Methods and functions of reactive power compensation

1. The use of over excited synchronous motor can improve the power factor of electricity consumption, but the equipment is complex and the cost is high, so it is only suitable for high-power driving device.

2. Using the condenser as the non power supply, this device has good adjustment performance, can maintain the system voltage level in the case of power system failure, and can improve the stability of power system operation, but it has high cost, large investment and high loss.

The loss of reactive power per kvar is about 1.8-5.5%. The operation and maintenance technology is complex, so it should be installed in the central substation of power system, which is rarely used by general users.

3. Asynchronous motor synchronization. This method has a certain effect, but its own loss is large, the loss of reactive power per kvar is about 4-19%, which is generally not used.

4. As a compensation device, power container has the advantages of convenient installation, short construction period, low cost, simple operation and maintenance, and low loss (the loss of reactive power per kvar is less than 0.3-0.4%).

The disadvantage of this method is that the service life of power capacitor is short;

The reactive power output is proportional to the square of the operating voltage. When the operating voltage of the power system decreases, the compensation effect decreases, and when the operating voltage increases, the end voltage of the electrical equipment is over compensated, which makes the terminal voltage increase too much, or even exceed the standard provisions. It is easy to damage the equipment insulation and cause equipment failure. To make up for this shortcoming, corresponding measures should be taken to prevent the reactive power from being sent back to the power system.

There are two ways to use power capacitor as compensation device

Series compensation and parallel compensation.

1) Series compensation is to connect capacitors directly to high voltage transmission lines, so as to improve transmission line parameters, reduce voltage loss, improve transmission capacity and reduce line loss. The capacitor of this compensation method is called series capacitor, which is used in high voltage long-distance transmission line, and rarely used by the electricity unit.

2) . parallel compensation is to connect the capacitor directly with the compensated equipment and connect it to the same circuit to improve the power factor. The capacitor used in this compensation method is called parallel capacitor, which is used by the power consuming enterprises.

Compensation for parallel capacitors:

The compensation form of capacitor shall be based on the principle of local balance of reactive power.

The reactive load of the power grid is mainly caused by the power consumption equipment and transmission and transformation equipment.

Besides the centralized installation of large and medium capacitor banks in the relatively dense power supply load center, it is convenient for the over-voltage control of the central grid and stability of the power supply voltage quality of the power grid. Besides, the medium and small capacitor banks shall be installed at the place close to the power consumption reactive load for local compensation.

When installing capacitor for reactive power compensation, it can be centralized, decentralized or individual compensation.

1) Individual compensation

Individual compensation is a method of nearby compensation for the reactive power required by a single power equipment. The capacitor is directly connected to the same electrical circuit of a single power equipment, controlled by the same switch, and put into operation or disconnected at the same time.

The compensation method has the best effect. The capacitor is close to the power equipment, and the reactive current can be balanced locally, which can avoid the over compensation when there is no load and the voltage quality can be guaranteed.

Individual compensation is usually used in high and low voltage motors with large capacity and other electrical equipment. However, when the power equipment is not running continuously, the capacitor utilization rate is low, and its compensation benefits can not be fully exerted.

2) Decentralized compensation:

The capacitor bank can be installed in groups on the outgoing lines of each branch of the workshop distribution room or substation. It can be put into operation or cut off at the same time as the change of part load of the factory. The compensation method also has good effect.

3) Centralized compensation:

The capacitor bank is installed on the bus of primary or secondary side of substation. This compensation method is simple to install, reliable in operation and high in utilization.

effect:

① Improve the user's power factor, so as to improve the utilization of electrical equipment;

② Reduce the active power loss of power network;

③ The reactive power flow of power system is controlled reasonably, so as to improve the voltage level, power quality and anti-interference ability of power system;

④ In the dynamic reactive power compensation device, the configuration of appropriate regulator can improve the dynamic performance of the power system, improve the transmission capacity and stability of the transmission line;

⑤ Static var compensator (SVS) can improve the voltage waveform, reduce the harmonic component and solve the problem of negative sequence current. For capacitors, cables, motors and transformers, it can also avoid the additional power loss and local overheating caused by high-order harmonics.