电力负载的无功测控电路设计毕业论文电力系统无功功率补偿.doc

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 compensation 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-voltage 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 . Reactive 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 directly 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 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 methods. 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 greater 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, timing, 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 high 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. Static 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 capacitor, 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 needs 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 relay 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-latency 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 quickly. 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 replaced 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 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 whole 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 the 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 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 following 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 value, 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 the current power factor is less than 0.9, to issue instructions, input of a compensation capacitor. If the compensated power factor <0, the reactive power sent back to the higher power, the controller will issue an order removal of a capacitor. When the detected power factor between 0.9 and 1.0, then regardless of the actual reactive power value is the amount of compensation are to maintain the current status quo. As the power factor value is a percentage value, so heavy duty Or light load, the compensation less effective. Heavy-duty, although the power factor to meet the requirements of 0.9-1, but the power required reactive power is still large, but not investment power capacitor to compensate, eventually reach the ideal effect on Energy Conservation. Power factor control is another problem switching under light load oscillation. Light loads, low power factor, when the reactive power compensation capacitor is less than 1 group capacity, in accordance with the principle of compensation will be invested in a group of capacitors, a result of compensation has been ahead of the power factor. Power factor as long as the lead, should immediately remove a capacitor, and removal of a group. Power factor after another is not sufficient, the formation of oscillation. Reactive power (reactive current) controller to control the reactive power (reactive current) control object, if more than one group reactive power compensation capacitor capacity of the input capacitor, when the higher power supply to the non- reactive power capacity is less than a group of capacitors, the capacitor will not invest. If when the reactive power sent back to the higher power, then remove a group of capacitors. The compensation method will make the grid reactive power (reactive current) is always maintained at a low level, therefore, does not appear the way the power factor control defects. Selected reactive power (reactive current) control mode is superior compared with power factor control mode. The performance of reactive power compensation device more practical application in a kind of reactive power compensation devices: power factor control of static VAR compensator; reactive power (reactive current) control of static VAR compensator; Dynamic power factor control power compensation device; reactive power (reactive current) controlled dynamic reactive power compensation device. In summary, reactive power (or reactive current) controlled dynamic reactive power compensation device has the advantages of the process without input capacitor inrush current impact, no over-voltage operation, the process of removal of non-arc capacitor renewed; machine life long, maintenance of small; dynamic response time fast, fast reactive power compensation; can be removed after the capacitor voltage discharge to any re-vote in person, and frequent switching; separable phase compensation, can be equipped with infrared acquisition and remote transmission device, and also harmonic components can be used for larger venues. In addition to the basic control functions, there are many additional features, such as: four quadrant operation, automatic manual switch, automatic identification of separate ways of power capacitors, automatic switching time under load regulation, over-voltage alarm and protection, alarm circuit resonance, voltage and current distortion measurement and power factor, voltage, current, apparent power, active power, reactive power, power grid frequency measurement and display. Some also have a printer interface, computer network interface. Therefore, reactive power (reactive current) controlled dynamic reactive power compensation devices on the network can really satisfy the requirements of reactive power compensation.Third, sum up        Combined with the main part of the intelligence information provided, we can see that the current martial power compensation, power system still major deficiencies. Do not use dynamic compensation of static compensation is superior than the use of reactive power control with power factor control is superior.       The main problem is that the current compensation schedule of compensation is not high, capacitor switching there is flow, easy to form oscillation, security is not high. So I think that the power system reactive power compensation will move toward a dynamic compensation, current control, and high-voltage and low voltage isolation, improve the security of direction.Fourth,references 1. Grid power factor measurement and automatic compensation of reactive power control Liu Junyue 2. On the low voltage reactive power compensation device of Yuzhao Rong Chen Xi 3. Reactive Power Compensation Scheme Comparison of Closed 前言补偿低压无功负荷是电网无功补偿的重要环节。搞好低压补偿，不但可以减轻上一级电网无功补偿的压力，而且可以提高用户配电变压器的利用率，改善用户功率因数和电压质量，并能有效地降低电能损失，减少用户电费支出。低压无功补偿对用户和供电部门均有益。现有的无功自动补偿装置种类很多，但基本上都是由检测单元、主控单元、执行单元和电源组成。检测单元的任务是从电网中检测与网络功率因数直接或间接相关的参数，并将此参数信号转换并送人主控单元，由主控单元将其与控制指标值进行比较。作出投切决策。执行单元则根据投切决策通过投切开关(交流接触)控制电容器的投切，完成补偿任务。本文利用单片机8051设计了一种全自动无功补偿控制器。它具有如下功能：(1)实时显示电网功率因数值，同时，还能够显示控制器的工作状态和电容器组的投切情况。(2)功率因数指标可以按不同的补偿要求设定和调整。如：以节能和减少电费支出为指标的无功参数补偿方案；以提高功率因数为目的的补偿方案和为改善电压偏差为主要指标的电压参数调节方案等。(3)利用可控硅做中间驱动单元，使强、弱电分离。提高了系统的可靠性。(4)采用电容器组循环投切方式，以免电容器组长期运行，温升过高等。(5)电容器组切换延时及延时调整等可防止电容器组投切时产生振荡现象。选题背景 电压质量是衡量电力系统电能质量的重要指标之一，它的好坏主要取决于电力系统无功潮流分布是否合理。这不仅关系到电力系统向电力用户提供电能质量的优劣问题，而且还直接影响电网的安全、经济运行。若无功电源容量不足，系统运行电压将难以保证。随着电网容量的不断增加，对电网无功功率的要求也与日增加。因此，还需考虑网络的功率因数和电压，因为网络功率因数和电压的降低会使电气设备得不到充分利用，从而降低网络的传输能力，并引起损耗增加。因此，解决好配电网络无功补偿的问题，对电网的安全和降损节能有着重要的意义。无功补偿点的合理选择以及补偿容量的确定，能够有效地维持系统的电压水平，提高系统的电压稳定性，避免大量无功功率的远距离传输，从而降低有功网损，减少发电费用。我国配电网长期以来无功匮乏，由其造成的网损严重，因此，进行无功功率补偿，能投资少回报高。通常采用的方法是在配电变压器低压侧进行补偿，既可降低线路损耗，也能降低配电变压器损耗，电压质量也有较大的改善。方案论证 功率因数的测量方法:在三相对称交流电路中UA UBC，即+ = 90°,(如图1所示。为提高测量精度，可测量一般情况下数值较大的值。由于直接测量日值很难，所以我们采用测量与成正比关系的时间t，再由t折算得到功率因数Cos。测量电路及其波形如图2和图3所示。检测单元通过电压互感器、电流互感器，将电网线电压UBC和相电流IA变换成适当的电压信号送人反相比较电路，得到相应的方波信号TBC和TA，再经与非门送到单片机INT0端。经单片机测得时间值T和t，求出与相位 对应的时问t 。UAUCUBUBCIA电压电流向量图-+- & 80C51IAubccccC测量电路图显然有，t=T/2-t0 = T/2 (T-t) >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，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<一>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: 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。<二>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