You know as well as power factor positive negative it?

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Do you know your LED lighting power factor equal to the number it? Most people would probably say they know the answer, ask one if you know what the power factor is not it? Most people also know what it is, because this is the basic electrician in common sense, but if you ask a question, you know your electronics power factor is positive or negative? Probably most people do not know.

Why is this so? Because the current digital power factor meter did not show the sign.

So why does this happen? This is a long story!

one. What is power factor?
We know that in electricians, all voltages and currents are sine wave, sine wave because it is so they can easily be represented by a vector. In the actual electric power system, not necessarily a purely resistive load, i.e., the current and the current is not necessarily in phase, if it is purely inductive, the current will lag the voltage by 90 degrees, if a purely capacitive, the current is It will lead the voltage by 90 degrees. If it is not purely inductive or purely capacitive, then there will be a phase angle φ, φ this may be positive, it could be negative, depending on the nature of the load. Inductive load φ is positive, capacitive load φ is negative.

Figure 1. The sine wave voltage and current represented by a vector

For inductive load or capacitive load because current and voltage are not in phase, active and reactive power are two different power occurs. Refers to the so-called active-phase voltage and current and voltage component of the product, so-called reactive power and voltage refers to the vertical component of current and voltage of the product. The real power is actually projected in the current vector on the voltage vector, the projection of the current vector is multiplied by the cosine of the angle between it and the voltage, which is Cosφ, and this Cosφ called the power factor. When φ is 0 degrees, Cosφ equal to 1, that is, pure resistance. Inductive load, 0 <Cosφ <1; and in the capacitive load, 0 <Cosφ <-1. Therefore, the power factor is certainly a positive or negative! And this is an important indicator to judge the load is capacitive or inductive! Power factor is Cosφ, Cosφ is the power factor, which is a matter of course.

In the power system, I hope all loads are purely resistive, but in fact it is impossible, but once Cosφ not equal to 1, wherein the reactive component is not really reactive power, voltage and even completely at right angles to the current I when it flows through the wire and still have I2R losses. Therefore, in the power system is to find ways to put the power factor correction, make it as close to 1. Because the actual load of the power system is a large part of the motor, it is an inductive load, in order to compensate this inductive loads, usually in the secondary parallel power transformer a large capacitance method can be very effective compensation. So for the power system and they do not care about power factor problem, because it is very easy to compensate.

II. Electronic system power factor

In electronic systems, there are many electronic devices, and almost all electronic devices are active DC power supply requirements, while in urban areas or in general as the power plants are based on AC. Therefore, almost all electronic systems need to have a whole rectifier to the AC to DC, usually in the back but also add a electrolytic capacitor filter (Figure 2).

Figure 2. The rectifier and electrolytic capacitors


Because this circuit includes a rectifier diode, so this is actually a non-linear circuit, which can be seen from its power supply and current waveform, this time the voltage and current waveforms shown in Figure 3.

3. The waveform rectifier voltage and current


Clearly, although voltage or sine wave, but has become a current pulse. For this non-linear system, inherently difficult to define its power factor, because the power factor was originally from a linear system come. Fortunately, most electronic systems are small household electrical appliances, it is for large power systems have little effect. So when the state 75 watts electronic system does not require power factor. It is also very reasonable. Even until now, the US Energy Star for general lighting system also provides 100W or less do not require power factor.


In the fluorescent lamp appears, he never raised any power factor requirements, so the use of inductive ballast fluorescent ordinary power factor of about 0.5, in the past there is no provision to limit.


However, to the national energy-saving lamps 15W or less on the provisions of the power factor is not required, but most energy-saving lamps are 15W or less, this provision has no effect because the large-scale promotion of energy-saving lamps. The provisions of the 5W LED but it does not require the following power factor. It seems to saving the better lighting, more demanding requirements for PF! It is really hard to understand!


