A comprehensive identification and control method for resonant overvoltage in shale gas field distribution network

Abstract

The present invention discloses a method for comprehensive identification and treatment of resonant overvoltage of a shale gas field distribution network. The method performs real-time impedance sweep and frequency impedance comparison on each node of the shale gas field distribution network. If the frequency impedance of the current node is less than the preset frequency impedance, the impedance sweep and frequency impedance comparison are performed on the next node; if the frequency impedance of the current node is greater than the preset frequency impedance, the node performs node voltage judgment, and performs harmonic suppression processing according to the judgment result; the bus zero-sequence voltage and zero-sequence component of each node are monitored in real time to screen out nodes where ferromagnetic resonance occurs; the bus zero-sequence voltage of the node where ferromagnetic resonance occurs is subjected to FFT decomposition, and after obtaining the ferromagnetic resonance frequency, the active inverter device is used to suppress the ferromagnetic resonance of the node. The present invention can identify and treat the resonant overvoltage of the shale gas field distribution network involving staged loads such as voltage cracking pumps and grid-electric drilling rigs, and the operation is simple, and the normal operation of the distribution network and the normal production of the shale gas field are not affected.

Description

Technical Field

[0001] The present invention relates to the field of power system safety analysis, and in particular to a method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network with staged loads such as a voltage cracking pump and a grid-powered drilling rig. Background Art

[0002] Resonant overvoltage problem has always been one of the common problems in power systems. With the commissioning of high-power voltage cracking pumps, grid-electric drilling rigs and other stage loads and their supporting frequency conversion equipment in shale gas fields, the power system has shown increasingly obvious power electronic characteristics. A large number of harmonics are introduced into the distribution network, which is very easy to induce harmonic resonance at a specific frequency, making the impedance value at this frequency extremely large. Only a small current value will cause a very large voltage value, resulting in harmonic resonance overvoltage, affecting the normal operation of the equipment or even burning the equipment; the operation of stage loads such as voltage cracking pumps and grid-electric drilling rigs is uncertain, and affected by the changes of other loads on the same feeder, the topological structure of the entire shale gas field distribution network is constantly changing. Under certain circumstances, capacitive and inductive impedance matching will cause ferromagnetic resonance. Ferromagnetic resonance occurs in the electromagnetic voltage transformer (PT) and causes saturation overcurrent. The overcurrent value may reach dozens of times the rated excitation current of the PT, which is very easy to cause the PT to burn. At the same time, the ferromagnetic resonance overvoltage lasts for a long time, which is easy to cause related equipment to burn, and even cause power outages, seriously affecting the stable operation of the shale gas field distribution network, and causing a great impact on the normal production of the shale gas field.

[0003] It is the first time that clean mining technologies such as grid-powered drilling rigs and voltage-fracture pumps have been widely used in shale gas mining. The resulting resonant overvoltage problem in shale gas fields urgently needs further research and control. Based on long-term research on harmonic resonance and ferromagnetic resonance, domestic and foreign scholars have proposed a series of control measures and corresponding detuning devices. These measures and devices can be mainly divided into two categories: one is to change the structural parameters of the power grid to keep the power grid away from the conditions for resonance and avoid the occurrence of resonance; the other is to consume the energy generated by the resonant overvoltage to avoid further damage to the power grid caused by overvoltage. However, the two methods have problems such as single application scenarios, large suppression blind spots, poor flexibility and high costs, and are not completely suitable for the control of resonant overvoltage problems in shale gas field distribution networks. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a comprehensive identification and control method for the resonant overvoltage of the shale gas field distribution network, which can identify and control the resonant overvoltage of the shale gas field distribution network taking into account the stage loads such as the voltage fracturing pump and the grid-powered drilling rig, and is simple to operate and does not affect the normal operation of the distribution network and the normal production of the shale gas field.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network, comprising:

[0007] S1, perform real-time impedance frequency sweep on each node of the shale gas field distribution network, and compare the node frequency impedance of each node with the preset frequency impedance. If the current node frequency impedance is less than the preset frequency impedance, perform impedance frequency sweep and frequency impedance comparison on the next node; if the current node frequency impedance is greater than the preset frequency impedance, proceed to step S2;

