31results about How to "Prevent misoperation of differential protection" patented technology

The method includes following steps: phase current at Y0 side of transformer and the zero sequence current of this side are used to build up the rate breaking component; when the rate value is less than setting value, the break signal of the phase is outputted to break the rate differential protection of relating transformer. The invention can avoid miss -protection caused by ground fault of Y0 side when error of three-phase current transformer is disagreeing.

The invention discloses a negative sequence synthesized integrated brake device for preventing multiple-branch voltage transformer differential protection unwanted operation by utilizing fault components, wherein the three-phase difference currents in the transformer differential protection constitute ratio braking element with the maximum value of zero-sequence current on each of the neutral point earthing end (or branches), when the positive input end signal is less than the negative input end signal on the comparators, the comparator outputs 0, the lateral area outer ground fault is determined, the three-phase differential protection exit is locked, otherwise the comparator 9 outputs 1, and the corresponding differential protection actuations are allowed. The advantage of the invention is, the transformer differential protection accidental operation resulted from ground fault outside the lateral area when the errors of the three-phase current transformer are in inconformity without influencing the correct actuation of the differential protection under the circumstance of in-area faults.

The present disclosure relates to a method for preventing a maloperation of differential protection of an optical fiber caused by saturation of a single Current Transformer (CT) of 3 / 2 connection. By applying a combination of the differential judgment and the sub-CT current judgment, reliable identification of internal and external faults is ensured, and the problem of misjudging of the internal fault as the external fault can be prevented as well.

This invention discloses a brake method of the maximum current zero-sequence fault component for preventing the transformer protection misoperation, which utilizes the maximum value of three-phase current fault components at its Yo side and a said zero-sequence current fault component to make up of ratio brake elements. When the rotio value is smaller than the setting, the brake signal is output to brake the ratio differential protection. PA three-phase current brake at Yo side with supply is collected to make up of a ratio brake element using the maximum value of the fault components and the zero-sequence current fault component to avoid the misoperation of the transformer differential protection resulted in earth fault.

The invention provides a valve bank differential protection method performing synthesis judgment based on difference stream waveforms. According to the invention, synthesis judgment is performed based on difference stream waveforms of the a valve bank and whether failures are in a protection range or not is identified according to features of the difference stream waveforms. Then adjustment is made on time delay of valve bank difference based on the synthesis judgment of difference streams and differential motion constant values of the valve bank. By adopting the invention, error action of valve bank differential protection due to discontinuous differential stream influence when an alternating current system meets failures can be prevented. At the same time, failures can be isolated with reliable action of differential protection when troubles inside the sample space occur. The method can be widely applied to a high voltage DC power transmission field.

The invention provides a method for preventing direct current magnetic bias from causing current transformer saturation and transformer differential protection malfunction. The method comprises the steps of judging whether differential protection is started according to phase current jump value start criteria, calculating the second harmonic content of the phase differential current after start, and shutting the differential protection if the second harmonic content is greater than 15%; otherwise judging whether the second harmonic trend criteria is met, determining that a current transformer is in partial transient saturation if the criteria is met and utilizing a corrected ratio brake characteristic curve; otherwise utilizing the conventional ratio brake characteristic curve. The method can identify the partial transient saturation of the current transformer caused by direct current magnetic bias and correct the ratio brake characteristic curve, thereby preventing differential protection malfunction caused by the partial transient saturation of the current transformer and solving the problem that malfunctions tend to occur based on the conventional ratio brake characteristic curve.

The invention discloses a method for identifying and preventing differential protection action of a transformer caused by inrush current. In the state of fault current, when the criterion is not satisfied, the differential protection is correctly blocked, and when the criterion is met, the protection is correctly opened; 2) Use the fundamental wave amplitude increment method to judge whether it is the inrush current, if the current is judged to be In response to inrush current, short-term enhancement of braking characteristics is adopted, and the next step is to judge TA saturation. If it is judged as exciting inrush current, the criterion of exciting inrush current is used to judge whether to act; 3) Use virtual braking criterion to judge TA saturation, if If the TA is saturated, the 2-level short-time enhanced braking characteristic is adopted, and if it is not saturated, the short-time enhanced braking characteristic is adopted; 4) The differential protection operates when the protection current falls in the action area, otherwise the differential protection does not operate. The invention can fundamentally solve the problem that the surge current will cause the differential protection to malfunction.

