, it is proposed to determine the setting boundary similar to artificial neural network (ANN) based on digital simulation; in addition, some scholars have analyzed in detail the case of distance protection misoperation caused by UPFC in double circuit lines, and proposed an adaptive distance protection for this problem method. Since UPFC can operate in a variety of working conditions and the operating parameters vary greatly under different working conditions, ANN-based adaptive distance protection requires a lot of testing and learning, while other distance protection methods require strict time synchronization at both ends of the system. There are high requirements on the communication system, so it is not easy to implement. Therefore, a new distance protection algorithm is urgently needed to solve the problem of accurate calculation of the fault distance when the UPFC line passes through the transition resistance fault.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, aiming at the impact of transition resistance and UPFC access on line distance protection, a line distance section I protection method suitable for unified power flow controller access is proposed. The geometric characteristics of the voltage and current of the system construct similar triangles and construct the fault distance solution equation based on this, and accurately solve the fault distance while combining the fault distance measurement volatility auxiliary criterion to correctly distinguish internal and external faults.

Technical method of the present invention is as follows:

A line distance section I protection method suitable for unified power flow controller access, comprising the following steps:

Step 1: Construct the fault distance measurement equation; according to the simplified system analysis diagram, construct a similar triangle based on the post-fault voltage and current phasor diagram; construct the fault distance percentage solution formula according to the principle that the corresponding side ratios of similar triangles are equal, and use the step-by-step search method to Calculate the fault distance percentage P;

Step 2: Solve the fault criterion; solve the fault distance mean p _m and fault distance variance D(p) according to the fault distance solution formula constructed in step 1;

Step 3: Judging the action condition; judging whether the calculation result of the fault ranging mean p _m and the fault ranging variance D(p) in step 2 satisfies the distance protection operating condition.

The formula for solving the fault distance percentage is as follows:

In the formula: Voltage measurement for end-of-line protection installations, For current measurement at end-of-line protection installations, is the positive-sequence impedance angle of the fault line, Z _L is the positive-sequence impedance of the full length of the line, and p is the percentage of the fault distance, that is, the ratio of the length of the line between the protection installation point and the fault point to the total length of the line;

When the system is a single-phase-to-ground short-circuit fault:

In the formula, Voltage measurement for end-of-line protection installations, For current measurement at end-of-line protection installations, is the phase voltage of the single-phase-to-ground short-circuit fault line, is the phase current of the single-phase-to-ground short-circuit fault line, is the zero-sequence current of the system, the intermediate variable Z ₁ is the line positive sequence impedance, Z ₀ is the line zero sequence impedance;

When the system is a phase-to-phase short circuit fault:

In the formula, Measure voltage at installations for end-of-line protection, For current measurement at end-of-line protection installations, is the phase-to-phase short-circuit fault line voltage, is the line current of the phase-to-phase short-circuit fault line,

The solution method of described fault ranging mean value p _m and fault ranging variance D(p) is as follows: determine the sampling frequency, solve the fundamental wave component of the sampling signal in the second cycle with the full-cycle Fourier algorithm, and calculate according to the fault distance solution formula The mean value p _m of fault distance measurement and the variance D(p) of fault distance measurement corresponding to each point constitute the auxiliary criterion.

The step 3 is specifically as follows:

Step 301: Enter p _m and D(p) to determine whether the distance protection action condition is satisfied:

In the formula, p _m ≤ p _set is the distance protection action equation; D(p) < 0.1 is the auxiliary criterion for distinguishing whether the fault range includes UPFC; p _m is the average value of fault distance measurement; p _set is the setting value of the traditional distance protection section I, in Z _L is the full length positive sequence impedance of the line; D(p) is the fault distance measurement variance;

Step 302: When both p _m and D(p) meet the operating conditions of the distance protection, it is determined that there is a fault within the protection range, and the protection of the distance section I on the opposite side of the UPFC trips.

The beneficial effects of the present invention are:

The distance protection section I of the present invention is not affected by the transition resistance and UPFC, can accurately locate the fault location only by using single-end electrical quantity information, and can reliably distinguish internal and external faults according to the fluctuation of the fault distance calculation result. In addition, the invention is applicable to distance elements of various fault types and various action characteristics, and is not affected by the operation mode of UPFC, has good universality, simple and reliable calculation, and has certain practical engineering significance.

