這是《有功功率和無功功率》教學反思，是優秀的物理教案文章，供老師家長們參考學習。

　　有功功率/無功功率Active power/reactive power 在交流電路中，由電源供給負載的電功率有兩種;一種是有功功率，一種是無功功率。

　　有功功率和無功功率

　　有功功率是保持用電設備正常運行所需的電功率，也就是將電能轉換為其他形式能量(機械能、光能、熱能)的電功率。比如：5.5千瓦的電動機就是把5.5千瓦的電能轉換為機械能，帶動水泵抽水或脫粒機脫粒;各種照明設備將電能轉換為光能，供人們生活和工作照明。有功功率的符號用P表示，單位有瓦(W)、千瓦(kW)、兆瓦(MW)。

　　無功功率比較抽象，它是用于電路內電場與磁場的交換，并用來在電氣設備中建立和維持磁場的電功率。它不對外作功，而是轉變為其他形式的能量。凡是有電磁線圈的電氣設備，要建立磁場，就要消耗無功功率。比如40瓦的日光燈，除需40多瓦有功功率(鎮流器也需消耗一部分有功功率)來發光外，還需80乏左右的無功功率供鎮流器的線圈建立交變磁場用。由于它不對外做功，才被稱之為“無功”。無功功率的符號用Q表示，單位為乏(Var)或千乏(kVar)。

　　無功功率決不是無用功率，它的用處很大。電動機需要建立和維持旋轉磁場，使轉子轉動，從而帶動機械運動，電動機的轉子磁場就是靠從電源取得無功功率建立的。變壓器也同樣需要無功功率，才能使變壓器的一次線圈產生磁場，在二次線圈感應出電壓。因此，沒有無功功率，電動機就不會轉動，變壓器也不能變壓，交流接觸器不會吸合。為了形象地說明這個問題，現舉一個例子：農村修水利需要開挖土方運土，運土時用竹筐裝滿土，挑走的土好比是有功功率，挑空竹筐就好比是無功功率，竹筐并不是沒用，沒有竹筐泥土怎么運到堤上呢?

　　在正常情況下，用電設備不但要從電源取得有功功率，同時還需要從電源取得無功功率。如果電網中的無功功率供不應求，用電設備就沒有足夠的無功功率來建立正常的電磁場，那么，這些用電設備就不能維持在額定情況下工作，用電設備的端電壓就要下降，從而影響用電設備的正常運行。 無功功率對供、用電產生一定的不良影響，主要表現在：

　　(1)降低發電機有功功率的輸出。

　　(2)降低輸、變電設備的供電能力。

　　(3)造成線路電壓損失增大和電能損耗的增加。

　　(4)造成低功率因數運行和電壓下降，使電氣設備容量得不到充分發揮。

　　從發電機和高壓輸電線供給的無功功率，遠遠滿足不了負荷的需要，所以在電網中要設置一些無功補償裝置來補充無功功率，以保證用戶對無功功率的需要，這樣用電設備才能在額定電壓下工作。這就是電網需要裝設無功補償裝置的道理。

　　電壓電流同相位，電源向負載供電，負載把電能轉換成其他能量，叫有功。

　　電壓電流不同相位部分，電源與負載之間交換電能，這部分(除線路損耗外)電能不轉換(電磁以外的)成其他能量，叫無功。 有功功率

　　有功功率是保持用電設備正常運行所需的電功率，也就是將電能轉換為其他形式能量(機械能、光能、熱能)的電功率。比如：5.5千瓦的電動機就是把5.5千瓦的電能轉換為機械能，帶動水泵抽水或脫粒機脫粒;各種照明設備將電能轉換為光能，供人們生活和工作照明。有功功率的符號用P表示，單位有瓦(W)、千瓦(kW)、兆瓦(MW)。定義：有功功率:在交流電路中，電源在一個周期內發出瞬時功率的平均值(或負載電阻所消耗的功率)，稱為"有功功率"。

　　有功功率過低導致線損增加、容量下降、設備使用率下降，從而導致電能浪費加大。

　　無功功率

　　電網中的感性負載(如電機，扼流圈，變壓器，感應式加熱器及電焊機等)都會產生不同程度的電滯，即所謂的電感。

　　感性負載具有這樣一種特性 -----即使所加電壓改變方向，感性負載的這種滯后仍能將電流的方向(如正向)保持一段時間。一旦存在了這種電流與電壓之間的相位差，就會產生負功率，并被反饋到電網中。電流電壓再次相位相同時，又需要相同大小的電能在感性負載中建立磁場，這種磁場反向電能就被稱作無功功率。

