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1、论电网中无功功率补偿许多电设备均是根据电磁感应原理工作的，如配电变压器、电动机等，它们都是建立交变磁场才能进行能量的转换和传递。为建立交变磁场和感应磁通而需要的电功率成为无功功率。因此，所谓的“无功”并不是“无用”的电功率。只不过它的功率并不转化为机械能、热能而已；因此在供电系统中除了需要有功电源外，还需要无功电源，两者缺一不可。在功率三角形中，有功功率P与视在功率S的比值，称为功率因数cos。其计算公式为：cos=P/S=P/（P2+Q2）1/2在电力网的运行中，功率因数反映了电源输出的视在功率被有效利用的程度，我们希望的是功率因数越大越好。这样电路中的无功功率可以降到最小，视在功率将大部分
2、用来供给有功功率，从而提高电能输送的功率。1、 影响功率因数的主要因素（1） 大量的电感性设备，如异步电动机、感应电驴、交流电焊机等设备是无功功率的主要消耗者。据有关的统计，在工矿企业所消耗的全部无功功率中，异步电动机的无功消耗占了60%70%，所以要改善异步电动机的功率因数就要防止电动机的空载运行并尽可能提高负载率。（2） 变压器消耗的无功功率一般约为其额定容量的10%15%，它的空载无功功率约为满载时的1/3，因而，为了改善电力系统和企业的功率因数，变压器不应空载运行或长期处于低负载运行状态。（3） 供电电压超过超出规定范围会对功率因数造成很大的影响当供电电压高于额定值的10%时，由于磁路
3、饱和的影响，无功功率将增长得很快，据有关资料统计，当供电电压为额定值的110%时，一般无功将增加35%左右。当供电电压低于额定值时，无功功率也相应减少而使它们的功率因数有所提高，但供电电压降低会影响电气设备的正常工作，所以，应当采取措施使电力系统的供电电压尽可能保持稳定2 无功补偿的一般方法无功补偿通常采用的方法主要有3种：低压个别补偿，低压集中补偿，高压集中补偿，下面简单介绍这三种补偿方式的适用范围及使用该补偿方式的优缺点。（1） 低压个别补偿：低压个别补偿就是根据个别用电设备对无功的需要量将单台或多台低压电容器组分散地与用电设备并接，它与用电设备公用一套断路器，通过控制、保护装置与电机，同
4、时投切，随机补偿适用于补偿个别大容量且连接运行（如大中型异步电动机）的无功损耗，以补励磁无功为主，低压个别补偿的优点是，用电设备运行时。无功补偿投入，用电设备停运时，补偿设备也退出，因此不会造成无功倒送，具有投资少、占位小、安装容易、配置方便灵活、维护简单、事故率低等优点。（2） 低压集中补偿：低压集中补偿是指将低压电容器通过低压开关接在配电变压器低压母线侧，以无功补偿投切装置作为控制保护装置，根据低压母线上的无功负荷而直接控制电容器的投切，电容器的投切是整组进行，做不到平滑的调节。低压补偿的优点：接线简单、运行维护工作量小，使无功就地平衡，从而提高配变利用率，降低网损，具有较高的经济性，是目
5、前无功补偿中常用的手段之一。（3） 高压集中补偿：高压集中补偿是指将并联电容器组直接装在变电所的610kv高压母线上的补偿方式适用于用户远离变电所或在供电线路的末端，用户本身又有一定的高压负荷，可以减少对电力系统无功的消耗并可以起到一定的补偿作用；不差个装置根据负荷的大小自动投切，从而合理地提高了用户的功率因数，避免功率因数降低导致电费的增加。同时便于运行维护，补偿效益高。3 采取适当措施，设法提高系统自然功率因数提高自然功率因数是不需要任何补偿设备投资，仅采取各种管理上或者技术上的手段来减少各种用电设备所消耗的无功功率，这是一种最经济的提高功率因数的方法。（1） 合理使用电动机；（2） 提高
6、异步电动机的检修质量；（3） 采用同步电动机：同步电动机啊消耗的有功功率取决于电动机上所带机械负荷的大小，而无功功率取决于转子中的励磁电流大小，在欠励状态时，定子绕组向电网“吸取”无功，在过励状态时，定子绕组向电网“送出”无功。因此。对于恒速长期运行的大型机构设备可以采取同步电动机作为动力。异步电动机同步运行就是将异步电动机三相转子绕组适当连接并通入直流励磁电流，使其呈同步电动机运行，这就是“异步电动机同步化”。（4） 合理选择配变容量，改善配变的运行方式：对负载率比较低的配变，一般采取“撤、换、并、停”等方法，使其负载率提高到最佳值，从而改善电网的自然功率因数。4 无功电源电力系统的无功电源
7、除了同步电动机外还有静电电容器、静止无功补偿器以及无功发生器，这4种装置又称为无功补偿装置，除电容器外，其余几种既能吸收容性无功又能吸收感性无功。（1） 同步电机：同步电机中有发电机、电动机及调相机3种。 同步发电机同步发电机是唯一的有功电源，同时又是最基本的无功电源，当其在额定状态发出无功功率：其中：Q、S、P、是相对应的无功功率、视在功率、有功功率和功率因数。发电机正常运行是，以滞后功率因数运行为主，向系统提供无功，但必要时，也可以减小励磁电流，使功率因数超前，即所谓的“进相运行”，以吸收系统多余的无功。 同步调相机：同步调相机是空载运行的同步电机，它能在欠励或过励的情况下向系统吸收或者供
8、出无功，装有自励装置的同步电机能根据电压平滑地调节输入或输出的无功功率，这是其优点，但它的有功损耗大、运行维护复杂、响应速度慢，近来已逐渐退出电网运行。 并联电容器：并联电容器补偿是目前使用最广泛的一种无功电源，由于通过电容器的交变电流在相位上正好超前于电容器极板上的电压，相反于电感中的滞后，有此可视为向电网“发”无功功率：其中：Q、U、分别为无功功率、电压、电容器容抗。并联电容器本身功耗很小，装设灵活，节省投资；由它向系统提供无功可以改善功率因数，减少由发电机提供的无功功率。 静止无功补偿器：静止无功补偿器是由晶闸管所控制投切电抗器和电容器组成，由于晶闸管对于控制信号反应极为迅速，而且通断次
9、数也可以不受限制，当电压变化静止补偿器能快速、平滑地调节，以满足动态无功补偿的需要，同时还能做到分相补偿；对于三相不平衡负荷及冲击负荷有较强的适应性；但由于晶闸管控制对电抗器的投切过程中会产生高次谐波，为此需加装专门的滤波器。 静止无功发生器：它的主体是一个电压源型逆变器，由可关断晶闸管适当的通断，将电容上的直流电压转换成为与电力系统电压同步的三相交流电压，再通过电抗器并联接入电网，适当控制逆变器的输出电压，就可以灵活地改变其运行工况，使其处于容性、感性或零负荷状态。与静止无功补偿器相比，静止无功发生器相应速度更快，谐波电流更少，而且在系统电压较低时仍能向系统注入较大的无功。5结束语本文集中探
10、讨了功率因数对广大供电企业的影响以及提高功率因数所带来的经济效益和社会效益，介绍了影响功率因数的主要因数和提高功率因数的几种方法，还讨论了目前所通用的几种无功电源及其特点，这对供电企业是十分有益的。Theory of grid planning of reactive power compensation Many electric equipment are according to the principle of electromagnetic induction and work, Such as distribution transformer, motor, etc， They a
11、re built to alternating magnetic field of energy conversion and transfer.To establish alternating magnetic field and inductive magnetic flux and need to be reactive power and power. Therefore, the so-called reactive and not useless theelectrohydraulic power. But it is not converted into mechanical e
12、nergy, power heat just; So in power supply system of meritorious power besides need outside, still need to reactive power, both are necessary.1, the main factors of influence power factor(1) a lot of inductive devices, such as induction motor, ac welders, induction, such equipment is reactive power
13、consumption is the main. According to the statistics, consumed in industrial and mining enterprises in all the reactive power, asynchronous motor of reactive power consumption accounted for 60% to 70%, so want to improve the power factor of asynchronous motor to prevent motor racing operation and ma
14、ximize load rate.(2) the consumption of reactive power transformer for its nominal capacity is typically about 10% 15%, its non-load reactive power for about one-third of full, therefore, in order to improve the power system and power factor of enterprise no-load transformer should not running or th
