In China's power system, especially in distribution networks below 35KV, there are a large number of electromagnetic voltage transformers in operation. Electromagnetic voltage transformers have nonlinear electromagnetic characteristics, and when they match parameters with capacitive components in the power grid, they will undergo ferromagnetic resonance, resulting in extremely high ferromagnetic resonance overvoltage. When overvoltage occurs, the saturation of the iron core of the transformer leads to a significant increase in the excitation current of the transformer, which can reach over a hundred times the normal excitation current in severe cases. This can cause the voltage transformer fuse to melt, spray oil, burn out, or even explode, posing a serious threat to the operation of the power grid.

At present, in the power grid, a primary harmonic eliminator is connected to the neutral point of the voltage transformer to limit the ferromagnetic resonance overvoltage. However, it is often found during operation that the PT secondary voltage imbalance phenomenon occurs after installing a primary harmonic eliminator, and the secondary voltage imbalance phenomenon basically disappears after removing the primary harmonic eliminator. After detailed on-site measurement and calculation analysis, it was found that the fundamental cause of this phenomenon is the presence of third harmonic in the power grid. Through the inductance formula of the transformer (XL=2 π f), we can know that the impedance of the transformer increases as the frequency increases, resulting in a greater difference in inductance among the three transformers. When the third harmonic current flows through the excitation winding and primary harmonic eliminator of the transformer, due to the different impedances, neutral point displacement voltage is generated, leading to three-phase voltage imbalance.

In order to solve the above problems, Hebei Taizhongyan Electrical Equipment Technology Co., Ltd. has developed the product TZY-THS voltage transformer third harmonic suppressor after years of research. The suppressor uses the high-speed CPU of American MSI as the core processing element, combined with modern power electronic control technology, which can effectively suppress the impact of third harmonic current on the voltage transformer and solve the problem of three-phase voltage imbalance after installing a harmonic eliminator in the voltage transformer.

3.1 Working environment conditions

3.1.1 Environmental temperature: -40 to+65 ℃;

3.1.2 Altitude: less than 5000 meters;

3.1.3 Seismic intensity: less than 8 degrees;

3.1.4 Relative humidity: not greater than 95%, no condensation;

3.1.5 Atmospheric pressure: 80-110kPa;

3.1.6 Other conditions: The air around the device should not contain corrosive or explosive substances containing acid or alkali, and should have lightning protection, rain and snow protection facilities.

3.2 Rated electrical parameters

3.2.1 Working power supply: built-in (low-power design, with a lifespan of over 20 years);

3.2.2 Rated input voltage: 100V;

3.2.3 Frequency: less than or equal to 150Hz.

3.3 Overload Capacity

3.3.1 1.2 times the rated input voltage can work for a long time;

3.3.2 1.5 times the rated input voltage allows for 2 hours.