138 results about "Current transformer saturation" patented technology

The present invention relates to a method to locate a fault in a section of a transmission line using measurements of current, voltage and angles between the phases at a first (A) and a second (B) end of said section. The invention is characterised by the steps of, after the occurrence of a fault along the section, calculating a distance (dA, dB) to a fault dependent on a fault current measured at one of said first and second ends and phase voltages measured at both of said first and second ends (A, B), where the distance to fault is calculated from the end (A or B) where the fault current is measured. The invention is particularly suitable when a current transformer at either of the first or second ends (A, B) is saturated. If so, then, a distance (d) to a fault is calculated dependent on a fault current measured at the non-affected end and phase voltages measured at both the affected end and the non-affected end.

The invention discloses a current transformer saturation detecting method and aims at solving the technical problem of improving the saturation detection accuracy of a current transformer. The current transformer saturation detecting method comprises the following steps: calculating the amplitude values of Im, I2m, I3m, I5m, In, I2n, I3n and I5n by a relay protection device; calculating according to the following equations: Id = Im + In, I2d = I2m + I2n, I3d = I3m + I3n, and I5d = I5m + I5n by the relay protection device; calculating according to the following equations: id = imp + inp, ir = imp - inp, and dir = | (imp - im ( p - N ) ) | + | ( inp - in ( p - N ) ) | by the relay protection device; meeting the following conditions: 1) dir > 0.8in, 2) the sample number meeting ir > 0.8in is smaller than N, 3) the sample number meeting id > 0.8in is smaller than 3, and the difference between the sample number meeting the condition 2) and the sample number meeting the condition 3) is bigger than 3; failing to meet the condition: I2d + I3d + I5d < 0.15Id; and judging that the current transformer is saturated. Compared with the prior art, the current transformer saturation detecting method has the advantages that the method not only ensures that false differential protection operation is not carried out during external major faults with CT (Current Transformer) saturation, but also can improve differential protection sensitivity during internal faults with CT saturation through the judgment of time difference between differential current and brake current and the harmonic properties of the differential current in combination with harmonic properties during the CT saturation.

The invention discloses current transformer remanence measurement system and method. An upper computer receives current transformer data signals transmitted by a data unit. Related data processing is performed to calculate remanence coefficient. Operation states of an operating unit are automatically judged during measurement, and on and off of a relay are controlled. When the primary side of a current transformer is open, the secondary side is sequentially subjected to positive charging, discharging and revere charging until the current transformer is saturated. Flux variations in positive charging process, discharging process and revere charging process are obtained by calculation. The three flux variations are then calculated to obtain accurate remanence coefficient. Therefore, errors in remanence coefficient measurement caused when initial core flux of the current transformer is not zero are eliminated, accuracy in remanence coefficient measurement for the current transformer is increased, and fairness in electric energy measurement and trade settlement for the current transformer is guaranteed. The current transformer remanence measurement system and method have promising application prospect.

This invention refers to a TA saturation identifying method and current differential protection method for same, which adopts the sectional wave shape integral method to judge whether the TA occurring, it needs a cycle and is simple and effective, said method does not influence protection action speed in area serious fault and effectively prevent error action in out area fault. Said invention is a self-adaptive method with very less influence to performance of protected unit.

The invention discloses a current transformer saturation recognition method based on the half-cycle integral characteristic of a differential current. The method is suitable for current differential protection of main equipment or power transmission lines. During an internal fault, a sliding data window half-cycle integral result of a differential current sampling value sequence is monotonically increased; when a current transformer is saturated during an external fault, the sliding data window half-cycle integral result of the differential current sampling value sequence has an obvious inflection point and is increased first and then decreased according to the variation tendency. According to the characteristic, after the fault is started, the variation tendency of the half-cycle integral value of the differential current is continuously judged in each fundamental wave cycle; once an obvious inflection point of the half-cycle integral value is found, the differential current is determined to be a false differential current caused by saturation of the current transformer; if no obvious inflection point of the half-cycle integral value is found, recognition and judgment are continuously carried out till saturation is determined, or the fault is removed and a complete protection device is reset. The recognition method is simple in logic, small in calculation amount and free of complex setting.

