The size of the power factor (Power Factor) and the nature of the load of the circuit, such as incandescent light bulbs, resistive loads such as resistance furnace power factor of 1, generally with inductive loads of the circuit power factor is less than 1. Power factor is an important technical data of the power system. Power factor is a coefficient that measures the efficiency of electrical equipment. Power factor is low, indicating that the circuit for alternating magnetic field conversion of reactive power, thus reducing the utilization of equipment, increasing the line power supply losses.
In an AC circuit, the cosine of the phase difference (Φ) between the voltage and the current is called the power factor, which is represented by the symbol cosΦ. Numerically, the power factor is the ratio of the active power to the apparent power, i.e., cosΦ=P/S.
Basic introduction Chinese name: power factor Alias: power phase difference factor Expression: cosΦ=P/S Applicable fields: Electricity Applicable fields: Physics Applicable fields: Physical Science Applicable fields: Electrical Engineering Applicable fields: Electricity Applicable fields: Electrical Science Applicable fields: Electrical Engineering Applicable fields: Electrical Science Applicable fields: Electrical Science Applicable fields: Electrical Science Applicable fields: Electrical Science Applicable fields: Electrical Science Scope of application ：Electricity Scope of application ：Thermal Calculation, requirements, basic analysis, basic analysis, advanced analysis, nonlinear loads, non-sinusoidal components, distortion power factor, switching power supply, improve, content, benefits, improve the power, how to improve, power factor, power factor, apparent power, reactive power, home appliances, Calculation The root cause of low power factor is the presence of inductive loads. For example, the most common AC asynchronous motor in the production of rated load power factor is generally 0.7 - 0.9, if the power factor in the light load is even lower. Other equipment such as frequency furnace, welding transformers and fluorescent lamps, etc., the power factor of the load is also low. From the power triangle and its interrelationship formula is not difficult to see, in the case of the apparent power is unchanged, the lower the power factor (the larger the angle), the active power is smaller, while the reactive power is larger. This makes the capacity of the power supply equipment can not be fully utilized, for example, the capacity of 1000kVA transformer, if cos = 1, that is, can send out 1000kW of active power; while in cos = 0.7, it can only send out 700kW of active power. Low power factor not only reduces the effective output of the power supply equipment, but also increases the loss of power supply equipment and lines, therefore, must be taken in parallel capacitors and other measures to compensate for reactive power to improve the power factor. Power factor since the total power expressed in the proportion of active power, obviously in any case the power factor can not be greater than 1. By the power triangle can be seen, when = 0 ° that is, the AC circuit voltage and current in phase, active power is equal to the apparent power. This is when the value of cos is maximum, i.e., cos = 1, which occurs when there is only a purely resistive load in the circuit, or when the inductive and capacitive reactances in the circuit are equal. Inductive circuit current phase is always lagging behind the voltage, this time 0 ° < < 90 °, this time that the circuit has a "lagging" cos; and capacitive circuit current phase is always ahead of the voltage, this time -90 ° < < 0 °, that the circuit has a "forward "of cos. There are many ways to calculate the power factor, the main direct calculation method and lookup table method. Commonly used formula for: power factor formula Requirements The most basic analysis of the equipment as an example. For example, the power of a device is 100 units, which means that there are 100 units of power delivered to the device. However, due to the inherent reactive power losses in most electrical systems, only 70 units of power can be used. Unfortunately, while only 70 units are used, 100 units are paid for. (With 70 units of active power used, you are paying for 70 units of consumption) In this example, the power factor is 0.7 (most equipment will be penalized if it has a power factor of less than 0.9) This reactive loss is found primarily in motor equipment (e.g., blowers, water pumps, compressors, etc.), also known as inductive loads. Power factor is a measure of motor efficiency. BASIC ANALYSIS Each motor system consumes two large amounts of power, the true active power (in watts) and the reactive power of the reactive (in spent). Power factor is the ratio of useful work to total power. The higher the power factor, the greater the ratio between useful work and total power, and the more efficiently the system operates. ADVANCED ANALYSIS In an inductively loaded circuit, the peak of the current waveform occurs after the peak of the voltage waveform. The separation of the two waveform peaks can be expressed in terms of power factor. The lower the power factor, the greater the separation between the two waveform peaks. Nonlinear Loads Common nonlinear loads on power systems include rectifiers (used in power supplies), or equipment