　　定義：在具有電感或電容的電路中，在每半個周期內，把電源能量變成磁場(或電場)能量貯存起來，然后，再釋放，又把貯存的磁場(或電場)能量再返回給電源，只是進行這種能量的交換，并沒有真正消耗能量，我們把這個交換的功率值，稱為" 無功功率"。

　　無功功率比較抽象，它是用于電路內電場與磁場的交換，并用來在電氣設備中建立和維持磁場的電功率。它不對外作功，而是轉變為其他

　　形式的能量。凡是有電磁線圈的電氣設備，要建立磁場，就要消耗無功功率。比如40瓦的日光燈，除需40多瓦有功功率(鎮流器也需消耗一部分有功功率)來發光外，還需80乏左右的無功功率供鎮流器的線圈建立交變磁場用。由于它不對外做功，才被稱之為“無功”。無功功率的符號用Q表示，單位為乏(Var)或千乏(kVar)。

　　無功功率過高的缺點 ：

　　1)無功功率會導致電流增大和視在功率增加，導致系統容量下降;

　　2)無功功率增加，會使總電流增加，從而使設備和線路的損耗增加;

　　3)使線路的壓降增大，沖擊性無功負載還會使電壓劇烈波動。

　　配電網中的電感性電氣設備如變壓器、電動機、電焊機、空調器、洗衣機、電冰箱、鈉燈、日光燈等投入運行后，不僅要從電力網中吸收有功功率用于做功，而且還要吸收無功功率建立磁場，這樣就導致電力客戶的自然功率因數一般都比較低。我國對電力客戶的用電，規定了必須達到的功率因數標準。

　　有功可以直接測量;有功與無功混在一起，無法直接區分開來，可以通過功率因數表測量。

　　In the circuit, the power supply by the two kinds of power load; One is the active power, one kind is reactive power.

　　Active power is to maintain the normal operation of the power equipment needed to power, is also to electric energy into other forms of energy (mechanical energy, light and heat energy) of power. For example: 5.5 kw motor is that of the 5.5 kw electrical energy into mechanical energy, drive the pumps pumping or the threshers threshing; Lighting equipment will be electric energy into light energy conversion, for people living and working lighting. The symbol of the active power with P says, the unit has watts (W), kilowatts (kW), megawatts (MW). Reactive power are abstract, it was used in the circuit of electric and magnetic field exchange, and used in electrical equipment to establish and maintain the magnetic field of power. It is not foreign energy, but changed into other forms of energy. Anyone with a magnetic coil of electrical equipment, to build a magnetic field, are about to use up reactive power. Such as 40 watts of fluorescent lamp, in addition to more than 40 tile active power (ballast also need to consume part of active power) to shine outside, still need to be around 80 lack of reactive power for ballast coil set up with alternating magnetic field. Because it is not foreign work, to be called "reactive power". Reactive power symbol using qq said, the unit is deficient (Var) or lack of thousands (kVar).

　　Reactive power is not useless power, it's very useful. Motor need to establish and maintain a rotating magnetic field, make the rotor, thus promote mechanical motion, motor rotor magnetic field is obtained from power by reactive power built. Transformer also require the reactive power, can cause the transformer a coil produce a magnetic field, at two times the voltage induction coil. Therefore, no reactive power, the motor does not turn, transformer cannot variable pressure, ac contactor won't suck $. In order to the image of the illustration of this problem, we give an example: rural water need to repair carried earth excavation earthwork, carried earth with ZhuKuang when filled with earth, the earth is like pick is active power, ZhuKuang carry empty is like a reactive power, ZhuKuang and not a useless, no ZhuKuang clay to DiShang how?

　　In normal circumstances, electrical equipment from power not only to get active power, which needs to be obtained from the power supply reactive power. If in the grid reactive power demand exceeds supply, power equipment is not enough reactive power to establish normal

　　electromagnetic fields, so, the electric equipment cannot be maintained in the rated work, electrical equipment will decline voltage, which affects the normal operation of the power equipment. Reactive power for electricity to produce a certain, bad influence, mainly displays in: (1) reduce the output of the active power generator.

　　(2) reduce the loss of power supply, the substation equipment.

　　(3) cause line voltage loss increase and the increase of the electric power. (4) cause low power factor operation and voltage fell, the electrical equipment capacity can not make full play. From the generator and the high voltage transmission line of reactive power supply, far meet the needs of the load, so in the power grid to set some of the reactive power compensation device to supplement the reactive power, in order to ensure that the user to the reactive power needed, so that power equipment can work under rated voltage. This is the power grid needs reactive power compensation devices of reason. Voltage current with phase, the power to load power supply, the load the energy conversion to other energy, called active.