[0008] S2, judging the node voltage of the node with impedance greater than the preset frequency according to the preset harmonic suppression voltage, and performing harmonic suppression processing according to the judgment result;

[0009] S3, real-time monitoring of the bus zero-sequence voltage of each node, the zero-sequence component of the PT primary opening side voltage and the zero-sequence component of the primary side current, and screening out the nodes where ferromagnetic resonance occurs according to the ferromagnetic resonance judgment conditions;

[0010] S4, performing FFT decomposition on the bus zero-sequence voltage of the node where ferromagnetic resonance occurs to obtain the ferromagnetic resonance frequency;

[0011] S5, using an active inverter device and a ferromagnetic resonance frequency to suppress ferromagnetic resonance at the node where ferromagnetic resonance occurs.

[0012] Specifically, step S2 is specifically as follows: for nodes with impedance greater than a preset frequency, node voltage is judged: if the node voltage is lower than 0.4 kV, an active filter is installed at the node where harmonics are likely to be induced and harmonic resonance is generated, and harmonics of various frequency bands are filtered out; if the node voltage is higher than 10 kV, a passive filter is installed at the node where harmonics are likely to be induced and harmonic resonance is generated, and harmonics of a specific frequency that is likely to induce resonance are filtered out. The preset frequency impedance of the present invention is 1000'Ω.

[0013] Furthermore, the passive filter adopts a single tuned filter model, and its harmonic impedance value is expressed as:

[0014]

[0015] In the above formula, Z LCh is the harmonic impedance value of the single tuned filter, R LC , X L , X C are the fundamental resistance, inductive reactance and capacitive reactance of the single tuned filter respectively, and h is the filtering order of the single tuned filter.

[0016] Further, the process of filtering out the harmonics of a specific frequency that is likely to induce resonance includes: when filtering out the harmonics of a specific frequency, satisfying Z LCh Minimum, that is, satisfying:

[0017]

[0018] At this time, the filtering times of the single tuned filter are:

[0019]

[0020] At this time, the quality factor of the single tuned filter is:

[0021]

[0022] In the formula, ω h is the resonant angular frequency of the single tuned filter, and the value range of the quality factor Q is 30Q 100;

[0023] When filtering out the hth harmonic, determine the reactive compensation capacity Q of the single tuned filter F , then the capacitor capacity is:

[0024] The fundamental reactance of the capacitor is:

[0025] The fundamental reactance of the inductor is:

[0026] The series resistance is:

[0027] According to the configuration principle of the passive filter, the quality factor Q is 30.

[0028] Specifically, step S5 is as follows: when ferromagnetic resonance occurs at the current node, a zero-sequence current signal having the same frequency as the ferromagnetic resonance frequency is injected into the distribution network node through an active inverter device, and the amplitude and phase of the injected zero-sequence current signal are changed in real time so that the zero-sequence voltage value of the node is zero, thereby suppressing the ferromagnetic resonance.

[0029] Furthermore, the ferromagnetic resonance judgment condition is: when the zero-sequence component of the PT primary opening side voltage and the zero-sequence component of the primary side current of the current node are less than 10% of the rated phase voltage and the rated phase current of the node, it is determined that ferromagnetic resonance occurs at the node.

[0030] Beneficial effects of the present invention: The present invention uses DIgSILENT and PSCAD software to simulate and analyze the method in a shale gas field distribution network taking into account a voltage fracturing pump and a grid-powered drilling rig. From the simulation results, it can be seen that the resonant overvoltage identification and control method proposed in the present invention can effectively find nodes that are prone to induce harmonic resonance and control them in time, thereby reducing the harmonic resonance overvoltage that may be caused by harmonics, and can quickly release the accumulated transient energy after ferromagnetic resonance occurs, effectively reducing the overvoltage level and shortening the fault recovery time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of the method of the present invention;

[0032] Figure 2 A flow chart for the identification and control of resonant overvoltage in shale gas field distribution network;

[0033] Figure 3 This is a schematic diagram of the internal frequency scanning results of a single system in the shale gas field distribution network;

[0034] Figure 4 This is a schematic diagram of the frequency scanning results of each node in the shale gas field distribution network;