Description of drawings

Accompanying drawing 1 is the flow chart of the line distance section I protection method of UPFC access;

Accompanying drawing 2 is the schematic diagram that contains UPFC system;

Accompanying drawing 3 is the schematic diagram of UPFC simplified model and fault location;

Accompanying drawing 4 contains the positive sequence network diagram of the system after the UPFC line failure;

Accompanying drawing 5 contains the negative sequence network diagram of the system after the UPFC line fault;

Accompanying drawing 6 contains the zero-sequence network diagram of the system after the UPFC line fault;

Figure 7 is the system voltage and current phasor diagram when fault occurs at F1;

Figure 8 is the system voltage and current phasor diagram when fault occurs at F2;

Attached figure 9 is the calculation result diagram of fault distance when Rg=30Ω;

Accompanying drawing 10 is the fault distance calculation result diagram when Rg=60Ω;

Attached Figure 11 is the fault distance calculation result diagram when Rg=100Ω;

Accompanying drawing 12 is the calculation result diagram of the fault distance when the F2 point is faulted;

Detailed ways

The main idea of this method is to construct a virtual similar triangle using the geometric characteristics of the voltage and current phasors of the system after a fault, and construct a new fault distance solution equation to accurately solve the fault distance, and then combine the fault distance measurement volatility auxiliary criterion to correctly distinguish internal and external faults . The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments. Accompanying drawing 1 is the flow chart of the protection method of line distance I section connected by UPFC. As shown in Fig. 1, the fault distance measurement equation is constructed first, and similar triangles are constructed based on the post-fault voltage and current phasor diagram according to the simplified system analysis diagram; According to the principle that the ratios of corresponding sides of similar triangles are equal, the fault distance percentage solution formula is constructed, and the fault distance percentage is solved by a step-by-step search method; secondly, the fault criterion is solved, and the fault distance percentage mean value p _m is calculated according to the fault distance solution formula constructed in step 1 And the variance D(p) of the fault distance percentage; finally judge the action condition, and judge whether the calculation result of the fault distance percentage mean p _m and its variance D(p) satisfies the distance protection action condition: If both p _m and D(p) meet the distance protection action conditions, it is judged to be a fault within the protection range, and the UPFC’s opposite distance section I protection trips, otherwise it exits directly and the judgment ends.

Further, in the process of constructing the fault location equation, the specific method is as follows: firstly, the schematic diagram of the system containing UPFC as shown in Figure 2 is simplified, and the simplified model and fault location are shown in Figure 3, and in Figure 3 A short-circuit fault occurs at point F1, the M side is the end of the line, and the UPFC is connected to the N side at the beginning of the line. Since the UPFC series-parallel converter transformer adopts the YY and Y-Δ wiring modes respectively, and the grid side of the two wiring modes is not grounded, the system zero-sequence current does not flow through the UPFC body device after the fault, that is, it will not change the system after the fault. Zero sequence network structure. Based on this, according to the simplified schematic diagram containing UPFC lines shown in Figure 3, the positive, negative, and zero three-sequence network diagrams of the system after the fault are drawn, as shown in Figures 4-6, and Figures 4-6 respectively show the positive and negative phases of the system after the UPFC line fault. Sequence network diagram, negative sequence network diagram and zero-sequence network diagram, it can be seen from Figure 4-6 that the connection of UPFC only introduces the zero-sequence leakage reactance of the series converter transformer in the zero-sequence network, but no zero-sequence potential connection , and then keep the network structure unchanged; however, in the positive and negative sequence networks, the positive sequence potential is introduced by the series converter transformer respectively and negative sequence potential The sequence network structure is changed, usually under the regulation of the three-level control system, the UPFC can operate in multiple modes according to the system requirements during steady-state operation, so as to achieve the control goal of the dispatching level. It can be known from UPFC control theory that UPFC output and control system parameters are electrical quantities such as system phase angle difference, frequency, voltage, and current. System failure will inevitably change the above electrical quantities and destroy the balance of power and voltage during normal operation. UPFC control system It is difficult to predict whether the original control target can be achieved and the original balance state can be restored. Even if the original balance is restored or a new balance is established, a dynamic adjustment process is required. Conservation methods make a big difference. For this reason the present invention carries out fault analysis to containing UPFC line fault analysis model according to Fig. 3:

Viewed from the M side of the line, when the fault is located at a position that does not include UPFC, such as F1 in Figure 3, the expression of the measured voltage at the protection installation on the M side of the line end is as follows:

In the formula, Z is the positive sequence impedance of the line between the protection installation point and the fault point; Measure the voltage and current at the line end protection installation respectively; is the fault point voltage;

When the system is a single-phase-to-ground short-circuit fault:

In the formula Z ₁ and Z ₀ are positive sequence and zero sequence impedance of the line respectively; Measure the voltage and current at the line end protection installation respectively; is the phase voltage of the single-phase-to-ground short-circuit fault line, is the phase current of the single-phase-to-ground short-circuit fault line, is the zero-sequence current of the system;

When the system is a phase-to-phase short circuit fault:

In the formula, Measure the voltage and measure the current at the protective installation at the end of the line respectively; is the phase-to-phase short-circuit fault line voltage, is the line current of the phase-to-phase short-circuit fault line,

