10kv resonance identification and harmonic elimination method

Abstract

The application discloses a 10KV resonance identification and harmonic elimination method, comprising the following steps: S1, collecting open delta voltage, and using different scales to carry out wavelet decomposition on the collected open delta voltage to extract signal components of different frequency bands; S2, establishing a signal component maximum absolute value M matrix according to the extracted signal components of different frequency bands; S3, comparing the signal component maximum absolute values of the frequency bands to complete amplitude, frequency identification and harmonic identification of waveform singularity; and S4, calculating to obtain a harmonic elimination condition and a damping resistance. The application can accurately identify resonance and select a harmonic elimination damping resistance, and has sensitivity and reliability for eliminating ferromagnetic resonance of a voltage transformer.

Description

Technical Field

[0001] This invention relates to the field of power system technology, specifically to a 10KV resonance identification and harmonic elimination method. Background Technology

[0002] In a 10kV ungrounded neutral power system, the busbar typically consists of three single-phase voltage transformers (PTs) connected in a Y / Y / Δ (open) configuration. The PT's inductance is non-linear, and its core's non-linear excitation characteristics are prone to saturation. When a single-phase ground fault occurs, capacitive current flows through the fault point, raising the voltage of the ungrounded phase to the line voltage. The phase's capacitance to ground is charged with a load corresponding to the line voltage. During the ground fault, this capacitive current flows through the grounding point between the power source, conductor, and earth. Due to the high excitation impedance of the PT, the current flowing through it is very small. Once the ground fault disappears, the current path is interrupted. The charge that the ungrounded phase had accumulated to the line voltage during the ground fault can only enter the earth through the PT winding and its originally grounded neutral point. During this transient process, a low-frequency saturation current with a high amplitude will flow through the high-voltage winding, causing severe saturation of the PT core and exciting a continuous high-amplitude ferroresonant overvoltage. Therefore, a nonlinear resistor is connected in series in the zero-sequence voltage circuit so that most of the PT saturation overvoltage also drops across the resistor, thereby avoiding core saturation and limiting the occurrence of saturation overvoltage. Considering that the neutral point zero-sequence current is small during normal grid operation and the sensitivity of the voltage transformer open delta voltage is satisfied during single-phase grounding, the neutral point resistor should be a nonlinear resistor or harmonic suppressor that meets certain characteristic requirements. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a 10KV resonance identification and harmonic elimination method, so as to accurately identify resonance and select harmonic elimination damping resistor to eliminate ferromagnetic resonance caused by the equivalent excitation inductance of voltage transformer.

[0004] To solve the above-mentioned technical problems, the present invention provides a 10KV resonance identification and harmonic cancellation method, comprising:

[0005] Step S1: Acquire the open triangle voltage and perform wavelet decomposition on the acquired open triangle voltage using different scales to extract signal components of different frequency bands.

[0006] Step S2: Based on the extracted signal components of different frequency bands, establish the maximum absolute value M matrix of the signal components;

[0007] Step S3: Compare the maximum absolute values ​​of signal components in each frequency band to complete the amplitude, frequency and harmonic identification of waveform singularity;

[0008] Step S4: Calculate and obtain the resonance elimination condition and damping resistance.

[0009] Furthermore, in step S1, acquiring the open delta zero-sequence voltage means acquiring the open delta voltage in real time and recording no less than five cycles of data in real time. When it is determined that the amplitude is greater than the ground fault judgment threshold, fault data recording is immediately started to acquire no less than 45 cycles of data, and at least three cycles of data before the fault are saved simultaneously.

[0010] Furthermore, in step S2, establishing the maximum absolute value M matrix of the signal components is done by dividing the high frequencies of the upper-level frequency division by 2. j Further frequency division, j=0~1, the wavelet decomposition scaling coefficient N array is as follows:

[0011] N=[K1,K2,K3,K4,K5,K6,K7,K8]

[0012] Wherein, K1~K8 are the scaling coefficients of wavelet decomposition. Based on a sampling frequency of 5000Hz, the scaling coefficient K1 corresponds to 2.5KHz~1.25KHz, K2 corresponds to 1.25K~625Hz, K3 corresponds to 625Hz~312.5Hz, K4 corresponds to 312.5Hz~156.25Hz, K5 corresponds to 156.25Hz~78.125Hz, K6 corresponds to 78.125Hz~39.0625Hz, K7 corresponds to 39.0625Hz~19.53125Hz, and K8 corresponds to 19.53125K~9.765625Hz. The fundamental frequency component in the analyzed signal is reflected by the scaling coefficient K6, the half-division frequency component is reflected by K7, the half-division frequency component is reflected by K8, and the third high-frequency component is reflected by K4.

