The issue of reactive power compensation in modern distribution networks cannot be ignored!

1. Compensation method issue.

At present, the starting point of reactive power compensation in many departments is still on the user side, that is, only paying attention to compensating the power factor of the user, rather than focusing on reducing the loss of the power grid. To increase the power factor of a certain power load, an additional compensation box should be installed. This will certainly be helpful for reducing losses. However, in order to achieve effective loss reduction, it is necessary to calculate the reactive power flow, determine the compensation amount and compensation method for each point, in order to make the limited funds effective. This is a method of considering problems from the perspective of the power system. Practical experience has shown that in order to reduce the losses of 10KV transmission lines, it is recommended to install compensation devices on the low-voltage side of distribution transformers, which is known as the decentralized on-site compensation method.

2. Harmonic issues.

Capacitors have a certain ability to resist harmonics and have a good filtering effect on harmonic pollution in the power grid, especially high-frequency harmonic pollution. However, excessive harmonic content can have an impact on the lifespan of capacitors, and even cause premature damage to capacitors; In addition, the control link of the dynamic reactive power compensation cabinet is easily affected by harmonic interference, resulting in control failure.

Therefore, in locations with significant harmonic interference and the need to compensate for reactive power, it is necessary to consider adding filtering devices. This issue is generally overlooked. Causing some compensation equipment to be inexplicably damaged. Therefore, when designing reactive power compensation, harmonic control must be considered.

3. The problem of selecting reactive power compensation capacity.

Overcompensation can cause reactive power backflow, which is not allowed in the power system because it will increase the losses of the line and transformer, and increase the burden on the line. Users who use fixed capacitor compensation methods may experience reactive power backflow during low load periods. For compensation cabinets controlled by contactors, the compensation amount is three-phase synchronous, in the case of three-phase load asymmetry. It may cause reactive power backflow. For compensation cabinets controlled by thyristors, although the compensation amount of the three phases can be adjusted separately, many manufacturers choose only one phase for sampling and reactive power analysis in order to save funds. So when choosing compensation methods, this should be fully considered.

4. The compensation equipment for voltage regulation methods brings problems.

Some reactive power compensation devices determine the amount of reactive power switching based on voltage, which helps to ensure the quality of electricity for users, but it is not advisable for the power system. Although the fluctuation of line voltage is mainly caused by changes in reactive power, the voltage level of the line is determined by the system situation. When the voltage reference of the line is too high or too low, the amount of reactive power switching may be far from the actual demand, resulting in reactive over compensation or under compensation.

5. Switching oscillation and prevention

Due to the capacitor grading compensation and closed-loop control method, switching oscillation may occur. When the reactive power of the load remains unchanged, the compensating capacitor is frequently switched on and off. Switching oscillation not only severely reduces the lifespan of switching contactors and compensating capacitors.