223 results about "Double circuit line" patented technology

The invention discloses a method for enabling a standby power supply automatic switching-in device with multiple power supplies and multiple incoming lines of a transformer substation to perform standby power supply automatic switching-in fast, efficiently and accurately. According to the method, the standby power supply automatic switching-in device is arranged on busbars and incoming lines in a centralized mode to collect operation information of a power supply network and determine detailed criteria on the states of all the incoming lines, busbar working power supplies and standby power supply automatic switching-in action logic, wherein the busbars and the incoming lines relate to single busbars, signal busbars with bypasses, single busbar segments and single busbar segments with bypasses. Thus, the standby power supply automatic switching-in device can automatically identify the operation states of all the incoming lines and the sources of power supplies of all the incoming lines of a multi-incoming-line power supply grid, identify standby circuits according to preference constant values, automatically select an action mode and preferably close circuits which have high preference constant value grades, ensure that circuits (such as double-circuit lines) of the same power supply source do not participate in mutual-switching-in, enable two systems to undergo loop closing, greatly improve the power supply reliability of the power supply network, achieve automatic power restoration of the power supply network and ensure safe operation of power systems.

A fault positioning method for a common-tower double-circuit line comprises the following steps: firstly, carrying out six-sequence decomposition for electrical quantity at two ends of the double-circuit line; next, calculating the fault distance by a long line equation of a transmission line of a same positive-sequence fault component of the six-sequence components, and obtaining six-sequence current of a fault point according to the electrical quantity at two ends of the double-circuit line, the fault distance and the long line equation; then converting the six-sequence current into six-phase current; and finally, judging a fault phase according to the amplitude value characteristic of the phase current of the fault point. According to the method provided by the invention, when fault phase-selection of the double-circuit line is carried out, the fault distance detection can be performed at the same time, and the advantages of clear principle, high distance detection accuracy, simple and reliable phase-selection logic and the like are provided. The method provided by the invention is free of the influence of fault point transitional resistance, circuit distributed capacitor current and load current, can automatically adapt to and regulate a definite value of the phase-selection criterion with the change of a system operation manner, and can provide effective phase-selection logic for distance protection of the common-tower double-circuit line.

The invention relates to the technical field of relay protection, and relates to a comprehensive phase selection method for double-circuit lines paralleled on the same tower: using the six-sequence component method to eliminate the mutual inductance current between the phases; according to the transformed six-sequence component, First distinguish the ground fault and non-ground fault, and then select the fault phase according to the following steps: According to the current amplitude characteristics of the single circuit fault, the non-identical phase cross-line fault and the same name phase cross-line fault, distinguish the non-identical phase span line fault, single circuit fault and phase line fault with the same name; for a single circuit fault, the phase angle of the positive and negative zero-sequence components in the same direction is 0° or 180° from the two The fault line is selected from three lines, and then the phase selection is carried out according to the negative sequence and zero sequence current phase selection principles; for the cross-line faults of the same name phase and non-same name phase, the fault type is judged respectively. The invention can make up for the disadvantages of incomplete phase selection function and even wrong phase selection of other phase selection methods currently used on double-circuit lines.

A method and a device for limiting secondary arc current of an extra-high voltage / ultra-high voltage double circuit line on the same tower. The method comprises the following steps: determining the type of a single-phase-to-ground fault when the extra-high voltage / ultra-high voltage double circuit line on the same tower has a single-phase-to-ground fault (S501); selecting a reactance value of a neutral grounding reactor according to the type of the single-phase-to-ground fault (S502); and switching the extra-high voltage / ultra-high voltage double circuit line on the same tower to the selected reactance value of the neutral grounding reactor (S503). Thus the reactance value of the neutral grounding reactor is not constant, but is changed along with the operating conditions of the power transmission line, that is, the reactance value of the neutral grounding reactor is controllable. In this way, when the operating conditions of the extra-high voltage / ultra-high voltage double circuit line on the same tower are different, a neutral grounding reactor with an optimal reactance value can be selected so as to be accessed to the power transmission line, thereby effectively limiting the secondary arc current caused by the single-phase-to-ground fault.

