Protection method for internal short circuit of rotor winding of variable-speed pumped storage unit

Abstract

The invention provides a protection method for internal short circuit of a rotor winding of a variable-speed pumped storage unit, and the method comprises the steps: determining the length of a data window according to the short-circuit protection action time limit requirement of the unit, and calculating the frequency spectrum resolution according to the length of the data window; determining a frequency range corresponding to each spectral line on a frequency axis of the spectrogram based on the spectral resolution, and collecting a slip ratio and a stator side transverse differential current of the unit; selecting a plurality of fractional harmonic magnetic fields in the transverse differential current on the stator side, obtaining harmonic induced by each magnetic field, calculating the frequency of each harmonic based on the slip ratio, and determining a spectral line corresponding to each harmonic; and performing FFT operation on the stator transverse differential current, calculating the total effective value of the spectral line corresponding to each harmonic wave, and performing rotor winding internal short circuit protection according to the total effective value. According to the method, main harmonic components on the stator side of the unit are extracted to realize short-circuit protection in the rotor winding, operation is performed in a short data window, and the timeliness and accuracy of short-circuit protection are improved.

Description

Technical Field

[0001] The present application relates to the technical field of short-circuit protection of variable-speed pumped-storage units, and in particular to a method for protecting a variable-speed pumped-storage unit from internal short circuit in a rotor winding. Background Art

[0002] In order to meet the construction needs of new power systems, it is necessary to vigorously develop intelligent equipment with energy storage functions. Among them, variable-speed pumped storage units can take into account the optimal efficiency of turbine and pump conditions, and can flexibly adjust the active power absorbed by the unit under pump conditions. Compared with fixed-speed pumped storage units, they are more suitable for the construction of new power systems.

[0003] In practical applications, the three-phase rotor windings of variable-speed pumped storage units are subjected to huge centrifugal forces during high-speed rotation and speed regulation, which causes extrusion and displacement deformation between the rotor windings, making the insulation of the rotor windings more susceptible to wear and tear, and the probability of internal short-circuit failure is higher than that of the stator windings. Therefore, short-circuit protection of variable-speed pumped storage units has become an issue that requires special attention.

[0004] In the related art, the rotor winding protection configured for the variable speed pumped storage unit usually includes rotor overvoltage protection, rotor overcurrent protection, and rotor winding short circuit protection achieved through a neural network algorithm, etc. However, the protection schemes in the above-mentioned related art, such as the scheme based on the neural network algorithm, take a long time in actual application, cannot achieve rapid protection against short circuit faults, and the fault factors considered are relatively single, and the protection effect cannot meet the actual needs. Summary of the invention

[0005] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0006] To this end, the first purpose of the present application is to propose a protection method for internal short circuit of the rotor winding of a variable-speed pumped-storage unit. The method collects the differential current on the stator side of the unit and extracts the main harmonic components on the stator side. It can complete the selection and amplitude calculation of the FFT spectrum lines corresponding to the extracted main harmonic components according to the measured slip rate within a shorter algorithm data window, thereby improving the timeliness, accuracy and reliability of short-circuit protection.

[0007] The second object of the present application is to provide a protection system for internal short circuit of rotor winding of a variable speed pumped storage unit;

[0008] A third object of the present application is to provide a non-transitory computer-readable storage medium.

[0009] To achieve the above-mentioned purpose, the first aspect of the present application is to provide a method for protecting a variable speed pumped storage unit rotor winding from internal short circuit, the method comprising the following steps:

[0010] Determine the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculate the spectrum resolution of the fast Fourier transform FFT according to the data window length;

[0011] Determine the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and collect the slip rate and stator side differential current of the target unit;

[0012] By performing an internal short-circuit fault simulation analysis on the target unit, multiple fractional harmonic magnetic fields in the stator side transverse differential current are selected, the harmonics induced by each of the fractional harmonic magnetic fields are obtained, and the frequency of each of the harmonics is calculated based on the slip rate, and the FFT spectrum line corresponding to each harmonic is determined according to the frequency range to which the frequency of each harmonic belongs, wherein the frequency components of the harmonics induced by the multiple fractional harmonic magnetic fields are greater than a preset component threshold;

[0013] Perform FFT operation on the stator side transverse differential current, calculate the total effective value of the FFT spectrum line corresponding to each harmonic, and use the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

[0014] Optionally, in one embodiment of the present application, the calculating the spectral resolution of the fast Fourier transform FFT according to the data window length includes: calculating the inverse of the data window length, and taking the inverse as the spectral resolution; after calculating the spectral resolution of the fast Fourier transform FFT, it also includes: numbering each FFT spectral line on the frequency axis in order from low to high frequency, and calculating the frequency of each FFT spectral line based on the spectral resolution and the number.

[0015] Optionally, in one embodiment of the present application, based on the spectrum resolution, the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum graph is calculated by the following formula:

[0016]

[0017] Where i is the number of the FFT line and Δf is the spectrum resolution.

