《有功功率和无功功率》教学反思

这是《有功功率和无功功率》教学反思，是优秀的物理教案文章，供老师家长们参考学习。

　　有功功率/无功功率Active power/reactive power 在交流电路中，由电源供给负载的电功率有两种;一种是有功功率，一种是无功功率。

　　有功功率和无功功率

　　有功功率是保持用电设备正常运行所需的电功率，也就是将电能转换为其他形式能量(机械能、光能、热能)的电功率。比如：5.5千瓦的电动机就是把5.5千瓦的电能转换为机械能，带动水泵抽水或脱粒机脱粒;各种照明设备将电能转换为光能，供人们生活和工作照明。有功功率的符号用P表示，单位有瓦(W)、千瓦(kW)、兆瓦(MW)。

　　无功功率比较抽象，它是用于电路内电场与磁场的交换，并用来在电气设备中建立和维持磁场的电功率。它不对外作功，而是转变为其他形式的能量。凡是有电磁线圈的电气设备，要建立磁场，就要消耗无功功率。比如40瓦的日光灯，除需40多瓦有功功率(镇流器也需消耗一部分有功功率)来发光外，还需80乏左右的无功功率供镇流器的线圈建立交变磁场用。由于它不对外做功，才被称之为“无功”。无功功率的符号用Q表示，单位为乏(Var)或千乏(kVar)。

　　无功功率决不是无用功率，它的用处很大。电动机需要建立和维持旋转磁场，使转子转动，从而带动机械运动，电动机的转子磁场就是靠从电源取得无功功率建立的。变压器也同样需要无功功率，才能使变压器的一次线圈产生磁场，在二次线圈感应出电压。因此，没有无功功率，电动机就不会转动，变压器也不能变压，交流接触器不会吸合。为了形象地说明这个问题，现举一个例子：农村修水利需要开挖土方运土，运土时用竹筐装满土，挑走的土好比是有功功率，挑空竹筐就好比是无功功率，竹筐并不是没用，没有竹筐泥土怎么运到堤上呢?

　　在正常情况下，用电设备不但要从电源取得有功功率，同时还需要从电源取得无功功率。如果电网中的无功功率供不应求，用电设备就没有足够的无功功率来建立正常的电磁场，那么，这些用电设备就不能维持在额定情况下工作，用电设备的端电压就要下降，从而影响用电设备的正常运行。 无功功率对供、用电产生一定的不良影响，主要表现在：

　　(1)降低发电机有功功率的输出。

　　(2)降低输、变电设备的供电能力。

　　(3)造成线路电压损失增大和电能损耗的增加。

　　(4)造成低功率因数运行和电压下降，使电气设备容量得不到充分发挥。

　　从发电机和高压输电线供给的无功功率，远远满足不了负荷的需要，所以在电网中要设置一些无功补偿装置来补充无功功率，以保证用户对无功功率的需要，这样用电设备才能在额定电压下工作。这就是电网需要装设无功补偿装置的道理。

　　电压电流同相位，电源向负载供电，负载把电能转换成其他能量，叫有功。

　　电压电流不同相位部分，电源与负载之间交换电能，这部分(除线路损耗外)电能不转换(电磁以外的)成其他能量，叫无功。 有功功率

　　有功功率是保持用电设备正常运行所需的电功率，也就是将电能转换为其他形式能量(机械能、光能、热能)的电功率。比如：5.5千瓦的电动机就是把5.5千瓦的电能转换为机械能，带动水泵抽水或脱粒机脱粒;各种照明设备将电能转换为光能，供人们生活和工作照明。有功功率的符号用P表示，单位有瓦(W)、千瓦(kW)、兆瓦(MW)。定义：有功功率:在交流电路中，电源在一个周期内发出瞬时功率的平均值(或负载电阻所消耗的功率)，称为"有功功率"。

　　有功功率过低导致线损增加、容量下降、设备使用率下降，从而导致电能浪费加大。

　　无功功率

　　电网中的感性负载(如电机，扼流圈，变压器，感应式加热器及电焊机等)都会产生不同程度的电滞，即所谓的电感。

　　感性负载具有这样一种特性 -----即使所加电压改变方向，感性负载的这种滞后仍能将电流的方向(如正向)保持一段时间。一旦存在了这种电流与电压之间的相位差，就会产生负功率，并被反馈到电网中。电流电压再次相位相同时，又需要相同大小的电能在感性负载中建立磁场，这种磁场反向电能就被称作无功功率。

　　定义：在具有电感或电容的电路中，在每半个周期内，把电源能量变成磁场(或电场)能量贮存起来，然后，再释放，又把贮存的磁场(或电场)能量再返回给电源，只是进行这种能量的交换，并没有真正消耗能量，我们把这个交换的功率值，称为" 无功功率"。