A digital travelling wave protecting method for electric power transmission lines and its relay and protection system is disclosed. The said system is composed of digital travelling wave relays containing hardware and firmed software and high-frequency carrier communication unit consisting of high-frequency transceiver and high-frequency carrier channel-power transmission lines. The said method features that the action results of said relays at both ends of a power transmission-line are compared with each other to judge if there is a failure on the line. Its advantages include fast response (5 ms for relay action and 15 ms for protection action).

The invention discloses a method for judging and compensating current transformer saturation. The method comprises the following steps of: firstly, judging whether an instantaneous value of current satisfies the condition for judging the saturation need of a current transformer or not; secondly, judging current transformer saturation if the instantaneous value of the current satisfies the condition for judging the saturation need of the current transformer; and at last, performing polarity and numerical compensation on the instantaneous value of the current when the current transformer is saturated according to judgment. Due to the adoption of the method for judging and compensating the current transformer saturation, the current transformer saturation of the current transformer secondarycurrent which attenuates according to an exponential law characteristic can be identified rapidly, and numerical and phase compensation can be performed on the current transformer saturation under the condition. By adopting the method disclosed by the invention, the polarity of fault component instantaneous current and the phase of a fault component current vector can be judged correctly, the protection of a phase comparison principle is not influenced by the current transformer saturation, and the rapidness, sensitivity, reliability and selectivity of phase comparison protection can be improved.

The invention provides an identification method for sympathetic inrush in transformer which belongs to power system main equipment relay protection technology field. The identification method has characteristic in that: the method identifies transformer sympathetic inrush by using non-saturation area equivalent instantaneous inductance. Phase current winding around primary-secondary sides of operating transformer and primary side phase voltage are collected by computer according with transformer sympathetic inrush generating reason, and difference of primary-secondary sides phase current is calculated, namely different current; next, non-saturation operation region is ensured according with max of different current absolute value; then, equivalent instantaneous inductance in non-saturation operation region is calculated, and sympathetic inrush in transformer is judged according with equivalent instantaneous inductance average value in non-saturation operation region, differential protection is closed locked for preventing misoperation. The method has merits of high reliability, strong saturability of anti-current transformer in comparison with secondary harmonic ratio inrush current locking criterion and third harmonic ratio current transformer saturation criterion.

Disclosed is a novel current transformer saturation identification method. The novel current transformer saturation identification method includes the steps that 1, three-phase voltage and electric current instantaneous value data at protective installation positions of current transformers are collected, and sampling results are recorded as ua(k), ub(k), uc(k), ia(k), ib(k) and ic(k); 2, the three-phase voltage and electric current fault component are calculated, namely, delta ua(k), delta ub(k), delta uc(k), delta ia(k), delta ib(k) and delta ic(k); 3, equivalent inductance and resistance parameters are calculated, namely, L(eq.j) and R(eq.j) (j=a, b ,c); 4, dispersion of the resistance parameters is calculated (j=a, b ,c); 5, whether all phases of mutual inductors are saturated is judged and recognized, if D(L(eq.a)) > epsilon, then the a-phase mutual inductor is judged to be saturated, if D(L(eq.b)) > epsilon, then the b-phase mutual inductor is judged to be saturated, and if D(L(eq.c)) > epsilon, then the c-phase mutual inductor is judged to be saturated. The novel current transformer saturation identification method is simple and reliable, and is not affected by system operation modes and fault initial phase angles because only short data windows are used.