[0035] Figure 5 This is a schematic diagram of the ferromagnetic resonance suppression principle;

[0036] Figure 6 This is the voltage waveform of the opening side of the 35kV voltage transformer when ferromagnetic resonance occurs;

[0037] Figure 7 This is the waveform of the primary side excitation current of a 35kV voltage transformer when ferromagnetic resonance occurs;

[0038] Figure 8 This is the waveform of 35kV bus voltage when ferromagnetic resonance occurs;

[0039] Fig. 9 This is the voltage waveform of the open side of the 35kV voltage transformer after treatment;

[0040] Fig.10 This is the waveform of the primary side excitation current of the 35kV voltage transformer after treatment;

[0041] Fig.11 This is the 35kV bus voltage waveform after treatment. DETAILED DESCRIPTION

[0042] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below. Obviously, the implementation cases described are part of the embodiments of the present invention, not all of the embodiments, and cannot be understood as limiting the scope of the implementation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0043] Embodiment 1:

[0044] In this embodiment, Figure 1 As shown, a method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network includes the following steps:

[0045] S1 performs real-time impedance frequency sweep on each node of the shale gas field distribution network. When the node frequency impedance is less than 1000'Ω, no harmonic suppression measures are required, and the process returns to this step to continue impedance frequency sweep on other nodes. If the impedance of the node is greater than 1000'Ω at a certain frequency, the process proceeds to the next step.

[0046] S2 judges the node voltage with frequency impedance greater than 1000′Ω: if the node voltage is low (0.4kV), an active filter is installed at the node where harmonics are likely to induce harmonic resonance to filter out harmonics of various frequency bands; if the node voltage is high (10kV), a passive filter is installed at the node where harmonics are likely to induce harmonic resonance to filter out harmonics of specific frequencies that are likely to induce resonance;

[0047] S3 monitors the zero-sequence voltage of each node bus, the zero-sequence component of the voltage on the primary opening side of the PT, and the zero-sequence component of the current on the primary side in real time: when the zero-sequence component is less than 10% of the rated phase voltage and rated phase current, ferromagnetic resonance occurs;

[0048] S4 performs FFT decomposition on the zero-sequence voltage to find the ferromagnetic resonance frequency;

[0049] When ferromagnetic resonance occurs in S5, a zero-sequence current signal of corresponding frequency is injected into the distribution network node through an active inverter device, and the zero-sequence voltage value of the node is made zero by changing the amplitude and phase of the injected zero-sequence current signal in real time, thereby suppressing ferromagnetic resonance.

[0050] For nodes that are prone to inducing harmonic resonance, if the voltage level is low (0.4kV), the present invention selects an active filter with appropriate parameters, and if the voltage level is high (10kV), selects an appropriate passive filter to filter out harmonics in time; for nodes that are prone to inducing ferromagnetic resonance overvoltage, the PT primary side excitation current, the open side voltage and the bus voltage measured at the node are subjected to FFT decomposition to find out the ferromagnetic resonance frequency, and a zero-sequence current signal of the corresponding frequency is injected into the node through an active inverter device, and the zero-sequence voltage value of the node is made zero by continuously changing the amplitude and phase of the injected zero-sequence current signal.

[0051] The method of the present invention is further described below:

[0052] Figure 2 is the equivalent circuit of the single tuned filter. The passive filter adopts the single tuned filter model. Ignoring the influence of the skin effect, the resistance, inductance and capacitance of the single tuned filter remain unchanged. Its harmonic impedance can be expressed as:

[0053]

[0054] In the above formula, Z LCh is the harmonic impedance value of the single tuned filter, R LC , X L , X C are the fundamental resistance, inductive reactance and capacitive reactance of the single tuned filter respectively, and h is the filtering order of the single tuned filter.

[0055] When filtering out harmonics of a specific frequency, the Z LCh Minimum, that is, satisfying:

[0056]

[0057] At this time, the filtering times of the single tuned filter are:

[0058]

[0059] At this time, the quality factor of the single tuned filter is:

[0060]

[0061] In the formula, ω h is the resonant angular frequency of the single tuned filter.

