PQ测量仪器与技术基础1.ppt
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1、3-Phase Power Systems 三相电力系统,Electricity is generated by conductors rotating though a magnetic 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 slo
2、ws. 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 the net 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! Thre
3、e phase motors have better starting torque, run more quietly, are more efficient and are smaller than singlephase 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 doesnt deliver significant performance improvements 如果相数多余三
4、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 resul
5、ting 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
6、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). PTs 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。
7、,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,From the Dam to Your Load 从发电站到负载,Transformer Connections 变压器的连接,Single-phase systems 单
8、相系统,Three-phase, Four wire systems 三相、四线系统,Three-phase, Three wire systems 三相、三线系统,Delta Configuration 三角型配置,Comprised of 3 voltages and 3 currents. 由三个电压和三个电流组成 No Neutral wire. 无零线 Sometimes has a ground wire. 有时有地线 Voltage is measure as “phase to phase”. 测量的电压为“相相”电压 Typically 480vrms. 一般为480vrms
9、.,Wye Configuration Y型配置,Almost all commercial and light industrial loads are supplied by Grounded-Y (4-wire Y) transformers. 几乎所有的商业和照明领域的负载都是由 接地的Y型(4线Y型)配置的变压器供电的,Comprised of 3 voltages and 3 currents. 由三个电压三个电流组成 Neutral wire and ground wire. 零线和地线 The Wye delivers two stable voltage levels fro
10、m one transformer 在Y性配置下,变压器可以提供两个电压 Phase to Neutral may be used for smaller loads 相零电压,小的负载可以使用这个电压 Phase to phase may be used for larger loads or longer wiring runs 相相电压,大负载或配线较长时可以使用该电压,Voltage Levels 电压,Standard voltage levels vary by country 各个国家的标准电压会不一样 Most distribution within buildings is
11、120V to 480V 建筑物内的绝大多数配电系统为120V到480V Residential standards vary considerably 各个国家与住宅有关的标准也不一样 US, Canada, Mexico use a 240V single phase system 美国、加拿大、墨西哥使用240V的单相系统 Europe, China, others use 230V single or 3-phase 欧洲、中国以及其它国家使用230V单相或三相系统 Typical Wye phase-to-phase and phase-to-neutral voltages are
12、 典型的Y型配置下相相和相零电压如下 240/120V (US, Canada, Mexico) 240/120V(美国、加拿大、墨西哥) 400/230V (China, Europe) 400/230V(中国、欧洲) 480/277V (US, Canada, Mexico) 480/277V(美国、加拿大、墨西哥) Voltages from 1kV to 100kV are used to serve large commercial buildings and for utility distribution 1kV到100kV的电压一般用于大的商业建筑和公用配电系统 Voltage
13、s over 100kV are used for transmission 超过100kV的电压一般用于电力传输,Color Codes 色标,Varies by country and territory. 各个国家和地区不一致 Not always done correctly. 不一定都正确使用 Bus bar usually not labeled. 通常并不标注母线 Australia & New Zealand: 澳大利亚和新西兰: Red / White / Blue / Black / Yellow Green Strip 红/白/蓝/黑/黄色卷带 USA: 美国: Blac
14、k / Red /Blue / White / Green 黑/红/蓝/白/绿 Europe: 欧洲: Red / Yellow / Blue / Black / Yellow Green strip 红/黄/蓝/黑/黄色卷带,Let us speak Power 关于功率,Three Kinds of AC Power 三种交流功率 True Power (W) 有效功率(W) Does useful work 做有用功 Reactive Power (VAR) 无功功率(VAR) Powers motor magnetic field, charges capacitor 驱动马达磁场、给
15、电容充电 Apparent Power (VA) 视在功率(VA) System capacity 系统负载量 PF = Watts Volt-Amps,Head = VARs 头部=乏,Beer = Watts 啤酒=瓦特,Glass = VA 玻璃杯=伏安,Power Triangle 功率三角形,Motors require “lagging” VARs, reducing PF. Greater system capacity (VA) is required. 马达需要“滞后” 乏,导致功率因数降低,需要更大的系统负载量(VA)。,Caps supply “leading” VARs
16、, improving PF, reducing VA requirement. 电容能使乏“提前”,提高功率因数,减小所需的伏安。,Reactive Power (VARs) 无功功率(乏),True Power (Watts) 有效功率(瓦特),Apparent Power (VA) 视在功率(伏安),What is Power Quality 什么是电能质量,“Any power problem manifested in voltage, current, or frequency deviations that results in failure or missed operati
17、on of utility or end user equipment” “电能质量就是指出现在导致公用设施或最终用户设备故障或工作不正常的电压、电流或频率偏移上的任何电能问题。,Dugan, McGranahan, Beaty; Electrical Power Systems Quality Dugan, McGranahan, Beaty;“电力系统的质量”,Power Problems 电能问题,Voltage sags and outages 电压骤降或断电 Overcurrent (tripping CBs) 过流(启动断路器) Utility Bills 电费 Energy co
18、nsumption 能量消耗 Peak Demand 最高负荷 Power Factor Penalties 功率因数的影响 Voltage swells 电压骤升 Transients 瞬态电压 Voltage imbalance/unbalance 电压失衡/紊乱 Excessive harmonics 谐波过多 Flicker 闪变 Noise 噪声 Ground currents or poor grounding 接地电流或接地不良,Severity of Voltage Events 电压时间的安全性,Most Power Quality events are really vol
19、tage events. 大多数电能质量时间其实是电压事件 Severity of a voltage event is characterized by magnitude and duration. 电压时间的严重程度是由幅度和持续时间表示的。 The larger the change, and the longer it takes place, the more likely it is that equipment will malfunction. 事件的变化越大、持续的时间越长,设备就越有可能出现故障 ITIC/CBEMA curves plot magnitude and d
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