　　Voltage current different phase part, source and load exchange between power, this part

　　(except the line loss outside) power not to convert (electromagnetic outside of the) into other energy, called reactive. Active power

　　Active power is to maintain the normal operation of the power equipment needed to power, is also to electric energy into other forms of energy (mechanical energy, light and heat energy) of power. For example: 5.5 kw motor is that of the 5.5 kw electrical energy into mechanical energy, drive the pumps pumping or the threshers threshing; Lighting equipment will be

　　electric energy into light energy conversion, for people living and working lighting. The symbol of the active power with P says, the unit has watts (W), kilowatts (kW), megawatts (MW). Definition: active power: in the circuit, the power supply in a cycle of inside an instantaneous power average (or load resistance of power consumption), known as the "active power". Active power is too low to increase capacity drops, and line loss, equipment utilization rate is reduced, which can lead to increased power waste.

　　Reactive power In the grid perceptual load (such as motor, choke, transformer, induction heater and electric) produce different degree of electricity sluggish, the so-called inductance. The perceptual load has such a characteristics-even if the voltage change of direction,

　　perceptual load this lag still current direction (such as positive) keep a period of time. Once existed for this current and voltage of the phase difference between, can produce negative power, and in the power to be feedback. Again the same in current voltage phase, and the need to same size of the electricity in the perceptual load established in magnetic field, the magnetic field reverse power is known as reactive power.

　　Definition: in a inductor or capacitance circuit, in each half a cycle, the power energy into the magnetic field (or electric field) energy stored, and then, then released, and the storage of the magnetic field (or electric field) energy returned to power again, just this energy exchange, and no real energy consumption, and we put the exchange value of power, called "reactive power". Reactive power are abstract, it was used in the circuit of electric and magnetic field exchange, and used in electrical equipment to establish and maintain the magnetic field of power. It is not foreign energy, but changed into other forms of energy. Anyone with a magnetic coil of

　　electrical equipment, to build a magnetic field, are about to use up reactive power. Such as 40 watts of fluorescent lamp, in addition to more than 40 tile active power (ballast also need to consume part of active power) to shine outside, still need to be around 80 lack of reactive power for ballast coil set up with alternating magnetic field. Because it is not foreign work, to be called "reactive power". Reactive power symbol using qq said, the unit is deficient (Var) or lack of thousands (kVar). Reactive power the shortcomings of high 1) reactive power will lead to current increases and installed power increase, cause the system capacity drops; 2) reactive power increase, can make the total current increase, which makes equipment and line loss increase; 3) make line pressure drop increases, impact reactive load will also make voltage sharp fluctuations.

　　The distribution network inductive electrical equipment such as transformer, electric motors,

　　electric welding machine, air conditioner, washing machines, refrigerators, sodium lamp, fluorescent lamp, and other inputs after the operation, not only to absorb the active power from the grid for work, but also to absorb reactive power establish magnetic field, this leads to electric power customer the natural power factor is compared commonly low. Our country to electric power customer the electricity, provisions must be met the power factor of standards. Active can be directly measured; Active and reactive mix together, not directly to distinguish, t 什么叫功率因數?

　　在電路由感性或讓性能源存儲設備,電壓和電流有相位差,流行講就是電壓和電流不相同的時間;

　　因此,表面看電壓、電流大小如何,實際的和沒有做那么大的工作,有權力和能源存儲設備的能源轉換;所謂的裝機功率。目前,電力有源+無功功率。

　　的意思是,無論有功功率和無功功率是多少,只能輸出電壓和電流太大。

　　是有功功率和無功功率適量,因為有功功率和無功功率成90度角,用鐵鉤電力變壓器容量安裝power稱,單位是current-voltage(VA)。

　　功率因數計算公式。有功功率與視在功率之比

　　如果你家里的“感性負載的“更重要的是,如汽車、微波爐……用電器,比如更,吸收的'反應將會更多,和功率因數小,電力部門是小(無功功率不消費,只是從電網到你的家庭電器在吸收)

　　對于企業,供電部門有監管權力的數值,高于彩票,下面的懲罰。哈哈。

　　相當復雜,其中涉及到安全的電力,電壓……當然,包括變電站設備投資和投入運行的可靠性、安全性和成本。而電力可以訪問為測量。

　　What is called power factor?