Because of the low-power LED power factor of the provisions, then such nonlinear system power factor should always have a definition. Otherwise, how to test? However, to the nonlinear system power factor to be defined it is too hard. For this reason, many people put forward various proposals:


1. Using the cosine of the phase difference of the fundamental current and voltage as the power factor. But because the current fundamental wave is derived from Fourier transform of the Fourier transform magnitude can only wait for it, but can not get its phase, the phase is relative, there must be a control to be able to obtain the phase. In doing Fourier transform is not the phase of the voltage as a reference, so the results obtained are also no phase. Therefore, this recommendation can not be achieved.


2. The current zero crossings as the starting phase of the current, the voltage of this phase and the cosine of the phase difference as the power factor. However, since the current waveform is not a sine wave, but the pulse wave. So put a pulse wave through zero as its starting phase is not justified.


3. finally someone came up with a very reluctant definition, the power factor is defined as the active and reactive power ratio.


PF = active / reactive power

Although the sine wave linear system, if this is defined, at least in absolute value and absolute value Cosφ is the same. Active power is projected onto the current axis voltage multiplied by voltage. Without power is the power to direct current vector and voltage vector is multiplied regardless of its phase. Clearly, the linear system and its absolute value is the absolute value Cosφ is consistent, but this ratio is no sign of.


Also, how to define the active and reactive power is also a big problem in a nonlinear system.


Most are now using the following formula:

:Called phase factor

What is a phase factor on no answer. Because this phase can not be obtained.

And if in nonlinear systems with this definition also lost power factor Cosφ the sign, because the power is not negative power. Since all digital power factor meter have adopted this definition, the results also lost sign. No sign of the power factor also lost power factor in the development of fundamental significance!

III. Found power factor

We will now look at the real world of power factor case. Because of the apparent power which is difficult to define, and it is difficult to measure in, so there have been different instruments measured results are not the same. For example, there is a 11-watt bulb, which uses a bridge rectifier coupled 10uF electrolytic capacitor using three instruments to measure

Three test instrument error of up to 8%, and completely unlike the measured current measuring power supply voltages so accurate!

So much error, if requested PF must be greater than 0.5, as long as the benefits of using the same power factor meter, but if detected Party must adhere to the use of remote data would fail the test. The result is simply to make people confused

After much deliberation should be used for electric system accredited by the most classic Cosφ meter to measure, the result was the most authoritative. And unlike digital Cosφ tester tester

also able to draw the sign.

IV. Analog power factor meter

Careful search can find the official system used a power factor meter mostly pointer, which is also known as the power factor meter Cosφ count. Single-phase, there are three phases. This electric rotating coil moving coil power factor table to two vertical moving coil. The magnetic field generated by the meter current in the load circuit. Vertical moving coil respectively A and B, the A coil in series with the load resistor in parallel to the line, after a series inductance coil B line in parallel with the load, so that a current B coil A coil would be more backward. At unity power factor 1, A coil currents and the load current are in phase, so the A coil generates maximum torque, the power factor meter pointer 1.0 scale. If the power factor to be 0, B coil currents and the load current are in phase, and therefore B coil will produce torque, power factor table pointer to 0. If the power factor is bounded between 0 and 1, the size of the torque generated is determined by the final position of the pointer two stitches. Its shape is as follows.

Analog power factor meter    Connection diagram when testing

102W light engine light engine rectifier (using 124 uF electrolytic capacitor) with a constant current source

The results obtained with digital meter power and power factor and power factor using the pointer as measured results are completely different.

Digital measured PF = 0.6590     pointer measured PF = +0.9

This result is very surprising, because no add any power factor compensation can be obtained +0.9 power factor! And this is the most authoritative results also should be officially recognized.


Fives. Conclusion


In fact, the power factor is defined for nonlinear systems in the international community also has a lot of controversy, it is said a total of 7 is defined as much. No wonder this issue in the United States is also the subject of a master's thesis in Sweden also serves as the subject of the doctoral thesis research. Baidu in China's academic years can also be found there are 3135 research paper in this issue. Oddly, for such an internationally are not conclusive indicators actually been identified as the official indicators must be strictly enforced, and the more energy-efficient lighting requires more demanding! I really do not know is how these officials think! If so, then I can only see "there are measures under the policy," the! I recommend everyone to use power factor meter pointer to get the official can not deny the power factor value!