[0013] Furthermore, in step S3, the amplitude, frequency identification, and harmonic identification of waveform singularities include decomposing the low-pass and band-pass equations of wavelets and comparing the energy of different frequency bands.

[0014] The low-pass equation for the decomposed wavelet is:

[0015]

[0016] The bandpass equation for decomposing wavelets is:

[0017]

[0018] in, G(k) These are the bandpass filter coefficients. H ( k ) represents the low-pass filter coefficients, and the orthogonality relationship between them is... G ( k )=( -1 ) K H ( 1-k ), n Indicates the harmonic order, 2 n This indicates that the high frequency of the higher-level frequency division is divided by 2. j (j=0~1) further divide the frequency; Z It is the set of positive integers; k The translation factor is the discrete wavelet transform factor. t It is a time variable.

[0019] Furthermore, the energy of different frequency bands is calculated, assuming... A=E ( k+1 ) / E ( k If A is the frequency band with the highest energy, then by comparing A, the frequency band with the highest energy is obtained, and this frequency band is the characteristic frequency band.

[0020] Furthermore, step S4 specifically includes:

[0021] Step S41: Obtain the piecewise linear current-magnetic flux linkage curves of the inductance of the three phases a, b, and c of the ferromagnetic voltage transformer PT coil.

[0022] Step S42: Determine the state equation of the ferroresonant equivalent circuit in the neutral-grounded power system;

[0023] Step S43: When the system is disturbed, both the magnetic flux and the system voltage will change, calculate the amount of change;

[0024] Step S44: Obtain the system of equations for the linear time-varying system based on the incremental differential equations;

[0025] Step S45: Based on the fact that the zero solution of the state equation of the ferromagnetic resonance equivalent circuit is asymptotically stable, and the steady state of the incremental differential equation is the only condition, corresponding to the condition that the system does not resonate, the piecewise slope values ​​of the inductances of the three phases a, b, and c in the linear time-varying system equations are obtained.

[0026] Furthermore, in step S41, the inductance of the three phases a, b, and c of the ferromagnetic voltage transformer PT coil... L 1, L 2, L 3 is a nonlinear inductor with the same current-flux flux linkage curve. Let the two different steady-state solutions of phase a be ψ. a1 (t), i a1 (t), ψ a2 (t), i a2 (t), the two different steady-state solutions of phase b and phase c are respectively ψ b1 (t), i b1 (t), ψ b2 (t), ib2 (t), ψ c1 (t), i c1 (t), ψ c2 (t), i c2 (t), then the equation for the slope K of the piecewise line is:

[0027] K a =(ψ a1 (t)-ψ a2 (t)) / (i a1 (t)- i a2 (t))

[0028] K b =(ψ b1 (t)-ψ b2 (t)) / (i b1 (t)- i b2 (t))

[0029] K c =(ψ c1 (t)-ψ c2 (t)) / (i c1 (t)- i c2 (t))

[0030] Where ψ is the flux linkage of the mutual inductor, and K a For phase a inductance L The slope of the piecewise line of 1, K b For phase b inductance L The slope of the piecewise line of 2, K c c-phase inductor L The slope of the piecewise line of 3.

[0031] Furthermore, in step S42, the state equation of the ferromagnetic resonant equivalent circuit is:

[0032] dψ a / dt =e a -u ca -(i La +i Lb +i Lc )R N

[0033] dψ b / dt = e b -u cb -(i La +i Lb +i Lc )R N

[0034] dψ c / dt = e c -ucc -(i La +i Lb +i Lc )R N

[0035] du ca / dt =i La / C

[0036] du cb / dt =i Lb / C

[0037] du cc / dt =i Lc / C

[0038] Among them, i La ~ψ a i Lb ~ψ b i Lc ~ψ c The relationship is determined by the current-magnetic flux curve; e a e b e c These are the three-phase voltage electromotive forces, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors, i La、 i Lb、 i Lc These represent the current flowing through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value of .