The invention discloses a phase selection method for faults of double-circuit lines on the same tower. The method includes the steps that the fault types and the fault phases are judged according to sequence voltage and voltage between phases, and different criteria are adopted for judging the physical fault phase of the local lines according to the fault type; the interphase impedance criterion and the ground impedance criterion are adopted for the two-phase grounding faults; the interphase impedance criterion and the impedance direction criterion are adopted for the two-phase non-grounding faults; the three-phase impedance direction is adopted for the three-phase faults. The phase selection method is simple and reliable in principle, the phase can be selected correctly under the single-return-wire faults and the overline faults, and the practical and feasible phase selection method is provided for protecting the lines on the same tower.

The invention relates to a power transmission line parameter online measurement method based on fault wave recording, which is characterized by comprising the steps: GPS clocks of wave recording devices are utilized for carrying out integral hour startup to obtain positive sequence voltage and current at two ends of a line and the voltage and the current are saved in the wave recording devices at two ends in the form of wave recording files respectively; when the double-circuit line with mutual inductance has an earth fault outside a region, the zero sequence current generated by the fault is utilized for simultaneously starting the wave recording devices at two ends of the line, the synchronous sampling of the zero sequence voltage and the current at two ends of the line in the region is carried out, and a zero sequence sensitive II segment startup element is further equipped; and a central dispatching computer reads the positive sequence voltage and the current values at the two ends and measures the positive sequence parameters of the line. The zero sequence voltage and the current values at two ends are read, thereby measuring the zero sequence parameters of the line. The method does not need to cut off the power, the operation is convenient, and the wave recording devices can be used for the power transmisison line parameter online measurment, thereby making up for the defects of non-synchronous problem when measuring the positive sequence parameters and no zero sequence power supply when measuring the zero sequence parameters by using the prior online measurment device, and improving the line parameter measurment times and the measurement precision.

The invention discloses a six-phase-sequence-impedance-based distance protection measurement method of double-circuit lines on the same pole. Two circuit lines are viewed as a whole body. Six single-phase ground impedance measuring elements, six interphase impedance measuring elements and six interline impedance measuring elements are formed by three voltages and six currents in the two circuit lines on the side of the whole body. Totally eighteen measuring impedances are formed. The measurement equation of the distance protection measuring method is as shown as the accompanying drawing, wherein UIAu, UIBu, UICu, UIIAu, UIIBu and UIICu respectively denote voltage drops of A, B and C on the unit length of a circuit line I and a circuit line II, ZS denotes line self-impedance, Zp denotes interphase mutual impedance of the same line, ZM denotes interline mutual impedance, L denotes line length, iIA, iIB, iIC, iIIA, iIIB and iIIC respectively denote A, B and C phase currents, and delta denotes interline zero-sequence mutual inductance compensation coefficient.

The invention discloses a ground line selection method for a small current grounding system. The method solves the problem that the prior line selection method is low in sensitivity and generates errors in line selection. The method comprises the following steps: 1, single-circuit lines and double-circuit lines are numbered and placed in a microcomputer; 2, the microcomputer judges whether the system is grounded or not and identifies a grounding phrase of the system; 3, according to the number of the single-circuit lines and the double-circuit lines, the microcomputer calculates a grounding transfer characteristic formula with zero sequence current which is measured during the normal operation of the system, zero sequence current of the single-circuit lines, zero sequence voltage of a bus and zero sequence current of the double-circuit lines which are measured when the system is grounded, and zero sequence voltage of a bus, zero sequence current of the double-circuit lines and zero sequence current of the single-circuit lines which are measured during grounding transfer of the system; the result of the calculation is compared with grounding current IJ passing through a split phase switch of the grounding phase during grounding transfer to determine a fault line. The method has the advantages of the characteristics of high sensitivity and accurate line selection and great significance on accurate identification of grounding circuit, grasp of grounding and arc-suppression coil conditions of the system, and promotion and improvement of safe and reliable operation of the system.