The invention provides a prediction method for current transformer saturation. The prediction method comprises the following steps: detecting a first current output from a high-voltage side current transformer of a transformer, and detecting a second current output from a low-voltage side current transformer of the transformer; calculating a first fundamental wave vector, a first DC (direct-current) component and a first total effective value of the first current, and calculating a second fundamental wave vector, a second DC component and a second total effective value of the second current; generating a current transformer saturation prediction signal according to the first fundamental wave vector, the first DC component, the first total effective value, the second fundamental wave vector, the second DC component and the second total effective value. By the method, the current transformer saturation can be predicted or detected effectively before the differential protection of the transformer caused by the current transformer saturation, so that the maloperation of the differential protection of the transformer can be effectively avoided.

The invention provides a current transformer saturation detection method based on a waveform area ratio method. Firstly secondary side current of a current transformer is sampled; then a standard sinusoidal current waveform is defined, normalization processing is performed on the actual saturated secondary side current with the maximum value acting as reference, and area formed by the actual saturated secondary side current waveform and a time axis and area formed by the standard sinusoidal current waveform and the time axis through enclosing are obtained via calculation; then ratio of area formed by the actual saturated secondary side current waveform and the time axis to area formed by the standard sinusoidal current waveform and the time axis is calculated; and finally a result is outputted and comparison and judgment are performed. Problems of low detection speed and low detection precision in saturation of the current transformer can be mainly solved, i.e. sampling data within a half cycle can be utilized to detect the saturation behavior of the CT sensitively through the area ratio, and stability of relay protection work can be enhanced to some extent.

The invention discloses a bus protection method based on the sudden-change direction of fault current containing power frequency bands, and belongs to the technical field of power system relay protection. When a bus or a circuit breaks down, three-phase current data of all circuits of the bus in a short time window existing after the bus or the circuit breaks down are extracted, and a line model current containing fault phases is obtained after calculation through the three-phase current data; db4 wavelet transform is conducted on the line model current, the frequency bands where power frequency amount exists are used for conducting straight line fitting, and whether the bus breaks down or the circuit breaks down is judged according to whether the slope polarities of straight lines obtained through fitting of all the circuits are the same or not. According to the bus protection method based on the sudden-change direction of the fault current containing power frequency bands, protection is formed by means of the variation tendency of power frequency band components of the current, the protection is reliable, the requirement for the sampling rate is low, and the head polarity of traveling waves does not need to be detected; the needed time window is short, the complete power frequency amount does not need to be extracted, the situations where a current transformer is saturated, and a power frequency current flows out of the fault bus cannot influence the method.

The invention discloses an instantaneous current characteristic based current transformer (CT) saturation recognition improvement method. On the basis of a combination of the conventional time-difference method and a virtual braking current method for recognizing the current transformer saturation, the alternating current / direct current component condition of the fault current before CT saturation is fitted according to the instantaneous sampling value of the fault current before saturation through a discrete sliding-window iterative Fourier algorithm; then an implicit expression relation between the fault current and the virtual braking current threshold value D is fitted by a BP neutral network which is trained by a genetic algorithm (GA); and finally, the instantaneous sampling value of the fault current which is measured in real time is input into an algorithm program to adaptively select the virtual braking current threshold value D. By adoption of the instantaneous current characteristic based current transformer (CT) saturation recognition improvement method, the problem of overlong locking differential protection time when a fixed threshold value is chosen by the conventional virtual braking current method under severe saturation is effectively solved; and in addition, the openness of differential protection can be accelerated under a condition of fault transferring from an extra-region to an intra-region.

The invention relates to a current transformer saturation identification method comprising the following steps: acquiring three-phase current data needed for current differential protection and preprocessing the data; setting a current transformer saturation identification plane and partitioning the current transformer saturation identification plane; identifying whether a current transformer is saturated or not according to the data and the saturation identification plane; and reopening the fault in the saturated period of the current transformer according to the saturation recognition judgment and the fault opening criterion. By adopting the technical scheme, the action performance of current differential protection is enhanced.