According to the relationship between the voltage and current after the fault shown above, the fault branch current after the fault is Measured currents at post-fault system protection installations for reference phasor plotting Measuring voltage fault point voltage fault branch current Line voltage between protection installation place and fault point Phasor diagram; Accompanying drawing 7 is the system voltage and current phasor diagram when fault occurs at F1, as shown in Fig. 7, extending and Intersect at point B, in the figure is a known quantity, and in the figure such as the fault point voltage Protect the line voltage between the installation place and the fault point The unknown quantities are represented by the percentage of fault distance, which is the ratio of the positive sequence impedance of the line between the protection installation point and the fault point to the positive sequence impedance of the full length of the line. Therefore, the fault distance percentage equation is established to solve the unknown quantity. According to the phasor diagram shown in Figure 7, add auxiliary lines in the figure according to the geometric characteristics of voltage and current to form similar triangles ΔOCD and ΔMAD, and solve the angles of the similar triangles. Since ΔOCD～ΔMAD, use the ratio of the corresponding sides of the similar triangle It can be seen The formula for solving the percentage of fault distance can be constructed by bringing in the expressions of various quantities in the formula:

In the formula, Measure the voltage and current at the line end protection installation respectively; is the positive-sequence impedance angle of the fault line, Z _L is the positive-sequence impedance of the full length of the line, and p is the percentage of fault distance, which is the ratio of the length of the line between the protection installation point and the fault point to the total length of the line.

When the system is a single-phase-to-ground short-circuit fault: In the formula Z ₁ and Z ₀ are the positive sequence and zero sequence impedances of the line respectively, Measure the voltage and current at the line end protection installation respectively; is the phase voltage of the single-phase-to-ground short-circuit fault line, is the phase current of the single-phase-to-ground short-circuit fault line, is the zero-sequence current of the system; when the system is short-circuited between phases, In the formula Measure the voltage and current at the line end protection installation respectively; is the phase-to-phase short-circuit fault line voltage, is the line current of the phase-to-phase short-circuit fault line, There is only one unknown quantity in f(p), that is, the fault distance percentage p, and it is sufficient to set f(p)=0 to solve it. Since f(p)=0 is a nonlinear equation, it can be solved by stepwise search method.

Further, in the process of solving the fault criterion, the specific method is as follows: the simplified model of UPFC and the schematic diagram of the fault location shown in Figure 3, when the fault is located in the position including UPFC such as F2 in Figure 3, the UPFC series branch is on the line A time-varying potential is inserted into the At this time, the measured voltage expression at the line end protection installation is as follows:

Where Z _T is the leakage reactance of the series transformer, Z _L is, is the compensation voltage for the UPFC series branch, Measure the voltage and current at the line end protection installation respectively, is the fault point voltage;

Figure 8 shows the phasor relationship of system voltage and current when F2 is faulty. It can be seen from Figure 8 that the connection of UPFC destroys the geometric relationship between ΔOC′D～ΔM′A′D′, so the fault measurement obtained by this method The distance cannot reflect the fault distance correctly, and there will be large fluctuations. However, when the fault occurs in a location that does not contain UPFC, the ranging is stable and the fluctuation is small. Therefore, the magnitude of the ranging fluctuation can be used to form an auxiliary criterion to distinguish internal and external faults. In summary, the opposite side distance protection criterion of UPFC after the UPFC line fault can be obtained: firstly, the sampling frequency is determined, and the fundamental wave component of the sampling signal in the second cycle is solved by the full-cycle Fourier algorithm, and calculated according to the fault distance solution formula The fault distance percentage mean p _m and variance D(p) corresponding to each point constitute the auxiliary criterion.

Further, in the process of judging the action conditions, the specific method is as follows: put p _m and D(p) into the distance protection action equation to judge whether the distance protection action conditions are satisfied:

In the formula, p _m ≤ p _set is the traditional distance protection action equation; D(p)<0.1 is the auxiliary criterion for distinguishing whether the fault range includes UPFC; where is the setting value of section I of the traditional distance protection; Z _L is the full-length positive sequence impedance of the line, p _m is the average value of fault distance measurement, and D(p) is the variance of fault distance measurement;

D(p) reflects the volatility of fault location, and constitutes an auxiliary criterion for judging whether the fault range includes UPFC, considering the influence of measurement errors, distributed capacitance and other factors that may cause fluctuations in fault location results, so the The criterion boundary was set at 0.1. When both p _m and D(p) meet the operating conditions of the distance protection, it is judged as a fault within the protection range, and the corresponding UPFC opposite side distance protection section I trips.