[0039] Further, in step S43, the calculated change is:

[0040] Δψ a =ψ a -ψ a ;Δu ca =u ca -u ca

[0041] Δψ b =ψ b -ψ b ;Δu cb =u cb -u cb

[0042] Δψ c =ψ c -ψc ;Δu cc =u cc -u cc

[0043] Where, ψ a ψ b ψ b These are the flux linkages before the three-phase disturbance, ψ a ψ b ψ c These are the flux linkages after three-phase disturbance, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors before the disturbance, u ca u cb u cc These are the voltage drops across the three-phase disconnected capacitors after the disturbance;

[0044] Based on the state equation obtained in step S42, the corresponding incremental differential equation is as follows:

[0045] dΔψ a / dt =Δu ca -(Δi La +Δi Lb +Δi Lc )R N

[0046] dΔψ b / dt =Δu cb -(Δi La +Δi Lb +Δi Lc )R N

[0047] dΔψ c / dt =Δu cc -(Δi La +Δi Lb +Δi Lc )R N

[0048] dΔu ca / dt =Δi La / C

[0049] dΔu cb / dt =Δi Lb / C

[0050] dΔu cc / dt =Δi Lc / C

[0051] Where, Δu ca , Δu cb , Δu cc These are the voltage drop changes across the three-phase disconnected capacitors, Δi La , Δi Lb , Δi Lc These represent the changes in current through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value;

[0052] In step S44, according to

[0053] Δi La = Δψ a Δi La / Δψ a = K a Δψ a

[0054] Δi Lb = Δψ b Δi Lb / Δψ b = K b Δψ b

[0055] Δi Lc = Δψ c Δi Lc / Δψ c = K c Δψ c

[0056] Rewrite the incremental differential equation as a system of equations for a linear time-varying system:

[0057] dΔu a / dt = K a R N Δψ a -(K b Δψ b +K c Δψ c )R N -Δu ca

[0058] dΔu b / dt = K b R N Δψb -(K a Δψ a +K c Δψ c )R N -Δu cb

[0059] dΔu c / dt = K c R N Δψ c -(K a Δψ a +K b Δψ b )R N -Δu cc

[0060] dΔu ca / dt = K a Δψ a / C

[0061] dΔu cb / dt = K b Δψ b / C

[0062] dΔu cc / dt = K c Δψc / C

[0063] Among them, R N It is a damping resistor.

[0064] Further, in step S45, the slope values ​​of the piecewise lines of the inductances of phases a, b, and c in the linear time-varying system equations are obtained as follows:

[0065] K a =K a0 +δK a

[0066] K b =K b0 +δK b

[0067] K c =K c0 +δK c

[0068] in K a0 、K b0 、K c0 for K a 、K b、K c Linear part, δK a、 δK b、 δK c Corresponding to K a 、K b 、K c The variation components surrounding the linear portion;

[0069] For different disturbances and different actual parameters, after substituting the state equations of step S42 and the linear time-varying system equations of step S44, the different damping resistances R are calculated. N Used to eliminate system resonance.

[0070] The present invention has the following beneficial effects: It provides a 10KV resonance identification and harmonic elimination method based on wavelet analysis, which can be used for monitoring and suppressing ferroresonance in power systems. It uses wavelet transform and energy comparison of open delta zero-sequence voltage transient signals to identify waveform singularities, harmonics, and resonant frequencies. The damping resistor is determined according to the system's resonance elimination conditions. It can accurately identify resonance and select the harmonic elimination damping resistor, and has sensitivity and reliability in eliminating ferroresonance in voltage transformers. Attached Figure Description

[0071] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0072] Figure 1 This is a schematic diagram of the wiring of a neutral-point ungrounded power system in an embodiment of the present invention.

[0073] Figure 2 This is a schematic diagram of the equivalent circuit of a neutral-point ungrounded power system in an embodiment of the present invention.

