Power factor of the motor: indicates that this motor can input % of the energy in the power grid to the motor as the input power of the motor.
Motor efficiency = motor output power/motor input power; indicates the ability of the motor to convert electrical energy into mechanical energy.
Power factor is the ratio of active power to apparent power, and is one of the main performance indicators of asynchronous motors. From the equivalent circuit, the asynchronous motor is an inductive circuit and must absorb inductive reactive power from the power grid, and its power factor is always less than 1.
The power factor of the motor refers to the ratio of the active power absorbed by the motor from the power grid to the apparent power. For the motor, the power factor can be understood as the ratio of the active current component in the stator current to the total stator current. The higher the power factor, the more useful work the motor does and the higher the utilization rate of the power supply.
1. Both power factor and efficiency are key indicators for reliable and economical operation of motor products. Customers hope that the larger the power factor, the better in order to save electricity or electricity bills.
2. The power factor considers the ability of motor products to convert the absorbed grid energy into useful work, which directly affects the utilization level of grid energy and the grid operation cost. For this reason, the state strictly controls the power factor of electrical equipment and has strict power factor assessment regulations in the technical conditions of continuous duty motors.
3. Motor efficiency reflects the ability of the motor body to convert the absorbed active power into mechanical power on the output shaft. GB18613, GB30253, and GB30254 respectively set limit control requirements for the efficiency of large-scale and wide-ranging motor products, and encourage enterprises to develop and produce high-efficiency motors through some policy inclinations.
4. The expression of power factor and efficiency is different. Although both are ratio relationships, the power factor uses a direct ratio, while efficiency is expressed in percentages.
The efficiency and power factor of the motor are mutually constrained. For motors with the same power and rated current, if the efficiency is high, the power factor is low; conversely, if the efficiency is low, the power factor is high.
The power factor has no effect on the end users of the motor, but it is of greatest concern to the power supply department because if there are too many customers with too low power factor, the grid loss will increase and the transmission efficiency will decrease; therefore, for AC induction motors, both the efficiency index and the power factor index are required to be high.
In an AC circuit, the cosine of the phase difference (Φ) between voltage and current is called the power factor, which is represented by the symbol cosΦ. In terms of numerical value, the power factor is the ratio of active power to apparent power, that is, cosΦ=P/S. The size of the power factor is related to the load nature of the circuit. For example, the power factor of a resistive load such as an incandescent bulb or a resistance furnace is 1. Generally, the power factor of a circuit with an inductive or capacitive load is less than 1. The power factor is an important technical data of the power system. The power factor is a coefficient that measures the efficiency of electrical equipment. A low power factor indicates that the reactive power used by the circuit for alternating magnetic field conversion is large, thereby reducing the utilization rate of the equipment and increasing the line power supply loss. Therefore, the power supply department has certain standard requirements for the power factor of power users.
1. The most basic analysis. For example, the power of the equipment is 100 units, that is, 100 units of power are delivered to the equipment. However, due to the inherent reactive power loss of most electrical systems, only 70 units of power can be used. Although only 70 units are used, 100 units of fees must be paid. In this example, the power factor is 0.7 (if the power factor of most equipment is less than 0.9, a fine will be imposed). This reactive power loss mainly exists in motor equipment (such as blowers, pumps, compressors, etc.), also known as inductive loads. Power factor is a measure of motor efficiency.
2. Basic analysis. Every motor system consumes two major powers, namely real useful power (called kilowatts) and reactive useless power. Power factor is the ratio between useful power and total power. The higher the power factor, the higher the ratio between useful power and total power, and the more efficient the system operation.
3. Advanced analysis. In an inductive load circuit, the peak of the current waveform occurs after the peak of the voltage waveform. The separation of the two waveform peaks can be expressed by the power factor. The lower the power factor, the greater the separation between the two waveform peaks.
The power loads in the power grid, such as motors, transformers, fluorescent lamps and arc furnaces, are mostly inductive loads. These inductive devices need to absorb not only active power from the power system during operation, but also reactive power. Therefore, after installing parallel capacitor reactive power compensation equipment in the power grid, it will be able to provide compensation for the reactive power consumed by the inductive load, reducing the reactive power provided by the inductive load on the power supply side of the power grid and transmitted by the line. Since the flow of reactive power in the power grid is reduced, the energy loss caused by the transmission of reactive power by transformers and buses in the transmission and distribution lines can be reduced. This is the benefit of reactive power compensation.
The main purpose of reactive power compensation is to improve the power factor of the compensation system. Because the power generated by the power supply bureau is calculated in KVA or MVA, but the charge is in KW, that is, the actual useful work done. There is a difference in reactive power between the two, generally speaking, it is reactive power in KVAR. Most of the reactive power is inductive, that is, the so-called motors, transformers, and fluorescent lamps. Almost all the reactive power is inductive, and capacitive is very rare. It is because of the existence of this inductance that a KVAR value is created in the system. The relationship between the three is a trigonometric function:
KVA squared = KW squared + KVAR squared
Simply speaking, in the above formula, if today's KVAR value is zero, KVA will be equal to KW, then 1KVA of electricity issued by the power supply bureau is equal to 1KW of user consumption, and the cost-effectiveness is the highest at this time, so the power factor is a coefficient that the power supply bureau cares about very much. If the user does not achieve the ideal power factor, it is relatively consuming the resources of the power supply bureau, so this is why the power factor is a regulatory restriction. At present, the power factor regulations in China must be between 0.9 and 1 of the inductance. If it is lower than 0.9 or higher than 1.0, it will be punished. This is why we must control the power factor within a very precise range, too much or too little is not acceptable.
refers to the data under which the motor is in the best working state.
The rated voltage is fixed, with an allowable deviation of 10%. The actual power and actual current of the motor vary with the size of the dragged load; the larger the dragged load, the larger the actual power and actual current; the smaller the dragged load, the smaller the actual power and actual current.
If the actual power and actual current are greater than the rated power and rated current, the motor will overheat and burn; if the actual power and actual current are less than the rated power and rated current, it will cause material waste.
Rated power = rated current IN*rated voltage UN*root 3*power factor
Actual power = actual current IN*actual voltage UN*root 3*power factor