71results about How to "Strong resistance to transition resistance" patented technology

The invention discloses a multi-terminal flexible DC power grid line direction pilot protection method. The method comprises steps: DC current and voltage at two ends of a DC reactor are measured and a DC current mutation rate di/dt and a voltage mutation rate du/dt are calculated; when the di/dt or the du/dt is larger than a threshold value K1-set and K2-set, a protection algorithm is started instantly; fault voltage at two sides of a DC reactor at a protection terminal is measured, and corresponding transient components UM_line and UM_bus (UN_line and UN_bus) are extracted; r1=UM_line/UM_bus (r2=UN_line/UN_bus) is calculated, and a fault direction is judged: if r1>1+epsilon (r2>1+epsilon), epsilon is a reliable margin, positive direction fault is judged and a direction signal RM is equal to 1 (RN=1), or otherwise, reverse direction fault is judged, and a direction signal RM is equal to 0 (RN=0); when RM&RN=1, internal fault is judged; and when RM&RN=0, external fault is judged. The method of the invention has the advantages that data synchronization is not needed; a sampling rate is lowly required; the fault resistance withstanding ability is strong; influences from line distributed capacitance do not exist; engineering implementation is facilitated; and the hardware investment cost is reduced.

The invention discloses a distribution network fault location method utilizing a natural frequency and an artificial neural network. In the method, fault location is performed by utilizing a principle that main natural frequencies of a line of a fault traveling wave are different when the line fails at different points; and simultaneously data processing is performed by utilizing a hierarchical distributed artificial neural network. After the line causes a single-phase ground fault, the sampling frequency is 1 MHz; a discrete zero-sequence transient signal with the sampling length of 2048 after the fault is selected; fast Fourier transform (FFT) is performed, wherein the transform result is a matrix of 2048*2; and an absolute value of the matrix is solved. According to the model adopted by the method, the fault location is performed by selecting 8 frequency values with large amplitude values as the sample attribute of the neural network, selecting a suitable transfer function and a learning rule, and setting appropriate neural network parameters to construct a back propagation (BP) network model. A large number of simulation results show that the method has a good effect.

The invention provides an extra-high voltage direct current line boundary element method adopting polar wave wavelet energy ratio, belonging to the technical field of relay protection of electric power systems. The method comprises the following steps: when the direct current line has fault, computing the anode line polar wave voltage and the cathode line polar wave voltage according to the direct current voltage and direct current of the two poles measured in the relay location; selecting the discrete polar wave voltage signal with sampling sequence length of 200 after fault to undergo wavelet transform to obtain a series of high/low frequency polar wave voltage wavelet transform parameters and computing the modules of the high/low frequency polar wave voltage wavelet transform parameters; computing the ratio of high/low frequency energy of polar wave voltage after extracting the high/low frequency components of polar wave voltage according to the obtained modules; and distinguishingthe area fault from the out-area fault according to the ratio of high/low frequency energy. Lots of simulation results show the method has good effect.

The invention relates to a single-phase permanent fault recognition method for an extra-high voltage AC transmission line using S transform energy. The method comprises the following steps: after fault occurs to an AC line, selecting a disperse voltage signal of which the recovery voltage sampling sequence length is 1,800 after the fault, and performing S transform to obtain a 901*1,800 time frequency complex matrix; and operating modulus of each element in the complex matrix to obtain the energy value under each frequency point. As too many frequency ranges are not good for recognition, every 9 rows from the 2nd row to the 901st row to obtain a 101*1 matrix, the 901 frequency ranges are integrated into 100 frequency ranges, and the frequency of each frequency range is 50 Hz. The single-phase permanent fault is judged according to the size of the first frequency range, namely the 50 Hz frequency range. A large number of simulation results indicate that the effect of the method is good.

The invention relates to a method for recognizing an internal fault and an external fault of an ultrahigh voltage alternating current transmission line. The method comprises the following steps of: after an alternating current line fails, starting a starting element, selecting the voltage of a fault component at the moment of 0.2ms before the fault and 0.8ms after the fault, and decoupling by using new phase mode transformation to acquire line mode voltage; performing S-transformation on the line mode voltage to acquire a result which is a time frequency complex matrix in a row -m and a column n; solving the modulus of each element in the complex matrix to acquire a modular matrix; calibrating the arrival time Tn of an initial voltage travelling wave according to an amplitude-time characteristic in the modular matrix; extracting the total high-frequency energy and the total low-frequency energy of the line mode voltage corresponding to 100 sampling points after the Tn from the modular matrix, and solving the ratio k of high-frequency energy to low-frequency energy; and distinguishing the internal fault from the external fault according to the ratio of the high-frequency energy to the low-frequency energy. In the method, sampling frequency is 250kHz, the length of a sampling sequence is 250 sampling points, the required data length is relatively short, calculated amount is low, and a real time property is relatively high. Whether the faults occur in a region is judged only by using single end amount without the usage of channels, so that the method is relatively high in applicability. A large number of simulation results prove that the method is high in transition resistance endurance capacity, is suitable for different fault types and has an obvious effect.

