Foreword

Efficiency and power factor are two different concepts. The efficiency of the motor refers to the ratio of the shaft output power of the motor to the power absorbed by the motor from the grid, and the power factor refers to the ratio of the active power of the motor to the apparent power. Low power factor will cause large reactive current and large line resistance voltage drop, resulting in low voltage. Active power increases due to increased line losses. The power factor is low, and the voltage and current are not synchronized; when there is reactive current flowing through the motor, the motor current increases, the temperature is high, and the torque is low, which increases the power loss of the grid.

Energy saving analysis of ultra-high efficiency permanent magnet motor

1. Comparison of energy saving effect

The three-level energy efficiency YX3 motor has higher efficiency and power factor than the traditional ordinary Y2 motor, and the permanent magnet synchronous motor has higher efficiency and power factor than the three-level energy efficiency YX3 motor, so the energy saving effect is better.

2. Example of energy saving

The input current of the permanent magnet motor with a nameplate power of 22 kW is 0.95, power factor 0.95 and Y2 motor efficiency 0.9, power factor 0.85 : I=P/1.73×380×cosφ·η=44A, the input of the permanent magnet motor Current: I=P/1.73×380×cosφ·η=37A, the current consumption difference is 19%

3. Apparent power analysis

Y2 motor P=1.732UI=29 kW permanent magnet motor P=1.732UI=24.3 kW power consumption difference is 19%

4. Part load energy consumption analysis

The efficiency of Y2 motors drops seriously below 80% load, and the power factor drops seriously. Permanent magnet motors basically maintain high efficiency and power factor between 20% and 120% loads. At partial loads, permanent magnet motors have Great energy saving advantages, even more than 50% energy saving

5. Consumption of useless work analysis

The reactive current of the Y2 motor is generally about 0.5 to 0.7 times the rated current, the power factor of the permanent magnet motor is close to 1, and no excitation current is needed, so the difference between the reactive current of the permanent magnet motor and the Y2 motor is about 50%.

6. Input motor voltage analysis

It is often detected that if the permanent magnet motor replaces the Y2 motor, the voltage will increase from 380V to 390V. Reason: The low power factor of the Y2 motor will cause a large reactive current, which in turn will cause a large voltage drop due to the line resistance, resulting in low voltage. The permanent magnet motor has a high power factor, consumes a low total current, and reduces the line voltage drop, resulting in a voltage rise.

7. Motor slip analysis

Asynchronous motors generally have a slip of 1% to 6%, and permanent magnet motors run synchronously with a slip of 0. Therefore, under the same conditions, the workmanship of permanent magnet motors is 1% to 6% higher than that of Y2 motors.

8. Motor self-loss analysis

22 kW Y2 motor has an efficiency of 90% and a self-loss of 10%. The self-loss of the motor is more than 20,000 kilowatts in one year of continuous uninterrupted operation; the efficiency of a permanent magnet motor is 95%, and its self-loss is 5%. About 10,000 kilowatts, the self-loss of Y2 motor is twice that of permanent magnet motor

9. Analysis of power factor national reward and punishment table

If the power factor of the Y2 motor is 0.85, 0.6% of the electricity fee will be charged; if the power factor is greater than 0.95, the electricity fee will be reduced by 3%. There is a 3.6% price difference in electricity charges for permanent magnet motors replacing Y2 motors, and the value of electricity for one year of continuous operation is 7,000 kilowatts

10. Analysis of the Law of Conservation of Energy

Power factor is the ratio of useful work to apparent power. Y2 motor has low power factor, poor absorption power utilization rate, and high energy consumption; permanent magnet motor has high power factor, good absorption utilization rate, and low energy consumption

11. National Energy Efficiency Label Analysis

Second-level energy efficiency of permanent magnet motor: the most energy-saving motor YX3 motor Level-three energy efficiency: ordinary Y2 motor is eliminated Motor: energy-consuming motor

12. From the analysis of national energy efficiency subsidies

The national subsidy for motors with second-level energy efficiency is much higher than that for third-level energy efficiency motors. The purpose is to save energy from the whole society, so as to ensure the country’s competitiveness in the world. From a global perspective, if permanent magnet motors are widely used, the power factor of the whole plant will be improved, with higher overall network voltage, higher machine efficiency, lower line loss, and lower line heat generation

The state stipulates that if the power factor is between 0.7-0.9, 0.5% will be charged for every 0.01 lower than 0.9, and 1% will be charged for every 0.01 lower than 0.7 between 0.65-0.7, and below 0.65, every lower than 0.65 If the user’s power factor is 0.6, then it is (0.9-0.7)/0.01 X0.5% + (0.7-0.65)/0.01 X1% + (0.65-0.6)/0.01X2%= 10%+5%+10%=25%

 

Specific principles

AC permanent magnet synchronous motor, the rotor has no slip, no electric excitation, and the rotor has no fundamental wave iron and copper loss. The rotor has a high power factor because the permanent magnet has its own magnetic field and does not require reactive excitation current. The reactive power is less, the stator current is greatly reduced, and the stator copper loss is greatly reduced. At the same time, since the pole arc coefficient of the rare earth permanent magnet motor is greater than that of the asynchronous motor, when the voltage and stator structure are constant, the average magnetic induction intensity of the motor is smaller than that of the asynchronous motor, and the iron loss is small. It can be seen that the rare earth permanent magnet synchronous motor saves energy by reducing its various losses, and is not affected by changes in working conditions, environment and other factors.

Characteristics of permanent magnet synchronous motor

1. High efficiency

The average power saving is more than 10%. The efficiency curve of the asynchronous Y2 motor generally drops rapidly at 60% of the rated load, and the efficiency is very low at light load. The efficiency curve of the permanent magnet motor is high and flat, and it is at a high level at 20% to 120% of the rated load. efficiency zone. According to on-site measurements by multiple manufacturers under different working conditions, the power saving rate of permanent magnet synchronous motors is 10-40%.

2. High power factor

High power factor, close to 1: permanent magnet synchronous motor does not need reactive excitation current, so the power factor is almost 1 (even capacitive), the power factor curve and efficiency curve are high and flat, the power factor is high, the stator current is small, and the stator copper loss is reduced ,Improve efficiency. The factory power grid can reduce or even cancel capacitor reactive power compensation. At the same time, the reactive power compensation of the permanent magnet motor is real-time on-site compensation, which makes the power factor of the factory more stable, which is very beneficial to the normal operation of other equipment, reduces the reactive power loss of cable transmission in the factory, and achieves the effect of comprehensive energy saving.

3. The motor current is small

After the permanent magnet motor is adopted, the motor current decreases significantly. Compared with the Y2 motor, the permanent magnet motor has a significantly reduced motor current through actual measurement.  The permanent magnet motor does not require reactive excitation current, and the motor current is greatly reduced. The loss in cable transmission is reduced, which is equivalent to expanding the capacity of the cable, and more motors can be installed on the transmission cable.

4. No slip in operation, stable speed

The permanent magnet motor is a synchronous motor. The speed of the motor is only related to the frequency of the power supply. When the 2-pole motor works under a 50Hz power supply, the speed is strictly stable at 3000r/min. No lost rotation, no slip, not affected by voltage fluctuation and load size.

5. The temperature rise is 15-20℃ lower

Compared with the Y2 motor, the resistance loss of the permanent magnet motor is small, the total loss is greatly reduced, and the temperature rise of the motor is reduced. According to the actual measurement, under the same conditions, the working temperature of the permanent magnet motor is 15-20°C lower than that of the Y2 motor.

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Post time: Apr-18-2023