Phase advance and lag problems in AC circuits

In the circuit analysis, often hear the so-called phase lead lag what, has been trying to understand, the voltage is added to the device at both ends, for the power output and device input is necessarily the same phase, Ah, why will appear ahead and lag of said.

Let's start by listing a few very clear concepts:

The coil load is called inductive, capacitive load is called capacitive, pure resistance load is called resistance; for example, the motor is inductive load, capacitance is capacitive load, electric furnace resistance wire, incandescent lamp, iodine dock light, etc. are resistive load.

In the electrical or electronic industry, the definition of load impedance characteristics is divided into pure resistance type, inductive type and capacitance type, for short, resistive, inductive, capacitive.

Several kinds of load in the DC circuit are characterized by:

Resistive load: The relationship of current and voltage conforms to the basic Ouyun law, i=u/r;

Inductive load: Allows the current to flow through, but the current lags behind the voltage, can be stored in the inductor;

Capacitive load: Prevents current flow and can also be stored in capacitance.

Several types of load in the AC circuit are characterized by:

Resistive load: the phase of the current voltage is the same;

Inductive load: The current lags behind the voltage;

Capacitive load: The current is ahead of the voltage.

So it can be understood that the so-called advance and lag is in the AC circuit, or the DC Circuit power instantaneous (the period of time the effect is equivalent to the AC circuit). The concept of lag and advance is not the relationship between the voltage phase relationship between the power supply and the load, or the current phase, but the relation of the current phase to the voltage phase from the point of view of the load. For example, for the inductive device, the current changes have a blocking effect, when the voltage is added at both ends of the current changes, and must be a voltage change, will then cause the current change, so is the voltage ahead of the current, and for capacitive load, because it is stored charge, it is after the charge transfer reflects the voltage change, That is, the current flow, and then reflected as the voltage changes, so is the current lead voltage.

Well, according to the explanation that the phase relationship between the load current and the load voltage, the concept of the so-called phase advance and lag is easy to understand.