The invention discloses an SV network sampling-based double-circuit line single-phase earth fault distance measurement method which is used for measuring the fault phase voltage mutational volume, the fault phase current mutational volume, the zero-sequence current and the other two normal phase voltages of an I-circuit line at the protection mounting position of a double-circuit line on the same pole, and measuring the zero-sequence current of a II-circuit line; calculating the fault phase voltage when the I-circuit line operates normally, sequentially calculating the positioning vector function of each point on the I-circuit line of the double-circuit line on the same pole until the full length of the I-circuit line of the double-circuit line on the same pole, and selecting the distance between the point with the smallest positioning vector function value on the I-circuit line of the double-circuit line on the same pole and the protection mounting position of the double-circuit line on the same pole as the fault distance. According to the method, the voltage of the circuit before the fault does not need to be remembered, and a voltage protection loop of the circuit before the fault does not need to be set; the influence of the zero-sequence mutual inductive impedance among the lines, the transition resistance and the load current on the precision of measurement of the fault distance is eliminated, and no fault distance measurement dead zone exists in protecting the single phase grounding fault of the outlet single-circuit line.

The invention discloses a double-circuit on the same tower double-circuit line fault distance measurement method which includes the following steps: (S1) using double-circuit three-phase transient currents which are obtained by sampling as original current signals for denoising; (S2) conducting six-phase phase-mode transformation to denoised current processing signals and extracting one mode of components to be used as fault analysis signals; (S3) conducting matching pursuit to the fault analysis signals which are obtained by applying a matching pursuit algorithm by using pulse signal atoms, comparing peak time of three optimum matching pulse atom signals with the largest energy, and taking the time which reaches a peak value at the earliest to be used as the time when a traveling-wave head reaches a measurement point; and (4) calculating and obtaining the distances respectively from measurement points at two ends and a fault point according to the obtained time during which the traveling-wave head can reach the measurement points at the two ends. By means of the double-circuit on the same tower double-circuit line fault distance measurement method, the characteristics of the traveling-wave head can be extracted accurately and reliably, and precision and reliability are achieved in the double-circuit on the same tower double-circuit line fault distance measurement.

The invention discloses a direct sampling and direct tripping communication mode-based double-circuit line single-phase earth fault positioning method, which comprises the steps: measuring the fault phase voltage, fault phase current and zero-sequence current of the circuit line I at the protection installation place of a common-tower double-circuit line, measuring the other two normal phase voltages, measuring the zero-sequence current of the circuit line II, and calculating the fault phase voltage when the circuit line I works normally by utilizing the two normal phase voltages of the circuit line I; starting from the protection installation place of the common-tower double-circuit line, sequentially calculating the phase angle that the fault phase voltage at each point of the circuit line I precedes the fault phase voltage when the circuit line I works normally in a fixed step length increment manner, and realizing the precise positioning of single-phase earth fault of the double-circuit line by virtue of the characteristic that the ratio of previous voltage to later voltage at the fault point has step change relative to the phase angle. According to the positioning method, the voltage before line fault does not need to be memorized, a voltage holding loop before the line fault does not need to be set; the influence of transition resistance, load current and interline zero-sequence mutual inductance on fault range accuracy is eliminated.

The invention provides a high-reliability unified power flow controller suitable for a double-circuit line. The high-reliability unified power flow controller comprises at least one parallel transformer, four converters, at least two series transformers, a parallel-side back brake loop, a series-side back brake loop and a direct-current public bus. At least one side of each series transformer is connected with at least one set of bypass switches in parallel. The alternating current side of at least one converter is connected with at least one series transformer through the series-side back brake loop to be connected into the line in series. The alternating current side of at least one converter is connected with the at least one parallel transformer through the parallel-side back brake loop to be connected into an alternating current system. The direct current sides of the converters are connected to the direct-current public bus through change-over switches. By means of the structure, multiple operation modes can be achieved, and when one converter breaks down, power flow of the double-circuit electric transmission line and the voltage of the parallel-side alternating current system can still be controlled; when two converters break down, control over the power flow of the double-circuit line can be achieved, and the good flexibility and the good reliability are achieved.

