pq测量仪器与技术基础(1).pptx

Electricity is generated by conductors rotating though a ic field电是由在磁场中旋转的导体产生的
Pick a point on a circle, rotating counterclockwise at a fixed speed. When the angle is small the change in height is rapid. As the angle increases towards 90° the change in height slows. The distance from the “the horizon” sweeps out a sine wave. 在圆周上选一个点,该点以固定速率在圆周上向逆时针方向旋转。当旋转的角度比较小时,高度的变化就比较明显;当旋转角度向90°方向增长时, 高度的变化也组件减缓。偏离“水平”方向的高度即形成了一个正弦波。
Why Sine Waves ?为什么会是正弦波?
Why 3-Phase?为什么为三相?
At any instant current on the neutral is zero. Try it!在任何情况下,零线上的净电流为零。试试看!
Three phase motors have better starting torque, run more quietly, are more efficient and are smaller than single—phase motors of similar hp rating三相马达具有更好的起动扭矩、运行更平顺、更有效率,并且体积比相同马力的单相马达更小。
If you add more than three phases it adds more cost but doesn’t deliver significant performance improvements如果相数多余三个,会增加很多费用,但是性能并没有明显改善。
Three individual voltage phases typically 120 degrees out of phase of each other.三个独立的电压相位彼此之间一般相差120度。
Three individual current phases typically 120 degrees out of phase of each other.三个独立的电流相位彼此之间一般相差120度。
Voltage and current will typically be shifted from each other resulting in “power factor”电压和电流的相位一般不一致,所以就有了“功率因数”
Vector Representation矢量表示
Note that the vectors go in the counterclockwise direction, like the circle in the previous slide注意:矢量呈逆时针运动,类似前面例子中的圆周。
From the Dam to Your Load从发电站到负载
From the Dam to Your Load从发电站到负载
High Voltage (over 100kV) is used for transmission. All 3-phase用于电力传输的高压线路(100kV以上)。全为三相系统
Substations use transformers to step down the voltage to medium voltage (4160 to 14kV).
PT’s are used to measure voltage levels.变电站利用变压器将电压变为中压(4160到12kV)。使用PT来测量电压。
Medium voltage is used for distribution. Mostly 3-phase.使用中压进行配电。大多数为三相系统。
Medium Voltage is stepped down to 240 or 480 for delivery to customers.中压又被变为240或480伏的电压,然后传输给用户。
Fuses and circuit breakers保险和电路断路器
Protective relays保护继电器
Lightning arrestors避雷器
Switches电闸
“Reclosure”
自动开关
Tra