[0018] Optionally, in one embodiment of the present application, the collecting of the slip rate and stator side differential current of the target unit includes: collecting the rotational speed and the slip rate of the target unit through a photoelectric encoder installed on the shaft of the generator motor of the target unit; and collecting the stator side differential current through a differential protection circuit transformer TA installed at the stator side winding of the target unit.

[0019] Optionally, in one embodiment of the present application, the internal short-circuit fault simulation analysis of the target unit is performed to select multiple fractional harmonic magnetic fields in the stator side differential current, including: establishing a mathematical model of the internal fault of the rotor winding of the target unit based on a multi-loop analysis method, and simulating the internal short-circuit fault of the rotor winding of the target unit through the mathematical model; performing a spectral analysis on the simulation results of the stator side differential current after the short-circuit fault to determine the frequency components of each fractional harmonic; and taking the fractional harmonic magnetic field corresponding to the harmonic whose frequency component is greater than the component threshold as the selected multiple fractional harmonic magnetic fields.

[0020] Optionally, in one embodiment of the present application, the calculation of the total effective value of the FFT spectrum lines corresponding to each harmonic includes: determining the amplitude of the FFT spectrum line corresponding to each harmonic through the FFT operation result of the stator side differential current; calculating the cumulative sum of the amplitudes of the FFT spectrum lines corresponding to each of the harmonics, and calculating the total effective value based on the cumulative sum.

[0021] Optionally, in one embodiment of the present application, using the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of a target unit includes: comparing the fault characteristic quantity calculated in real time with a preset protection setting current threshold, and controlling the target unit to trip when the fault characteristic quantity is greater than the current threshold and the duration exceeds a preset delay value.

[0022] To achieve the above-mentioned purpose, the second aspect of the present application further proposes a protection system for internal short circuit of rotor winding of a variable speed pumped storage unit, comprising the following modules:

[0023] A calculation module, used to determine the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculate the spectrum resolution of the fast Fourier transform FFT according to the data window length;

[0024] An acquisition module, used for determining the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and acquiring the slip rate and stator side lateral differential current of the target unit;

[0025] A determination module is used to select multiple fractional harmonic magnetic fields in the stator side transverse differential current by performing internal short-circuit fault simulation analysis on the target unit, obtain the harmonics induced by each of the fractional harmonic magnetic fields, calculate the frequency of each of the harmonics based on the slip rate, and determine the FFT spectrum line corresponding to each harmonic according to the frequency range to which the frequency of each harmonic belongs, wherein the frequency components of the harmonics induced by the multiple fractional harmonic magnetic fields are greater than a preset component threshold;

[0026] The protection module is used to perform FFT operation on the stator side differential current, calculate the total effective value of the FFT spectrum line corresponding to each harmonic, and use the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

[0027] In order to implement the above-mentioned embodiments, the third aspect embodiment of the present application also proposes a non-temporary computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the protection method for internal short circuit of the rotor winding of the variable-speed pumped-storage unit in the above-mentioned first aspect is implemented.

[0028] The technical solution provided by the embodiment of the present application brings at least the following beneficial effects: the present application first collects the transverse differential current on the stator side through the transverse differential protection TA on the stator side of the variable speed pumped storage unit, and can accurately measure the current without adding additional detection equipment. Then, the main harmonic components on the stator side are extracted, and the frequencies of the extracted harmonics are calculated according to the measured unit slip, and then the main harmonic components are respectively corresponded to an FFT spectrum line. Then, by performing FFT operation on the stator transverse differential current, the total effective value of each selected FFT spectrum line is calculated, and trip protection is performed according to the fault characteristic quantity. Therefore, the present application can quickly complete the selection and amplitude calculation of the FFT spectrum line corresponding to the extracted main harmonic component according to the measured slip within a shorter algorithm data window, which can meet the rapidity requirements of the main protection of the rotor winding, and consider the influence of the slip rate on the fault characteristics, and select different FFT spectrum lines for calculation under different slip rates. Therefore, the present application improves the timeliness, accuracy and reliability of the internal short-circuit fault protection of the rotor winding, which is beneficial to ensuring the safe and stable operation of the rotor winding of the variable-speed pumped storage unit.

[0029] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0031] Figure 1 A flow chart of a method for protecting a variable-speed pumped-storage unit rotor winding from internal short circuits proposed in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of the structure of a variable speed pumped storage unit proposed in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of a current transformer configuration method for a stator winding of a unit proposed in an embodiment of the present application;

[0034] Figure 4 A schematic diagram of a rotor winding tap of a unit proposed in an embodiment of the present application;

[0035] Figure 5 A flowchart of a specific variable speed pumped storage unit rotor winding internal short circuit protection method proposed in an embodiment of the present application;

[0036] Figure 6 A schematic diagram of calculation results of the total effective value of an FFT spectrum line using a zero-sequence transverse differential current as input proposed in an embodiment of the present application;

