First, what is the power factor?
When the AC current is overloaded, the AC voltage applied to the load and the AC current passing through the load cause a phase difference, and the concept of the power factor is drawn from it.
People use electricity from production and living from the power grid, and the grid provides AC power with a frequency of 50 Hz or 60 Hz. As the load of the alternating current, there are three types of resistors, inductors, and capacitors. When the alternating current is passed through a purely resistive load, the alternating voltage applied to the resistor is in phase with the alternating current through the resistor, that is, the phase angle between them is ?? = 0?°, and the active power is consumed on the resistive load. The grid has to supply energy. When the AC power passes through the pure inductive load, the phase of the AC voltage on the AC current is 90?° ahead of the phase, and the angle between them is ??=90?°, which generates reactive power on the inductive load, and the power supplied by the grid changes in the inductance. After the magnetic field can be stored for a short time and then fed back to the grid to become electric energy, the periodic cycle is endless. As a result, the grid does not supply energy, so it is called a€?reactive powera€?, but the a€?reactive currenta€? that generates a€?reactive powera€? is actually existing. When the AC power is passed through a pure capacitive load, it is similar to this, except that the phase of the AC voltage on it lags the phase of the AC current by 90?°, and the angle between them is ?? = -90?°. Here, the phase angle is defined as positive and the phase angle lag is negative.
The actual load is the three types of composites of the resistance, the inductance of the inductor, and the capacitive reactance of the capacitor. After compounding, it is called a€?impedancea€?, and the mathematical formula is: impedance Z=R+j(XLa€“XC). Where R is the resistance, XL is the inductive reactance, and XC is the capacitive reactance. If (XLa€“XC) > 0, it is called a€?inductive loada€?; otherwise, if (XLa€“XC) < 0 is called a€?capacitive loada€?. When the AC power passes through the inductive load, the phase of the AC voltage leads the AC current phase (0?°<??<90?°); when the AC power passes through the capacitive load, the phase of the AC voltage lags the AC current phase (-90?°<??< 0?°); Electrotechnical defines that the angle ?? is the power factor angle, and the cosine of the power factor angle ??, Cos??, is called the power factor.
For a resistive load, the phase difference between voltage and current is 0?°. Therefore, the power factor of the circuit is 1 max (Cos 0?°=1); and for purely inductive circuits, the phase difference between voltage and current is 90?°, and The voltage leads the current; in the pure capacitor circuit, the phase difference between the voltage and the current is -90?°, that is, the current leads the voltage. In the latter two circuits, the power factor is zero (Cos 90?° = 0). For a general load circuit, the power factor is between 0 and 1.
By the mathematical impedance Z = R + j ( XL - XC), if XL = XC, then Z = R, that is, the impedance Z becomes a pure resistance, and the power factor is equal to 1. That is to say, the inductive load and the capacitive load can compensate each other. The inductive reactance value of the inductive component in one circuit is exactly equal to the capacitive reactance value of the capacitive component, which can be completely compensated. The power factor compensation method is derived from this.
When the alternating current passes through the impedance load, the total power generated S is called "apparent power", and the apparent power S includes two components of the active power P and the reactive power Q. Among them, the active power P = S*Cos?? and the reactive power Q = S*Sin??. Only when the power factor Cos?? value is equal to the maximum value 1, that is, ?? = 0?°, the reactive component Q is equal to zero, and the active power P is equal to the value of the apparent power S.
However, the actual working capacity of the load is only related to the active power. For example, the cooling capacity of the air conditioner and the illumination of the luminaire are only proportional to the active power. Therefore, people certainly want a higher power factor.
Second, the harm of low power factor
1) The load capacity of the power supply equipment is discounted, that is, the load capacity is reduced. If a device can supply 100KVA of apparent power, if the power factor is 0.7, only 70KW of active power can be supplied. If the power factor is 0.9, 90KW of active power can be supplied. It can be seen that it is meaningful to improve the power factor.
2) Due to the existence of reactive current, the transmission line increases the loss of the transmission line. For example, if the power factor is 0.7, to supply 70KW of active power, it is necessary to supply 100KVA of apparent power. The current of the transmission line increases, and the line loss must increase.
