Power transmission line ultra-high speed protection method based on fault feature compensation

Abstract

The application is a power transmission line super-high-speed protection method based on fault feature compensation. A new type of differential fault direction feature is constructed by the polarity of the amplitude difference of the high-frequency signal of the line and bus voltage due to the hindering characteristics of the wave trap on high-frequency signals. The polarity is positive when the fault is in the positive direction and negative when the fault is in the negative direction. The adaptive fault direction feature is obtained by compensating the fault direction feature according to different fault state parameters when the fault occurs, effectively solving the problem of insufficient reliability and sensitivity of the transient protection under weak fault. The transient protection method has super-high-speed operation performance, is not affected by the distributed capacitance current of the power transmission line, the saturation of the current transformer, the power system oscillation and the transition resistance and the like, and overcomes the influence of the fault initial angle and the transition resistance on the transient protection, greatly improving the protection reliability.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and particularly relates to a transmission line protection method based on transient signals. Background Technology

[0002] The power system is gradually transitioning to a new type of power system dominated by new energy sources. However, in China, energy production areas and load centers are distributed in reverse, resulting in a large amount of electricity needing to be transmitted over long distances. This has led to a gradual increase in the use of ultra-high voltage (UHV) and extra-high voltage (UHV) lines to achieve large-scale long-distance power transmission. This presents new challenges to the power system. UHV and UHV networks need to quickly and selectively clear faults to reduce damage to electrical equipment, improve power transmission capacity and system transient stability, especially given the widespread adoption of power electronic equipment in new energy grids. Traditional protection systems based on power frequency have excessively long sampling times and are facing severe challenges such as declining performance or even failure to operate due to factors such as the non-constant internal impedance of new energy sources, weak feedback, limited short-circuit current amplitude, controlled phase angle, and frequency deviation.

[0003] Traditional protection systems based on power frequency quantities have limited potential for further improvements in operating speed and reliability. Transient-based protection systems, utilizing high-frequency fault information, can rapidly detect high-frequency components, achieving ultra-high-speed protection. Furthermore, their occurrence is solely related to faults. Therefore, constructing protection criteria based on transient quantities is one of the effective ways to improve the reliability and speed of protection in new power systems.

[0004] Traditional transient protection performance is affected by the fault initial angle or transition resistance. When the fault initial angle is small or the transition resistance is large, the transient protection performance is severely affected, and the reliability and sensitivity cannot meet the requirements. Furthermore, traditional traveling wave directional protection relies on the wavefront detection of the traveling wave, and since the subsequent traveling wave is affected by reflected and refracted waves, traditional transient directional protection exhibits insufficient sensitivity and unacceptable reliability within 18° before and after the fault initial angle crosses zero. Therefore, we need to research new methods for transient protection of transmission lines. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and to provide a method for ultra-high-speed protection of transmission lines based on fault characteristic compensation.

[0006] The present invention adopts the following technical solution:

[0007] In my country, power line carrier equipment, including wave traps and coupling capacitors, is installed on 100kV and above transmission lines, as well as some 35kV transmission lines. Wave traps are connected in series between the transmission line carrier signal point and adjacent system components (such as buses and transformers) to filter out high-frequency signals without affecting power frequency current transmission. Therefore, transient high-frequency signals are significantly attenuated by the wave trap, resulting in a significantly larger high-frequency signal entering the wave trap than the filtered-out signal, creating a noticeable difference. Based on this characteristic, a fault characteristic compensation-based ultra-high-speed protection method for transmission lines is proposed.

[0008] The ultra-high-speed protection method for transmission lines based on fault characteristic compensation includes:

[0009] Step 1. Collect the fault voltage u on the inside of the protected line bus and on the bus.

[0010] Step 2. Extract transient high-frequency components u using signal processing techniques. h Wavelet transform, mathematical morphology, empirical mode decomposition, etc., can be used.

[0011] Step 3. Calculate the transient high-frequency component processing quantity. Calculate the transient high-frequency component processing quantity A1 inside the local busbar, the transient high-frequency component processing quantity A2 on the local busbar, and calculate their difference DA. 12 =A1-A2. Calculate the transient high-frequency component processing amount A3 on the inner side of the opposite busbar, the transient high-frequency component processing amount A4 on the opposite busbar, and calculate their difference DA. 34 =A3-A4. The transient high-frequency component processing quantity can be energy, or entropy, or signal complexity, or signal singularity, or Li's exponent, or instantaneous amplitude integral, or instantaneous amplitude, or instantaneous amplitude summation, or singularity, or other transient high-frequency component processing quantity, one of them.

