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. The load as an alternating current has three types: resistance, inductance, and capacitance:
1. When the alternating current passes 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 ф = 0°, and the active power is consumed on the resistive load. Power, the grid has to supply energy.
2. 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 Ñ„=90°, which generates reactive power on the inductive load, and the power supplied by the grid is in the inductor. In the middle, the magnetic field can be stored for a short time and then fed back to the grid to become electric energy. This cycle is cyclical. As a result, the grid does not supply energy, so it is called “reactive powerâ€, but the “reactive current†that produces “reactive power†is still Actually exists.
3. When the AC power passes through the 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 resistance of the resistor, the inductance, and the capacitive reactance of the capacitor. After compounding, it is called “impedanceâ€. It is written as a mathematical formula: impedance Z= R+j ( XL – XC, where R is the resistance XL is the inductive reactance and XC is the capacitive reactance. If (XL–XC, > 0, it is called “inductive loadâ€; otherwise, if (XL – XC, < 0 is called “capacitive loadâ€).
When the AC power passes through the inductive load, the phase of the AC voltage leads the AC current phase (0°<ф<90°); when the AC power passes through the capacitive load, the phase of the AC voltage lags the AC current phase (-90°<ф< 0°); Electrotechnical defines that the angle ф is the power factor angle, and the cosine of the power factor angle ф, Cosφ, 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 (Cos 0°=1, and the pure inductance circuit, the phase difference between voltage and current is 90°, and The voltage leads the current; in the pure capacitor circuit, the phase difference between voltage and current is -90°, that is, the current leads the voltage. In the latter two circuits, the power factor is zero (Cos 90° = 0. For generality) The 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, power The 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*Cosф and the reactive power Q = S*Sinф. Only when the power factor Cosф value is equal to the maximum value 1, that is, ф = 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.
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