Phase Relationships in AC Circuits

Phase

相

When capacitors or inductors are involved in an AC circuit, the current and voltage do not peak at the same time. The fraction of a period difference between the peaks expressed in degrees is said to be the phase difference. The phase difference is <= 90 degrees. It is customary to use the angle by which the voltage leads the current. This leads to a positive phase for inductive circuits since current lags the voltage in an inductive circuit. The phase is negative for a capacitive circuit since the current leads the voltage. The useful mnemonic ELI the ICE man helps to remember the sign of the phase. The phase relation is often depicted graphically in a phasor diagram.

当电容器或电感器参与交流电路时，电流和电压并不在相同的时间达到峰值。峰值之间周期的分数差，以度数表示，称为相位差。相位差小于或等于90度。通常习惯使用电压领先电流的角度。这导致在电感电路中相位为正，因为电流滞后于电压。而在电容电路中，相位为负，因为电流领先于电压。有用的记忆法ELI the ICE man有助于记住相位的符号。相位关系通常在相量图中图形化表示。

Phasor Diagrams

相量图

It is sometimes helpful to treat the phase as if it defined a vector in a plane. The usual reference for zero phase is taken to be the positive x-axis and is associated with the resistor since the voltage and current associated with the resistor are in phase. The length of the phasor is proportional to the magnitude of the quantity represented, and its angle represents its phase relative to that of the current through the resistor. The phasor diagram for the RLC series circuit shows the main features.

有时将相视为定义在一个平面上的矢量是有帮助的。通常将零相的参考方向取为正x轴，并与电阻器相关联，因为电阻器上的电压和电流是同相的。矢量的长度与所表示量的幅度成正比，其角度表示它与通过电阻器的电流的相位关系。RLC串联电路的相量图展示了主要特征。

Note that the phase angle, the difference in phase between the voltage and the current in an AC circuit, is the phase angle associated with the impedance Z of the circuit.

注意，交流电路中电压与电流之间的相位差，即为电路阻抗Z的相位角。