The current transformer saturation detecting process based on correlation coefficient method includes: 1. the sampling step of sampling the phase currents in the principal side of the current transformer in the set rate and storing the sampled result in the memory; 2. the calculation step of calculating the real part, the imaginary part of the phase current in cycle Fourier conversion algorithm and DC component average value in the cycle, and calculating the correlation coefficient of the phase current sampling value in one cycle; and 3. the comparison and judgment step of comparing the obtained correlation coefficient with one set threshold and judging as the current phase TA saturation in condition of the calculated correlation coefficient smaller than the set threshold. The technology may be applied in high voltage line protecting system.

The invention provides a protective current transformer saturation detection method based on skewed distribution. Firstly CT secondary current is sampled; then current waveform is intercepted near the waveform peak by adopting short data windows so that local current waveform symmetrical about the peak is obtained; waveform mirror image transformation is performed on the intercepted waveform and then coefficient of skewness of the waveform is calculated by skewed distribution; and the coefficient of skewness is compared with the fixed value of the pre-set coefficient of skewness so that saturation of a current transformer is judged. Problems of low detection speed and low detection precision in saturation of the current transformer can be solved, and the CT saturation situation can be rapidly and accurately detected only by utilizing sampling data of half cycle so that reliability of relay protection can be enhanced to some extent, and thus the method also has certain reference significance in the actual engineering application.

The invention provides a method for identifying sympathetic inrush current of a transformer based on online voltage integrating. The method comprises the following steps: step 1, reading current and voltage sampling values of the transformer; step 2, judging whether to start sympathetic inrush current identification or not; step 3, calculating the magnetic flux of the transformer; step 4, calculating the amplitude of the magnetic flux of the transformer; step 5, judging flux saturation on line; step 6, carrying out adaptive adjustment on the fixed value of a differential protection action platform; and improving the original fixed value of the action platform operating transformer differential protection to k1 times higher than the original fixed value, wherein k1 is more than 1. The method disclosed by the invention is not subject to the effects of sympathetic inrush current type and saturation of a current transformer, which prevents false action of transformer differential protection during the generation of sympathetic inrush current and facilitates the engineering application.

The invention relates to a transformer protection method based on double-side unsaturated zone equivalent instantaneous inductance, belonging to the electric power system primary device relay protection technical field. The invention is characterized in that: unsaturated zone equivalent instantaneous inductance at two sides of a transformer is utilized to realize transformer protection, which is a novel transformer protection method unrelated to excitation inrush current; when an internal fault of the transformer happens, equivalent instantaneous inductance in an unsaturated zone calculated from the prior secondary are all very small; when an external fault of the transformer happens, the equivalent instantaneous inductance in the unsaturated zone calculated from the prior secondary is very small on the fault side, while the equivalent instantaneous inductance is very big on the non fault side; whether a fault happens in the transformer can be judged according to the characteristic of the equivalent instantaneous inductance in an unsaturated zone calculated from two sides of the prior secondary being less than a threshold value at the same time, and internal fault and external fault can be identified; the protection has strong antisaturation capability of a current transformator.

The invention discloses a global-and-local-feature-combined current transformer saturation detection method, which comprises the following steps: if meeting emergency variable startup judging criteria, entering the saturation detection step immediately; calculating harmonic ratio alpha of secondary current waveform within a period starting from an extreme point; calculating integral areas of equal four sections of waveforms of secondary current of a current transformer within the period starting from the extreme point after fault starts and calculating the ratio Sc of the maximum area and the minimum area; comparing the obtained ratio Sc and the harmonic ratio alpha with corresponding preset threshold values respectively, and when both the ratio Sc and the harmonic ratio alpha are larger than the preset threshold values, judging that the current transformer enters a saturation state; and when detecting saturation, carrying out comprehensive analysis on the calculating results of the waveform area ratio and the harmonic ratio immediately to obtain exact saturation degree. The method retains the sensitivity of harmonic ratio to mild saturation, and meanwhile, can also use the ratio of sectional integrals to better reflect the degree of saturation; and through combination of the two modes, the method is allowed to be high in sensitivity and improves identification efficiency.

