Upgrading a conventional motor to a high-efficiency motor can lead to an issue of excessive current during operation. This necessitates replacing the entire motor, which in turn increases power consumption. This article analyzes the reasons for the excessive current in high-efficiency motors and their power consumption, comparing the power consumption with the actual operating current to determine the motor's current components.
1. High-efficiency motor design
High-efficiency energy-saving motors are essentially traditional electric motors with added high efficiency. These motors utilize new processes and materials to reduce the consumption of mechanical, electromagnetic, and thermal energy, thereby increasing actual output efficiency. Compared to ordinary motors, high-efficiency motors offer more significant energy savings, typically increasing efficiency by up to 4%. During the actual conversion of electrical energy in an electric motor, mechanical energy is generated, resulting in energy loss. Electric motor losses occur in five ways: stator losses, stray losses, rotor losses, windage losses, and iron losses. Compared to ordinary motors, high-efficiency motors undergo significant design adjustments, primarily reducing these five losses and greatly improving actual efficiency. A detailed analysis follows.
1.1 Stator Loss
The stator consists of two parts: the stator core and the stator coils. The stator core is a crucial component in the motor's magnetic flux circuit. Compared to ordinary motors, high-efficiency motors use silicon steel sheets with excellent magnetic permeability, significantly reducing the thickness of the silicon steel sheets. Therefore, the stator core made of cold-rolled silicon steel sheets has very low induced current loss. In the design and manufacturing of the stator coils, high-efficiency motors use relatively thicker, better-insulated wires, which also increases the number of stator slots. At the same time, the length of the stator winding ends is greatly reduced, thus minimizing end losses.
1.2 Rotor Losses
Rotor losses operate on the same principle as stator losses; therefore, high-efficiency motors need to minimize rotor losses.
1.3 Iron Loss
High-efficiency motors significantly reduce iron losses by employing the following methods: 1. Using cold-rolled silicon steel sheets with good magnetic permeability; 2. The length of the iron core greatly reduces the magnetic flux density; 3. Using high-performance iron cores.
1.4 Stray Losses Stray losses in high-efficiency motors include the following: 1. Increasing the length of the air gap; 2. Reducing the length of the coil ends; 3. Strengthening the surface insulation of the rotor slots; 4. Reducing harmonics in the rotor slot design.
1.5 Wind friction loss
There are two main ways to reduce wind wear in high-efficiency motors: 1. Reduce friction in high-efficiency bearings and lubricants; 2. Use smaller fan blades to reduce wind resistance.
2. Analysis of motor operating current
To analyze the operating current of a motor, it is necessary to analyze and compare the actual operating currents of ordinary motors and high-efficiency motors.
2.1 No-load current
The no-load current of a motor is mainly determined by the magnetic flux density and the length of the air gap between the stator and rotor. A lower magnetic flux density will result in a shorter air gap, and thus a lower no-load current.
Typically, the air gap length of a motor is relatively small, usually only a few millimeters. Therefore, the main magnetic flux passes through the loop, and the length of the air gap becomes a small percentage, typically one percent of the total magnetic loop length. Because the permeability of silicon steel sheets is greater than that of air, the density of the magnetic flux, when considering the motor's no-load current, significantly affects the length of the air gap.
2.1.1 Regarding magnetic flux density
High-efficiency motors require increased core length, necessitating the use of cold-rolled silicon steel sheets for magnetic permeability. Consequently, the magnetic flux density of high-efficiency motors decreases, resulting in a smaller no-load current compared to ordinary motors.
2.1.2 Air gap length square
For low-power motors, stray losses can significantly affect the actual efficiency of the motor. Therefore, in the design of high-efficiency motors, the length of the air gap needs to be controlled. Since the parameters of the motor are determined by the air gap, the effect of the air gap length on the actual no-load current can be ignored when comparing low-power motors.
For high-power motors, efficiency is affected by additional losses. Therefore, in the design of high-efficiency motors, the air gap length needs to be larger than that of ordinary motors. With a longer air gap, high-efficiency motors, compared to ordinary motors, will have a higher no-load current and lower power output.
2.1.3 Comprehensive Analysis
For low-power motors, the magnetic flux density is usually reduced because the air gap is not long enough. Therefore, the actual no-load current of a high-efficiency motor is much smaller compared to that of an ordinary motor.
For high-power motors, although the magnetic flux density of high-efficiency motors changes significantly, the air gap length of high-efficiency motors will increase. As a result, the magnetic flux density will affect the air gap length, and the no-load current of high-efficiency motors will increase.
2.2 Load Current
Formula for calculating the output shaft power of a motor:
First, measure the line voltage and line current. Set the power factor to 0.85 and the mechanical efficiency to 0.85.
Output shaft power = √3 * line voltage * line current * power factor 0.85 * efficiency 0.85. This is the actual shaft power.
Solution: Measurement and selection of four parameters: line voltage and line current, power factor, and mechanical efficiency.
Depending on the operating conditions, such as voltage, temperature, and output power, in actual operation of a motor, voltage and output shaft power are constants, therefore K is also a constant.
Under the same operating conditions, when comparing the current of a high-power motor and an ordinary motor, the operating current of a high-efficiency motor is determined by the difference between the motor's excitation current and its efficiency.
The efficiency difference between high-power motors and ordinary motors is analyzed and compared. The efficiency values of high-efficiency motors are very small. Therefore, under the same operating conditions, the active current of a high-efficiency motor is much smaller than that of an ordinary motor, but it remains unchanged. Thus, in actual operation, the current variation of a high-efficiency motor is determined by the variation of the excitation current; however, this only applies to the operating current.
3. Power Consumption Analysis of the Motor
The power consumption of a motor consists of the sum of the motor's output shaft power and actual losses. Tests were conducted on the same motor running on the same belt under no-load conditions, with identical operating voltages. Therefore, the actual operating conditions of the two motors were identical, including the same output shaft power. Combining the above calculation methods, the power consumption of ordinary motors and high-efficiency motors can be accurately calculated.
3.1 The theoretical calculation of the power consumption ratio between high-efficiency motors and ordinary motors is as follows:
The input electrical power (apparent power) is √3 × U × I
The input power is =√3×U×I×cosφ
The shaft power of the motor is =√3×U×I×η×cosφ = 160KW
3.3 Comparative Analysis
Based on the above calculations, it can be analyzed that, compared with the power consumption of ordinary motors, the power consumption of high-efficiency motors is 97.15%, and the final measured actual data is 96.05%. Analyzing the two sets of data, it can be concluded that the power consumption of high-efficiency motors is the lowest under load. However, there is still a certain error in the actual measurement. The reason for the error is that the wear and tear of ordinary motors decreases after a long period of time.
Conclusion
Analyzing the actual power consumption of the motors reveals that variations in design parameters will affect the performance of both ordinary and high-efficiency motors. A comparison shows no direct correlation between the ratio of actual operating current and the motor's power consumption; the primary factor is the motor's active current component. Analyzing the motor current, high-efficiency motors typically have higher actual operating currents than ordinary motors. Compared to ordinary motors, high-efficiency motors have significantly lower active currents. Under identical operating conditions, the power consumption of high-efficiency motors is significantly lower than that of ordinary motors.