such as fluorescent lamps, welders, or arc furnace arc discharges. Because the current in these systems is interrupted by switching components, the current can contain harmonics at frequencies that are integer multiples of the power system. The Distortion Power Factor is used to measure the effect of harmonic distortion on the average power of a current. The distortion power factor of a computer power supply is 0.75 for sinusoidal voltages and non-sinusoidal currents. Non-sinusoidal Components Non-linear loads distort the current waveform from a sinusoidal waveform to other waveforms. The input current of a nonlinear load contains many high-frequency harmonic currents in addition to the original power supply frequency (fundamental frequency). Filters consisting of linear components such as capacitors and inductors can reduce the harmonic currents entering the power system from the load side. If the voltage in a circuit made of linear components is a sine wave, the current is also a sine wave of the same frequency. The power factor is simply due to the phase difference between the voltage and the current, and can also be called the displacement power factor (Displacement Power Factor). If the current or voltage is not sinusoidal and the apparent power includes all harmonic components, the power factor will not only have the displacement power factor due to the phase difference between voltage and current, but also the distortion power factor corresponding to the harmonic components. A normal triple meter cannot measure the input current of a nonlinear load. A triple meter measures the average of the rectified waveform. If you use a meter that measures the root mean square (RMS) value, you can measure the RMS value of the actual current and voltage, and therefore also calculate the apparent power. To measure active or reactive power, a wattmeter designed for non-sinusoidal currents is used. Distortion Power Factor The Distortion Power Factor measures the effect of harmonic distortion on the average power of a current. It is the total harmonic distortion of the load current. The above definition assumes that the voltage remains sinusoidal and free of distortion, an assumption that is close to what is usually applied in practice. is the fundamental frequency component of the current, and is the total current, both expressed as root-mean-square values. If the distortion power factor is multiplied by the displacement power factor (Displacement Power Factor, or DPF), the total power factor can be obtained, which can also be called the true power factor, or simply referred to as the power factor. Switching Power Supplies Switching power supplies are a common nonlinear load, and are found in at least a few million personal computers around the world, with power outputs ranging from a few watts to a kilowatt. Early inexpensive switching power supplies had a full-wave rectifier, which would conduct only when the voltage at the power supply terminals exceeded the voltage of the internal capacitors, resulting in a high peak factor, a low distortion power factor, and the potential for excessive neutral loading in a three-phase current system, where its mid-linear current would not be zero [6]. A typical switching power supply will first use a rectifier diode to generate a DC voltage, which in turn generates an output voltage. Since the rectifier is a nonlinear component, its input current will have many high harmonic components. This situation causes problems for the power company because it is not possible to compensate for the high frequency harmonics by adding capacitors and inductors. Therefore, some regions have begun to legislate to require all power supplies with power greater than a certain value to have a power factor correction function. In order to improve the power factor, the European Union has set standards for harmonics. To comply with the current EU standard EN61000-3-2, all switching power supplies with an output power greater than 75W need to have at least passive PFC (Passive Power Factor Correction). The 80 PLUS switching power supply certification requires a power factor of at least 0.9 [7]. Improvement Power loads in the power grid, such as motors, transformers, fluorescent lamps and arc furnaces, etc., are mostly inductive loads, and these inductive devices not only need to absorb active power into the power system during operation, but also absorb reactive power at the same time. Therefore, after installing shunt capacitor reactive power compensation equipment in the power grid, it will be able to provide compensation for the reactive power consumed by inductive loads, reducing the reactive power provided by the power side of the grid to the inductive loads and delivered by the line. Since the flow of reactive power in the grid is reduced, the power loss caused by the transformer and bus in the transmission and distribution lines due to the delivery of reactive power can be reduced, which is the benefit of reactive power compensation. The main purpose of reactive power compensation is to improve the power factor of the compensation system. Because the power supply bureau sends out electricity in kVA or MVA, but the charge is in kW, that is, the actual useful work done to charge, there is a difference between the two ineffective power, generally speaking, is the unit of reactive power in kvar. Most