Calculating method of impedance value of three-winding transformer based on short circuit current restraint

Abstract

The invention relates to a calculating method of an impedance value of a three-winding transformer based on short circuit current restraint. The method includes: firstly, a target function is set, and relations between an equivalent positive-sequence impedance XH [sigma]1 and an equivalent zero-sequence impedance XH [sigma]0 from a system to a short circuit point and system positive-sequence impedances Hx1 and Mx1, zero-sequence reactances, and transformer three-side equivalent reactances x1, x2, and x3 are established; relations between XH [sigma]1 and a high-voltage side three-phase short circuit current IHf3, a medium-voltage side three-phase short circuit current IMf3, and XH [sigma]1, XH [sigma]0 and a high-voltage single-phase grounding short circuit current IHf1, a medium-voltage single-phase grounding short circuit current IMf1 are established; a relation between a low-voltage side three-phase short circuit current ILf3 and x1, x2, x3, Hx1 and Mx1 is established; and limit values of short circuit current of each voltage grade side of a substation are set, the ranges of initial values of positive-sequence and zero-sequence impedances of each voltage grade are obtained, and the optimal parameter values of impedances at each side of the transformer are calculated. The beneficial effects of the method are that optimized design of the impedances of the transformers for various types of substations can be realized, and the applicability is high.

Description

technical field [0001] The invention relates to the field of environmental monitoring, in particular to a method for calculating the impedance value of a three-winding transformer based on short-circuit current constraints. Background technique [0002] The design of impedance parameter values ​​of power transformers is an important link in the engineering design of power plants and substations. At present, most substations with three voltage levels use three-winding transformers. The selection of the impedance value directly affects the short-circuit current level of the three-side voltage level, and the size of the short-circuit capacity indirectly determines the single group of reactive power compensation equipment on the low-voltage side of the substation. The capacity and the number of groups are closely related to the economic benefits of project construction. [0003] Such as figure 1 Shown is a schematic diagram of short-circuit current calculation for a typical 22...

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Problems solved by technology

However, for substations in different regions, their positions and positions in the power system are different, especially for terminal substations with low grid coupling, because the system impedance is relatively high, if the general impedance value (standard impedance value), will limit the short-circuit current to a too low level, and the excessive reduction of the short-circuit capacity of the low-voltage side will cause voltage fluctuations caused by switching of reactive power compensation equipment: after the system short-circuit capacity is reduced, if the reactive power compensation equipment If the capacity of a single group is large, the voltage fluctuation of the system during switching will not meet the power quality requirements. At this time, the problem of voltage fluctuation can only be compensated by increasing the number of groups of reactive power compensation equipment. The investment and substation area greatly increase the construction cost: currently 220kV substations in Jiangsu generally use general-purpose impedance transformers with relatively high impedance values, and at the same time use a single group of capacitors with a small capacity of 6000kvar as reactive power compensation. Large area and high one-time investment cost

This method is accidental, and the designer may be able to find a relatively reasonable parameter range through a few trials, or it may not be able to meet the requirements after many trials, and even if this method is used to find a relatively reasonable value, the optimization goal must be not optimal value

[0012] In summary, the current three-winding transformer impedance design optimization method has no theoretical support, manual calculation is complicated (multiple trial calculations are required, irregularity), and design parameters are not effective (unable to achieve optimization, high construction costs, and poor economic benefits).

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