Third, power factor compensation method
The power supplied by the power supply department is calculated by "apparent power", but the power collection fee is calculated by "active power", and the user's "electricity meter" is actually "active power meter". A "power factor" discount, so the power factor is a data that the power supply department is very concerned about. If the user does not reach the ideal power factor, the user is relatively consuming resources in the power supply department. At present, the power factor regulation in China must be between 0.9 and 1 inductive. Power factor compensation can be done in the following ways:
1) Semi-concentrated and centralized compensation method, all power distribution rooms of power companies must be equipped with power factor automatic control devices, real-time detection of power factor, automatic input or removal of the number of compensation power capacitors, for motor operation compensation (due to enterprises) The main electrical load is the motor), so that the local power network power factor is up to standard. This method has been enforced since the late 1970s and early 1980s, and has been said for more than 20 years. In addition, each power supply station is also equipped with a power factor automatic control device to further compensate the power supply area under its jurisdiction.
2) The decentralized compensation method requires that each electrical appliance be designed with advanced technology to meet the power factor compliance, so that the power factor can be guaranteed whenever and wherever electricity is used. However, this will increase the cost and increase the size of the appliance, while some appliances have strict restrictions on the size and size, which increases the design difficulty.
Fourth, electric light source lighting fixtures and power factor compensation
The electric light source is started by an incandescent light bulb, which is a purely resistive load with no power factor compensation. After the 1950s, fluorescent lamps became popular as the main lighting fixtures. The ballasts used silicon steel sheet inductors, which have high reliability and long life. They are still used in small quantities. Most of them have no power factor compensation measures. Affected by cost factors, or people do not know much about power factor compensation, energy-saving awareness is not strong. There are also capacitors with appropriate capacity for power factor compensation, which are mostly used on 30W, 40W large wattage fluorescent lamps, and rarely used below 20W.
After the 1990s, people's awareness of environmental protection and energy conservation increased, and the development of three primary color fluorescent powder energy-saving lamps has higher light efficiency. Electronic ballasts were also introduced later, with three primary color fluorescent powder tubes, the energy saving effect is more significant. Some integrated circuit manufacturers at home and abroad have introduced lamp chips with source power factor compensation for electronic ballasts, which have excellent performance, but increase the cost and volume of electronic ballasts. The people can't accept the price, only about Used in high-end lighting products. A large number of popular electronic ballasts, including energy-saving lamps, do not add any power factor compensation measures, which can be seen everywhere in the market for energy-saving lamps and fluorescent lamps. That is to say, the previous lamps basically have no power factor compensation measures, but everyone is using them.
Five, power factor and LED lighting
The LED consumes less power and the lamp power is smaller than the energy-saving lamp. LED lighting is of course more advanced, and it is more suitable for environmental protection, energy conservation and emission reduction. Whether the LED lamp adds power factor compensation, the author's opinion is:
1) According to expert analysis, LED is a capacitive load. There are many inductive loads on the grid, such as motors, transformers, and so on. It is often necessary to access a capacitive load for compensation, and the power factor automatic control device is used for this purpose. LED is a capacitive load, which just compensates for the problem that the power grid has low power factor due to the inductive load. It is just what it is. From this understanding, the author believes that LED lighting fixtures do not need to add power factor compensation measures in principle.
2) Single-turn LED lamps for indoor lighting are all low-power, and the power will not exceed 30W. The small power of the luminaire has little impact on the power grid. I believe that such luminaires can completely eliminate the power factor compensation measures. Adding the opposite is not good, but will lose the LED luminaire. The capacitive load can compensate the grid due to the inductive load and the power factor is low. The function. These small power lamps are mostly compact and compact, and the internal space is very limited. For example, MR16, PAR30, PAR38 lamp cups, power PCB board can not be placed after the increase, it is good intention to add power factor compensation measures can not be added. There is also the side effect of the efficiency reduction caused by the addition of power factor compensation, or the cloud is not worth the loss. Then the cost increase affects sales. What's more, the power supply department has taken countermeasures to compensate for the grid power factor, and the lamp manufacturers do not have to add more.
3) Power factor compensation measures can be considered for power above 100W. Powerful loads have a large impact on the power grid, such as LED street lights from one hundred watts to hundreds of watts. The street lamp belongs to the public welfare undertaking, and the cost is slightly increased without any problem. The power PCB board has a larger position and can be placed. Adding power factor compensation measures can help the power supply department to alleviate some adjustment burden and prevent excessive compensation due to excessive capacitive load.
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