The invention discloses a series-compensation double-circuit line fault locating method based on a distributed parameter model. The method comprises a step I, a six-sequence component method is adopted to perform decoupling, and a reverse voltage cross a bus on two sides is zero when a fault occurs in a circuit after the decoupling is performed; a step II, according to characteristics that voltages at a fault spot are equal and currents at two ends of a series compensation device are reverse and which are respectively reckoned from the two sides, a series compensation voltage and the currents at the two ends in a transmission equation are eliminated; and a step III, by utilizing a pure resistance property of a transition resistor at a position of the fault spot and a fault timing sequence network boundary condition, a fault locating function when double-circuit lines containing series compensation are erected on the same pole is constructed, and a fault distance is solved by utilizing the fault locating function when the fault occurs. The method does not rely on a model of the series compensation device and is not influenced by MOV nonlinearity, a position of the fault spot relative to the series compensation does not need to be known in advance, the ranging principle is simple, one-dimensional searching for the fault distance is needed only, and a pseudo root discrimination problem does not exist.

The invention discloses a grounding fault distance protecting method of double circuit lines on the same tower. The grounding fault distance protecting method of the double circuit lines on the same tower comprises the steps of estimating the phase of voltages of a grounding fault point by using a fault syntropy zero sequence current phase, directly calculating a fault distance x according to the fact that the voltage drop of a protecting mounting portion to the grounding fault point is in linear relation with the fault distance, and comparing the size relationship of the fault distance x and a protection setting range xset. If a I circuit line of the double circuit lines on the same tower is in single-phase grounding fault, and the fault distance x is smaller than the protection setting range xset, the I circuit line of the double circuit lines on the same tower is protected to send an action tripping signal. If a II circuit line of the double circuit lines on the same tower is in single-phase grounding fault, and the fault distance x is smaller than the protection setting range xset, the II circuit line of the double circuit lines on the same tower is protected to send the action tripping signal. According to the grounding fault distance protecting method of the double circuit lines on the same tower, a symmetrical component method and a six-sequence component method are used comprehensively, and accurate measuring of the fault distance of the single-phase grounding fault of the single circuit line of the double circuit lines on the same tower is achieved.

The invention relates to a common-tower double-circuit line vertical fault zero sequence pilot protection error operation prevention method. The method comprises steps that zero sequence criteria are constructed and comprise main zero sequence direction criteria and zero sequence current start criteria; negative sequence criteria are constructed and comprise negative sequence direction auxiliary criteria, negative sequence compensation voltage start criteria, negative sequence current start criteria and a negative sequence voltage threshold; if the zero sequence criteria and the negative sequence criteria are simultaneously satisfied, a fault is determined to be a positive direction fault; if the zero sequence criteria are satisfied, the negative sequence current start criteria are not satisfied, and the negative sequence voltage threshold is satisfied, and the fault is determined to be an internal fault of an outgoing wire of a weak power source and is further a positive direction fault; if two ends of the line are determined to have positive direction faults, an internal ground fault of the line is generated, and a protection outlet is tripped. The method is advantaged in that through introducing negative sequence components and improving a compensation voltage, a zero sequence pilot protection error operation problem of a healthy line during generation of the common-tower double-circuit line vertical fault can be effectively prevented.