The current transformer saturation detecting technology based on phase comparison method includes: 1. the sampling step of synchronously sampling the phase currents in the principal side and the opposite side of the current transformer in the set rate and transmitting the phase current of the opposite side to the principal side for storing; 2. the calculation step of calculating the instantaneous value, Fourier conversion amplitude, integrated various, etc of the phase current to obtain one phase comparison coefficient; and 3. the comparison and judgment step of comparing the obtained phase comparison coefficient with one set threshold and judging as outside fault saturation in condition of the phase comparison coefficient smaller than the set threshold or inside fault in other conditions. The technology performs phase comparison judgment with cycle data window, and is simple, reliable and fast.

The present invention discloses a method for distinguishing saturation of current transformer for buslar protection equipment in power system-busbar protection current trasformer saturation mutational load difference current dynamic recollecting method. The method uses mutational load difference current as main distinguishing basis and collects the output end current of every current transformer in high-voltage and ultrahigh-voltage equipment according to the interval of a certain time, and utilizes the A / D conversion mode to convert the output end current into digital quantity from analog quantity, then utilizes there digital quantities to make correspondent calculation and uses the distinguishing basis to correctly distinguish the fault source.

The invention discloses a transmission line fault detection method based on a spearman correlation coefficient. The method comprises the following steps of: acquiring three-phase current instantaneousvalues on two sides of a line at each moment; calculating to obtain instantaneous values of a positive sequence fault component current, a negative sequence current and a zero sequence current on twosides of the line; constructing a fault component comprehensive current on a certain side of the line to be the superposition of the instantaneous values of the positive sequence fault component current, the negative sequence current and the zero sequence current at the same moment; using one cycle as a time window, utilizing the fault component comprehensive current in the time window to construct two characteristic sequences of a certain line, and calculating the spearman correlation coefficient between the two characteristic sequences; and calculating the spearman correlation coefficient of the line once when the time window moves forwards by one point, and judging that the line is a fault line when the correlation coefficient is larger than a threshold value 0. The transmission line fault detection method of the invention has the beneficial effects that: the transmission line fault detection method is not influenced by transition resistance, abnormal data, current transformer saturation and the like, and the fault line can be detected when a fault occurs in open-phase operation and flow transferring, and the requirement on information synchronism is not high.

The invention discloses a busbar sampling value differential protection method based on a current transformer linear transmission area. The regularity rule of current transformer saturation is used, according to a current known linear transmission area position, the linear transmission area position after a cycle wave, and sampling value differential criterion judgment is applied a predicted linear transmission area. If a fault is developed in the area, sampling value differential is on exit. If sampling value differential criterion does not act, the actual linear transmission area position is used to predict the linear transmission area position of a next time, and so on until protection action or starting return. According to the method, reliable locking is achieved in external fault current transformer saturation, a conversion fault can be correctly identified, the rapid action is achieved in a current transformer linear saturation process, the sensitivity is high, and the ability of resistance to outflow current and development fault external fault point fault current shunt is improved.

The invention belongs to the technical field of relay protection of power systems, and particularly relates to a differential protection method for a partition inverse-time transformer by considering DC bias effects. The method is characterized by comprising the following steps: judging whether a partition signal is sent out or not by detecting a DC of a neutral point; if a microprocessor protection device does not receive the signal, judging an internal fault or an external fault according to an original ratio braking characteristic, judging saturation of a current transformer by a time-difference method and blocking the external fault; if the signal is received, partitioning an action region of the ratio braking characteristic into two blocks, if a serious internal fault is generated, enabling the signal to drop into a no-delay action region and if a light internal fault is generated, enabling the signal to drop into an inverse-time action region; and if the external fault is generated, enabling the current transformer to quickly retreat from the inverse-time action region, returning an action instruction within a time delay, retreating and entering a brake region and blocking differential protection. After the fault is removed, a brake current is a load current; the minimum action current of the ratio braking characteristics is lifted on the basis of the partition signal; and a relatively high differential current after the fault is removed is evaded.

