Capacitance-current measuring system and method of power distribution network with ungrounded neutral point

Abstract

The invention relates to a capacitance-current measuring system and method of power distribution network with an ungrounded neutral point, and relates to capacitance and current measuring technology of the power distribution network. The measuring system comprises a bus voltage transformer, an adjustable resistor, a frequency-variable voltage source and a voltage measuring instrument, the adjustable resistor and the frequency-variable voltage source are connected in series and then connected to the two ends of a third winding of the bus voltage transformer, and the voltage measuring instrument is also connected to the two ends of the third winding of the bus voltage transformer. The method by which the measuring system is used for measurement solves the problem that short-circuit impedance of the bus voltage transformer influences the measuring precision, influence of zero sequence voltage on the capacitance and current measured by a signal injection method caused by imbalance degree of the electrical network is taken into consideration, the capacitance and current measuring accuracy of the power distribution network is improved, an accurate Thevenin's equivalent circuit model is used, and the grounding capacitance of the system is solved. A measuring process is carried out in the third winding side of the transformer, wiring of primary equipment needs not to be changed, the measuring method is safe and convenient, and a result is accurate and reliable.

Description

technical field [0001] The invention belongs to the technical field of capacitive current measurement of a distribution network, and in particular relates to a system and method for measuring a capacitive current of a neutral point ungrounded distribution network. Background technique [0002] The early medium and low-voltage distribution networks in my country mostly adopted the neutral point ungrounded mode. When a single-phase ground fault occurs, the grounding arc can be self-extinguished under the condition that the grid capacitive current is not large, and the distribution network can continue to supply power with faults for 1~ 2 hours. With the continuous development of the distribution network of the power system, especially the large number of cable lines in the urban power grid, the capacitive current of the line to the ground continues to increase, resulting in a sharp increase in the single-phase ground fault current of the distribution network line, and it is dif...

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Problems solved by technology

However, considering that there will be a certain zero-sequence voltage during the actual operation of the power grid, the zero-sequence voltage will be reflected on the open triangle end of the transformer, which will have a great impact on the measurement of the voltage, often making the measurement results more inaccurate

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