[0037] Figure 7 A schematic diagram of the calculation results of the total effective value of the FFT spectrum line using the A-phase split phase differential current as input proposed in an embodiment of the present application;

[0038] Figure 8 A schematic diagram of the calculation results of the total effective value of the FFT spectrum line using the B-phase split phase differential current as input proposed in an embodiment of the present application;

[0039] Fig. 9 A schematic diagram of the calculation results of the total effective value of the FFT spectrum line using the C-phase split phase differential current as input proposed in an embodiment of the present application;

[0040] Fig.10 A structural schematic diagram of a fault locating system for a rotor winding of a variable-speed pumped-storage unit proposed in an embodiment of the present application. DETAILED DESCRIPTION

[0041] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0042] It should be noted that the rotor winding protection configured for the variable-speed pumped storage unit in the related technology is generally rotor overvoltage protection, rotor overcurrent protection and injection-type rotor grounding protection. Among them, the dead zone of the rotor overcurrent protection is relatively large. If differential protection is used on the rotor side, the corresponding increase in slip rings and current transformers (TA) will affect the mechanical stability of the rotor, and the low-frequency current on the rotor side is difficult to be accurately measured by the electromagnetic TA. For short-circuit protection related technologies, there are also protection schemes based on fast Fourier transform (FFT) and neural networks, as well as main protection schemes based on the total effective value of harmonics.

[0043] However, since the large short-circuit current generated when the variable speed pumped storage unit rotor winding has an internal fault will generate a destructive electromagnetic force, and may also cause overheating, burning the winding and core, the rotor winding internal short-circuit protection scheme needs to act quickly to avoid further damage to the unit. In the related art, the protection scheme based on FFT and neural network sets the data window length of the algorithm to a long 1s to ensure a sufficiently small (1Hz) spectral resolution, so it is impossible to achieve rapid protection against faults.

[0044] In addition, the main protection scheme based on the total effective value of harmonics takes all harmonic components except the DC component and the fundamental component into account, and cannot purposefully extract one or several characteristic harmonic components, and the corresponding unbalanced component is small during normal operation. At the same time, the frequency of the stator side circulating current during a fault is a function of the slip rate, and the algorithm of this protection does not change with the group slip rate, so it fails to consider the impact of the slip rate on the fault characteristics such as the circulating current frequency.

[0045] That is, the existing rotor winding internal short-circuit fault protection schemes include protection schemes based on FFT and LSTM neural networks and harmonic total effective value main protection schemes. However, the data window length of the protection algorithm based on FFT and LSTM neural networks is too long, resulting in slow action speed. The harmonic total effective value main protection scheme ignores the change of fault characteristic frequency with slip rate during actual operation of the unit, and cannot purposefully select characteristic subharmonics to further improve the sensitivity of the rotor winding main protection.

[0046] To this end, in view of the problem that the rotor winding protection scheme in the related art cannot act quickly and does not consider the impact of slip rate on characteristic harmonics, the present application proposes a method for internal short-circuit protection of the rotor winding of a variable-speed pumped-storage unit based on extracting the main harmonic components on the stator side. The method extracts the main harmonic components on the stator side of the unit to achieve internal short-circuit protection of the rotor winding, performs calculations within a shorter data window, and improves the timeliness and accuracy of short-circuit protection.

[0047] A method and system for protecting a variable-speed pumped-storage unit rotor winding from internal short circuit according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0048] Figure 1 This is a flow chart of a method for protecting a variable speed pumped storage unit rotor winding from internal short circuits proposed in an embodiment of the present application, as shown in FIG. Figure 1 As shown, the method comprises the following steps:

[0049] Step S101, determining the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculating the spectrum resolution of the fast Fourier transform FFT according to the data window length.

[0050] Specifically, the variable-speed pumped-storage unit that is currently to undergo internal short-circuit protection for the rotor winding is taken as the target unit. The fixed data window length T in the subsequent calculation process is determined according to the short-circuit protection action time limit requirements of the target unit, and then the FFT spectrum resolution Δf is calculated according to the fixed data window length T of the algorithm.

[0051] Among them, the selection of the data window length needs to ensure that it can meet the rapidity requirements of the main protection of the rotor winding. The data window length T can be determined based on the maximum allowable protection action time of the current operating conditions of the target unit. For example, to ensure the protection action speed, this application can select T=60ms.

[0052] In one embodiment of the present application, the spectrum resolution of the fast Fourier transform FFT is calculated according to the data window length, including: calculating the reciprocal of the data window length, and using the reciprocal as the spectrum resolution. For example, when the data window length T is selected as 60ms according to the above example, the spectrum resolution of the FFT is Δf=1 / T=16.67HZ.

[0053] Furthermore, in this embodiment, after calculating the spectrum resolution of the fast Fourier transform FFT, it also includes: numbering each FFT spectrum line on the frequency axis in order from low to high frequency, and calculating the frequency of each FFT spectrum line based on the spectrum resolution and the number.

