The difference and connection between the active power and the rated power of the three-phase asynchronous motor:
The rated power is the mechanical power output of the motor running at the rated point.
Rated power = sqrt (3) * rated voltage * rated current * power factor * efficiency. This refers specifically to the rated point.
Apparent power = sqrt(3) * voltage * current.
Active power = sqrt (3) * voltage * current * power factor, this active power is the electrical power input of the motor, which is different from the apparent power is caused by the intersection difference of AC voltage and current, or caused by the inductance of the energy storage element in the motor.
Efficiency is a completely different concept caused by the copper loss, iron loss and mechanical loss of the stator and rotor in the motor. There is no power loss in reactive power, but there is energy stored in the energy storage element in the form of a magnetic field, which is not transmitted to the mechanical power output, and the loss of efficiency is all converted into heat energy, which will cause the temperature rise of the motor.
The motor absorbs electrical energy from the power grid through the provisions of the law of electromagnetic induction, and becomes the rotor of the motor to rotate, driving the load machinery to do work, so that the electrical energy is converted into mechanical energy.
The energy output of the motor is the rated power of the motor.
When the motor is running, many losses such as coil heating and bearing friction are motor losses.
Add up the rated power and all the losses to the active power that the motor absorbs from the grid.
The conversion of electric energy into mechanical energy by the motor is inseparable from the magnetic field, the establishment of the magnetic field is formed by the electrification of the motor coil, then the formation of the magnetic field also requires energy, this part of the energy is not converted into mechanical energy and thermal energy, equivalent to the medium, this part of the energy is the reactive power of the motor.
Active power Reactive power Apparent power, note: This is a vector addition.
Efficiency Rated Power Active Power 100 is always less than 1
1. The concepts of active power, reactive power, apparent power, power factor and peak factor.
1.Active power: Energy that can be converted into other forms of energy (heat, light, kinetic energy). It is expressed in p and the unit is w. In general, active power is relative to a purely resistive load.
2.Reactive power: The power that is transmitted from the energy source to the load and can reflect the power exchange is reactive power. It is expressed in q and is expressed in var. It arises due to inductive loads, capacitive loads, and distortions of voltage and current. This power can result in additional current loss.
3.Apparent power: The geometric sum of active and reactive power (i.e., the root mean square of the sum of squares), which is used to express the capacity of an electrical device. It is expressed in s and is in va.
4.Power factor: The phase difference between the sinusoidal AC voltage and the current is called the power factor angle, so it is expressed, there is no unit, and the cosine value of this power factor angle is called the power factor. It is determined by the parameters of the circuit elements and the operating frequency, the power factor of the pure resistive circuit is 1, and the power factor of the pure inductor capacitor circuit is 0. Power factor cosine = p s.
5.Crest factor: As shown in the figure on the right, the blue sine wave is the voltage waveform and the red is the current waveform. The crest factor is the ratio of the peak value of the instantaneous value of the current to its RMS. It is used to describe an inrush current. If the peak factor of the power supply equipment is higher, it indicates that the equipment is more resistant to shock.
Active power: in AC circuits. The average amount of instantaneous power (or power consumed by the load resistance) emitted by a power supply over a cycle. It is called "active power". Reactive power: In circuits with inductors or capacitors. In each half cycle. The energy of the power supply is stored as magnetic (or electric field) energy. And then. Re-release. The stored magnetic field (or electric field) energy is then returned to the power supply. Just do this exchange of energy. And it doesn't really consume energy. Let's swap this for the power value. It is called " reactive power". Apparent power: In an AC circuit with impedance. The product of the rms voltage and the rms current. This is called "apparent power". It is not an average of the actual work done. Nor is it the maximum rate at which energy is exchanged. It is only an easier way to design and calculate electrical equipment in the motor or electrical equipment.
Relationship: the square of the apparent power = the square of the active power + the square of the reactive power The apparent power s=ui or s=p cos and the capacity of the transformer is also s=ui thus. The rated capacity of the transformer is equal to the rated apparent power. Or that the two are equivalent. If the rated capacity is 100kvaThen the rated apparent power is also 1000kva
1. Active power: the electrical power required to maintain the normal operation of electrical equipment, that is, the electrical power required to directly convert electrical energy into other forms of energy. In alternating current, the active power is expressed as: p=uicos p represents the active power unit: watts (w) kilowatts (kw) megawatts (mw) u represents voltage, i represents current, cos represents power factor.
2. Reactive power: It is used for the exchange of electric field and magnetic field inside the circuit, and is used to establish the electrical power required to maintain the magnetic field. It does not do external work, but only converts energy inside the circuit. Reactive power is expressed by q Unit: Lack (var) Thousand Lack (kvar) All electrical equipment that has an electromagnetic coil and needs to establish and maintain a magnetic field must have reactive power. For example, a 40 watt fluorescent lamp requires 40 watts of active power and 80 watts of var reactive power to establish and maintain the electromagnetic sound field.
3. Apparent power: that is, the total power on the circuit. Expressed in S, the unit: volt-ampere (va) kilovolt-ampere (kva), which is the product of voltage and current in alternating current: s=ui4, power factor: cos is a coefficient to measure the efficiency of electrical equipment. 0 ≤ cosφ ≤1 。is a ratio of active power to apparent power. cos φ =p/s 。Represents the phase difference (phase angle) between voltage and current. The magnitude of the COS value is related to the nature of the load on the electrical equipment.
1) Pure resistance electrical equipment, because it directly consumes power to convert electrical energy into heat energy, there is no phase difference, =0 cos =1 so p=s resistive electrical appliances only consume active power.
2) The phase difference (phase angle) of inductive electrical appliances (electrical appliances with inductance coils) 0 ° 90 ° Capacitive electrical appliances (electrical appliances with capacitance) -90 ° 0 ° The relationship between apparent power, active power, reactive power and power factor (as shown in Figure 1): s 2 =q 2 +p 2cos =p s Conclusion: If the power factor is improved, the output of reactive power on the line is reduced, and the apparent power is reduced, the electric energy is saved, and the apparent power current is reduced.
5. The principle of reactive power compensation: the harm of excessive reactive power
1) Reduce the output of active power of power generation equipment.
2) Reduce the power supply capacity of wire equipment.
3) Cause the increase of voltage loss and power loss on the line.
4) Cause the electrical equipment to operate inefficiently at low power, and the voltage drops and even cannot work normally. Adopt artificial methods to set up reactive power compensation devices to ensure the reactive power required by electrical equipment and reduce the reactive power provided on the line. Reactive power compensation is to connect a device with capacitive power and an inductive power load in parallel on the same line.
6. Method of reactive power compensation:
1) Centralized compensation: the method of compensating all electrical equipment by centralizing the capacitive power load device.
2) Local compensation: for a single electrical equipment Our power saver is to use the principle of reactive power compensation to compensate for a single or local electrical equipment on the spot, improve the power factor of electrical equipment, reduce the reactive power provided by the line, so as to reduce the active power loss caused by the apparent power current caused by reactive power, and achieve the purpose of saving electricity.