Abstract: When an ordinary motor is upgraded and replaced with a high efficiency motor, there is a problem of high current in the total operation, for which the motor needs to be completely replaced, and the power consumption increases. In this paper, we analyse the reasons for the high current of high efficiency motors and the power consumption of the motors, and compare the power consumption of the motors with the actual current values in order to derive the current components of the motors.
Keywords: high efficiency motors; no-load current; load current
Introduction
1 High efficiency motor design
Energy efficient motors are motors that add high efficiency to traditional motors. High efficiency motors use new processes and materials to reduce the consumption of mechanical, electromagnetic and thermal energy and increase the actual output efficiency. In comparison with ordinary motors, the use of high-efficiency motors has a significant energy saving effect, generally increasing efficiency by up to 4%. The actual conversion of electrical energy in motors results in the formation of mechanical energy, which results in the loss of some of the energy. Compared with ordinary motors, university motors have been designed with great adjustments, mainly to reduce the amount of these five losses, and the actual efficiency of the motor is greatly improved. The following is a specific analysis.
1.1 Stator losses The stator is made up of two components, the stator core and the stator coil. The stator core is a key component in the magnetic flux circuit of the motor. In contrast to ordinary motors, high-efficiency motors use silicon steel sheets with good magnetic conductivity and reduce the thickness of the sheets considerably. As a result, stator cores made from cold-rolled silicon steel sheets have very low induction current losses. In the design and manufacture of the stator coils, the wire used in high-efficiency motors is a relatively thick, better insulated wire, which also increases the stator slots, while at the same time the length of the stator winding ends is greatly reduced in order to reduce the end losses.
1.2 Rotor losses The rotor losses are the same as the stator losses and for this reason high efficiency motors need to minimise rotor losses.
1.3 Iron losses High efficiency motors reduce the iron loss considerably by using the following forms: 1. cold rolled silicon steel sheets with good magnetic permeability; 2. the length of the core so that the flux density is greatly reduced; 3. the use of effective iron chips.
1.4 Stray losses Stray losses, high-efficiency motors have the following kinds: 1, the length of the air gap needs to be increased; 2, reduce the length of the end of the coil; 3, for the rotor slot to strengthen the surface insulation; 4, the rotor slot in the design of harmonics to reduce.
1.5 Wind friction High-efficiency motors to reduce wind wear, mainly in two ways: 1, to reduce the friction of high-efficiency bearings and lubricants; 2, the loss of wind resistance can use small fan blades.
2 Motor running current analysis For the motor running current to take the analysis, need to ordinary motor and high efficiency motor of the actual running current to take the analysis and comparison.
2.1 No-load current The no-load current of a motor is mainly determined by the flux density and the length of the air gap between the stator and rotor, where a low flux density will result in a smaller air gap length and the no-load current of the motor will be reduced. Normally, the air gap length of a motor is relatively small, usually a few millimetres. For this reason, the main magnetic flux passes through the circuit, where the length of the air gap is a small percentage of the length of the entire magnetic circuit. Because the permeability of the silicon steel sheet is greater than the permeability in the air, for this reason, the no-load current of the motor, where the density of the magnetic flux is influencing the length of the air gap.
2.1.1 Flux density aspects High efficiency motors need to increase the length of the core, then the magnetic permeability needs to choose cold-rolled silicon steel sheet, for this reason, high efficiency motors in the flux density will become smaller, and the ordinary motor no-load electricity popular comparison, high efficiency motors no-load current will become smaller.
2.1.2 Air gap length For the motor small power specifications, due to stray dissipation loss will seriously affect the actual efficiency of the motor, for this reason, high efficiency motor in the design process, it is necessary to control the length of the air gap, because the motor parameters are air gap caused by, therefore, the small power motor for comparison, in the air gap length to target the actual role of no-load current can be ignored.
For high-power motors, the efficiency of the motor will be affected by additional losses, so the length of the air gap needs to be chosen to be larger than normal in the design of high-efficiency motors. In the case of high power motors, the length of the air gap of the high efficiency motor increases, so that the no-load current of the high efficiency motor increases and the power is very low compared to that of an ordinary one.
2.1.3 Comprehensive analysis In the case of small power motors, it is usually due to the insufficient length of the air gap that the flux density becomes smaller, so that the actual no-load current of a high-efficiency motor is small compared to that of a normal motor. For high power motors, although the flux density of high efficiency motors has changed significantly, the air gap length of high efficiency motors has increased, resulting in the flux density causing the air gap length to be affected, and the no-load current of high efficiency motors will then increase.
2.2 Load current The formula for calculating the output shaft power of a motor: Depending on the operating conditions, e.g. voltage, temperature and output power, the voltage and output shaft power are a constant in the actual operating motor, and for this reason K is also a constant. When comparing the current of a high-power motor with that of an ordinary motor under the same conditions, the operating current of a high-efficiency motor is determined by the difference between the motor's excitation current and the motor's efficiency. High power motors, and ordinary motor efficiency difference to take the analysis and comparison, high efficiency motor value is very small, so the same working conditions, and ordinary motor current value, high efficiency motor active current is very small, but no change. For this reason, in the actual operation of high-efficiency motors, the change in current is determined by the change in excitation current, but only in the operating current.
3 Analysis of the power consumption of the motor The power consumption of a motor consists of the sum of the shaft power output of the motor and the actual losses. The test is taken on the same belt, both are running at no load and the operating voltage is the same, therefore, the actual operating conditions of both motors are the same and the output shaft power is the same. Combined with the above calculation method, the power consumption of the common motor and the power consumption of the high efficiency motor can be accurately calculated.
3.1 The theoretical calculation of the ratio of power consumption between a high-efficiency motor and an ordinary motor is as follows: The formula for calculating the output shaft power of a motor:
3.3 Comparative analysis After the above calculation, it can be analysed that, compared with the ordinary motor power consumption, the power consumption of the high-efficiency motor 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 under load is the smallest at this time, but the actual measurement still has a certain error, the reason for the error is that after a long period of time, the ordinary motor in the loss of the motor will decline.
Conclusion In response to the analysis of the actual power consumption of the motor, it can be concluded that the change of parameters in the design of the two motors will cause changes in the ordinary motor and the high efficiency motor, take a comparison can be analysed that the ratio of the actual operating current and the power consumption of the motor does not exist in connection eh, the main is the motor active current component. For the motor current to take the analysis, high efficiency motors in the actual operating current is often greater than the ordinary motor, and the ordinary motor, high efficiency motor active current is obviously lower, in the same working conditions, ordinary motor and high efficiency motor power consumption compared to the high efficiency motor to significantly lower.