The invention discloses a method for setting the reclosing time on the basis of secondary arc currents and recovery voltages. The method includes judging types of single-phase earth faults when the single-phase earth faults of double-circuit lines of the same towers occur; computing numerical values of the secondary arc currents and the recovery voltages by the aid of the types of the single-phase earth faults, selecting the appropriate reclosing time and switching the reclosing time of the double-circuit lines of the same towers to the reclosing time corresponding to the current fault types. The secondary arc currents and the recovery voltages correspond to the current fault types. The method has the advantages that the corresponding reclosing time can be selected according to the types of the specific single-phase earth faults of the power transmission lines and can be changed along with running conditions of the power transmission lines instead of being fixed, accordingly, the optimal reclosing time can be selected when the running conditions of the ultrahigh-voltage double-circuit lines of the same towers are different, the problem of reclosing failures during temporary faults can be effectively solved, and the single-phase automatic reclosing success rate can be increased.

The invention discloses a crossover line permanent fault recognizing method for double circuit lines on a same tower. The crossover line permanent fault recognizing method comprises the steps of: 1. judging whether an amplitude of a difference of voltage at tripping phase ends of different circuit lines is less than or equal to a voltage setting value after the double circuit lines on the same tower have crossover line faults, if so, executing a step 4, if not, executing a step 2; 2. judging whether a phase of the difference of the voltage at the tripping ends of the different circuit lines is more than or equal to a setting phase after the double transmission lines on the same tower have the crossover line faults, if so, executing the step 4, if not, executing a step 3; 3. when the double circuit lines on the same tower have the crossover line temporary faults, reclosing by the tripping phases in delay, and ending a process; and 4. when the double circuit lines on the same tower have the crossover line permanent faults, interlocking reclosing, and ending the process. According to the crossover line permanent fault recognizing method provided by the invention, through analyzing whether the double circuit lines on the same tower have the crossover line faults, according to the characteristics of the voltage at the tripping phase ends after fault phases trip, whether a line operates in a light load or a heavy load, the crossover line permanent faults are effectively identified, and thus success rate of reclosing the line can be effectively increased.

The invention discloses a method for calculating a single-phase earth fault point of a parallel double-circuit line in the technical field of power system relay protection. The method comprises the steps that a voltage instantaneous value and a current instantaneous value of the line are collected and phase voltage of a distance protection installation portion fault line, a phase current of the distance protection installation portion fault line and a zero-sequence current of the distance protection installation portion fault line are obtained through Fourier transform; according to the operation state of the parallel double-circuit line, single-phase earth fault impedance Z of the parallel double-circuit line is calculated; according to the single-phase earth fault impedance Z of the parallel double-circuit line, the distance between a distance protection installation portion and the fault point is calculated. According to the method for calculating the single-phase earth fault point of the parallel double-circuit line, the position of the fault point is calculated according to single-ended voltage and a single-ended current of the protected line, the influence of single-phase earth fault impedance measurement of zero sequence mutual inductance of the parallel line is eliminated, and the measurement accuracy of single-phase earth protection and the reliability of single-phase earth protection of the parallel line are greatly improved.

The invention discloses a method for distinguishing fault types of a non-transposition same-tower double-circuit line. The method comprises the steps that firstly, when the non-transposition same-tower double-circuit line fails, voltage information and current information at the protection installation position of the non-transposition same-tower double-circuit line are collected in real time through a current transformer and a voltage transformer; secondarily, positive-phase-sequence identical-phase-sequence current components, positive-phase-sequence differential-phase-sequence current components, negative-phase-sequence identical-phase-sequence current components, negative-phase-sequence differential-phase-sequence current components, the zero-phase-sequence identical-phase-sequence current components and zero-phase-sequence differential-phase-sequence current components of the double-circuit line are extracted by using the six-sequence component conversion method, and the relative phase angle between the differential-phase-sequence components and the identical-phase-sequence components of positive-phase-sequence currents and the relative phase angle between the differential-phase-sequence components of negative-phase-sequence currents and the differential-phase-sequence components of the positive-phase-sequence currents are calculated; then whether the non-transposition same-tower double-circuit line has a same-name-phase crossing-line fault or a single-circuit-line fault or a non-same-name-phase crossing-line fault is judged. By means of the method, the single-circuit-line fault, the same-name-phase crossing-line fault and the non-same-name-phase crossing-line fault of the non-transposition same-tower double-circuit line can be distinguished correctly. Excellent fault distinguishing capacity can be still kept when non-transposition parameters and line parameters of the same-tower double-circuit line are seriously unsymmetrical.

