Control method of three-phase load in distribution network

Abstract

The invention discloses an optimized three-phase load automatic adjustment device for distribution network and its control method, including a three-phase unbalance adjustment controller, a switch circuit, and an inter-line compensation unit controlled by the three-phase unbalance adjustment controller. Phase-to-phase compensation unit, the line-to-line compensation unit is a plurality of compensation capacitor groups set according to the size of the three-phase unevenness in the distribution network, and the phase-to-phase compensation unit is a plurality of compensation reactances set according to the size of the reactive power of the distribution transformer device. The three-phase unbalance regulating controller can automatically calculate the active power and reactive power of the three-phase lines of the distribution network online, select the appropriate line-to-line compensation capacity and phase-to-phase compensation capacity, and then control the automatic switching of the composite switch, and the power distribution Each phase of the distribution network is compensated to ensure the load balance between the phases of the distribution network; the unidirectional reactor is used in the phase-to-phase compensation unit, which not only has the function of reactive power compensation but also has the function of reducing the power factor to ensure that the power in each phase The factor is less than 1.

Description

technical field [0001] The invention relates to a method for controlling three-phase loads of a distribution network, which is suitable for controlling three-phase unbalanced loads in a low-voltage power supply system, and belongs to the fields of electric power technology and electronic technology. Background technique [0002] In the power system, the consumption of electric energy is mainly realized by the distribution network, especially by the low voltage of the distribution network. my country's low-voltage power load usually refers to the load carried by the AC 220V / 380V system. AC 220V / 380V system usually consists of three-phase four-wire, namely A phase, B phase, C phase and N phase. The low-voltage electric energy of the distribution network is transmitted and distributed by a certain distance of cable lines or wire lines, and the inductance in the low-voltage lines is inevitable. Thus, the reactive power in the load does exist. The loads on the low-voltage side...

AI Technical Summary

Problems solved by technology

[0003] The unbalanced three-phase load, the first major harm to the power system is the increase of line loss

For the power sector, it increases the number of emergency repairs and operation and maintenance costs, and reduces the reliability of power supply

[0004] The unbalanced three-phase load, the second biggest harm to the power system is the increase of transformer core loss

Distribution transformers with Y / Y0 or △ / Y0 wiring mostly adopt a three-core column structure. When the three-phase current imbalance occurs, there is no zero-sequence current on the primary side, but there is zero-sequence current on the secondary side. The current is Pure excitation current produces zero-sequence magnetic flux, because the magnetic flux does not have a closed magnetic circuit, it needs to pass through the tank wall to close, thus generating heat and loss in the iron core, fuel tank and magnetic accessories

[0005] Unbalanced three-phase loads, the third major harm to the power system is voltage offset, which will lead to unbalanced three-phase voltages in severe cases, affecting the output of three-phase motors and even burning the motors

It can be seen from the above formula that after the common compensation capacitor is connected, because the U / X values ​​of each phase are equal, the current of each phase has the same amount of change in value, so it cannot play the role of balancing the load, and can only change a certain amount on the vector. Angle

The traditional sub-compensation method is to connect different capacitors between phases of the three-phase system. The capacitor current on a certain phase is perpendicular to the active current on this phase, and the projection of the capacitor current on the active current is zero, so the active current and active current cannot be changed. power

Images