15、e long-term at low load operation.(3) power supply voltage exceed within the prescribed scope of power factor will have a big impactWhen the power supply voltage when the 10% higher than the ratings, due to the influence of magnetic saturation, reactive power will grow fast, according to the statist
16、ics, when the power supply voltage of ratings, generally for 110% of the reactive power will increase about 35%. When the power supply voltage is lower than ratings, reactive power when they drop accordingly improve the power factor, but the power supply voltage lowering will affect the normal work
17、of the electrical equipment, so, shall adopt measures to prevent power system voltage supply as remained stable2 the general method of reactive power compensationReactive compensation the usual method basically has 3 kinds: low voltage individual compensation concentrated compensation, high pressure
18、, low pressure concentrated compensation, the following simple introduce this three kinds of compensation methods applicable scope and the advantages and disadvantages of using this method for compensation.(1) low-pressure individual compensation:Low voltage individual compensation is according to t
19、he individual of reactive power equipment will be a single stage because of the low voltage capacitor set or more sets with electrical equipment and scattered with electrical equipment pick, it public a set of circuit breaker, through the control and protection device and motor, meanwhile shots, ran
20、dom compensation applicable to cut large capacity and compensation individual connect operation, such as large and medium-sized asynchronous motor) reactive loss to recover the excitation reactive power is given priority to, the advantages of low voltage individual compensation, electricity equipmen
21、t in operation. Reactive compensation investment, electrical equipment, compensation equipment and action, and therefore wont cause from reactive delivers the placeholder, has less investment, small, easy installation, configuration is convenient and flexible, simple maintenance and accidents etc.(2
22、) low-pressure concentrated compensation:Low voltage concentrated compensation refers to low voltage capacitor through the low pressure switch will pick up in distribution transformer, low-pressure busbar side reactive power compensation threw cutting device as control protection device, according t
23、o the low-pressure busbar reactive load and direct control capacitors, capacitors cast cut, cut the cast is less than smooth adjustment. Do Low voltage compensation advantages: wiring is simple, operation and maintenance, small amount of reactive power balance, so as to improve the in situ with vari
24、able utilization, decrease network loss, high efficiency, is currently reactive compensation in one of the common method.(3) high-pressure concentrated compensation:High-pressure concentrated compensation refers to will shunt capacitors installed directly in the substation of 6 to consumers 10kv hig
25、h-pressure busbar compensation way suitable for user from substation or the end of the power supply line, user itself also has the certain high-voltage, can reduce on power system reactive power consumption and can play a certain role; the compensation Not bad, according to the size of a device to l
26、oad auto-switching, thus reasonable improve users power factor, avoid power factor caused by the increase of electricity. Also facilitate operation and maintenance, high compensation benefits.3 take appropriate measures to try to improve the system of natural power factorImprove natural power factor
27、 is not to need any compensation equipment investment, only take various management or technical means to reduce power consumption equipment of reactive power, this is a kind of the most economic improving power factor method.(1) reasonably using the motor;(2) improve the maintenance quality of asyn
28、chronous motor;(3) using synchronous motor: synchronous motor ah the active power consumed by motor with depends on the size of the mechanical load, and reactive power depends on the excitation currents, rotor shunt state in owe to the power grid, stator winding drain reactive, stator winding shunt