of the ineffective power is inductive, which is generally known as motor, transformer, fluorescent lamps ......, almost all of the ineffective power is inductive, capacitive is very rare, for example: inverter is capacitive, inverter power supply end of the reactor can be added to improve the power factor. Contents The presence of inductive, capacitive or nonlinear loads results in the presence of reactive power in the system, which leads to the fact that the active power is not equal to the apparent power, and the relationship between the three is as follows: S^2=P^2+Q^2; S is the apparent power, P is the active power, and Q is the reactive power. The units of the three are VA (or kVA), W (or kW), var (or kvar). An active power factor correction circuit Simply put, in the above formula, if the value of kvar is zero today, kVA will be equal to kW, then the power supply bureau sends out 1kVA of electricity is equal to the user's consumption of 1kW, at this time, the most cost-effective, so the power factor is the power supply bureau is very concerned about a coefficient. If the user does not achieve the desired power factor, it is relatively consuming the resources of the power supply bureau, so this is why the power factor is a regulatory limit. In the country, the power factor must be between 0.9 and 1 inductive, with penalties below 0.9. Benefits The power supply department requires the customer to improve the power factor in order to improve cost-effectiveness, so what are the benefits of improving the power factor to the customer side? ① By improving the power factor, the total current in the line and the capacity of electrical components in the power supply system, such as transformers, electrical equipment, wires, etc., are reduced, so not only the investment costs are reduced, but also reduces its own loss of electrical energy. ② A good power factor value is ensured, thus reducing the voltage loss in the power supply system, which can make the load voltage more stable and improve the quality of electric power. ③ The margin of the system can be increased, and the potential of the generating and supplying equipment can be tapped. If the power factor of the system is low, the installation of capacitors can improve the power factor and increase the capacity of the load while the capacity of the existing equipment remains unchanged. For example, if the power factor of a 1000kVA transformer is increased from 0.8 to 0.98: Before compensation: 1000×0.8=800kW After compensation: 1000×0.98=980kW The same 1000kVA transformer can carry 180kW more load after the power factor is changed. ④ Reduction of the user's electricity expenses; through the reduction of the losses of each of the above components and the power factor improvement of the electricity tariff concessions. In addition, some power electronic equipment such as rectifiers, inverters, switching power supplies, etc.; saturable equipment such as transformers, motors, generators, etc.; arc equipment and electric light source equipment such as arc furnaces, fluorescent lamps, etc., which are the main sources of harmonics, will generate a large number of harmonics during operation. Harmonics on the engine, transformers, motors, capacitors and other electrical equipment connected to the power grid have varying degrees of harm, mainly manifested in the generation of harmonic additional loss, making the equipment overload and overheating and harmonic overvoltage accelerate the aging of the equipment's insulation and so on. Capacitors connected in parallel to the line for reactive power compensation will have an amplifying effect on harmonics, making the system voltage and current distortion more serious. In addition, the harmonic current superimposed on the fundamental current of the capacitor will increase the effective value of the current of the capacitor, resulting in increased temperature and reducing the service life of the capacitor. Harmonic currents increase the copper loss of the transformer, causing local overheating, vibration, increased noise and additional heating of the windings. Harmonic pollution also increases losses in transmission lines such as cables. And harmonic pollution has an impact on the quality of communication. When the current harmonic component is high, it may cause the over-voltage protection and over-current protection of relay protection to operate incorrectly. Therefore, if the measured harmonic content of the system is too high, in addition to the capacitor terminal needs to be connected in series with the appropriate detuned reactance, and the load characteristics need to be specifically designed for the installation of harmonic improvement devices. Improvement of electrical energy Why is it said that improving the power factor of consumers can improve voltage quality? The voltage supplied by the power system to the consumer varies with the active and reactive power delivered by the lines. When the line delivers a certain amount of active power, such as the more reactive power delivered, the greater the voltage loss of the line. That is, the lower the voltage delivered to the user terminal. If the line below 110kV, its voltage loss can be approximated as: △U = (PR + QX)/Ue where: △U - voltage loss of the line, kV Ue - rated voltage of the line, kV P - the line delivery of active power, kW Q - line delivery of