When the AC current is over load, the AC voltage on the load and the alternating current of the load generate phase difference, and the concept of power factor is introduced. People produce and live electricity from the electricity grid, which provides alternating current frequencies of 50Hz or 60Hz. As an alternating current load has three types of resistors, inductors and capacitors:
1, when the AC power through the pure resistor load, the AC voltage added to the resistance and the AC current through the resistance is the same phase, that is, the phase angle between them ф=0°, at the same time in the resistance load consumption of active power, the power grid to provide energy.
2, when the AC power through the pure inductance load, the alternating current phase of the AC voltage is 90°, the angle between them is ф=90°, the reactive power is generated on the inductance load, and the electric energy supplied by the grid can be changed into a magnetic field in the inductor and then returned to the power grid for a short period of time, so that the periodic cycle, Results The power grid does not provide energy, so it is called "reactive force", but the "reactive power current" which produces the "Var" still exists.
3, when the AC power through the pure capacitor load, also similar to this, except that the AC voltage on the phase hysteresis AC current phase 90°, the angle between them ф=-90°.
Here, the definition of phase angle is positive and phase angle lag is negative. The actual load is resistance, inductance inductance, capacitance resistance three kinds of complex, after the composite collectively referred to as "impedance", written as the mathematical formula is: Impedance z=r+j (XL–XC,. where R is resistor, XL is inductance, XC is capacitive resistance. if (XL–XC, 0, called "perceptual load"; Conversely, if (Xl–xc, < 0 is called "Capacitive load").
Alternating current phase (0°< ф< 90°), alternating current phase of AC voltage when AC power passes through the inductive load, alternating currents phase hysteresis ( -90°< ф< 0°); The electrician defines the angle ф as the power factor angle, The cosine value of the power factor angle ф is called the Cosф power factor. For resistive loads, the difference between the voltage and current is 0°, therefore, the power factor of the circuit is 1 max (Cos 0°=1, while the pure inductance circuit, the voltage and current bit difference is 90°, and is the voltage advance current; In the pure capacitor circuit, the voltage and current position is -90°, that is, the current advance voltage. In the latter two kinds of circuit, the power factor is 0 (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, impedance z into a pure resistance, power factor is equal to 1.
That is to say, the perceptual load and capacitive load can compensate each other, the inductance value of the perceptual element in a circuit is exactly equal to the tolerance value of capacitive element can be completely compensated, the method of power factor compensation originates from this. When alternating current is carried by impedance load, the total power generated by S is called "apparent power", depending on power s including active power p and reactive energy Q two components. Which active power P=s*cosф, reactive q=s*sinф. Only when the power factor Cosф value equals the maximum value of 1 or ф=0°, the reactive component Q equals zero, and the active power p equals to the value of the power S. But the actual working ability of the load is only related to active power.
Power factor and LED illumination
In this paper, the concept of power factor and power factor compensation is described, and the conclusion that the power factor compensation circuit does not need to be increased in LED lighting is demonstrated by the characteristics of capacitive load of LED lamps.
The harm of low power factor
(1) The load-carrying capacity of the power supply equipment has been discounted, which reduces the load-carrying capacity. If a device can supply 100KVA of the apparent power, if the power factor is 0.7, then can only provide 70KW of active power; If the power factor is 0.9, then the active power of 90KW can be provided, so it is significant to improve the power factor.
(2) The transmission line loss is increased due to the existence of reactive current. For example, the power factor is 0.7, to provide 70KW of active power, it is necessary to provide 100KVA of the apparent power, transmission lines of the current increase, the line loss is bound to increase.
Power Factor Compensation Method
Electricity supplied by the power supply department is calculated as "apparent power", but the charge is the "active power" to calculate, the user's "Watt-hour meter" is actually "active power meter", between the two there is a "power factor" discount, so the power factor is a very concerned about the supply sector data. If the user does not achieve the ideal power factor, the relative is consumes the power supply department resources. At present, at home, the power factor regulation must be between 0 of the electrical sensibility. Aged.
Power factor compensation can be done in the following ways:
(1) Semi-centralized and centralized compensation method, requiring the power-supply enterprises of each distribution room must be installed power factor automatic control device, real-time detection of power factor size, automatic input or removal of the number of compensating power capacitors for motor operation compensation (because the main electric load is the motor, to achieve local power network power This approach has been enforced since the late 70 and early 80, and has so far been less than more than 20 years. There are also various power supply units installed power factor control device, to its jurisdiction of the power supply area further compensation.
(2) The decentralized compensation method, requires that each electrical appliance design will use advanced technology to meet the power factor standards, so that whenever and wherever electricity can ensure the power factor standards. But this will increase the cost, increase the volume of electrical appliances, and some appliances to the size of the limit is very strict, increase the design difficulty.
Review of light source lighting and power factor compensation The electric lamp is started by the incandescent bulb, the incandescent bulb is pure resistance load, there is no power factor compensation problem. In the late 50, fluorescent lamp quickly became the main lighting, the ballast used silicon steel inductors, high reliability, long life, still have a small number of use, most of the power factor compensation, may be affected by cost factors, or people do not understand the power factor compensation, energy-saving awareness is not strong. Also have to add the appropriate capacity of capacitors for power factor compensation, used in 30W, 40W large wattage fluorescent lamp, 20W is less used. After the 90 's, people's environmental protection, energy-saving awareness, the development of a three-color fluorescent powder energy-saving lamps, its light efficiency is higher. Electronic ballast was subsequently introduced, with a three-color fluorescent powder lamp, energy-saving effect more significant. Some IC manufacturers at home and abroad have introduced the lamp with the source power factor compensation chip, uses in the electronic ballast, the performance is excellent, but increased the cost and the electronic ballast volume, the populace cannot accept its price, about only uses in the high-end lamp product. A large number of popular electronic ballasts, including energy-saving lamps do not add any power factor compensation measures, which are popular in the market energy-saving lamps, fluorescent lamps everywhere. In other words, the past lamps basically do not have any power factor compensation measures, but everyone is using.
LED power consumption is more province, lighting than energy-saving lamps are smaller. LED lighting Of course more progress, environmental protection, energy saving and emission reduction more appropriate.
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