　　无功功率比较抽象，它是用于电路内电场与磁场的交换，并用来在电气设备中建立和维持磁场的电功率。它不对外作功，而是转变为其他

　　形式的能量。凡是有电磁线圈的电气设备，要建立磁场，就要消耗无功功率。比如40瓦的日光灯，除需40多瓦有功功率(镇流器也需消耗一部分有功功率)来发光外，还需80乏左右的无功功率供镇流器的线圈建立交变磁场用。由于它不对外做功，才被称之为“无功”。无功功率的符号用Q表示，单位为乏(Var)或千乏(kVar)。

　　无功功率过高的缺点 ：

　　1)无功功率会导致电流增大和视在功率增加，导致系统容量下降;

　　2)无功功率增加，会使总电流增加，从而使设备和线路的损耗增加;

　　3)使线路的压降增大，冲击性无功负载还会使电压剧烈波动。

　　配电网中的电感性电气设备如变压器、电动机、电焊机、空调器、洗衣机、电冰箱、钠灯、日光灯等投入运行后，不仅要从电力网中吸收有功功率用于做功，而且还要吸收无功功率建立磁场，这样就导致电力客户的自然功率因数一般都比较低。我国对电力客户的用电，规定了必须达到的功率因数标准。

　　有功可以直接测量;有功与无功混在一起，无法直接区分开来，可以通过功率因数表测量。

　　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 什么叫功率因数?

　　在电路由感性或让性能源存储设备,电压和电流有相位差,流行讲就是电压和电流不相同的时间;

　　因此,表面看电压、电流大小如何,实际的和没有做那么大的工作,有权力和能源存储设备的能源转换;所谓的装机功率。目前,电力有源+无功功率。

　　的意思是,无论有功功率和无功功率是多少,只能输出电压和电流太大。

　　是有功功率和无功功率适量,因为有功功率和无功功率成90度角,用铁钩电力变压器容量安装power称,单位是current-voltage(VA)。

　　功率因数计算公式。有功功率与视在功率之比

　　如果你家里的“感性负载的“更重要的是,如汽车、微波炉……用电器,比如更,吸收的'反应将会更多,和功率因数小,电力部门是小(无功功率不消费,只是从电网到你的家庭电器在吸收)

　　对于企业,供电部门有监管权力的数值,高于彩票,下面的惩罚。哈哈。

　　相当复杂,其中涉及到安全的电力,电压……当然,包括变电站设备投资和投入运行的可靠性、安全性和成本。而电力可以访问为测量。

　　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. 什么叫视在功率?

　　在交流电路中，由于有感性或容性储能设备，电压与电流有相位差，通俗讲就是电压与电流不在同一时间到达;因此，表面看电压有多大、电流有多大，实际并没有做那么大的功，有电源与储能设备的能量转换; 所以称为视在功率。既，有功功率+无功功率。

　　电力变压器就用视在功率表示容量，单位为伏安(VA)。

　　意思是不管有功功率与无功功率是多少，只能输出这么大的电压与电流。 视在功率:在具有阻抗的交流电路中，电压有效值与电流有效值的乘积值，称为"视在功率"，它不是实际做功的平均值，也不是交换能量的最大速率，只是在电机或电气设备设计计算较简便的方法。

　　关系:视在功率的平方=有功功率的平方+无功功率的平方

　　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有功功率和无功功率 simple method. Relationships: installed power square = active power of square + reactive power square

　　如图所示，电源电压U=220V，频率50Hz，求电流I，I1和I2，及电路有功，无功，视在功率，和功率因数 Z1=10Ω Z2=5Ω，总电抗Z=10//5=10/3Ω

　　总电流I=U/Z=66A，I1=22A,I2=44A

　　有功功率P=I1?R1+I2?R2=2904+5808=8712W

　　视在功率S=UI=14520VA

　　无功功率Q=11616VAR

　　功率因数=P/S=0.6 有功功率、无功功率、视在功率三者之间的关系是怎样的?计算公式是?

　　容量620KW,功率因数0.8,视在功率542KVA,无功功率应该是多少?有公式吗?

　　悬赏分：0 - 离问题结束还有 5 天 22 小时

　　无功功率是怎样算出来的?

　　提问者： 2007xinwei2007 - 经理 四级

　　视在功率=(有功功率的平方+无功功率的平方)开根号

　　有功功率=视在功率×功率因数

　　在本计算中 P有功=S视在×cosφ=542×0.8=433.6KW

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

　　或者根据cosφ求出sinφ 得出φ=37 sinφ=0.6

　　Q=S× sinφ=542×0.6=325.2KVAR

　　回答者：womyn5 - 千总 五级 7-3 17:59

　　这个有具体的数值，希望能够更方便你理解