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1、电力负载的无功测控电路设计目录毕业设计任务书.I文献综述II指导老师审查意见答辩会议记录评阅教师评语中外文摘要Reactive power load measurement and control circuit design Reactive power load measurement and control circuit design literature review Fist. Introduction I wrote this article is to introduce the current status of power system and power compensa
2、tion in power system problems. Mainly related to the power system reactive power compensation in the area. Reactive power load measurement and control circuit design literature review Low-voltage reactive power compensation reactive power load is an important part of compensation. Improve low-voltag
3、e compensation, not only can reduce the level of reactive power compensation on the pressure, but also improve the utilization of the user distribution transformers to improve power factor and voltage quality of the user, and can effectively reduce power losses, thus reducing electricity bills . Rea
4、ctive power compensation and power supply departments of user benefit. Existing reactive power compensation device type a lot, but basically by the detection unit, control unit, execution units, and power component. The task detection unit is detected from the network and network power factor direct
5、ly or indirectly related to the parameters, and to give as gifts this parameter signals and control unit, the control unit to be compared with the control target value. Make switching decisions. Implementation unit is based switching decisions by switching switch (AC Contactor) Control of capacitor
6、switching, compensation to complete the task.Second, the main At present, the low voltage reactive power compensation devices are static and dynamic compensation device compensation of two, the control method are: power factor control, reactive Power (or reactive current) control and other control m
7、ethods. Static and dynamic reactive power compensation reactive power compensation. Static Var Compensator SVC means that when the reactive changes, control changes to control the capacitor according to the group switching to achieve the required reactive power compensation, the response normally gr
8、eater than 5 seconds. Capacitor switching is accomplished by the contactor, due to capacitor inrush current withstand capability and the discharge time, capacitor grade, contactors operating frequency, life and other factors, so there is much to be desired: ( 1) there is a level of compensation, tim
9、ing, and thus compensation accuracy, the time when the load changes frequently (such as rolling, high-power electric furnace, etc.), to follow is not strong. (2) The input capacitor can be no surge. For contactor + reactor program, a larger increase in losses for capacitive touch device program, a h
10、igh accident rate, but also a great influence on the life of the capacitor. (3) run noisy. (4) As part of the load control contactor coil is in the switching process, will produce sparks and high harmonics, resulting in interference, affect the compensation device reliability and service life. Stati
11、c reactive power compensation equipment and some use of composite switch as the Closing and breaking circuit current component, which uses silicon and contacts (or high-capacity relays) in parallel, when you need input capacitor, the first by the SCR conduction circuit, no inrush current into the ca
12、pacitor, and then contacts (or high-capacity relays) conduction circuit, controllable Silicon out of operation. Removal of the action when the capacitor is the opposite order. Because of the inherent characteristics of the components used, limitations, when the controller detects reactive change nee
13、ds switching capacity of the capacitor must, we must delay a certain time (response time greater than 5 s) for switching. Therefore, static reactive power compensation is a longer delay switching for reactive compensation. In addition, the operation was found, due to high current flows through the r
14、elay contacts regularly, and frequent switching, make contact burning, bonding occurs. Relay contacts will occur shake off timely, high harmonic generation, on the controller to work greater impact. Dynamic reactive power compensation (Thyristor Switched Capacitor TSC): As the SVC is kind of long-la