[0074] Figure 3 This is a schematic diagram of the wiring of a neutral-grounded power system in an embodiment of the present invention.

[0075] Figure 4 This is a schematic diagram of the equivalent circuit of a neutral-grounded power system in an embodiment of the present invention.

[0076] Figure 5 This is a flowchart illustrating a 10KV resonance identification and harmonic elimination method according to an embodiment of the present invention.

[0077] Figure 6 This is a schematic diagram of the piecewise linear form of the i-ψ current-magnetic flux linkage curve in an embodiment of the present invention. Detailed Implementation

[0078] The following description of the embodiments is taken with reference to the accompanying drawings, which illustrate specific embodiments in which the invention can be implemented.

[0079] In practical applications, for neutral-point ungrounded power systems, such as Figure 1 , Figure 2 As shown, Ea, Eb, and Ec are the electromotive forces of the three-phase symmetrical power supply, L is the voltage transformer, C0 is the capacitance to ground of each phase conductor and bus, and RN is the damping resistor. Based on the Petersen curve theory and the harmonic oscillation region curves plotted using the PT excitation characteristics, the ratio of the system's phase-to-ground capacitive reactance to the excitation inductive reactance of the voltage transformer winding under rated line voltage changes as the ratio increases. The system is in the 1 / 2 harmonic, fundamental, and 3rd harmonic resonance regions, respectively. The minimum critical excitation voltage gradually increases in different frequency resonance regions, with the 1 / 2 harmonic resonance requiring the lowest excitation voltage and the higher harmonic resonance requiring the highest. That is, under actual operating conditions, as long as certain parameter conditions are met, the cascading resonance phenomenon is most likely to occur.

[0080] Typical wiring diagram of ferroresonant power system with neutral grounding Figure 3 , Figure 4 As shown, PT is the voltage transformer, C is the bus-to-ground capacitance, K1 is the break point of circuit breaker K2 and the equalizing capacitor C1, E is the power supply, and RN is the damping resistor connected in the open delta configuration. When the voltage transformer is switched to an empty bus, all its outgoing lines are disconnected. When circuit breaker K2 is closed and K1 is opened (disconnecting the empty bus), or when K1 is open and K2 is closed (connecting the empty bus), a series three-phase ferroresonant circuit will be formed. According to domestic and international operational experience data, this is a typical scenario frequently occurring in substations.

[0081] Therefore, please refer to Figure 5 As shown, this embodiment of the invention provides a 10KV resonance identification and cancellation method, including:

[0082] Step S1: Acquire the open triangle voltage and perform wavelet decomposition on the acquired open triangle voltage using different scales to extract signal components of different frequency bands.

[0083] Step S2: Based on the extracted signal components of different frequency bands, establish the maximum absolute value M matrix of the signal components;

[0084] Step S3: Compare the maximum absolute values ​​of signal components in each frequency band to complete the amplitude, frequency and harmonic identification of waveform singularity;

[0085] Step S4: Calculate and obtain the resonance elimination condition and damping resistance.

[0086] Therefore, this invention is applied in harmonic suppression equipment to accurately identify resonance and select the harmonic suppression damping resistor RN to eliminate the ferromagnetic resonance caused by the equivalent excitation inductance of the voltage transformer.

[0087] Specifically, in step S1, acquiring the open delta zero-sequence voltage refers to real-time acquisition and recording of at least five cycles of open delta voltage data. When its amplitude is determined to be greater than the ground fault judgment threshold, fault data recording is immediately initiated to acquire at least 45 cycles of data, while simultaneously saving at least three cycles of data prior to the fault. Wavelet decomposition of the acquired open delta voltage is performed using different scales, employing the orthogonal real wavelet basis function of DB5, with a sampling frequency of 5000Hz.

