摘要:
Disclosed is a relaying method for protecting a transformer by using a difference of current. A decision function, related to the rate of change of a primary current, a secondary current, or a differential current, is used for determining whether a detected abnormal current is due to the inrush or internal fault.
摘要:
Disclosed herein is a method of compensating for the distorted secondary/ current of a current transformer. The method includes steps (a), (b) and (c). At step (a), the saturated section of the current transformer is detected. At step (b), fault current generated during a fault in a power system is represented using an AutoRegressive (AR) model, with the fault current being assumed to be a combination of a Direct Current (DC) offset component, a fundamental wave component and harmonic components. At step (c), coefficients of the AR model are estimated and the secondary current during saturation of the current transformer is compensated, based on the secondary current data sampled in the unsaturated section.
摘要:
Disclosed is a method for detecting saturation of a current transformer. The method determines whether or not a change of a secondary current generated in a current transformer is due to the saturation of the current transformer.
摘要:
Disclosed is a compensated current differential relaying method and system for protecting a transformer more correctly by calculating and estimating an exciting current including a core-loss current and a magnetizing current, and, in particular, to a compensated current differential relaying method and system which can protect the transformer correctly irrespective of the level of remanent flux.
摘要:
A method for preventing the unwanted maloperation of a protective relay system that is caused by the imprecise detection of an actual secondary current value resulting from a measured secondary current being distorted comprises the steps of calculating difference values for sampled secondary currents; comparing absolute values of the difference values with a predetermined critical value, and determining a saturation starting moment of a current transformer when one of the absolute values exceeds the predetermined critical value; obtaining a magnetizing current at the saturation starting moment using the difference values if the saturation starting moment is determined, and obtaining a magnetic flux value in a steel core of the current transformer from a magnetization curve using the magnetizing current; calculating a magnetic flux value at a time after the saturation starting moment using a secondary current value measured at that time and the magnetic flux value obtained at the saturation starting moment so as to obtain a secondary current value consistent with a current transformation ratio at that time; obtaining a magnetizing current at that time from the magnetization curve using the magnetic flux value calculated at that time; and obtaining the secondary current value consistent with the current transformation ratio by adding the obtained magnetizing current and the measured secondary current value.
摘要:
The present invention relates to a relaying method using the ratio of induced voltages or the ratio of flux linkage increments. The protective relaying method for power transformers with one or more phases includes the first step of obtaining primary and secondary voltages and currents of the transformer; the second step of calculating induced voltages, induced voltage differences, ratio of primary and secondary induced voltages, or ratio of primary and secondary induced voltage differences from the currents and the voltages; the third step of calculating at least one predetermined decision parameter derived from at least one predetermined equation; the fourth step of deciding whether an internal winding fault occurs by comparing the decision parameter to the induced voltages, the induced voltage differences, the ratio of primary and secondary induced voltages, or the ratio of primary and secondary induced voltage differences.
摘要:
The present invention relates to a method and system for controlling a wind farm when a ramp up or ramp down rate of the wind farm does not satisfy a grid-code or corresponding criteria due to an abrupt change in wind speed. The method and system for controlling a wind farm includes the steps of measuring speed and direction of wind performed outside the wind farm, sequentially controlling wind turbines if the wind speed abruptly changes considering a time for the wind to arrive at the wind turbines, determining the number of wind turbines to be controlled simultaneously so that the wind farm may satisfy the grid-code at this point, grouping the wind turbines, determining a control sequence and a control time of each group, and adjusting a control end time if stopping times of adjacent groups are overlapped when the wind turbines are stopped.
摘要:
The present invention relates to a method and system for controlling a wind farm when a ramp up or ramp down rate of the wind farm does not satisfy a grid-code or corresponding criteria due to an abrupt change in wind speed. The method and system for controlling a wind farm includes the steps of measuring speed and direction of wind performed outside the wind farm, sequentially controlling wind turbines if the wind speed abruptly changes considering a time for the wind to arrive at the wind turbines, determining the number of wind turbines to be controlled simultaneously so that the wind farm may satisfy the grid-code at this point, grouping the wind turbines, determining a control sequence and a control time of each group, and adjusting a control end time if stopping times of adjacent groups are overlapped when the wind turbines are stopped.
摘要:
Provided an error compensating method for an instrument transformer, in which an error of an instrument transformer is compensated by reflecting hysteresis characteristics of iron core. When such error compensation is performed, a hysteresis loop indicating the relationship between magnetic flux and excitation current is not used as it is, but core-loss resistances and magnetic flux-excitation current curves are used, thereby achieving more precise compensation. According to the present invention, an error of an instrument transformer can be significantly reduced. Therefore, it is possible to manufacture an instrument transformer with high accuracy and to significantly reduce the size of the instrument transformer. Further, a material with high permeability does not need to be used in order to increase the accuracy.
摘要:
The present invention relates to a method for preventing the unwanted maloperation of a protective relay system that is caused by the imprecise detection of an actual secondary current value resulting from a measured secondary current being distorted. The method comprises the steps of calculating difference values having at least second order for sampled secondary currents; comparing absolute values of the difference values with a predetermined critical value, and determining a saturation starting moment of a current transformer when one of the absolute values exceeds the predetermined critical value; obtaining a magnetizing current at the saturation starting moment using the difference values if the saturation starting moment is determined, and obtaining a magnetic flux value in a steel core of the current transformer from a magnetization curve using the magnetizing current; calculating a magnetic flux value at a time after the saturation starting moment using a secondary current value measured at that time and the magnetic flux value obtained at the saturation starting moment so as to obtain a secondary current value consistent with a current transformation ratio at that time; obtaining a magnetizing current at that time from the magnetization curve using the magnetic flux value calculated at that time; and obtaining the secondary current value consistent with the current transformation ratio by adding the obtained magnetizing current and the measured secondary current value.