[0054] Specifically, the spectra on the frequency axis of the spectrum graph are numbered in order from low to high frequency, and each horizontal axis on the frequency axis corresponds to a spectrum line, that is, spectrum line m i The number of the spectrum line is i. The spectrum line m can be calculated by the following formula i Frequency:

[0055] f mi =(i-1)Δf, i=1,2,3...

[0056] It should be noted that the horizontal coordinate value of each spectral line on the spectrum axis is only determined by the spectrum resolution. Therefore, when the spectrum lines are sorted and numbered according to frequency, there is no need to perform FFT calculation first, that is, the specific height of each spectrum line and the complete spectrum diagram are not required. For example, when the spectrum resolution is 16.67Hz, it can be calculated by substituting the above formula that the first spectrum line is 0Hz, the second is 16.67Hz, the third is 33.33Hz, and so on. Therefore, since the frequency of the FFT spectrum line is only determined by the spectrum resolution, in this step, after calculating the spectrum resolution, the spectrum lines can be sorted from left to right on the horizontal axis of the spectrum diagram according to the size of the spectrum.

[0057] Step S102, determining the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and collecting the slip rate and stator side differential current of the target unit.

[0058] Specifically, the frequency axis is divided into multiple continuous non-overlapping frequency ranges, and each frequency range is corresponded to an FFT spectrum line in turn according to the "rounding" principle, that is, a frequency range corresponding to each FFT spectrum line on the frequency axis is determined. When determining the frequency range corresponding to each FFT spectrum line, the frequency of the midpoints of two adjacent spectrum lines is classified as follows to avoid involving new spectrum lines in actual calculations as much as possible.

[0059] In one embodiment of the present application, based on the spectrum resolution, the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum graph can be calculated by the following formula:

[0060]

[0061] Where i is the number of the FFT line and Δf is the spectrum resolution.

[0062] For example, continuing to refer to the above example, when the spectrum resolution is 16.67 Hz, the frequency range corresponding to each FFT spectrum line calculated according to the above formula is shown in the following Table 1.

[0063] Table 1 Frequency range corresponding to each FFT spectrum line

[0064]

[0065]

[0066] Among them, the above Table 1 only lists the frequency ranges corresponding to the first 6 spectral lines as an example, and the frequency ranges corresponding to the remaining spectral lines can be calculated according to the above method, which will not be repeated here.

[0067] Furthermore, the slip rate and stator side differential current of the target unit are collected to facilitate the calculation of subsequent fault characteristic quantities.

[0068] In one embodiment of the present application, the slip rate and stator-side differential current of the target unit are collected, including: collecting the speed and slip rate of the target unit through a photoelectric encoder installed on the shaft of the generator motor of the target unit; collecting the stator-side differential current through a differential protection circuit transformer TA installed at the stator-side winding of the target unit.

[0069] Specifically, if Figure 2As shown, the embodiment of the present application pre-installs a speed measurement module, a current measurement module, and an acquisition and calculation module in the variable speed pumped storage unit. Among them, the speed measurement module includes a photoelectric encoder installed at the shaft of the generator motor, and the photoelectric encoder is used to measure the speed and slip rate of the unit. The current measurement module includes a transverse differential protection TA installed at the stator winding, and the current transformer TA is used to measure the stator side transverse differential current. The acquisition and calculation module is used to collect the signals measured by the speed measurement module and the current measurement module, so as to obtain the slip rate and stator transverse differential protection current of the variable speed pumped storage unit, and input the measured signal, and then use the algorithm to calculate the total effective value of the FFT spectrum line corresponding to the main harmonic components on the stator side, so as to realize the protection of the internal short circuit fault of the rotor winding.

[0070] Step S103, by performing internal short-circuit fault simulation analysis on the target unit, multiple fractional harmonic magnetic fields in the stator side differential current are selected, the harmonics induced by each fractional harmonic magnetic field are obtained, and the frequency of each harmonic is calculated based on the slip rate, and the FFT spectrum line corresponding to each harmonic is determined according to the frequency range to which the frequency of each harmonic belongs.

[0071] Among them, the frequency components of the harmonics induced by multiple fractional harmonic magnetic fields are greater than a preset component threshold. The component threshold is a preset judgment threshold for distinguishing whether the current fractional harmonic has a high content in the stator transverse differential current. When the frequency component of a harmonic is greater than the preset component threshold, it indicates that the harmonic has a high content in the stator transverse differential current and is the main harmonic component on the stator side.

[0072] Specifically, the present application extracts the main harmonic components of the stator transverse differential current when the rotor winding of the variable speed pumped storage unit is short-circuited internally, and selects different FFT spectrum lines for calculation according to each main harmonic component under different slip rates.

[0073] It should be noted that through the simulation analysis of the multi-loop model and the internal fault experiment of the rotor winding on the AC excitation prototype, the internal fault characteristics of the rotor winding of the variable-speed pumped storage unit can be determined, that is, when the internal short circuit of the rotor winding occurs, the fractional harmonic magnetic field will cause a circulating current in the stator branch, and the frequency of the circulating current can be calculated by the following formula:

[0074]

[0075] Wherein, P is the number of pole pairs of the stator winding of the variable speed pumped storage unit; k / P is the number of fractional harmonic magnetic fields; s is the slip rate of the motor; f N is the rated frequency of the stator current.