[0088] In step S2, establishing the maximum absolute value M matrix of the signal components is done by dividing the high frequencies of the upper-level frequency division by 2. j (j=0~1) After further frequency division, the scaling coefficient N array of wavelet decomposition is as follows:

[0089] N=[K1,K2,K3,K4,K5,K6,K7,K8]

[0090] Wherein, K1~K8 are the scale decomposition coefficients of wavelet decomposition. Based on a sampling frequency of 5000Hz, decomposition coefficient K1 corresponds to 2.5KHz~1.25KHz, K2 to 1.25K to 625Hz, K3 to 625Hz~312.5Hz, K4 to 312.5Hz~156.25Hz, K5 to 156.25Hz~78.125Hz, K6 to 78.125Hz~39.0625Hz, K7 to 39.0625Hz~19.53125Hz, and K8 to 19.53125K to 9.765625Hz. In terms of the decomposition scale, the fundamental frequency component of the analyzed signal is reflected by decomposition coefficient K6, the half-division component by K7, the third-division component by K8, and the third high-frequency component by K4.

[0091] In step S3, the amplitude, frequency and harmonic identification of waveform singularities include the low-pass and band-pass equations of decomposed wavelets and the energy comparison of frequency bands.

[0092] Specifically, the low-pass and band-pass equations of the decomposed wavelet are as follows:

[0093] Wavelet low-pass equation:

[0094]

[0095] Wavelet bandpass equation:

[0096]

[0097] in, G(k) These are the bandpass filter coefficients. H ( k ) represents the low-pass filter coefficients, and the orthogonality relationship between them is... G ( k )=( - 1 ) K H ( 1-k ), n Indicates the harmonic order, 2 n This indicates that the high frequency of the higher-level frequency division is divided by 2. j (j=0~1) further divide the frequency; Z It is the set of positive integers; k The translation factor is the discrete wavelet transform factor. t It is a time variable.

[0098] Calculate the energy in different frequency bands, assuming A=E ( k+1 ) / E ( k If A is a frequency band with the highest energy, then by comparing A, we can find the frequency band with the highest energy. This frequency band is the characteristic frequency band. It can be understood that energy is a parameter that reflects the characteristics of resonance; the higher the energy, the greater the probability of resonance.

[0099] Step S4 specifically includes:

[0100] Step S41: Obtain the piecewise linear current-magnetic flux linkage curves of the inductance of the three phases a, b, and c of the ferromagnetic voltage transformer PT coil.

[0101] The inductance of the three phases (a, b, and c) of the ferromagnetic voltage transformer (PT) coil. L 1, L 2, L 3 ( L 1>0, L 2>0, L (3>0) is a nonlinear inductor, with the same i-ψ current-magnetic flux linkage curve, and can be expressed as follows: Figure 6 The piecewise linear form shown.

[0102] Let ψ be the flux linkage of the mutual inductor, and let ψ be the two different steady-state solutions of phase a. a1 (t), i a1 (t), ψ a2 (t), i a2 (t), similarly, the two different steady-state solutions of phase b and phase c are ψb1 (t), i b1 (t), ψ b2 (t), i b2 (t), ψ c1 (t), i c1 (t), ψ c2 (t), i c2 (t), then the equation for the slope K of the piecewise line is:

[0103] K a =(ψ a1 (t)-ψ a2 (t)) / (i a1 (t)- i a2 (t))

[0104] K b =(ψ b1 (t)-ψ b2 (t)) / (i b1 (t)- i b2 (t))

[0105] K c =(ψ c1 (t)-ψ c2 (t)) / (i c1 (t)- i c2 (t))

[0106] Among them, K a For phase a inductance L The slope of the piecewise line of 1, K b For phase b inductance L The slope of the piecewise line of 2, K c c-phase inductor L The slope of the piecewise line of 3.

[0107] Step S42, determine the state equation of the ferroresonant equivalent circuit in the neutral-grounded power system:

[0108] dψ a / dt =e a -u ca -(i La +i Lb +i Lc )R N

[0109] dψ b / dt = e b -u cb -(i La +i Lb +i Lc )R N

[0110] dψ c / dt = e c -u cc -(i La +i Lb +i Lc )R N

[0111] du ca / dt =i La / C

[0112] du cb / dt =i Lb / C

[0113] du cc / dt =i Lc / C

[0114] Among them, i La ~ψ a i Lb ~ψ b i Lc ~ψ c The relationship is determined by the current-magnetic flux curve; e a e b e c These are the three-phase voltage electromotive forces, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors, i La、 i Lb、 i Lc These represent the current flowing through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value of .

