Method for calculating equivalent load line impedance of three-phase three-wire system unbalanced system

Abstract

The invention discloses a method for calculating equivalent load line impedance of a three-phase three-wire system unbalanced system. The method includes the steps that firstly, a bus voltage phasor and a general incoming line current phasor of a three-phase unbalanced power system are acquired, the voltage phasor and the current phasor are resolved according to a symmetrical component method, and therefore a bus voltage positive-sequence component, a general incoming line current positive-sequence component and a general incoming line current negative-sequence component of the three-phase unbalanced power system are acquired; secondly, the minimum phase of a general incoming line current phasor module value serves as a reference phase, and the general incoming line current negative-sequence component is rotated in the positive sequence, so that the general incoming line current negative-sequence component in the positive sequence is acquired; the general incoming line current negative-sequence component in the positive sequence is subtracted from an original general incoming line current negative-sequence component of a non-reference phase, so that a current component passing through the non-reference interphase is acquired; thirdly, the bus voltage positive-sequence component, the general incoming line current positive-sequence component, the general incoming line current negative-sequence component in the positive sequence and the interphase current component are used for calculation, so that positive-sequence impedance, negative-sequence impedance in the positive sequence and interphase impedance of the non-reference phase of a load are acquired, the positive-sequence impedance and the negative-sequence impedance in the positive sequence of the load are equivalently converted in an angle joint mode and combined with the interphase impedance together, and therefore the equivalent load line impedance of the three-phase three-wire system unbalanced system can be calculated through a impedance parallel formula.

Description

technical field [0001] The invention relates to a three-phase three-wire power system with an ungrounded neutral point, in particular to a calculation method for the equivalent load line impedance of an unbalanced three-phase three-wire system. Background technique [0002] With the continuous construction and development of my country's power system, some three-phase unbalanced loads and single-phase large-capacity loads appear in the power system, such as traction transformers in electrified railways, AC electric arc furnaces and electroslag furnaces for steelmaking in steel plants, Spot welding machines in automobile factories, etc. The negative-sequence current generated during the operation of these unbalanced loads is injected into the power system to cause negative-sequence voltage. The negative-sequence voltage not only increases the extra loss of the motor and transformer, reduces its service life, but may also cause malfunction of relay protection and automatic devi...

AI Technical Summary

Problems solved by technology

When there are many load feeders, the equivalent line impedance of the system side is calculated according to the PT and CT measurement signals of many load incoming lines. The hardware cost is high, the calculation workload is large, and it is difficult to meet the real-time compensation and control on the algorithm operation time. requirements

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