[0062] As the formula As shown, R is inversely proportional to C. When the inductance and capacitance of the filter are determined, the larger the Q, the smaller the R, and the more obvious the filtering effect. It is usually 30Q 100.

[0063] When filtering out the hth harmonic, the parameter design process of the single tuned filter is as follows:

[0064] Determine the reactive power compensation capacity Q of a single tuned filter F , then the capacitor capacity is:

[0065]

[0066] The fundamental reactance of the capacitor is:

[0067]

[0068] The fundamental reactance of the inductor is:

[0069]

[0070] The series resistance is:

[0071]

[0072] According to the configuration principle of passive filters, the quality factor Q value of single-tuned filters should be made consistent as much as possible, and the Q value should be taken as 30.

[0073] The active filter can select the appropriate capacity based on the actual compressor rated power, compressor rated voltage, load rate, total current distortion rate, harmonic current and reliability factor. For the inverter, the total current distortion rate is 0.3 and the reliability factor is 1.3.

[0074] Figure 3 The ferromagnetic resonance suppression principle diagram of the shale gas field distribution network is shown in Figure 1. Assume that the three phases in the figure are symmetrical with respect to the ground. A 、E B 、E C are the three-phase power supply voltages of A, B, and C in the power grid, r0 is the leakage resistance of a single phase to ground, C0 is the capacitance of a single phase to ground, u0 is the zero-sequence voltage, I i is the injected current, L A , L B , L C is the magnetizing inductance of the voltage transformer.

[0075] The excitation current on the high voltage side of the voltage transformer is recorded as in the form of is the magnetic flux, assuming that the number of turns of the coil windings on the high and low voltage sides of the voltage transformer are m1 and m2 respectively,

[0076] The three-phase winding can be written as:

[0077] In the formula, i a 、i b 、i care the primary side excitation current of the voltage transformer respectively.

[0078] According to KCL, we can get:

[0079]

[0080] From the above formula, we can know that the zero-sequence voltage u0 and the injected current I i A certain functional relationship is presented. The active inverter device modulated by PWM wave is used to inject zero-sequence current into the node where ferromagnetic resonance occurs. This absorbs the zero-sequence transient energy in the shale gas field distribution network during the fault recovery process, thereby providing a new release path for the excess charge accumulated in the line-to-ground capacitance, thereby suppressing the generation of overvoltage and improving the stability of the power grid.

[0081] Embodiment 2:

[0082] In order to verify the reliability of the harmonic resonance impedance monitoring of the shale gas field distribution network described in the present invention, the DIgSILENT software is used to perform frequency scanning on each node of the shale gas field distribution network.

[0083] Figure 3 , Figure 4 From the frequency sweep results of a single node and each node, it can be seen from Figure 3 that the larger impedance frequency is mainly concentrated in each frequency conversion device. Different types of filters are designed for each main frequency conversion device according to different voltage levels to reduce the resonant impedance. Figure 3 It can be seen that the nodes with higher frequency impedance are mainly the fracturing and drilling platforms. The frequency is swept inside each platform in turn to control the internal harmonic sources of the fracturing and drilling platforms.

[0084] Figure 5 This is an embodiment of the ferromagnetic resonance control system for the shale gas field distribution network in the present invention, including an active inverter device installed between the neutral point of the distribution network and the ground, and an active inverter device zero-sequence voltage model predictive control device composed of a voltage detection circuit, a controller and a PWM drive circuit connected in sequence, the detection circuit is external and the current u0 and I0 of the neutral point of the distribution network, and the drive circuit directly drives the active inverter device.

[0085] Figure 6 , Figure 7 , Figure 8They are the 35kV PT primary side opening voltage, primary side excitation current and 35kV bus voltage waveforms after ferromagnetic resonance occurs. At this time, the system has a frequency division resonance with a resonance frequency of 14.28z. The PT primary side excitation current is obviously distorted, and the amplitude increase of the higher frequency resonance and fundamental frequency resonance is the largest, which is 0.006A in normal operation and 0.063A when ferromagnetic resonance occurs, with an overcurrent multiple of 10.5 times. The bus voltage is 35kV in normal operation and 61.433kV during resonance, with an overvoltage multiple of 1.743 times, and the fault recovery time is 0.5s.