The invention provides a recognition method for transformer saturation under the condition of complex surge. The recognition method comprises the following steps of (1) reading three-phase current sampling values at the two sides of protected equipment; (2) judging whether transformer-saturation recognition criterion is started according to the read three-phase current sampling values at the two sides of the protected equipment, if the judgment result is yes, starting the transformer-saturation recognition criterion and executing the step (3), or returning the step (1); (3) judging whether the aperiodic component of current becomes lower; (4) judging whether differential protection acts; and (5) carrying out self-adaptive adjustment on a constant value of a differential-protection acting platform. The recognition method provided by the invention has the advantages that TA saturation can be effectively recognized, differential-protection false action caused by TA saturation in the period of complex surge is prevented, the internal fault condition can not be misjudged as TA saturation, and the sensitivity of protection when the internal faults occur is not influenced.

The invention discloses a three-phase integrated brake device for preventing multiple-branch voltage transformer differential protection unwanted operation, wherein the three-phase difference currents in the transformer differential protection constitute ratio braking element with the maximum value of zero-sequence current on each of the neutral point earthing end (or branches), when the positive input end signal is less than the negative input end signal on the comparator 51-53, the comparator outputs 0, the corresponding differential current is judged to be the error current caused by the faults outside the area, the signal is outputted through an OR gate 6, or when the OR gate 6 outputs 0, the three-phase differential protection exit is locked, otherwise the OR gate 6 outputs 1, and the corresponding differential protection actuations are allowed. The advantage of the invention is, the transformer differential protection accidental operation resulted from ground fault outside the lateral area when the errors of the three-phase current transformer are in inconformity without influencing the correct actuation of the differential protection under the circumstance of in-area faults.

The invention discloses a positive sequence synthesized brake device for preventing multiple-branch voltage transformer differential protection unwanted operation by utilizing fault components, wherein the three-phase difference currents in the transformer differential protection constitute ratio braking element with the maximum value of zero-sequence current on each of the neutral point earthing end (or branches), when the positive input end signal is less than the negative input end signal on the comparators, the comparator outputs 0, the lateral area outer ground fault is determined, the three-phase differential protection exit is locked, otherwise the comparator 8 outputs 1, and the corresponding differential protection actuations are allowed. Tthe transformer differential protection accidental operation resulted from ground fault outside the lateral area when the errors of the three-phase current transformer are in inconformity.

The positive sequence current failure components of first harmonic at Y0 side of transformer and the zero sequence current failure components are used to build up the rate break component. When the rate value is less than setting value, the break signal is outputted to break the rate differential protection of relating transformer. The invention can avoid miss -protection caused by ground fault of Y0 side when error of three-phase current transformer is disagreeing.

The invention discloses a phase-splitting zero-sequence brake method for preventing multiple-branch voltage transformer differential protection unwanted operation, wherein the three-phase difference currents in the transformer differential protection constitute ratio braking element with the maximum value of zero-sequence current on each of the neutral point earthing end (or branches), when the ratio value is less than a setting value K, the corresponding differential current is judged to be the error current caused by the faults outside the area, brake the corresponding phase ratio differential protection, thus preventing the differential protection accidental operation of the transformer. The transformer differential protection accidental operation resulted from ground fault outside the lateral area when the errors of the three-phase current transformer are in inconformity.

The invention discloses a phase-splitting difference stream method for preventing voltage transformer differential protection unwanted operation by utilizing fault components, wherein the three-phase difference current variation in the transformer differential protection constitute ratio braking element with the zero-sequence current variation, when the ratio of the differential current variation and the zero-sequence current variation is smaller than a setting value K, the corresponding differential current is judged to be the error current caused by the faults outside the area, and outputs corresponding brake signal, brake the corresponding phase ratio differential protection, thus preventing the differential protection accidental operation of the transformer, The advantage of the invention is, the transformer differential protection false operation resulted from neutral ground lateral area outer earth fault can be fully prevented, without influencing the correct actuation of the differential protection under the circumstance of in-area faults.