[0115] Step S43: When the system is disturbed, both the magnetic flux and the system voltage will change. Let the changes be:

[0116] Δψ a =ψ a -ψ a ;Δu ca =u ca -u ca

[0117] Δψ b =ψ b -ψ b ;Δu cb =u cb -u cb

[0118] Δψ c =ψ c -ψ c ;Δu cc =u cc -u cc

[0119] Where, ψ a ψ b ψ b These are the flux linkages before the three-phase disturbance, ψ a ψ b ψ c These are the flux linkages after three-phase disturbance, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors before the disturbance, u ca u cb u cc These are the voltage drops across the three-phase disconnected capacitors after the disturbance.

[0120] Based on the state equation obtained in step S42, the corresponding incremental differential equation is as follows:

[0121] dΔψ a / dt =Δu ca -(Δi La +Δi Lb +Δi Lc )R N

[0122] dΔψ b / dt =Δu cb -(Δi La +Δi Lb +Δi Lc )R N

[0123] dΔψ c / dt =Δu cc -(Δi La +Δi Lb +Δi Lc )R N

[0124] dΔu ca / dt =Δi La / C

[0125] dΔu cb / dt =Δi Lb / C

[0126] dΔu cc / dt =Δi Lc / C

[0127] Where, Δu ca , Δu cb , Δu cc These are the voltage drop changes across the three-phase disconnected capacitors, Δi La , Δi Lb , Δi Lc These represent the changes in current through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value of .

[0128] Step S44: Obtain the system of equations for the linear time-varying system;

[0129] because:

[0130] Δi La = Δψ a Δi La / Δψ a = K a Δψ a

[0131] Δi Lb = Δψ b Δi Lb / Δψ b = K b Δψ b

[0132] Δi Lc = Δψ c Δi Lc / Δψ c = K c Δψ c

[0133] Therefore, the incremental differential equation can be written as a system of equations for a linear time-varying system:

[0134] dΔu a / dt = K a R N Δψ a -(K b Δψ b +K c Δψ c )RN -Δu ca

[0135] dΔu b / dt = K b R N Δψ b -(K a Δψ a +K c Δψ c )R N -Δu cb

[0136] dΔu c / dt = K c R N Δψ c -(K a Δψ a +K b Δψ b )R N -Δu cc

[0137] dΔu ca / dt = K a Δψ a / C

[0138] dΔu cb / dt = K b Δψ b / C

[0139] dΔu cc / dt = K c Δψc / C

[0140] Among them, R N It is a damping resistor.

[0141] Step S45: Based on the fact that the zero solution of the state equation of the ferromagnetic resonance equivalent circuit is asymptotically stable, and the steady state condition of the incremental differential equation is unique, corresponding to the condition that the system does not resonate, the linear time-varying system equations contain:

[0142] K a =K a0 +δK a

[0143] K b =K b0 +δK b

[0144] K c =K c0 +δK c

[0145] in K a0 、K b0 、K c0 for K a 、K b 、K c The linear part corresponds to Figure 6 In L 1 section, and δK a、 δK b、 δK c Corresponding to K a 、 K b 、K c The variation components surrounding the linear part.

[0146] Therefore, the only steady-state condition is:

[0147] ;

[0148] Therefore, for different disturbances and different actual parameters, by substituting the state equations of step S42 and the linear time-varying system equations of step S44, the different damping resistances R can be calculated. N Used to eliminate system resonance.

[0149] The implementation of this invention patent realizes the identification of the resonance region, the determination of the resonance elimination condition, the determination of the open triangular damping resistor, and the calculation of the simulation condition, thus obtaining the parameter conditions for eliminating resonance.

[0150] As can be seen from the above description, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a 10KV resonance identification and harmonic elimination method based on wavelet analysis, which can be used for monitoring and suppressing ferroresonance in power systems. It uses wavelet transform and energy comparison of the transient signal of the open delta zero-sequence voltage 3U0 to identify waveform singularities (amplitude and frequency) and harmonic identification and resonance frequency determination. The damping resistor is obtained according to the system's resonance elimination conditions. It can accurately identify resonance and select the harmonic elimination damping resistor RN, and has sensitivity and reliability in eliminating ferroresonance in voltage transformers.