29、state, to the power grid send reactive. Therefore. For constant speed long-term operation of large institutions equipment can take synchronous motor as power.Asynchronous motor synchronization operation is three-phase asynchronous motor rotor windings appropriate link and access to dc exciter curren
30、t, to assume the synchronous motor running, it is a asynchronous motor synchronization.（5） (4) rational choice, improve with variable volume with the operation mode: to change the load factor lower with variable, generally take withdraw, change, and methods, stop, make its load rate increased to bes
31、t value, thereby improve the natural power factor.Four reactive powerPower system reactive power except for synchronous motor and electrostatic capacitor, static outside of reactive power compensator and reactive generator, the four devices called reactive compensation devices, except capacitor outs
32、ide, the rest several can absorb capacitive reactive and can absorb perceptual reactive.(1) synchronous motor:Synchronous motor are generators, motors and in three adjustable camera.(1) the synchronous generatorsSynchronous generator is the only active power, and is the most basic reactive power, wh
33、en its rated condition in issued reactive power:Among them: Q, S, P, phi is corresponding reactive power, ShiZai power, active power and power factor.Generators in the normal operation of power factor is lagging, mainly to run, system to provide the reactive power, but when necessary, also can reduc
34、e excitation current, make the power factor ahead, the so-called under-excitation operation, to absorb system redundant reactive.(1) the synchronous adjustable cameras:Synchronous adjustable camera is no-load running synchronous motor, it can shunt or excitation in owe to the system under the condit
35、ion of the absorption of reactive power, or for the synchronous motor with motivated device can smoothly according to the voltage regulation input or output of reactive power, this is its advantages, but its active loss is big, operation &maintenance complex, slow response, recently has gradually ex
36、it the power network operation.(2) the parallel capacitor:Parallel capacitor compensation is the most widely used a reactive power, because through the capacitors in alternating current in advance exactly in the phase of voltage capacitor plates, as opposed to the lag, there is the inductance can be
37、 regarded as to the grid hair reactive power:Among them: Q and U, respectively, reactive power, voltage, capacitor RongKang.Parallel capacitor itself power consumption is small, furnish flexible, save investment; By its system to provide reactive to can improve power factor, reduce by generators pro
38、vide reactive power. (1) the static reactive power compensator:Static reactive power compensator is cast by ZhaGuanSuo control wafer cut reactor and capacitors because of thyristor reaction to control signal is rapidly, but hige number are also can not restricted, when voltage changing static compen
39、sator can fast and smooth to adjust to meet the needs of dynamic reactive compensation, also can achieve points phase compensation; For unbalanced three-phase load and impact load have strong adaptability; But because thyristor controlled the shots of reactor will generate cut process, therefore hig
40、her harmonic to add special filter.(2) the static reactive power generators:Its subject is a voltage source type inverter, by can shut off the thyristor appropriate hige, will the dc voltage capacitance converted into and power system voltage synchronized three-phase ac voltage, again through the re
41、actor parallel access, appropriately control inverter power output voltage, can the flexibility to change its running condition, subjecting capacitive, perceptual or zero load conditions.And static reactive power compensator, static reactive power generator compared the corresponding velocity faster
42、, harmonic current less, and in the system at low voltage to the system can still be injected larger reactive.5 closingThe paper focuses on the discussion to the power factor of power supply enterprises and improving power factor influence brought by economic and social benefits, this paper introduces the main factor influence power factor and improve the power factor, also discussed several methods of several now general supply reactive power and characteristics of the power supply enterprise, which is very useful.