The invention relates to a method for differentiating the fault properties of a same-rod double-circuit line with a paralleling reactor. According to an existing same-rod double-circuit line self-adaption reclosure scheme, the fault properties of all faults can not be differentiated and an adopted fault property differentiating principle requires long time. According to the method, the voltage of a disconnected phase recovery terminal is integrated within a power frequency period, so that the property of the ground fault is differentiated; the voltage difference of the synonym overline fault phase recovery terminal is integrated, so that the property of a synonym overline fault is differentiated; meanwhile, with the combination of the reclosing time sequence, the properties of the inter-phase and synonym overline faults are differentiated. According to the method, sensitivity is high, an adopted data window is short, and the method is suitable for various possible faults in the same-rod double-circuit line with the paralleling reactor.

The invention discloses a zero sequence voltage compensation element locking method for a double-circuit same-tower line. The zero sequence voltage compensation element locking method comprises the following steps: firstly, after the protection device of the line is powered on, acquiring the zero sequence current, negative sequence current and zero sequence voltage vector and amplitude of the protected line, judging whether the zero sequence current amplitude meets a threshold value or not, and if so, starting zero sequence direction protection; and secondly, judging whether the zero sequence voltage amplitude meets a threshold value or not, if the zero sequence voltage amplitude is lower than the threshold value, comparing the negative sequence current amplitude with the zero sequence current amplitude, when the ratio of the negative sequence current amplitude to the zero sequence current amplitude is greater than 0.8, starting a zero sequence voltage compensation element, performing zero sequence direction calculation by using a compensated zero sequence voltage vector, or else performing zero sequence direction calculation by using the locked zero sequence voltage compensation element directly. By adopting the zero sequence voltage compensation element locking method, a long-distance double-end co-bus same-tower double-circuit line can be ensured, and in case of an asymmetric longitudinal fault of one circuit line, the zero sequence direction protection of the other circuit line has no mal-operation but can act reliably when a grounding fault happens in an area.

The invention discloses a nonsynchronous fault range-finding method for a double-circuit line, comprising series compensation, on the same tower, and the method comprises the steps: employing a six-sequence component method for decoupling for each sub-algorithm, and eliminating a series compensation voltage at a side nearby a fault and series compensation currents at two sides in a transmission equation according to the characteristics that the voltages, deduced from two sides, of a fault point are equal and the currents at two sides of a series compensation device meet the Kirchhoff's Current Law; constructing a fault positioning function through employing the pure resistance of a transition resistor at the fault point when the double-circuit line on the same tower comprises the series compensation; inputting double-end data into an M-side sub-algorithm and an N-side sub-algorithm at the same time for calculation, and directly achieving the precise positioning of a fault without the discrimination of a fault section. The method is applicable to all types of faults, does not need to carry out synchronous sampling, is independent of a series compensation device model, is not affected by MOV nonlinearity, does not need to know the position of the fault point relative to the series compensation in advance, is simple in range-finding principle, just needs to carry out the one-dimensional search of the fault distance, and does not have a problem of false root discrimination.

A unified power flow controller for a double-circuit transmission line comprises at least one parallel-connection transformer, three current converters, at least two series-connection transformers, a parallel-connection side switching circuit, a series-connection side switching circuit and a direct current common bus. The series-connection transformers connected with at least one group of by-pass switches in parallel. The three current converters connected to each loop line in series after being connected with at least one series-connection transformer through the series-connection side switching circuit. The three current converters connected to an alternating current system after connected with at least one parallel-connection transformer through a parallel-connection side switching circuit starting circuit. The three current converters are connected to the direct current common bus through a transfer switch.