[0076] That is, when the rotor winding is short-circuited, the transverse differential current contains multiple-order fractional harmonic magnetic fields, and each fractional harmonic magnetic field can induce corresponding fractional harmonics. N There are two operation symbols, addition and subtraction, in front of it, so a k / P-order fractional harmonic magnetic field strictly corresponds to two harmonic frequencies, and the two circulating current frequency components induced by the same k / P-order fractional harmonic magnetic field are equal.

[0077] In specific implementation, the present application can determine the main harmonics on the stator side with a higher content by means of simulation. In one embodiment of the present application, by performing internal short-circuit fault simulation analysis on the target unit, multiple fractional harmonic magnetic fields in the stator side transverse differential current are selected, including the following steps: first, a mathematical model of the internal fault of the rotor winding of the target unit is established based on the multi-loop analysis method, and the internal short-circuit fault of the rotor winding of the target unit is simulated by the mathematical model; then, the simulation results of the stator side transverse differential current after the short-circuit fault are subjected to spectrum analysis to determine the frequency components of each fractional harmonic; and then, the fractional harmonic magnetic field corresponding to the harmonic whose frequency component is greater than the component threshold is used as the selected multiple fractional harmonic magnetic fields.

[0078] Specifically, for the specific target unit currently under study, a mathematical model of the internal fault of the rotor winding of the unit is established based on the multi-loop analysis method, and a large number of simulations are performed on the actual possible internal rotor short circuit. Then, based on the simulation of the internal fault of the rotor winding of the multi-loop model, the spectral analysis of the simulation results of the stator side differential current after the fault is performed, and the frequency components of the harmonics with higher frequency components are statistically summarized to determine the fractional harmonic magnetic field corresponding to several main harmonic frequency components after the internal short circuit of the rotor winding. For other types of units, the magnetic field can be selected according to this method. By simulating different types of units, different magnetic field selection rules for different units can be summarized.

[0079] For example, in general, for k / P harmonics, the two frequency components induced when k=1 are the highest of all frequency components, followed by k=2, and k=3 is the third highest if P is not equal to 3, otherwise it is k=4 (k / P needs to be a fraction).

[0080] Referring to the above example, the present application can start from a lower magnetic field order and select fractional harmonics with higher content in the stator transverse differential current, that is, the 6 harmonics induced by the first 3 lower-order fractional magnetic fields.

[0081] Furthermore, after obtaining the harmonics induced by each selected fractional harmonic magnetic field, the frequency of each harmonic is calculated based on the measured slip rate, and then the FFT spectrum line corresponding to each harmonic is determined according to the frequency range to which the frequency of each harmonic belongs on the frequency axis in step S102.

[0082] For example, from the calculation formula of the above circulating current frequency, it can be known that after s and P are determined, the frequency value of the harmonic can be calculated. Therefore, the frequencies of the six harmonics induced by the first three lower-order fractional magnetic fields can be obtained based on the actual unit slip rate s and the number of stator winding pole pairs P. Then, according to the frequency range to which the frequency of each harmonic belongs on the frequency axis, and in accordance with the correspondence between the determined FFT spectrum line and the frequency range, each harmonic is sequentially matched to the corresponding FFT spectrum line.

[0083] Step S104, performing FFT operation on the stator side transverse differential current, calculating the total effective value of the FFT spectrum line corresponding to each harmonic, and using the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

[0084] Specifically, the collected stator transverse differential current is subjected to FFT operation to obtain the amplitudes of each FFT spectrum line corresponding to the selected multiple stator-side main harmonics, and then the total effective value is calculated based on the amplitudes of each FFT spectrum line. The total effective value is used as the fault characteristic quantity to determine whether short-circuit protection is performed on the target unit.

[0085] In one embodiment of the present application, the total effective value of the FFT spectrum lines corresponding to each harmonic is calculated, including: determining the amplitude of the FFT spectrum line corresponding to each harmonic through the FFT operation result of the stator side differential current; calculating the cumulative sum of the amplitudes of the FFT spectrum lines corresponding to each harmonic, and calculating the total effective value based on the cumulative sum.

[0086] For example, continue to refer to the above example, and take the union of the spectrum line numbers corresponding to the selected 6 harmonics, and the set is I. Perform FFT operation on the stator transverse differential current to obtain the amplitude of all spectrum lines in set I. The amplitudes are superimposed and converted into effective values ​​by the following formula to obtain the fault characteristic value H rms :

[0087]

[0088] Where I is the set of spectral line numbers selected under the current slip rate, Amp mi is the spectrum line m i The amplitude, H rms is the total effective value of the selected spectral line.