reactive power, kvar R - line resistance, ohm X - line reactance, ohm As seen in the above formula, when the user's power factor is increased, it is to the As can be seen from the above equation, when the power factor of the user is improved, the reactive power it draws from the power system has to be reduced, and therefore the voltage losses have to be reduced, thus improving the voltage quality of the user. In a DC circuit, voltage times current is active power. But in the AC circuit, voltage times current is apparent power, and can play a part of the power (i.e., active power) will be less than the apparent power. The ratio of active power to apparent power is called the power factor and is expressed as COSΦ. In fact, the simplest way to measure this is to measure the phase difference between the voltage and the current, and the result is the power factor. How to improve (1) Improve the natural power factor. The natural power factor is the power factor of an electric device without any compensation. Methods to improve the natural power factor: rational selection of asynchronous motors; avoid transformer no-load operation; rational arrangement and adjustment of process flow, improve the operation of electromechanical equipment; in the production process allows conditions, the use of synchronous motors instead of asynchronous motors. (2) Adopt artificial compensation of reactive power. Installation of reactive power compensation equipment for artificial compensation, power users commonly used reactive power compensation equipment is power capacitors. Improve the power factor of the way to improve the power factor is mainly in how to reduce the various parts of the power system requires reactive power, in particular, to reduce the load to take the reactive power, so that the power system in the delivery of a certain amount of active power, which can reduce the through the reactive current to improve the power factor of a lot of methods, but in general can be summarized in two categories: Improvement of natural power factor method The use of reactive power compensation equipment is commonly used by electric power users is power capacitors. Methods The use of reducing the reactive power required by the power equipment to improve its power factor measures, known as the improvement of the natural power factor of the method are: 1, the correct choice of asynchronous motor type and capacity. According to relevant information, China's small and medium-sized asynchronous motor load accounts for more than 80% of the total load of the grid, a few major power grids, motor energy consumption accounted for the entire industrial power consumption of 60% to 68% or so 1 Therefore, do a good job of motor loss reduction and energy saving is of great economic significance Correctly selected asynchronous motor, so that the rated capacity and the load with the matching, for the improvement of the power factor is very important. In terms of selection, attention should be paid to the selection of energy-saving, eliminating high energy consumption of the motor, and according to the specific requirements of the motor mechanical work on the starting torque, the number of starts, speed regulation, etc., the selection of different models. Motor efficiency η and power factor cosφ is to reflect the motor economic operation level of the main indicators, are closely related to the load rate β 1 GB / T 12497 - 90 on the three-phase asynchronous motor three operating regions are as follows: when the load rate β between 70 % ~ 100 %, for the economic operation area; when 40 % ≤ β ≤ 70 %, for the general operation area; when β < 40 %, for the non-economic operation area; when β < 40 %, for the economic operation area. When 40 % ≤ β ≤ 70 %, for general operation area; When β < 40 %, for non-economic operation area; 2, according to the load selection of matching transformer. Power transformer primary side power factor is not only related to the power factor of the load, but also related to the load rate if the transformer is running full load, the primary side power factor is only lower than the secondary side of about 3 ~ 5 %; if the transformer is running light load, when the load is less than 0. 6, the primary side power factor is a significant drop, down to 11 ~ 18 %, so the power transformer load rate of 0. 6 or more than the operation of the economy, should generally be 60 % ~ 70 %, the transformer should be used for the operation of the power factor of the primary side. Generally should be in 60% ~ 70% is more appropriate in order to fully utilize the equipment and improve the power factor, power transformers are generally not suitable for light load operation. When the power transformer load factor is less than 30%, should be replaced with a smaller capacity transformer (3, rationalize and adjust the process. Reasonable arrangements and adjust the process, improve the operating status of motor equipment, limit the welding machine and tool machine motor no-load operation 1 such as no-load automatic power-off delay device process, etc. 4, asynchronous motor synchronization operation. For the load factor is not greater than 0. 