Example 1

The present invention will be further described below with specific examples. In the 220KV dual power supply system including UPFC shown in Figure 2, The length of the line is 100km, the distance protection is set to 80% of the total length of the line, and the rated capacity of UPFC is 100MVA. According to the common knowledge in this technical field, the maximum possible transition resistance of the system after a 220KV system fault is 100Ω, so the three transition resistance values of the system are respectively 30Ω, 60Ω, and 100Ω, and a single-phase grounding short circuit fault near the end of the protection range is taken as an example for analysis. , assuming that the fault occurs after the system runs for 7s. Both the experimental data and the simulation results take 7s as the timing zero point at the initial time of the fault, and use MATLAB to take the sampling data in the second cycle and filter it with the full-cycle Fourier algorithm to calculate it. The simulation results are shown in Figure 9-Figure 11. The simulation results of the fault at _F2 shown in Figure 3 are shown in Figure 12, where Rg is the transition resistance, and pF is the actual fault distance percentage.

From the analysis of the simulation results shown in Figures 9 to 11, it can be known that the protection method of the present invention is less affected by fault transients, and can quickly obtain the correct ranging result with an error of less than 3%, which meets the requirements of the high-voltage system for the quickness of the protection device; At the same time, the ranging fluctuation is small, and the ranging standard deviation is about 10 ^-4 . Therefore, the fault distance can be calculated correctly, thereby ensuring that the distance I section will not refuse to operate or malfunction. It can be seen from Figure 12 that when the F2 point is faulty outside the protection zone, the fault distance measurement is relatively large, all of which are greater than the set value of 0.1. It can be seen that the main and auxiliary criteria of the method of the present invention complement each other, can accurately distinguish internal and external faults, and can overcome the influence of transition resistance and UPFC on distance protection.

This embodiment is only a preferred specific implementation of the present invention, but the scope of protection of the present invention is not limited thereto, any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention , should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (3)

1. a kind of I segment protection method of route distance suitable for THE UPFC access, which is characterized in that including following step It is rapid:

Step 1: building fault localization equation；It is basic structure with voltage and current phasor diagram after failure according to network analysis figure is simplified Make similar triangles；Fault distance percentage solution formula is constructed according to the corresponding sides ratio equal principle of similar triangles, is led to Search one by one method is crossed to solve fault distance percentage P；

Voltage and current phasor diagram is with fault branch electric current after failure after the failureFor the post-fault system drawn with reference to phasor Installation place is protected to measure electric currentMeasure voltageFault point voltageFault branch electric currentProtect installation place to event Line electricity between barrier pointPhasor diagram；

Step 2: failure criterion solves；Fault localization mean value p is solved according to the fault distance percentage P that step 1 is calculated_mAnd Fault localization variance D (p)；

The fault localization mean value p_mAnd the method for solving of fault localization variance D (p) is as described below:

It determines sample frequency, the fundametal compoment of sampled signal in the second cycle is solved with full-wave fourier algorithm, is obtained according to solution Fault distance percentage P, calculate the corresponding mean value of each point and variance to get fault localization mean value p is arrived_mAnd fault localization variance D (p), wherein D (p) constitutes assistant criteria；

Step 3: judging operation condition；Fault localization mean value p described in judgment step two_mThe calculating knot of its fault localization variance D (p) Whether fruit meets distance protection operation condition.

2. a kind of I segment protection method of route distance suitable for THE UPFC access according to claim 1, It is characterized in that, the fault distance percentage solution formula is as follows:

In formula:Installation place is protected to measure voltage for line end,Installation place is protected to measure electric current for line end,For Faulty line positive sequence impedance angle, Z_LFor total track length positive sequence impedance, p is fault distance percentage, i.e. protection installation place to failure The ratio of line length and total track length between point；

When system is single-phase grounding fault,

In formula,Installation place is protected to measure voltage for line end,Installation place is protected to measure electric current for line end,For The phase voltage of single-phase grounding fault route,For the phase current of single-phase grounding fault route, To be System zero-sequence current, intermediate variableZ₁For route positive sequence impedance, Z₀For route zero sequence impedance；

When system is phase fault,

In formula,For line end protect installation place measure voltage,Installation place is protected to measure electric current for line end,For The line voltage of phase fault route,For the line current of phase fault route,

3. a kind of I segment protection method of route distance suitable for THE UPFC access according to claim 1, It is characterized in that, the step 3 is specific as follows:

Step 301: by p_mAnd D (p) is brought into, judges whether to meet distance protection operation condition:

In formula: p_m≤p_setFor distance protection operation equation；D (p) < 0.1 is to distinguish whether fault coverage includes that the auxiliary of UPFC is sentenced According to；p_mFor fault localization mean value；p_setFor I section of setting valve of traditional distance protection, whereinZ_LFor the resistance of total track length positive sequence It is anti-；D (p) is fault localization variance；

Step 302: working as p_m, D (p) is when being all satisfied distance protection operation condition, be determined as protection scope internal fault, the opposite side of UPFC I section of trip protection of distance.