Low-voltage power electronic on-load tap-changer

Abstract

The invention discloses a low-voltage power electronic on-load tap-changer, and belongs to the technical field of distribution transformer manufacturing and low-voltage dynamic reactive compensation. The low-voltage power electronic on-load tap-changer is composed of a switch body and a controller. The switch body is composed of a working thyristor, a switching thyristor and a current-limiting resistor. The controller is composed of a single board computer and has different control programs according to different control targets. The input signals are current and voltage of the transformer, and the output signals are conduction and switching control signals of the thyristor of the switch body. The output voltage is determined by the conduction position of the working thyristor, and when the voltage needs to be adjusted, the switching thyristor is matched to complete switching. The low-voltage power electronic on-load tap-changer can automatically adjust the output voltage of the distribution transformer according to the voltage change, and the voltage qualification rate is improved. And meanwhile, the method can be used for dynamic reactive compensation of the distribution transformer, improves operation power factors, reduces loss and realizes energy conservation.

Description

Technical Field

[0001] This invention patent belongs to the technical field of distribution transformer manufacturing and low-voltage dynamic reactive power compensation. It can be widely used in distribution systems and urban street lighting and can be used as a low-voltage on-load tap-changer. Background Art

[0002] If the output voltage of the grid distribution transformer is low during the daytime peak period and high during the nighttime low period, it cannot operate economically. The operating power factor of the distribution transformer is relatively low, only about 0.7 - 0.8, and the loss is very large. Currently, there is no reliable dynamic reactive power compensation device. The voltage of urban street lighting is high in the late night, and there is no voltage regulation means, which wastes energy and shortens the service life of lighting devices.

[0003] The distribution system needs to ensure the voltage qualification rate, which requires an automatic voltage regulation device. The voltage qualification rate of rural power grids and urban street lighting is relatively low, not meeting the national standard, and there is no automatic voltage regulation means. Existing distribution transformers are only equipped with off-load tap-changers, which cannot achieve automatic voltage regulation, and the existing 10kV on-load tap-changers are large in volume and high in price, and cannot be used on small distribution transformers.

[0004] In the field of reactive power compensation, the existing on-load tap-changers above 10kV can basically meet the requirements of voltage regulation type dynamic reactive power compensation technology, but there is currently no voltage regulation type dynamic compensation device in the 400V system. The operating power factor is generally low, which cannot meet the needs of economic operation. The operating energy consumption of the distribution system is very large, and the annual loss of the distribution transformer itself reaches more than 170 billion kwh, which is equivalent to the annual power generation of a Three Gorges Power Station.

[0005] The domestic on-load tap-changer manufacturing technology can only meet the requirements of voltage regulation above 10kV. So far, no 400V on-load tap-changer has been produced. On-load tap-changers are divided into mechanical and electronic types. Currently, the on-load tap-changers produced by domestic tap-changer enterprises are all mechanical types. Since the 400V system has a low voltage and a small current, it can just use a power electronic on-load tap-changer to meet the requirements of voltage regulation and dynamic reactive power compensation of the distribution system. Summary of the Invention

[0006] The following technical solutions are adopted to achieve the purpose of the present invention:

[0007] Manufacture a low-voltage power electronic on-load tap-changer, which consists of a switch body and a controller. The switch body consists of working thyristors, switching thyristors, and current-limiting resistors. The controller consists of a single-board computer and has different control programs according to different control objectives. Its input signals are the current and voltage of the transformer, and its output signals are the conduction and switching control signals of the thyristors of the switch body. The conduction position of the working thyristors determines the output voltage, and when the voltage needs to be adjusted, the switching thyristors cooperate to complete the switching.

[0008] The invention can automatically adjust the output voltage of a distribution transformer according to voltage changes, improving the voltage qualification rate. At the same time, it can be used for dynamic reactive power compensation of distribution transformers, improving the operating power factor, reducing losses, and achieving energy conservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further described below in conjunction with the accompanying drawings.

[0010] Figure 1 : Schematic wiring diagram of the switch body principle of the present invention

[0011] Figure 2 : Schematic wiring diagram of the controller principle of the present invention DETAILED DESCRIPTION OF THE INVENTION

[0012] As shown in the accompanying drawings Figure 1 , according to actual needs, we designed a 5-step on-load tap-changer with a voltage difference of 5%-8% of the rated voltage of the transformer between adjacent steps. The tap-changer can only be adjusted step by step. Thyristors T1, T2, T3, T4, and T5 are working thyristors, K2 and K4 are switching thyristors, and R2 and R4 are current-limiting resistors. The voltage switching is controlled by the controller to meet the operating requirements, achieve stable voltage output, and improve the voltage qualification rate. When used for dynamic reactive power compensation, it can adjust the working voltage of the compensation capacitor, adjust the reactive power output, improve the power factor, reduce the operating losses, and achieve energy conservation.

[0013] The controller is as Figure 2 , and is composed of a single-board computer. Controllers for voltage control and power factor control have different control programs.

[0014] The following takes the 3-step (T3 is conducting, others are off) and the transformer output voltage being at the 3-step as an example to illustrate the switching process. When the voltage is lower than the specified value, the controller issues a control signal to command K2 to conduct. After 40 milliseconds, it commands to turn off T3, turn on T2, and then turn off K2. The output voltage changes from the 3-step to the 2-step, and the output voltage increases by 5%-8%. When the output voltage is too high, the controller issues a command for K4 to conduct. After 40 milliseconds, it turns off T3, conducts T4, and then turns off K4. The output voltage decreases from the 3-step to the 4-step.

[0015] When the output voltage needs to be adjusted when the transformer is operating at the 2nd or 4th step, the controller issues an instruction to conduct the switching thyristor of this step. After 40 milliseconds, it conducts the working thyristor of the adjacent step, turns off the working thyristor T2 or T4 of this step, and then turns off the switching thyristor K2 or K4 of this step. The output voltage is switched to the adjacent step. The voltage switching is completed.

Claims

1. A low voltage power electronic on-load tap changer, characterized in that This low-voltage power electronic on-load tap changer consists of a switch body and a microcomputer controller. It is installed inside the distribution transformer and connected to the transformer voltage tap to complete automatic voltage regulation of the distribution transformer and improve the voltage qualification rate.

2. The switch body according to claim 1. Its characteristics are It consists of thyristors and transition resistors. Thyristors are divided into conduction thyristors T1, T2, T3, T4, and T5 according to different uses. When working, only one is turned on and the others are turned off. The conduction thyristor determines the output voltage of the distribution transformer. When switching voltage, the switching thyristors K2 and K4 act according to the control program and cooperate with the conduction thyristor to complete the voltage switching. The function of the transition resistor is to limit the circulating current during switching.

3. The microcomputer controller according to claim 1. It consists of a single-board computer. Its input signal is the current and voltage of the distribution transformer, and its output signal is the control signal of the thyristor. According to the change of the output voltage of the distribution transformer, when the voltage is unqualified, it issues an adjustment command to control the switching of the thyristor and the conduction of the thyristor according to the control program to complete the switching and change the output voltage of the distribution transformer. The microcomputer controller is equipped with a telecontrol interface, which can upload the operation data of the distribution transformer and receive instructions.

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