Low voltage residential area transformer three-phase load automatic balancing system and automatic balancing method thereof

Abstract

The invention provides a low voltage residential area transformer three-phase load automatic balancing system and an automatic balancing method thereof. The system comprises an intelligent central controller and several intelligent phase changers. The intelligent central controller is installed at the beginning of a to-be-balanced line. The intelligent phase changers are installed at the branch lines of a three-phase transformer. The intelligent central controller is only responsible for the communication with the intelligent phase changers installed in the branch lines. The intelligent phase changers is treated as the slave machines of the intelligent central controller. According to the low voltage residential area transformer three-phase load automatic balancing system, the change of the three phase voltages and currents of a to-be-monitored line are collected to achieve the assessment of the unbalance level of the three phase load lines. An balance logic algorithm and a random sampling method is started based on the unbalance level of the three phase load lines to control the load switch of the three phase monitoring lines to achieve the goal of balancing the three phase loads.

Description

Technical field: [0001] The invention belongs to the technical field of electric power distribution, and in particular relates to an automatic balancing system and an automatic balancing method for three-phase loads in a low-voltage station area. Background technique: [0002] As my country's modern industrial development continues to accelerate, the unbalanced nonlinear loads in the power system also increase. Usually, the three-phase unbalanced operation of the grid for a long time will seriously affect the power quality of the grid, and will have adverse effects on both power supply and electricity consumption. For example, in production and domestic electricity consumption, affected by three-phase imbalance, The transformer is in an asymmetric operation state, which causes the loss of the transformer to increase, and the unbalanced three-phase load will also cause the zero-sequence current of the transformer to be too large, the local metal temperature will increase, and...

AI Technical Summary

Problems solved by technology

[0008] 1) The active power or power loss of the line increases

When the three-phase load is unbalanced, the load current of each phase is not equal, and an unbalanced current is generated between the phases. These unbalanced currents will not only cause losses on the phase lines, but also cause losses on the neutral line, which increases total line loss

[0009] 2) Increased power loss of distribution transformers

In the case of the same output capacity of the distribution transformer, the power loss of the transformer is greater when the low-voltage three-phase load current is unbalanced than balanced.

[0010] 3) The output of the distribution transformer is reduced

The design and manufacture of the distribution transformer capacity are determined based on the three-phase load balance condition. If the three-phase load is unbalanced, the maximum output of the distribution transformer can only be limited to the maximum one phase of the three-phase load not exceeding the rated capacity, and the load is light. There is a surplus capacity in the phase of the distribution transformer, so that the output of the distribution transformer is reduced

[0011] 4) The operating temperature of the distribution transformer rises and the service life is shortened

When the neutral line current is too large, the zero-sequence magnetic flux generated by the zero-sequence current will pass through the oil tank wall and steel structural parts, causing a large power loss, which will increase the operating temperature of the distribution transformer and accelerate the internal insulation of the transformer. Ageing

In more serious cases, the neutral wire current may exceed the allowable current carrying capacity, the neutral wire is blown, the three-phase voltage differs greatly, and the voltage on the light-loaded phase is too high, even reaching the line voltage, which may easily lead to distribution transformer failure.

[0012] 5) The neutral point is displaced, and the three-phase voltage of the distribution transformer is unbalanced

The three-phase load is unbalanced, and the neutral line has zero-sequence current passing through the iron core to generate zero-sequence magnetic flux, but it cannot be offset by the primary-side magnetic flux, and it is superimposed on the original positive-phase-sequence main magnetic flux

[0013] Based on the above existing problems, the usual improvement measures in the power system are to adjust the load by manually changing the line regularly according to the actual load situation of the line. The problem of unbalanced three-phase, it is difficult to meet the requirements of smart grid for instantaneous load adjustment

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