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 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 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 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 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 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 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.

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, 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.