江苏春晨电缆有限公司生产JFEYH10KV高压电机引接线电机绕组线，在比较两个正弦量的相位时，其超前或滞后的角度，习惯上不应大于180°。而对于不同频率的正弦量，就不能用相位差来比较，因为这时相位差将随时间而变化。JFEYH10KV高压电机引接线电机绕组线
When comparing the phase of two sinusoids, the angle of advance or lag should not be more than 180 degrees. For the sinusoidal quantity of different frequencies, the phase difference can not be compared, because the phase difference will change with time.
例题：试计算下列u与i在t=0时的数值u0及i0；并比较其相位关系，已知：JFEYH10KV高压电机引接线电机绕组线
Example: try to calculate the following values of u and I at t=0, U0 and I0; and compare their phase relations, known as:
u=311sin（ωt+30°）伏；
U=311sin (omega t+30) volt;
i=5sin（ωt-30°）安；
I=5sin (omega T-30 degrees);
解：当t=0时：
Solution: when t=0:
u0=311sin（0+30°）=311sin30°=155.5伏；
U0=311sin (0+30) =311sin30 degree =155.5 volt;
i0=5sin（0-30°）=5sin（-30°）=-2.5安；
I0=5sin (0-30 degree) =5sin (-30) =-2.5 an;
u与i的相位差：
Phase difference between u and I:
△Φ=（ωt+30°）-（ωt-30°）=30°-（-30°）=60°
Delta phi = (omega t+30 DEG) - (omega T-30 DEG) =30 degrees (-30 degrees) =60.
即，电压超前于电流60°，或电流滞后于电压60°。
That is, the voltage is ahead of the current 60 degrees, or the current is lagging behind the voltage 60 degrees.