[0012] Step 4. Calculate the initial fault angle θ and the transition resistance R.

[0013] Step 5. Construct fault direction characteristic quantities. Process the transient high-frequency component DA based on the initial fault angle θ and transition resistance R. 12 DA 34 Compensation is performed to obtain the fault characteristic quantity NDA. 12 NDA 34 The compensation method is as follows:

[0014]

[0015] Where k is the compensation coefficient, and a1, a2, b1, and b2 are constants.

[0016] Step 6. Fault direction determination, if NDA 12>0 indicates positive polarity and the fault direction at this end is positive; otherwise, the fault direction at this end is negative. If NDA 34 >0 indicates positive polarity and the direction of the fault at the other end is positive; otherwise, the direction of the fault at the other end is negative.

[0017] Step 7. Construct the protection criteria for the system:

[0018] NDA 12 >0 (1)

[0019] NDA 34 >0 (2)

[0020] If formula (1) is satisfied, it indicates a positive direction fault at this end; if formula (2) is satisfied, it indicates a positive direction fault at the opposite end. Based on the fault direction determination results at both ends, a corresponding trip command is issued. If both ends are determined to be positive direction faults, the fault is within the protection zone, and a trip command is sent. If one end is determined to be a reverse direction fault, the protection is blocked.

[0021] Furthermore, the transient high-frequency component refers to the portion of the fault voltage or current that differs from the power frequency component.

[0022] Furthermore, the term "local end" refers to the end that first receives the fault information, while the other end is referred to as the "reciprocal end".

[0023] Furthermore, the positive direction refers to the direction within the protected area, and the negative direction refers to the direction outside the protected area.

[0024] The beneficial effects of this invention are:

[0025] (1). This invention is based on transient information generated by faults. The protection method based on this principle is not affected by the distributed capacitance current of the transmission line, the saturation of the current transformer, the oscillation of the power system and the transition resistance, and has ultra-high speed operation performance.

[0026] (2). The present invention compensates for the fault characteristic quantity based on the fault initial angle and the transition resistance. The fault characteristic quantity difference between the positive direction fault and the reverse direction fault is significant and the boundary of the interval is relatively clear. This makes the protection easy to set, highly reliable and highly sensitive, and the protection performance is not affected by the fault initial angle, transition resistance, fault type, etc.

[0027] (3) An adaptive directional relay of the present invention can simultaneously determine the positive direction of the fault in two related lines, and the protection area is twice that of the traditional protection area. Attached Figure Description

[0028] Figure 1 A schematic diagram of a power grid system for implementing transient high-frequency component differential polarity direction protection. Detailed Implementation

[0029] The following uses examples of transient high-frequency component processing quantities—the amplitude of transient high-frequency components of fault voltage, and wavelet transform, a signal processing technique, to further describe the present invention in detail with reference to embodiments and accompanying drawings. However, the embodiments of the present invention are not limited thereto.

[0030] Example

[0031] Figure 1 The diagram shows a power grid system implementing transient high-frequency component differential polarity directional protection. In this model, line L1 is 210km long, line L2 is 110km long, line L3 is 140km long, line L4 is 160km long, and line L5 is 140km long. Wave traps are installed at both ends of each line, and the impedance of the wave traps is above 800Ω for signals in the 40-500kHz range.

[0032] Step 1. Collect the fault voltages u1 and u2 on the inside of the busbar and on the busbar at this end, and the fault voltages u3 and u4 on the inside of the busbar and on the busbar at the opposite end.

[0033] Step 2. Use wavelet transform to extract the transient high-frequency components u on the inner side of the local bus and on the bus. h1 u h2 The transient high-frequency component u on the inner side of the opposite bus and on the bus. h3 u h4 In this embodiment, the sampling frequency is 400kHz, and the transient high-frequency component u h1 u h2 u h3 u h4 The frequency is 50-100kHz.