7 and the maximum load is not greater than 90% of the rated power of the winding asynchronous motor, if necessary, can be synchronized, that is, when the winding asynchronous motor in the start-up is completed, the rotor three-phase windings into DC excitation, that is, the torque generated by the asynchronous motor into the synchronous operation of the operating state and synchronous motor similar to the over-excitation of the case, the motor can be sent out to the grid In the case of overexcitation, the motor can send reactive power to the grid, thus achieving the purpose of improving the power factor. Compensation method to improve power factor The use of reactive power supply equipment to compensate for the reactive power required by the power equipment, in order to improve the power factor of the measures, known as the compensation method to improve the power factor. To improve the power factor by the compensation method, it is necessary to add new equipment and to increase the demand for non-ferrous and ferrous metals. In addition, the compensation equipment itself also has power loss, so from an overall perspective, should first be used to improve the natural power factor of power equipment. However, when the power factor is not up to the value required by the Technical Specification for Electric Power Design, it is necessary to use specialized compensation equipment to improve the power factor. Applied artificial compensation of reactive power is usually applied phase-shifting capacitors (i.e., electrostatic capacitors), the use of synchronous motors and the use of synchronous regulator three methods. Synchronous motor in the overexcitation mode of operation (0.8 ~ 0.9 ahead of schedule), the reactive power to the power system, improve the power factor of industrial enterprises General in order to meet the process conditions, with or without the use of synchronous motors to improve the power factor of the enterprise, should be a technical and economic comparison. Usually for low-speed, constant speed and long-term continuous operation of the larger capacity of the motor, it is appropriate to use synchronous motor unit, such as steel rolling motor unit, ball mill, air compressor, blower, pumps and other equipment These equipments use synchronous motors as the prime mover, its capacity is generally more than 250 kW, the environment and the start-up conditions are able to meet the requirements of synchronous motors, and less stopping time, and therefore improve the power factor can play a great role in the power factor, but the synchronous motors can play a significant role in the improvement of power factor. But synchronous motor structure is complex, and with a set of start-up control equipment, maintenance workload, the price is more expensive than asynchronous motor, and high-voltage phase-shifting capacitors prices are generally reduced, which correspondingly improves the "asynchronous motor plus phase-shifting capacitor compensation program" superiority phase-shifting capacitors because of power loss, operation and maintenance is very convenient. Shift capacitor because of the power loss is small, operation and maintenance is very convenient, short-circuit current is small and other advantages in industrial enterprises are widely used as artificial compensation device. To sum up, improve the power factor is bound to the country's energy use, the economic benefits of enterprises to play a role in promoting, is to ensure that the power system power quality, voltage quality, reduce network losses and safe operation of the indispensable conditions should be based on the different situations to take appropriate measures to improve the power factor, to reduce reactive power loss, thereby improving economic efficiency. Power factor 1, diesel generator oscillation out of step characteristics 1) stator current exceeds the normal value, the ammeter pointer will be violently bumping block. (2) The stator voltmeter pointer will swing rapidly. (3) The active power meter pointer will swing on the whole dial of the dial. 4) The rotor ammeter pointer swings rapidly around the normal value. (5) The generator emits a chirping sound, and the change in the chirping sound corresponds to the frequency of the swing of the meter pointer. (6) other parallel operation of the generator meter also has a corresponding swing 2, generator oscillation out of step when the treatment method generator oscillation out of synchronization should pay attention to the following: 1) to increase the excitation current to produce the conditions for the restoration of synchronization; 2) to be appropriate to the adjustment of the load of the machine in order to help restore the synchronization; 3) when the whole power plant is out of synchronization with the system, all generators in the plant will oscillate, in addition to trying to increase the excitation current of each generator, in the event that synchronization cannot be restored, in order to save the generators from the damage of the continuous current, should be in accordance with the regulations of the plant and the system in 2 minutes after the delinking of the power plant. Power factor The power factor characterizes the ability of a luminaire to deliver active power. Power is a measure of the rate of transfer of energy. In a DC circuit it is the product of voltage V and current A. In an AC system it is more complicated. In an AC system, it is a little more complicated: there is a portion of the AC current circulating in the load that does not transfer energy, called reactance current