[0089] Furthermore, the total effective value is used as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit, including: comparing the fault characteristic quantity calculated in real time with a preset protection setting current threshold, and controlling the target unit to trip when the fault characteristic quantity is greater than the current threshold and the duration exceeds a preset delay value.

[0090] Specifically, during the operation of the variable speed pumped storage unit, when H rmsThe calculated value exceeds the current threshold I set When the duration exceeds the delay setting, a trip signal will be issued to protect the rotor winding from internal short circuit. set Current threshold set for protection.

[0091] In summary, the protection method for the internal short circuit of the rotor winding of the variable speed pumped storage unit of the embodiment of the present application first collects the transverse differential current on the stator side through the transverse differential protection TA on the stator side of the variable speed pumped storage unit, and can accurately measure the current without adding additional detection equipment. Then, the main harmonic components on the stator side are extracted, and the frequencies of the extracted harmonics are calculated according to the measured unit slip, and then the main harmonic components are respectively corresponded to an FFT spectrum line. Then, by performing FFT operation on the stator transverse differential current, the total effective value of each selected FFT spectrum line is calculated, and trip protection is performed according to the fault characteristic quantity. Therefore, the method can quickly complete the selection and amplitude calculation of the FFT spectrum line corresponding to the extracted main harmonic component according to the measured slip within a shorter algorithm data window, which can meet the rapidity requirements of the main protection of the rotor winding, and consider the influence of the slip rate on the fault characteristics, and select different FFT spectrum lines for calculation under different slip rates. Therefore, the method improves the timeliness, accuracy and reliability of the rotor winding internal short-circuit fault protection, which is beneficial to ensure the safe and stable operation of the rotor winding of the variable-speed pumped storage unit.

[0092] Based on the above embodiments, in order to more clearly illustrate the implementation process and obtainable calculation results of the protection method for internal short circuit of the rotor winding of the variable speed pumped storage unit of the present application, a specific embodiment of short circuit protection for a variable speed pumped storage unit is described in detail below.

[0093] In this embodiment, a 12kW dynamic model machine with a rotor winding internal short circuit is used as an example to illustrate the protection method. The current transformer configuration of the stator winding of the unit is as follows: Figure 3 As shown, the rotor winding of the unit and its fault tap are as follows Figure 4 As shown, the composition of the four types of transverse differential currents on the stator side is shown in the following Table 2.

[0094] Table 2 Current transformer settings and differential current meters for 12kW dynamic prototype

[0095]

[0096] It should be noted that in actual applications, multiple transverse differential currents as shown in Table 2 above may be collected. The total effective value of each transverse differential current is calculated respectively, and a tripping judgment is performed under each current. The judgment logic of the tripping protection is an "or" logic, that is, as long as any of the calculation results of the four transverse differential currents meets the action conditions, the protection action is performed.

[0097] When carrying out protection, Figure 5 The short-circuit protection method shown in the figure is used to protect the unit from short-circuit. Figure 5 It can be seen that the unit meets the general rules described in the embodiment of the above step S103. Therefore, this embodiment calculates the frequencies of the six harmonics induced by the first three lower-order fractional magnetic fields, and corresponds them to the FFT spectrum lines in turn according to the frequency axis range to which the harmonic frequencies belong.

[0098] Further according to Figure 5 The protection method shown can obtain the spectrum line selection scheme of the 12kW prototype as shown in Table 3 below.

[0099] Table 3 Spectral line selection scheme for 12kW prototype

[0100]

[0101] Furthermore, the multi-loop analysis method is used to simulate the situation that the U1 tap of the rotor winding U phase is short-circuited to the V1 tap of the V phase when the unit is running at no-load at a slip rate of 8%. The simulation results are input into Figure 5 The protection algorithm shown in the figure can finally calculate the total effective value of the selected FFT spectrum line under the slip rate as follows: Figures 6 to 8 shown.

[0102] in, Figure 6 It is the total effective value of the selected FFT spectrum line with zero-sequence differential current as input before and after the U1 tap of the 12kW dynamic prototype rotor winding is short-circuited to the V1 tap. Figure 7 It is the total effective value of the selected FFT spectrum lines with the A-phase split-phase differential current as input before and after the U1 tap of the 12kW dynamic prototype rotor winding is short-circuited to the V1 tap. Figure 8 It is the total effective value of the selected FFT spectrum lines with the B-phase split-phase differential current as input before and after the U1 tap of the 12kW dynamic prototype rotor winding is short-circuited to the V1 tap. Fig. 9 It is the total effective value of the selected FFT spectrum lines with the C-phase split-phase differential current as input before and after the U1 tap of the 12kW dynamic prototype rotor winding is short-circuited to the V1 tap. Figures 6 to 9 Different colors are used to distinguish the calculated fault characteristic quantity H rms The curve of the protection setting current threshold I set curve.