[0034] Step 3. Calculate the transient high-frequency component processing quantity. Calculate the transient high-frequency component processing quantity A1 inside the local busbar, the transient high-frequency component processing quantity A2 on the local busbar, and calculate their difference DA. 12 =A1-A2. Calculate the transient high-frequency component processing amount A3 on the inner side of the opposite busbar, the transient high-frequency component processing amount A4 on the opposite busbar, and calculate their difference DA. 34 =A3-A4. A1, A2, A3, and A4 are obtained by the following formula (7):

[0035]

[0036] n is the length of the data window; in this embodiment, n is 200.

[0037] Step 4. Calculate the initial fault angle θ and the transition resistance R.

[0038] Step 5. Construct fault direction characteristic quantities. Process the transient high-frequency component DA based on the initial fault angle θ and transition resistance R. 12 DA 34 Compensation is performed to obtain the fault characteristic quantity NDA. 12 NDA 34 The compensation method is as follows:

[0039]

[0040] In this embodiment, a1, a2, b1, and b2 are 0.0438, 0.9835, -0.2467, and -0.006548, respectively.

[0041] Step 6. Fault direction determination, if NDA 12 >0 indicates positive polarity and the fault direction at this end is positive; otherwise, the fault direction at this end is negative. If NDA 34 >0 indicates positive polarity and the direction of the fault at the other end is positive; otherwise, the direction of the fault at the other end is negative.

[0042] Step 7. Construct the protection criteria for the system:

[0043] NDA 12 >0 (1)

[0044] NDA 34 >0 (2)

[0045] If formula (1) is satisfied, it indicates a positive direction fault at this end; if formula (2) is satisfied, it indicates a positive direction fault at the opposite end. Based on the fault direction determination results at both ends, a corresponding trip command is issued. If both ends are determined to be positive direction faults, the fault is within the protection zone, and a trip command is sent. If one end is determined to be a reverse direction fault, the protection is blocked.

[0046] The above embodiments are typical implementations of the present invention. However, the implementation of the present invention is not limited to the embodiments described. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for ultra-high-speed protection of transmission lines based on fault characteristic compensation, characterized in that, include: Step 1. Collect the fault voltage u on the inside of the protected line bus and on the bus itself; Step 2. Extract transient high-frequency components u using signal processing techniques. h ; Step 3. Calculate the transient high-frequency component processing quantity. Calculate the transient high-frequency component processing quantity A1 inside the local busbar, the transient high-frequency component processing quantity A2 on the local busbar, and calculate their difference DA. 12 =A1-A2. Calculate the transient high-frequency component processing amount A3 on the inner side of the opposite busbar, the transient high-frequency component processing amount A4 on the opposite busbar, and calculate their difference DA. 34 =A3-A4; Step 4. Calculate the initial fault angle θ and the transition resistance R. Step 5. Construct fault direction characteristic quantities. Process the transient high-frequency component DA based on the initial fault angle θ and transition resistance R. 12 DA 34 Compensation is performed to obtain the fault characteristic quantity NDA. 12 NDA 34 . Step 6. Fault direction determination, if NDA 12 >0 indicates positive polarity and the fault direction at this end is positive; otherwise, the fault direction at this end is negative. If NDA 34 >0 indicates positive polarity and the direction of the fault at the other end is positive; otherwise, the direction of the fault at the other end is negative. Step 7. Construct the protection criteria for the system: NDA 12 >0 (1) NDA 34 >0 (2) If formula (1) is satisfied, it indicates a positive direction fault at this end; if formula (2) is satisfied, it indicates a positive direction fault at the opposite end. Based on the fault direction determination results at both ends, a corresponding trip command is issued. If both ends are determined to be positive direction faults, the fault is within the protection zone, and a trip command is sent. If one end is determined to be a reverse direction fault, the protection is blocked.

2. The method according to claim 1, characterized in that, Methods for extracting transient high-frequency components in step 2 include wavelet transform, mathematical morphology, and empirical mode decomposition.

3. The method according to claim 1, characterized in that, Step 3 involves processing one of the following transient high-frequency components: energy, entropy, signal complexity, signal singularity, Li's exponent, instantaneous amplitude integral, instantaneous amplitude, instantaneous amplitude summation, or singular value.

4. The method according to claim 1, characterized in that, Step 5: Processing quantity DA of transient high-frequency components based on the initial fault angle θ and transition resistance R. 12 DA 34 Compensation is performed to obtain the fault characteristic quantity NDA. 12 NDA 34 The specific compensation methods are as follows: Where k is the compensation coefficient, and a1, a2, b1, and b2 are constants.

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