or harmonic current, which makes the apparent power (voltage Volt by current Amps) greater than the real power. The inequality between apparent power and real power leads to the power factor, which is equal to the ratio of real power to apparent power. So the real power in an AC system is equal to the apparent power multiplied by the power factor. That is: power factor = real power / apparent power. Only electric heaters and light bulbs and other linear loads of the power factor of 1, the actual power of many devices and the apparent power of the difference in the value of a very small, negligible, and like capacitive devices such as lamps and lanterns of this difference is very large, very important. PC Magazine magazine, a study shows that the typical power factor of lamps and lanterns is 0.65, that is, the apparent power (VA) than the actual power (Watts) is 50% larger! Apparent power Apparent power: that is, the product of AC voltage and AC current. Expressed in the formula: S = UI. where S is the rated output power in VA (volt-ampere); U is the rated output voltage in V, such as 220V, 380V, etc.; I is the rated output current in A. Apparent power consists of two parts: active power (P) and reactive power (Q). Active power is the part that directly does work. For example, it makes a lamp glow, makes a motor turn, makes an electronic circuit work, and so on. Because this power to do work are turned into heat, can be directly felt by people, so some people have an illusion, that is, the active power as the apparent power, do not know that the active power is only a part of the apparent power, expressed in the formula: P = Scosθ = UIcosθ = UIF. in which P is the active power in units of W (watt); F = cos θ is called the power factor, and θ is the phase difference when the voltage and current are in different phases at a nonlinear load. Reactive power is the part of the power stored in the circuit but does not directly do work, expressed by the formula: Q = Ssinθ = UIsinθ. In the formula, Q is the reactive power, the unit is var (lack of). Reactive power for lamps and lanterns and all other electronic circuits working on DC voltage, leaving the reactive power is simply not work. Users generally think that equipment such as lamps and lanterns only need active power, but not reactive power. Since the reactive power does not do work, to it what use! So of course they think that a luminaire with a power factor of 1 is best. Because it gives the maximum output power. However, this is not the case. If there is a lamp, when the AC mains input rectification, you get a pulsating DC voltage, if the pulsating voltage without any processing, it is provided directly to the lamp, no doubt, the circuit simply can not work properly. Although the power factor of the luminaire is close to 1 at this time, but what is the use of it. In order for the luminaire circuit to work properly, it must be supplied with a smoothed DC voltage. This "smoothing" must be connected to the back of the lamp rectifier filter capacitor to complete. This filter is like a reservoir, and the capacitor must hold a sufficient amount of charge to keep the operating voltage on the circuit uninterrupted and at a normal level during the gap between the rectifier half-waves. In other words, even when there is no input power between the two pulsating half-waves, there is no significant change in the voltage level of Uc. This function is realized by the energy stored in the capacitor, and this part of the energy stored in the capacitor is the reactive power. Therefore, the lamps and lanterns are supported by reactive power to ensure that the circuit correctly using active power to achieve normal use. Therefore, it can be said that the lamps not only need active power, but also need reactive power, both are indispensable. Home Appliances Common Home Appliances Power Factor Some people have tested the power consumption and power factor of various household appliances, the results are as follows: No. Name Equipment Capacity (W) Power Factor Reactive Power (var) Apparent Power (VA) 1 Lighting 200 0.90 96.86 222.22 2 Air Conditioning 3000 0.80 2250.00 3750.00 3 Electric Freezer 150 0.60 200.00 250.00 4 Microwave 1000 0.90 484.32 1111.11 5 Electric water heater 2000 1.00 0.00 2000.00 6 Rice cooker 1000 1.00 0.00 1000.00 7 Computer 300 0.80 225.00 375.00 Measurement of the power factor of a computer 8 Printer 250 0.80 187.50 312.50 9 Television 200 0.80 150.00 250.00 10 Washing machine 200 0.60 266.67 333.33 11 Range hood 50 0. 80 37.50 62.50 12 Speaker 300 0.60 400.00 500.00 13 Drinking fountain 600 1.00 0.00 600.00 Power factor of drinking fountains 14 Sanitary equipment 1000 1.00 0.00 1000.00 15 Health care equipment 600 0.80 450.00 750.00 16 VCR 200 0.90 96.86 222.22 17 DVD\VCD 100 0.90 48.43 111.11 These figures are of course for reference only. 1. The power factor of all electric appliances is equal to 1 because they are resistive loads. 2. 2. all household appliances with motors (most white goods) are inductive loads. 3. 3. any household appliance with a transformer (TV, stereo) is also an inductive load. 4. an electric freezer, which operates continuously for 24 hours, is an inductive load that consumes a lot of power and has a very low power factor. 5. The lighting fixtures in them have a power factor close to 1 because they are mainly incandescent.