A fault direction judgment method based on positive-sequence polarization voltage phase comparison includes the steps that the measuring voltage Um, the measuring current Im and the bus positive-sequence voltage Um1 at the installation position of a directional element are respectively acquired after a smart distribution network breaks down; a working voltage Uop is set; the direction of the fault is judged. The fault direction judgment method has the advantages that due to limitation of the minimum value, it can be guaranteed that correct actions can be carried out when a short circuit occurs at the tail end of the protection range due to the resistance smaller than the largest transition resistance, and the reverse-direction fault can be judged with high reliability. The fault direction judgment method has the advantages that a voltage dead area does not exist, the capacity for resisting transition resistance is high, the working characteristics are stable, and influences cannot be caused by large changes of the operating mode of a power distribution network system or obvious difference between distributed power supplies or complex load types or other working conditions.

A high-voltage DC power transmission line single-end protecting method based on wavelet energy relative entropy mainly comprises the steps of 1), performing data acquisition and preprocessing, acquiring a current signal by a current measuring device, performing phase-model transformation by a protective data processing device by means of an orthogonal transformation matrix, and obtaining the inside 1-mode current xa(n) of a line boundary and the outside 1-mode current xb(n) of the line boundary; 2) calculating the wavelet energy relative entropy, namely performing wavelet transformation on the inside 1-mode current Xa and the outside 1-mode current Xb, and calculating the wavelet energy relative entropy M between the inside 1-mode current vector Xa and the outside 1-mode current vector Xb; and 3), performing high-voltage DC power transmission line single-end protection, namely determining whether the wavelet energy relative entropy M is larger than a preset protecting threshold epsilon, if M is larger than the epsilon, determining a fact that the fault occurs in the high-voltage DC power transmission line area by a protecting device. The high-voltage DC power transmission line single-end protecting method has advantages of high identification rate for line faults, more accurate and reliable protection action, and higher capability of ensuring safe and stable operation of the power transmission line.

The invention discloses a distance protection method making use of voltage distribution under a distributed parameter model. The distance protection method comprises the following steps of: 1, taking a mutational volume current as a protection starting element: Img>0.2Ie (1), and when the mutational volume current meets the formula (1), judging that an mn power transmission line has a fault, wherein Img is the mutational volume current amplitude of the m end in the mn power transmission line, and Ie is the rated current amplitude; 2, solving the voltage amplitudes at 80% and 100% places of the line, for the fault phase, by combining a fault phase selection result and by utilizing the voltage of a relay-installed place under the distributed parameter model, and judging whether the voltage amplitudes accord with a formula (2): U1>=U0.81, wherein the U1 is the voltage amplitude at the 100% place of the line, and the U0.81 is the voltage amplitude at the 80% place of the line; and 3, if the formula 2 is set up, judging the fault is an internal fault and protecting actuating-tripping, or protecting non-actuating. The distance protection method disclosed by the invention is not influenced by distributed capacitive current of the line by adopting the distributed parameter model, has strong transition resistance endurance capability, capability of judging the fault just by judging the voltage trend at the terminal of the line and has less computation amount.

The invention discloses a time domain model identification pilot protection method suitable for a wind power system. The method comprises the following steps: collecting three-phase voltage and current at the protection installation place and forming differential voltage and differential current; judging whether to start time domain model identification pilot protection according to the differential current value; calculating each phase of differential current and correlation coefficient rho of a first-order derivative of the differential voltage obtained after zero sequence compensation; judging internal and external faults by comparing the value of each correlation coefficient rho with a set threshold value; if the correlation coefficient rho of any phase is smaller than the set threshold value, judging that the fault is the internal fault, and then, pilot protection at the two ends of a line is carried out to protect the device to act reliably; or otherwise, judging that the fault is the external fault so as protect the device not to act reliably. The time domain model identification pilot protection method is easy to realize, can carry out split-phase judgment, is fast in action speed, is not influenced by line distributed capacitive current and fault resistance, and can be widely applied to the wind power system.