[0151] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for identifying and eliminating 10kV resonances, characterized in that, include: Step S1: Acquire the open triangle voltage and perform wavelet decomposition on the acquired open triangle voltage using different scales to extract signal components of different frequency bands. Step S2: Based on the extracted signal components of different frequency bands, establish the maximum absolute value M matrix of the signal components; Step S3: Compare the maximum absolute values ​​of signal components in each frequency band to complete the amplitude, frequency and harmonic identification of waveform singularity; Step S4: Calculate and obtain the resonance elimination condition and damping resistance; In step S1, acquiring the open delta zero-sequence voltage means acquiring the open delta voltage in real time and recording no less than five cycles of data in real time. When it is determined that its amplitude is greater than the ground fault judgment threshold, fault data recording is immediately started to acquire no less than 45 cycles of data, and at least three cycles of data before the fault are saved simultaneously. In step S2, establishing the maximum absolute value M matrix of the signal components is done by dividing the high frequencies of the upper-level frequency division by 2. j Further frequency division, j=0~1, the wavelet decomposition scaling coefficient N array is as follows: N=[K1,K2,K3,K4,K5,K6,K7,K8] Wherein, K1 ~ K8 are the scaling coefficients of wavelet decomposition. Based on a sampling frequency of 5000Hz, the scaling coefficients K1 correspond to 2.5KHz~1.25KHz, K2 to 1.25K to 625Hz, K3 to 625Hz~312.5Hz, K4 to 312.5Hz~156.25Hz, K5 to 156.25Hz~78.125Hz, K6 to 78.125Hz~39.0625Hz, K7 to 39.0625Hz~19.53125Hz, and K8 to 19.53125K to 9.765625Hz. The fundamental frequency component in the analyzed signal is reflected by the scaling coefficient K6, the half-division frequency component by K7, the third-division frequency component by K8, and the third high-frequency component by K4. In step S3, the amplitude, frequency and harmonic identification of waveform singularities include decomposing the low-pass and band-pass equations of wavelets and comparing the energy of frequency bands. The low-pass equation for the decomposed wavelet is: The bandpass equation for decomposing wavelets is: in, G(k) These are the bandpass filter coefficients. H ( k ) represents the low-pass filter coefficients, and the two satisfy the orthogonal relationship: G ( k )=( -1 ) k H ( 1-k ), n Indicates the harmonic order, 2 n This indicates that the high frequency of the higher-level frequency division is divided by 2. j Further divide the frequency, j = 0~1; Z It is the set of positive integers; k The translation factor is the discrete wavelet transform factor. t It is a time variable; Calculate the energy in different frequency bands, assuming Then by comparison The frequency band with the highest energy is the characteristic frequency band. Step S4 specifically includes: Step S41: Obtain the piecewise linear current-magnetic flux linkage curves of the inductance of the three phases a, b, and c of the ferromagnetic voltage transformer PT coil. Step S42: Determine the state equation of the ferroresonant equivalent circuit in the neutral-grounded power system; Step S43: When the system is disturbed, both the magnetic flux and the system voltage will change, calculate the amount of change; Step S44: Obtain the system of equations for the linear time-varying system based on the incremental differential equations; Step S45: Based on the fact that the zero solution of the state equation of the ferromagnetic resonance equivalent circuit is asymptotically stable, and the steady state of the incremental differential equation is the only condition, corresponding to the condition that the system does not resonate, the piecewise slope values ​​of the inductances of the three phases a, b, and c in the linear time-varying system equations are obtained.

2. The method according to claim 1, characterized in that, In step S41, the inductance of the three phases a, b, and c of the ferromagnetic voltage transformer PT coil... L 1, L 2, L 3 is a nonlinear inductor with the same current-flux flux linkage curve. Let the two different steady-state solutions of phase a be ψ. a1 (t), i a1 (t), ψ a2 (t), i a2 (t), the two different steady-state solutions of phase b and phase c are respectively ψ b1 (t), i b1 (t), ψ b2 (t), i b2 (t), ψ c1 (t), i c1 (t), ψ c2 (t), i c2 (t), then the equation for the slope K of the piecewise line is: K a =(ψ a1 (t)-ψ a2 (t)) / (i a1 (t)- i a2 (t)) K b =(ψ b1 (t)-ψ b2 (t)) / (i b1 (t)- i b2 (t)) K c =(ψ c1 (t)-ψ c2 (t)) / (i c1 (t)- i c2 (t)) Where ψ is the flux linkage of the mutual inductor, K a For phase a inductance L The slope of the piecewise line of 1, K b For phase b inductance L The slope of the piecewise line of 2, K c c-phase inductor L The slope of the piecewise line of 3.