The invention discloses a test method of a main transformer CT (Current Transformer). The test method comprises the steps of: in the case that the current transformers have all secondary loop current, leads are used for respectively connecting the high-voltage side, the middle-voltage side and the low-voltage side of the main transformer, and stride over the transformer; an isolation switch at one side and a breaker and an earthing isolation switch at the other two sides are closed; three-phase current is applied to the current transformer side of the side with the unclosed breaker and earthing isolation switch, so that the current flows through the current transformers at three sides of the transformer so as to simulate load current states at the three sides when the transformer operates normally; the current value, phase and differential current of each side are detected at the differential protection device for the main transformer, if the differential current is equal to 0, the ratio of transformation, the polarity and the wiring of the differential loop of each current transformer are correct. According to the test method of the main transformer CT, the correctness of the current value, phase and differential current of each main transformer CT can be simultaneously tested, so that the work efficiency and test quality are improved, and the electrical device is ensured to operate reliably.

Provided is a method for detecting the saturation of a current transformer (CT) on the basis of a third-order central moment. The method comprises: sampling current at the secondary side of the CT; acquiring a current waveform from a position near the peak value of a waveform by using a data window in order to obtain a waveform symmetric about the peak value and with less sampling points; computing a dispersion coefficient by using the third-order central moment after the acquired waveform is subjected to waveform mirror image transformation; and outputting a detected result. In the method, a dispersion coefficient after a standard sinusoidal current waveform is subjected to mirror image transformation. By means of analysis and computation, the dispersion coefficient can be considered as a fixed value so as to be used as a comparison basis. The method mainly solves problems of low detection rate and low detection precision when the CT saturation occurs, may fast and accurately detect the generation of the CT saturation just by using sampled data in half cycle so as to improve relay protection reliability to a certain extent and have certain practical significance in the aspect of guaranteeing the accurate and reliable operation of the CT.

A method for differential protection by waveform shaping includes: a differential protection device samples the current waveform of a current mutual-inductor to get a transient value to shape the deformed AC waveform to square to sum vectors of other side current except that of the saturated mutual-inductor to get the composed current vector to compare the above basic square waveform phase with that of the composed current basic waveform to get the cosine of its included angle. If taking the positive current direction to the transformer as the positive then the rest cosine value is positive, which refers to internal fault the differential protector is switched-on, or the outside fault, the protector is switch-off.

A method, device and computer program product for determining at least one property of a current (Ip) running through the primary winding of a transformer operating in saturation using an unreliable detected current (Is) running through the secondary winding of the transformer. According to the invention a first reliable extreme point (EP1) of a cycle of the current in the secondary winding is detected and compared with an absolute time reference. Based on the comparison a first property of the current running through the primary winding in the form of the phase angle is then determined.

In the field of current differential protection relays there is a need for improvements in or relating to the protection relays to allow them to accommodate current transformer saturation while maintaining a desired degree of reliability. A method of operating a current differential protection relay (10, 26) following a fault, the protection relay (10, 26) being electrically coupled to a protection zone of an electrical power system, comprises the steps of establishing a fault condition by discriminating between an internal fault inside the protection zone and an external fault outside the protection zone; and modifying the sensitivity of the protection relay (10, 26) according to the nature of the fault condition. A current differential protection relay (10, 26) comprises a fault discriminator module (20) to establish a fault condition by discriminating between an internal fault inside a protection zone of an electrical power system and an external fault outside the protection zone; and a sensitivity modifying module (22) to modify the sensitivity of the protection relay according to the nature of the fault condition.