15、tency switching method, which is determined by its reactive change frequently and vary greatly in the case, can not meet the requirements. In modern power electronic devices and digital control technology support, with fast switching capability of dynamic reactive power compensation device can quick
16、ly. Tracking compensation of reactive power changes. Static and dynamic compensation equipment circuit structure is the same, but the dynamic compensation is dynamic compensation controller to control the fast-pass thyristor .Broken, no surge in power capacitor switching. Reactive power regulator re
17、placed electromagnetic AC contactors to change this component, making the performance of the compensation device has been a qualitative leap to a capacitor bank switching time reduced by a few hundred milliseconds to 20,30 ms . That is, l 2 个 a cycle is complete a capacitor bank switching, so do the
18、 amount of reactive power compensation can quickly follow changes in actual demand. As the reactive power regulator is a non-contact capacitive switch long life, so that no surge capacitors impact the process of investment, no operating over-voltage, arc-free capacitor renewed removal process, the w
19、hole long life, maintenance of small and can be removed in the capacitor after the discharge to any What input voltage again. Frequent switching capacitor can be divided into phase compensation. Power factor control and reactive power (reactive current) control whether static VAR compensation, or th
20、e dynamic reactive power compensation, require a controller to complete the network parameters of the measurement, control capacitor banks switching. Most of static reactive power compensation device is a contactor switch element, the controller issued a traffic signal switches to control contactors
21、 or off Closing Open. Dynamic reactive power compensation device to thyristors as switching elements, the controller issued a trigger signal to the thyristor. Reactive power compensation device has power factor control and reactive power (no Reactive current) control in two ways, each of the followi
22、ng features: Power factor control power factor control is to meet the requirements for power factor control objectives, so that the grid power factor to meet the requirements. Power Factor Controller on the grid voltage and current sample testing, analysis and calculation of power by the current val
23、ue, with the current power factor values with the switching threshold set for comparison to determine whether investment, removal of capacitors, or maintaining the status quo unchanged. Suppose the power factor before compensation 0.9. When the input threshold is set to = 0.9, the controller detects
24、 the current power factor is less than 0.9, to issue instructions, input of a compensation capacitor. If the compensated power factor 0(负载呈感性) =t-T/2= =0(负载呈阻性) 0(负载呈容性) 功率因数的计算：为使CPU有能力和时间实施自诊断和二次开发，本文对Cos 的运算采用查表技术c设市电工频5O Hz(周期20ms)，T=10ms，则Cos=c0弧节 Cos*t=Cos（*t/T-/2）事先离线使 按一定步长 递增，并由上式计算得tCos查询表
25、，存人EPROM。其中把t折算为地址，地址内容为Cos 值。这样当采样回路测得 时，就可将其转化为地址，查表即得对应的Cos 。过程论述理解关于无功功率补偿的几个概念1.1 正弦交流电中的无功功率定义正弦电流中的无功功率定义为: 习惯上认为它是由电路中的储能元件(电容或电感)引起。在交流电一个周期的一部份时间内，储能元件从电源吸收能量，另一部时间内将能量返回电源，理想的无损失储能元件在整个周期q平均功率是零。也就是说在外电路和电感或电容之间虽有能量的来回交换，但在储能元件上并没有能量的消耗。无功功率与储能元件相关联。我们可计算功率因数： 1.2 电力系统中无功功率及功率因数电力网除了要负担用电
26、负荷的有功功率P，还要负担负荷的无功功率Q。 无功功率O和视A功率S之间存在下述关系: 然而：被定义为电力网的功率囚数，其物理意义是线路的视在功率S供给有功功率的消耗所占百分数。在电力网的运行中，我们所希望的是功率因数越大越好，如能做到这一点，则电路中的视在功率将人部分用来供给有功功率，以减少无功功率的消耗。1.2.1 如何提高电力系统功率因数功率因数还可以表示成个述形式:注：U:为线电压，L为:线电流。 可见，在一定的电压和电流卜，提高Cos，其输出的有功功率将增大。因此，改善功率因数是充分发挥没备潜力，提高设备的利用率的有效方法。1.2.2 补偿电容以减少线路损失电力网的电压损失可以表示为
27、: 可看出，影响U的因数四个:线路的有功功率P、无功功率o,电阻R和电抗X。如果采用容抗为X。的电容来补偿，则电压损失为:故采用补偿电容提高功率因数后，电压损失U减小，改善了电压质量。电力系统无功补偿的原理 2. 3. 1配电网无功补偿问题的提出 在电力系统中，由于电感、电容元件的存在，不仅系统中存在着有功功率，而且存在无功功率。虽然无功功率本身不消耗能量，它的能量只是在电源及负载间进行传输交换，但是在这种能量交换的过程会引起电能的损耗。并使电网的视在功率增大，这将对系统产生以下一系列负面影响:(1) 电网总电流增加，从而会使电力系统。中的元件，如变压器、电器设备、导线等容量增大，使用户内部的起动控制设备、量测仪表等规格、尺寸增大，因而使初投资费用增大。在传送同样的用功功率情况下，总电流的增大，使设备及线路的损耗增加，使线路及变压器的电压损失增大。(2) 电网的无功容量不足，会造成负荷端的供电电压低，影响正常生产和生活用电;反之，无功容量过剩，会造成电网的运行电压过高，电压波动率过大。(3) 降低了电网的功率因数造成大量电能损耗，当功率因数由0.8下降到0.6时，电能损耗将近提高了一倍。(4) 对电力系统的发电设备来说，无功电流的增大，对发电机转子的去磁效应增加，电压降低，如过度增加励磁电流，则使转子绕组超过允许温升。为了保证转子绕组正常工作，发电