3. The method according to claim 2, characterized in that, In step S42, the state equation of the ferromagnetic resonant equivalent circuit is: dψ a / dt =e a -u ca -(i La +i Lb +i Lc )R N dψ b / dt = e b -u cb -(i La +i Lb +i Lc )R N dψ c / dt = e c -u cc -(i La +i Lb +i Lc )R N you ca / dt =i La / C you cb / dt =i Lb / C you cc / dt =i Lc / C Among them, i La ~ψ a i Lb ~ψ b i Lc ~ψ c The relationship is determined by the current-magnetic flux curve; e a e b e c These are the three-phase voltage electromotive forces, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors, i La、 i Lb、 i Lc These represent the current flowing through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value of R N It is a damping resistor.

4. The method according to claim 3, characterized in that, In step S43, the calculated change is: Dp a =ψ a -ψ a * ;No ca =u ca -u ca * Dp b =ψ b -ψ b * ;No cb =u cb -u cb * Dp c =ψ c -ψ c * ;No cc =u cc -u cc * Where, ψ a ψ b ψ c These are the flux linkages before the three-phase disturbance, ψ a * ψ b * ψ c * These are the flux linkages after three-phase disturbance, u ca、 u cb、 u cc These are the voltage drops across the three-phase disconnected capacitors before the disturbance, u ca * u cb * u cc * These are the voltage drops across the three-phase disconnected capacitors after the disturbance; Based on the state equation obtained in step S42, the corresponding incremental differential equation is as follows: dΔψ a / dt =Δu ca -(Δi La +Δi Lb +Δi Lc )R N dΔψ b / dt =Δu cb -(Δi La +Δi Lb +Δi Lc )R N dΔψ c / dt =Δu cc -(Δi La +Δi Lb +Δi Lc )R N dΔu ca / dt =Δi La / C dΔu cb / dt =Δi Lb / C dΔu cc / dt =Δi Lc / C Where, Δu ca , Δu cb , Δu cc These are the voltage drop changes across the three-phase disconnected capacitors, Δi La , Δi Lb , Δi Lc These represent the changes in current through the three-phase coil inductance, and C is the voltage equalization capacitor at the break point. a、 C b、 C c The value; In step S44, according to Yes La = Δψ a* Yes La / Dpψ a = K a Dp a Yes Lb = Δψ b* Yes Lb / Dpψ b = K b Dp b Yes Lc = Δψ c* Yes Lc / Dpψ c = K c Dp c Rewrite the incremental differential equation as a system of equations for a linear time-varying system: dΔu a / dt = K a R N Dp a -(K b Dp b +K c Dp c )R N -Yes ca dΔu b / dt = K b R N Dp b -(K a Dp a +K c Dp c )R N -Yes cb dΔu c / dt = K c R N Dp c -(K a Dp a +K b Dp b )R N -Yes cc dΔu ca / dt = K a Δψ a / C dΔu cb / dt = K b Δψ b / C dΔu cc / dt = K c Δψc / C Among them, R N It is a damping resistor.

5. The method according to claim 4, characterized in that, In step S45, the slope values ​​of the piecewise lines of the inductances of phases a, b, and c in the linear time-varying system equations are obtained as follows: K a =K a0 +δK a K b =K b0 +δK b K c =K c0 +δK c in K a0 、K b0 、K c0 for K a 、K b 、K c Linear part, δK a、 δK b、 δK c Corresponding to K a 、K b 、K c The variation components surrounding the linear portion; For different disturbances and different actual parameters, after substituting the state equations of step S42 and the linear time-varying system equations of step S44, the different damping resistances R are calculated. N Used to eliminate system resonance.

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