A single / double-circuit power-transmission-line whole-line high-precision fault range finding method is disclosed. Range finding precision of many existing range finding schemes of a general long-distance power transmission line middle section fault is not easy to control because the fault is far away from a measurement apparatus and there are a plurality of range finding influence factors. In the invention, through listing a two-end calculation voltage amplitude ratio under a fault line equivalence network, a proportion function of a distance from a fault point to a line end in a whole length of the line is derived so as to realize accurate range finding to the power transmission line fault. In addition, in order to widen an application scope of the fault range finding method, through considering electrical characteristic differences of a double-circuit line and a single-circuit line, according to a network structure characteristic of a double-circuit power transmission line, and from an aspect of equivalent transformation, a terminal voltage amplitude comparison range finding method adapting to the double-circuit power transmission line is provided. By using the method, range finding operation is simple; a range finding result is not influenced by a transition impedance; a whole line range finding precision is high and a suitable scope is wide. A problem that power transmission line middle section range finding precision is poor can be well solved.

The invention discloses an accurate fault locating method for double circuit lines on the same pole, which is used for solving the problems of locating errors caused by unavailability of avoiding mutual impedance and mutual susceptance phase difference among leads and the realization of fault location in any fault existing in the conventional fault locating method for double circuit lines on the same pole. According to the accurate fault locating method, an accurate fault calculation method is adopted. The accurate fault locating method comprises the following steps of: 1, calculating measured values of current and voltage vectors before and after a fault with a Fourier algorithm; 2, calculating impedance matrixes and potentials of systems on both sides; 3, calculating to obtain a transfer matrix ranging from fault points of the double circuit lines on the same pole to a bus by using different fault distance values with a feature modulus decomposition method; 4, constructing a resistance matrix of the fault points by using different fault resistance values; 5, solving an equation to obtain calculated values of voltage vectors of buses on both sides and current vectors from a circuit to a bus; and 6, calculating an error quadratic sum of each vector calculated value and measured value. In different values of a fault distance and fault resistance, the error quadratic sum calculated by using a fault distance and a fault resistance value which are most proximate to a practical fault distance and practical fault resistance in the step 6 is least.

The invention relates to a common-tower double-circuit T-type power transmission line fault distance measurement method based on positive sequence current difference. The method is characterized in that firstly, a current transformer at a protection mounting portion is utilized to acquire each phase current data of three ends of a double-circuit T-type power transmission line system, and a positive sequence current component of a double-circuit line is solved through a symmetric component method; secondly, distance measurement functions of the three branches are calculated according to the positive sequence current component of the double-circuit T-type power transmission line, and a fault branch can be determined according to difference of the distance measurement functions of two ends of each branch; and lastly, a fault distance analysis expression is utilized to calculate a fault distance on a fault branch.

The invention discloses a double-circuit line non-in-phase cross-line earth fault judgment method based on a trigonometric function. The method comprises the steps that the fault phase voltage, the fault phase current and the zero-sequence current at the protection installing position of the line I of same-tower double-circuit lines are firstly measured the zero-sequence compensating current of the line I of the same-tower double-circuit lines is calculated, the phase angle of the fault phase voltage of the protection installing position of the line I of the same-tower double-circuit lines ahead of the zero-sequence current injected in a non-in-phase cross-line earth fault point is calculated, the fault phase voltage of the line I of the same-tower double-circuit lines within the protection setting range is calculated, and the accurate judgment on a double-circuit line non-in-phase cross-line earth fault is achieved through the amplitude characteristic of the trigonometric function of the vector relation between electrical quantities of single ends after the double-circuit line non-in-phase cross-line earth fault happens. The judgment result is not influenced by factors such as zero-sequence mutual inductance between lines, transition resistance, load currents and electric power system operation modes, and the double-circuit line non-in-phase cross-line earth fault judgment method based on the trigonometric function is applicable to same-tower double-circuit line single-end electric quantity backup protection.