Reactive power compensation methods and some existing problems in power system

In recent years, with the leapfrog development of the national economy, the power industry has also developed rapidly, especially the construction of power grids. The rapid growth of loads has also greatly increased the demand for reactive power. Reactive compensation plays an important role in improving voltage quality. The use of advanced reactive compensation devices can achieve dynamic automatic stepless adjustment of reactive power, while achieving the purpose of reducing system losses and improving system power supply efficiency. The use of automatic stepless reactive power compensation devices can achieve automatic, smooth and continuous control of reactive power in the power grid. There is a filter circuit inside to ensure safe and reliable operation of the system. At present, reactive power compensation in power systems mainly adopts the following methods:

1. Synchronous condenser: Synchronous condenser is a typical representative of early reactive power compensation devices. It can not only compensate fixed reactive power, but also dynamically compensate for changing reactive power.

2. Parallel compensation device: Parallel capacitors are the most widely used reactive compensation device in the field of reactive power compensation. However, capacitor compensation can only compensate fixed reactive power. Although the use of capacitor group switching can more effectively adapt to the dynamic changes of load reactive power than the fixed capacitor compensation method, the capacitor compensation method still belongs to a stepped reactive power regulation and cannot achieve smooth and stepless reactive power regulation.

3. Shunt reactor: The capacity of the reactor currently used is fixed. In addition to absorbing the system capacitive load, it is used to suppress overvoltage. Adjustable shunt reactors are now under development, and problems such as harmonics, noise, control, and heat dissipation need to be solved.

The above methods have been used in power systems for many years and have achieved certain results. However, there are also some problems in the actual reactive power compensation work, mainly:

Compensation method problem: At present, many power departments take on-site compensation as the starting point for reactive power compensation, and do not return reactive power to the system. That is, they only pay attention to compensating power factors, and are not based on reducing the loss of the system network.

Harmonic problem: Capacitors have a certain ability to resist harmonics, but when the harmonic content is too large, it will affect the life of the capacitor and even cause premature damage to the capacitor; and because capacitors have an amplifying effect on harmonics, the harmonic interference of the system is more serious.

Reactive power reverse transmission problem: Reactive power reverse transmission is not allowed in the power system, especially when the load is low, reactive power reverse transmission causes the voltage to be too high.

Problems caused by voltage regulation compensation equipment: Some reactive power compensation equipment determines the reactive power switching amount based on voltage, which helps to ensure the power quality of users, but is not desirable for the power system. Because although the fluctuation of line voltage is mainly caused by the change of reactive power, the voltage level of the line is determined by the system conditions. When the line voltage reference is too high or too low, the reactive power switching amount may be far from the actual demand, resulting in over-compensation or under-compensation of reactive power.