[0086] Fig. 9 , Fig.10 , Fig.11 They are the 35kV PT primary side opening voltage, primary side excitation current and 35kV bus voltage waveforms after treatment. The overcurrent multiple is 3.8 times; the overvoltage multiple is 0.743 times, and the fault recovery time is 0.12s. The overcurrent multiple, overvoltage multiple and fault recovery time have been significantly improved compared with those before treatment.

[0087] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of the present invention to be protected is defined by the attached claims and their equivalents.

Claims

1. A method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network, characterized in that: include: S1, perform real-time impedance frequency sweep on each node of the shale gas field distribution network, and compare the node frequency impedance of each node with the preset frequency impedance. If the current node frequency impedance is less than the preset frequency impedance, perform impedance frequency sweep and frequency impedance comparison on the next node; if the current node frequency impedance is greater than the preset frequency impedance, proceed to step S2; S2, judging the node voltage of the node with impedance greater than the preset frequency according to the preset harmonic suppression voltage, and performing harmonic suppression processing according to the judgment result; S3, real-time monitoring of the bus zero-sequence voltage of each node, the zero-sequence component of the PT primary opening side voltage and the zero-sequence component of the primary side current, and screening out the nodes where ferromagnetic resonance occurs according to the ferromagnetic resonance judgment conditions; S4, performing FFT decomposition on the bus zero-sequence voltage of the node where ferromagnetic resonance occurs to obtain the ferromagnetic resonance frequency; S5, using an active inverter device and a ferromagnetic resonance frequency to suppress ferromagnetic resonance at a node where ferromagnetic resonance occurs; The step S2 is specifically as follows: determining the node voltage of the node with an impedance greater than a preset frequency: if the node voltage is lower than 0.4 kV, an active filter is installed at the node where harmonics are likely to be induced and harmonic resonance is likely to be generated, so as to filter out harmonics of various frequency bands; if the node voltage is higher than 10 kV, a passive filter is installed at the node where harmonics are likely to be induced and harmonic resonance is likely to be generated, so as to filter out harmonics of a specific frequency that is likely to induce resonance; The passive filter adopts a single tuned filter model, and its harmonic impedance value is expressed as: In the above formula, Z LCh is the harmonic impedance value of the single tuned filter, R LC , X L , X C are the fundamental resistance, inductive reactance and capacitive reactance of the single tuned filter respectively, and h is the filtering order of the single tuned filter; The process of filtering out harmonics of a specific frequency that is likely to induce resonance includes: when filtering out harmonics of a specific frequency, satisfying Z LCh Minimum, that is, satisfying: At this time, the filtering times of the single tuned filter are: At this time, the quality factor of the single tuned filter is: In the formula, ω h is the resonant angular frequency of the single tuned filter, and the value range of the quality factor Q is 30≤Q≤100; When filtering out the hth harmonic, determine the reactive compensation capacity Q of the single tuned filter F , then the capacitor capacity is: The fundamental reactance of the capacitor is: The fundamental reactance of the inductor is: The series resistance is: According to the configuration principle of passive filter, the quality factor Q is 30; In the above formula, Z LCh is the harmonic impedance value of the single tuned filter, ω0 is the resonant angular frequency for filtering out a specific frequency, L, C, R are the inductance, capacitance, and resistance of the single tuned filter at the frequency to be filtered out, respectively, and U is the voltage value across the capacitor.

2. The method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network according to claim 1 is characterized in that: The step S5 is specifically as follows: when ferromagnetic resonance occurs at the current node, a zero-sequence current signal having a frequency the same as the ferromagnetic resonance frequency is injected into the distribution network node through an active inverter device, and the amplitude and phase of the injected zero-sequence current signal are changed in real time so that the zero-sequence voltage value of the node is zero, thereby suppressing the ferromagnetic resonance.

3. The method for comprehensive identification and control of resonant overvoltage in a shale gas field distribution network according to claim 1 is characterized in that: The ferromagnetic resonance judgment condition is: when the zero-sequence component of the PT primary opening side voltage and the zero-sequence component of the primary side current of the current node are less than 10% of the rated phase voltage and rated phase current of the node, it is determined that ferromagnetic resonance occurs at the node.

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