The present invention relates to a direct current power transmission line fault identification method by employing a filter branch current and principal component analysis method, belonging to the electric power system protection technology field. The method comprises: firstly, building a sample database, along the full line of the UHVDC, setting a fault position for faults in an area along a line, setting fault positions at a rectification side and an inversion side for the faults out of the area, taking the filter branch current curve cluster in the six sample points obtained by the electromagnetic transient simulation as sample data to perform the PCA cluster analysis, building the PCA cluster space, and forming obviously distinguished line faults and the cluster point cluster of two fault modal out of the area; secondary, after the starting component is started, taking polar fault current data in the six sample points as test samples, calculating the test sample data, and calculating the projection value q1 of the PCA cluster space; and finally, determining whether the faults are located in the area or out of the area, and the UHVDC is configured to transmit power for the extra-high voltage direct current.

The invention discloses a method for detecting a multi-terminal DC(direct current) system fault based on transient high frequency energy, characterized by establishing an analytical expression of a fault component current of a multi-terminal DC system line; obtaining the transient high frequency energy of the current according to the analytical expression of the fault component current; and if thetransient high frequency energy of a line exceeds a preset protection threshold, determining that the line is a fault line. The invention has the following advantages: the threshold setting is easy to be realized, the robustness of the fault detection of the multi-terminal DC system is improved, the sampling frequency is low, and the transition resistance is good.

The invention discloses a method for projecting traveling wave of a same-tower double-circuit HVDC transmission line. The method includes employing different criteria for and setting the upper and lower layers of pole wires respectively, eliminating outer-zone faults of the upper-layer pole wire through voltage change rate and current direction, eliminating outer-zone faults of the lower-layer pole wire through ground-mode change rate, employing voltage integration ratio to distinguish the fault of the very pole wire, for the upper-layer pole wire, from that of the other pole wire, and employing voltage integration ratio and modulus integration ratio to distinguish the fault of the very pole wire, for the lower-layer pole wire, from that of the other pole wire. The method has the advantage of high sensitivity, less operation burden and short determination time, the information of the very round is needed, communication between different rounds is not required, and influence of transition resistance is minimal. The fault pole wire of a same-tower double-circuit DC transmission line can be rapidly determined, and misjudgement hardly occurs.

The invention discloses a same-tower double-circuit direct current transmission line fault line selection method based on single pole information. The method includes the following steps: 1. voltage variations of four polar lines are calculated; 2. if the upper layer polar lines satisfy conditions, step 3 is carried out, and if the lower layer polar lines satisfy conditions, a step 4 is carried out; 3. If the low frequency harmonic wave amplitude satisfies a minimum value requirement, an amplitude ratio of low frequency and high frequency harmonic waves is continued to be obtained, if a specific value is larger than 1, the line of the pole is judged to be in fault, and otherwise travelling wave protection of the pole is locked; and 4. a voltage variation delay is sampled, if only one mutation wave head is detected in a data processing time window, the step 3 is carried out, if at least two mutation wave heads are detected in the data processing time window, polarity and amplitude relations of two continuous wave heads are compared, if the polarities are both positive and the amplitude relation satisfies a condition of a certain multiple, the line of the pole is judged to be in a non-near-end fault, and otherwise, travelling wave protection of the pole is locked. The same-tower double-circuit direct current transmission line fault line selection method based on single pole information has the advantages of high sensitivity, strong quick-action performance, difficult occurrence of misjudgment and the like.

The invention discloses a high-voltage direct-current power transmission line fault distance measurement method. The method comprises the following steps: S1, decoupling a power transmission line equation in a Bergeron model, and respectively obtaining a transient voltage component of a high-voltage direct-current power transmission line and transient current components of a rectification side andan inversion side; S2, determining voltage and current distribution along the line based on the obtained transient voltage and the transient current components of the rectification side and the inversion side, and calculating voltage and current ratio distribution along the line according to the obtained voltage and current distribution along the line; and S3, sampling the voltage-current ratio distribution along the line, calculating the standard deviation of the voltage-current ratio along the line obtained by sampling, and taking the distance corresponding to the voltage-current ratio along the line with the minimum standard deviation as a fault distance. According to the method, a filtering algorithm does not need to be involved, the inversion side auxiliary increasing current is introduced when the fault current is determined, the required data time window is short, and when fault distance measurement is carried out in a complex environment, the accuracy of fault distance measurement is high; and the method has better stable distance measurement performance.

The invention discloses a single-phase grounding fault distance protection method for a line overloaded and resistant to maloperation and high impedance. The method uses a fault phase voltage, a fault phase current, a fault phase negative sequence current and a zero sequence current on a protected installation place of a transmission line to calculate the line distance between the setting protection range of the transmission line and a single-phase grounding fault point, and then whether the line distance between the setting protection range of the transmission line and the single-phase grounding fault point is greater than zero is judged. If the line distance is greater than zero, the single-phase grounding fault point is determined to be located within the setting protecting range of the transmission line, an action tripping signal is sent, and circuit breakers on both ends of the transmission line trip. The method eliminates the influence of transition resistance on protection action performance in principle, and the method has the strong ability to resist the influence of the transition resistance.