　　In the circuit, the voltage and the phase

　　difference between the current (Φ) called the cosine power factor, with symbols cos Φ said, in numerical, power factor is active power and installed power

　　http://baike.baidu.com/view/56022.htm > ratio, namely cos Φ = P/S What is installed power?

　　In the circuit, with perceptual or let sexual energy storage equipment, the voltage and current with a phase difference, popular speak be voltage and current is not the same time;

　　Therefore, the surface see voltage is, how current size, actual and didn't do so big of work, there are power and energy storage equipment energy conversion; So called installed power. Already, the active power + reactive power.

　　Mean, whatever the active power and the reactive power is how much, can only output voltage and current so big.

　　Is the active power and the reactive power and right amount, because the active power and the reactive power into a 90 degree Angle, with hook power transformer installed with power said capacity, the unit is current-voltage (VA).

　　Stocks can calculate theorem. Active power/installed power = power factor,

　　If your home "perceptual load" is more, such as motor, microwave oven... With electric

　　equipment such as more, the absorption of reactive will more, and power factor is small, the electricity power department is little (reactive power is not consume, just from the power grid to your home electrical appliances in the absorption) Regarding the enterprise, power supply departments have the regulation of power for numerical values, higher than the lottery, below to the punishment. Ha ha. Quite complicated, which relates to safety of power, voltage... And, of course, involves the transformer substation equipment investment and put into operation reliability, safety and cost. hrough power can access for measurement. 什么叫視在功率?

　　在交流電路中，由于有感性或容性儲能設備，電壓與電流有相位差，通俗講就是電壓與電流不在同一時間到達;因此，表面看電壓有多大、電流有多大，實際并沒有做那么大的功，有電源與儲能設備的能量轉換; 所以稱為視在功率。既，有功功率+無功功率。

　　電力變壓器就用視在功率表示容量，單位為伏安(VA)。

　　意思是不管有功功率與無功功率是多少，只能輸出這么大的電壓與電流。 視在功率:在具有阻抗的交流電路中，電壓有效值與電流有效值的乘積值，稱為"視在功率"，它不是實際做功的平均值，也不是交換能量的最大速率，只是在電機或電氣設備設計計算較簡便的方法。

　　關系:視在功率的平方=有功功率的平方+無功功率的平方

　　What is installed power?

　　In the circuit, with perceptual or let sexual energy storage equipment, the voltage and current

　　with a phase difference, popular speak be voltage and current is not the same time; Therefore, the surface see voltage is, how current size, actual and didn't do so big of work, there are power and energy storage equipment energy conversion;

　　So called installed power. Already, the active power + reactive power. Power transformer installed with power said capacity, the unit is current-voltage (VA).

　　Mean, whatever the active power and the reactive power is how much, can only output voltage and current so big. Installed power: in a circuit impedance, RMS voltage and current is the product of the RMS values, called "installed power", it is not the average of the actual work, also not the biggest energy exchange rate, just in the motor or electrical equipment design and calculation, a有功功率和無功功率 simple method. Relationships: installed power square = active power of square + reactive power square

　　如圖所示，電源電壓U=220V，頻率50Hz，求電流I，I1和I2，及電路有功，無功，視在功率，和功率因數 Z1=10Ω Z2=5Ω，總電抗Z=10//5=10/3Ω

　　總電流I=U/Z=66A，I1=22A,I2=44A

　　有功功率P=I1?R1+I2?R2=2904+5808=8712W

　　視在功率S=UI=14520VA

　　無功功率Q=11616VAR

　　功率因數=P/S=0.6 有功功率、無功功率、視在功率三者之間的關系是怎樣的?計算公式是?

　　容量620KW,功率因數0.8,視在功率542KVA,無功功率應該是多少?有公式嗎?

　　懸賞分：0 - 離問題結束還有 5 天 22 小時

　　無功功率是怎樣算出來的?

　　提問者： 2007xinwei2007 - 經理 四級

　　視在功率=(有功功率的平方+無功功率的平方)開根號

　　有功功率=視在功率×功率因數

　　在本計算中 P有功=S視在×cosφ=542×0.8=433.6KW

　　Q無功=√(542×542-433.6×433.6)=325.2KVAR

　　或者根據cosφ求出sinφ 得出φ=37 sinφ=0.6

　　Q=S× sinφ=542×0.6=325.2KVAR

　　回答者：womyn5 - 千總 五級 7-3 17:59

　　這個有具體的數值，希望能夠更方便你理解