[0103] Depend on Figures 6 to 9 It can be seen that the protection method of the present application based on extracting the main harmonic components on the stator side can successfully extract the fault characteristic quantity induced on the stator side when the rotor winding of the variable-speed pumped-storage unit is short-circuited internally, thereby realizing protection against internal short-circuit faults in the rotor winding and improving the current status of "weak protection" of the rotor winding of the variable-speed pumped-storage unit.

[0104] It should be noted that the specific implementation of each step in the method of this embodiment can also refer to the relevant description of the above embodiment, and the implementation principle is similar, which will not be repeated here.

[0105] In order to implement the above embodiment, the present application also proposes a fault location system for rotor windings of a variable speed pumped storage unit. Fig.10 This is a structural schematic diagram of a fault location system for a rotor winding of a variable speed pumped storage unit proposed in an embodiment of the present application, such as Fig.10 As shown, the system includes: a calculation module 100 , a collection module 200 , a determination module 300 and a protection module 400 .

[0106] The calculation module 100 is used to determine the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculate the spectrum resolution of the fast Fourier transform FFT according to the data window length.

[0107] The acquisition module 200 is used to determine the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and to acquire the slip rate and stator side differential current of the target unit.

[0108] The determination module 300 is used to perform internal short-circuit fault simulation analysis on the target unit, select multiple fractional harmonic magnetic fields in the stator side differential current, obtain the harmonics induced by each fractional harmonic magnetic field, and calculate the frequency of each harmonic based on the slip rate, and determine the FFT spectrum line corresponding to each harmonic according to the frequency range to which the frequency of each harmonic belongs, wherein the frequency components of the harmonics induced by the multiple fractional harmonic magnetic fields are greater than a preset component threshold.

[0109] The protection module 400 is used to perform FFT operation on the stator side transverse differential current, calculate the total effective value of the FFT spectrum line corresponding to each harmonic, and use the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

[0110] Optionally, in one embodiment of the present application, the calculation module 300 is specifically used to: calculate the inverse of the data window length, and use the inverse as the spectrum resolution; number each FFT spectrum line on the frequency axis in order from low to high frequency, and calculate the frequency of each FFT spectrum line based on the spectrum resolution and the number.

[0111] Optionally, in one embodiment of the present application, the acquisition module 200 is specifically used to calculate the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution by the following formula:

[0112]

[0113] Where i is the number of the FFT line and Δf is the spectrum resolution.

[0114] Optionally, in one embodiment of the present application, the acquisition module 200 is also used to: collect the rotational speed and slip rate of the target unit through a photoelectric encoder installed on the shaft of the generator motor of the target unit; and collect the stator side differential current through a differential protection circuit transformer TA installed at the stator side winding of the target unit.

[0115] Optionally, in one embodiment of the present application, the determination module 300 is specifically used to: establish a mathematical model of the internal fault of the rotor winding of the target unit based on the multi-loop analysis method, and simulate the internal short-circuit fault of the rotor winding of the target unit through the mathematical model; perform spectral analysis on the simulation results of the stator side differential current after the short-circuit fault to determine the frequency components of each fractional harmonic; and use the fractional harmonic magnetic field corresponding to the harmonic whose frequency component is greater than the component threshold as the selected multiple fractional harmonic magnetic fields.

[0116] Optionally, in one embodiment of the present application, the protection module 400 is specifically used to: determine the amplitude of the FFT spectrum line corresponding to each harmonic through the FFT operation result of the stator side differential current; calculate the cumulative sum of the amplitudes of the FFT spectrum lines corresponding to each harmonic, and calculate the total effective value based on the cumulative sum.

[0117] Optionally, in one embodiment of the present application, the protection module 400 is specifically used to: compare the fault characteristic quantity calculated in real time with a preset protection setting current threshold, and control the target unit to trip when the fault characteristic quantity is greater than the current threshold and the duration exceeds a preset delay value.

[0118] It should be noted that the above explanation of the embodiment of the protection method for internal short circuit of the rotor winding of the variable speed pumped storage unit is also applicable to the system of this embodiment and will not be repeated here.

[0119] In summary, the protection system for internal short circuit of the rotor winding of the variable speed pumped storage unit of the embodiment of the present application can quickly complete the selection and amplitude calculation of the FFT spectrum corresponding to the extracted main harmonic components according to the measured slip rate within a relatively short algorithm data window, and can meet the rapidity requirements of the main protection of the rotor winding, and consider the influence of the slip rate on the fault characteristics, and select different FFT spectrum lines for calculation under different slip rates. As a result, the system improves the timeliness, accuracy and reliability of the protection of the internal short circuit fault of the rotor winding, which is conducive to ensuring the safe and stable operation of the rotor winding of the variable speed pumped storage unit.

[0120] In order to implement the above-mentioned embodiments, the present application also proposes a non-temporary computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, a method for protecting the rotor winding of a variable-speed pumped-storage unit from internal short circuit is implemented as described in any one of the above-mentioned first aspect embodiments.