The invention discloses a single-end electrical quantity protection method suitable for a hybrid bipolar direct current transmission line, and constructs a direct current line fault discrimination method based on a signal transient high and low frequency energy ratio by using a specific boundary structure of a hybrid bipolar direct current transmission system. A hybrid bipolar high-voltage direct-current power transmission system is built through a PSCAD/EMTDC simulation platform, fault conditions under different working conditions are simulated, voltage characteristic signals are extracted, wavelet packet transformation is carried out, transient energy of each node is obtained, a protection criterion is constructed by using a ratio of specific low-frequency energy to partial high-frequency energy, and thus internal and external faults of a region are identified and fault line selection is carried out. The method is high in transition resistance resistance, the protection reliability, selectivity, quickness and sensitivity are all met, high precision is achieved, and faults can be accurately recognized. According to the invention, calculation related to the wavelet packet can be realized by adopting a high-performance CPU (Central Processing Unit) or a hardware circuit such as an FPGA (Field Programmable Gate Array) or a CPLD (Complex Programmable Logic Device), so that the fault identification speed, precision and reliability are improved.

The invention relates to an MMC (Modular Multilevel Converter) DC transmission line protection method based on voltage correlation, which belongs to the technical field of power system relay protection. When a fault occurs in a DC transmission line, the positive and negative voltages at both ends of the line are collected and a correlation coefficient is obtained. Then, whether the fault is a single-pole grounding fault is judged according to the correlation coefficient. If the fault is judged to be a non-single-pole grounding fault, the inter-pole voltage is calculated, and the change rate ofthe inter-pole voltage is obtained. Finally, whether there is a short circuit between the two poles is judged according to the change rate of the voltage. The method of the invention has strong transition resistance endurance, and the data window is only 3ms. The method is quick in operation, and has a strong application prospect.

The invention relates to a multi-fractal spectrum ultra-high voltage direct current line fault identification method based on filter branch current and belongs to the technical field of direct current line protection. When a direct current line has a fault, a sampling frequency is 6.4kHz, and a filter branch measurement end is used for obtaining current data; and k (k>=2) squares of proper edges of [Epsilon] 1, [Epsilon] 2, ...[Epsilon] k are selected to over current i(t), so as to obtain the quality distribution probability pk ([Epsilon]) and the non-uniform degree index [delta][alpha], and finally faults inside and outside a direct current line area are identified according to that whether the non-uniform degree index [delta][alpha] is larger than a fixed value [delta][alpha]set or not. The invention generates time domain waveforms in case of faults inside and outside the direct current line area based on the multi-fractal spectrum, constructs protection criteria hereby, and achieves the stronger traveling wave protection transition-resisting resistance capability.

The invention discloses a flexible direct-current distribution line protection device based on direct-current circuit breakers. The flexible direct-current distribution line protection device comprises (M+N) direct-current circuit breakers, a circuit breaker control unit, M bus fault detection units and N line fault detection units; the circuit breaker control unit combines the magnitudes of current on all direct-current buses and the magnitudes of current on a power distribution line, the current break variable and the current direction are taken as protection characteristics to construct a fault criterion, a fault occurrence position is judged, whether a fault action signal is sent out or not is judged, and a corresponding direct-current circuit breaker is tripped off according to the obtained fault action signal. According to the method, the break variable and the power direction of the fault current can be comprehensively considered, and the action characteristics of the novel direct-current circuit breakers are combined, so that the bus fault and the line fault of a net-shaped direct-current power distribution network are quickly protected and distinguished.

This invention relates to an earth faulty distance protection technology of high voltage transmission line, which is an adaptive earth direction impedance relay taking the residual voltage Uo at the faulty protection installation place as the polarized volume, which not only has the strong ability of bearing the transient impedance, but also has the advantage of protecting residual component.

The invention belongs to the technical field of high-frequency transient component direction pilot protection, and discloses a high-frequency transient component direction pilot protection method andsystem. The system comprises a current detection module, a voltage detection module, a fault detection module, a main control module, a change curve drawing module, a transient component extraction module, a fault identification module, an electric energy quality signal analysis module, a highest frequency component solving module, a phase difference solving module, a data storage module, a terminal module and a display module. According to the invention, the clear analytical expression of the fault component current of a multi-terminal direct-current system line is established through a faultdetection module, so that threshold setting is easy to realize, and the robustness and accuracy of multi-terminal direct-current system fault detection are improved; various typical transient electric energy quality signals, such as sudden voltage rise, sudden voltage drop, transient change, harmonic waves, transient pulses and the like in an electric power system can be rapidly and accurately analyzed through an electric energy quality signal analysis module; and calculation is simple, and the system can be used for real-time online analysis.