Explore The Importance Of Reactive Power Compensation For Factory Power Supply Systems

With the vigorous promotion of national energy conservation and emission reduction, industrial factories have their own waste heat power generation and power supply and distribution systems. The factory power supply and distribution system runs in parallel with the external power grid, which improves the safety and reliability of the factory power supply and distribution system. At the same time, various inductive loads consume a large amount of reactive power in the system, and it is of great significance to perform reactive compensation and power factor adjustment.

1. Introduction to reactive power and power factor

(1) Reactive power is the electrical power that establishes and maintains the magnetic field in electrical equipment by exchanging the electric field and magnetic field in the circuit. It does not do work to the outside, but converts electrical energy into other forms of energy. Any electrical equipment with electromagnetic coils consumes reactive power to establish a magnetic field. The magnetic field of the motor rotor is established by obtaining reactive power from the power supply. The transformer also needs reactive power to generate a magnetic field in the primary coil of the transformer and induce voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not be able to change voltage, and the AC contactor will not be attracted. Under normal circumstances, electrical equipment not only absorbs active power from the power supply, but also reactive power from the power supply. If the reactive power in the power grid is in short supply, the electrical equipment will not have enough reactive power to establish a normal electromagnetic field. Then, these electrical equipment cannot maintain operation under rated conditions, and the terminal voltage of the electrical equipment will drop, thus affecting the normal operation of the electrical equipment. Capacitive reactive power can compensate for the inductive reactive power lost due to reactive exchange, so that the reactive power can be effectively balanced. The reactive power supplied by generators and high-voltage transmission lines is far from meeting the needs of the load, so some reactive power compensation devices must be installed in the power grid to supplement the reactive power to ensure that users' demand for reactive power is met. This is why the power grid needs to be equipped with reactive power compensation devices.

(2) The power loads in the power grid, such as motors and transformers, are resistive and inductive loads. There is a phase difference between the voltage and current phases of the inductive load, which is usually expressed by the cosine of the phase angle. This is called the power factor. The power factor is an important indicator that reflects the reasonable use of electrical equipment by power users, the degree of electric energy utilization, and the level of power management. The power factor is divided into natural power factor, instantaneous power factor, and weighted average power factor. The natural power factor refers to the power factor when the electrical equipment is not equipped with reactive power compensation equipment, or the power factor of the electrical equipment itself. The level of the natural power factor mainly depends on the load nature of the electrical equipment. The power factor of resistive loads (incandescent lamps, resistance furnaces) is relatively high, equal to 1, while the power factor of inductive loads (motors, welding machines) is relatively low, both less than 1. The instantaneous power factor refers to the power factor read by the power factor meter at a certain moment. The instantaneous power factor changes all the time with the type of electrical equipment, the size of the load, and the voltage. The weighted average power factor refers to the average value of the power factor over a certain period of time.

2. Methods of reactive power compensation

In the power system, there are many ways to compensate reactive power, including synchronous generators, synchronous motors, synchronous condensers, shunt capacitors and SVC. In the power supply systems of many projects, since the resistive and inductive loads are mostly, the total equivalent load is inductive, and shunt capacitors are usually used to compensate reactive power and improve the power factor. When using self-provided generator sets for power supply, they are equipped with automatic excitation voltage regulation devices to automatically adjust reactive power and voltage.

According to the different installation positions, there are three compensation methods for parallel capacitors: one is centralized compensation, which installs the capacitor group on the bus to improve the power factor of the entire substation and reduce the reactive loss of the feeder line, the second is to install the capacitor groups on the busbars in areas with lower power factors for partition compensation, which has better compensation effect. The disadvantage is that the compensation range is smaller than the centralized compensation range, the third is to install the capacitor group near the load equipment and perform reactive compensation on-site. For inductive equipment such as asynchronous motors and lighting circuits mainly based on fluorescent lamps, this method has the advantage of improving the power factor of the power supply circuit and improving the voltage quality of the electrical equipment itself. The disadvantage is that the capacitors are dispersedly arranged and the maintenance workload is large. With the improvement of domestic self-healing capacitor technology and production level, conditions have been created for the promotion of on-site compensation methods.

3. Calculation of improving power factor

Connecting capacitors in parallel with inductive loads can improve the power factor. The current in the inductive load circuit lags behind the voltage. After connecting capacitors in parallel, a capacitor branch current with a voltage lead of 900 can be generated to offset the current that lags behind the voltage, reducing the total current of the circuit, thereby reducing the impedance angle and improving the power factor. The power factor of the circuit can also be improved by connecting capacitors in series, but connecting capacitors in series reduces the total impedance of the circuit and increases the total current, thereby increasing the burden on the power supply. Therefore, the method of connecting capacitors in series is not used to improve the power factor.

Suppose the terminal voltage of the load is U, the voltage frequency is f, the power supplied to the load by the power supply is P, and the power factor is. To increase the power factor of the load from to, how large a capacitor should be connected in parallel across the load?

summary

In actual work, the factory power supply and distribution system consumes a lot of reactive power. Reactive power compensation and improving the power factor can save costs and improve economic benefits for the factory itself, and also provide reliable protection for the safe operation of the power system outside the factory.