[0121] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0122] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0123] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0124] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute the instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purpose of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0125] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0126] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0127] In addition, each functional unit in each embodiment of the present application may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0128] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for protecting a variable speed pumped storage unit rotor winding from internal short circuit, characterized in that: The following steps are involved: Determine the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculate the spectrum resolution of the fast Fourier transform FFT according to the data window length; Determine the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and collect the slip rate and stator side differential current of the target unit; By performing an internal short-circuit fault simulation analysis on the target unit, multiple fractional harmonic magnetic fields in the stator side transverse differential current are selected, the harmonics induced by each of the fractional harmonic magnetic fields are obtained, and the frequency of each of the harmonics is calculated based on the slip rate, and the FFT spectrum line corresponding to each harmonic is determined according to the frequency range to which the frequency of each harmonic belongs, wherein the frequency components of the harmonics induced by the multiple fractional harmonic magnetic fields are greater than a preset component threshold; Perform FFT operation on the stator side transverse differential current, calculate the total effective value of the FFT spectrum line corresponding to each harmonic, and use the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

2. The method according to claim 1, characterized in that The calculating the spectrum resolution of the fast Fourier transform FFT according to the data window length comprises: Calculating the reciprocal of the data window length, and using the reciprocal as the spectrum resolution; After calculating the spectrum resolution of the fast Fourier transform FFT, the method further comprises: Each FFT spectrum line on the frequency axis is numbered in order from low to high frequency, and the frequency of each FFT spectrum line is calculated based on the spectrum resolution and the number.

3. The method according to claim 2, characterized in that Based on the spectrum resolution, the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum graph is calculated by the following formula: Where i is the number of the FFT line and Δf is the spectrum resolution.

4. The method according to claim 1, characterized in that: The collecting of the slip rate and stator side differential current of the target unit includes: The rotation speed and the slip rate of the target unit are collected by a photoelectric encoder installed on the rotating shaft of the generator motor of the target unit; The stator side transverse differential current is collected through the transverse differential protection circuit transformer TA installed at the stator side winding of the target unit.

5. The method according to claim 1, characterized in that The method of performing an internal short circuit fault simulation analysis on the target unit and selecting a plurality of fractional harmonic magnetic fields in the stator side transverse difference current comprises: Establishing a mathematical model of the rotor winding internal fault of the target unit based on a multi-loop analysis method, and simulating the rotor winding internal short-circuit fault of the target unit through the mathematical model; Perform spectrum analysis on the simulation results of the stator side differential current after a short-circuit fault to determine the frequency components of each fractional harmonic; The fractional harmonic magnetic field corresponding to the harmonic whose frequency component is greater than the component threshold is used as the selected multiple fractional harmonic magnetic fields.

6. The method according to claim 1, characterized in that The calculating the total effective value of the FFT spectrum lines corresponding to each harmonic includes: Determine the amplitude of the FFT spectrum line corresponding to each harmonic through the FFT calculation result of the stator side transverse differential current; The accumulated sum of the amplitudes of the FFT spectrum lines corresponding to the harmonics is calculated, and the total effective value is calculated according to the accumulated sum.

7. The method according to claim 1, characterized in that The method of using the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit includes: The fault characteristic quantity calculated in real time is compared with a preset protection setting current threshold value, and when the fault characteristic quantity is greater than the current threshold value and the duration exceeds a preset delay value, the target unit is controlled to trip.

8. A variable speed pumped storage unit rotor winding internal short circuit protection system, characterized in that: include: A calculation module, used to determine the data window length according to the short-circuit protection action time limit requirement of the target unit to be protected, and calculate the spectrum resolution of the fast Fourier transform FFT according to the data window length; An acquisition module, used to determine the frequency range corresponding to each FFT spectrum line on the frequency axis of the FFT spectrum diagram based on the spectrum resolution, and to acquire the slip rate and stator side lateral differential current of the target unit; A determination module is used to select multiple fractional harmonic magnetic fields in the stator side transverse differential current by performing internal short-circuit fault simulation analysis on the target unit, obtain the harmonics induced by each of the fractional harmonic magnetic fields, calculate the frequency of each of the harmonics based on the slip rate, and determine the FFT spectrum line corresponding to each harmonic according to the frequency range to which the frequency of each harmonic belongs, wherein the frequency components of the harmonics induced by the multiple fractional harmonic magnetic fields are greater than a preset component threshold; The protection module is used to perform FFT operation on the stator side differential current, calculate the total effective value of the FFT spectrum line corresponding to each harmonic, and use the total effective value as a fault characteristic quantity to perform internal short-circuit protection on the rotor winding of the target unit.

9. The system according to claim 8, characterized in that The computing module is specifically used for: Calculating the reciprocal of the data window length, and using the reciprocal as the spectrum resolution; Each FFT spectrum line on the frequency axis is numbered in order from low to high frequency, and the frequency of each FFT spectrum line is calculated based on the spectrum resolution and the number.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, a method for protecting a variable-speed pumped-storage unit rotor winding from internal short circuit is implemented as described in any one of claims 1 to 7.

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