Furthermore, frequency converter is the mainstream at present.
Put the energy-saving project of motor system in a very important position. In fact, almost every one of the ten key energy-saving projects is related to motor energy saving, and motor is a kind of terminal energy-using equipment with * * *.
In view of the serious waste of electric energy in the current motor operation, the "Implementation Opinions" proposes to vigorously promote the frequency conversion speed regulation technology or permanent magnet speed regulation technology in electrical drives in various industries. This is absolutely correct. Because for variable load conditions, the motor can output the force required by the dragged equipment, thus truly achieving the purpose of energy saving.
However, in the industrial production process, many dragged loads are basically stable, and there is no need for speed regulation, and most working conditions are overloaded. At this time, for the motor, the main contradiction is how to solve the problem of starting with heavy load. Therefore, wound induction motors have been widely used at home and abroad. Its starting scheme is to connect the resistance in series on the winding circuit of the motor rotor through the slip ring brush cable. This is a very practical technical scheme. However, after the motor starts running, although the series resistance is short-circuited, the strong rotor induced current still flows in the slip-ring brush cable, which not only wastes electric energy, but also greatly reduces the reliability of the motor, which is the price paid for obtaining large starting torque. Can this starting scheme be completely negated, so as to save energy and reduce consumption and make the motor run reliably and safely for a long time? The answer is yes.
After years of repeated practice, we have developed a new type of motor-pole-changing start anti-slip wound rotor induction motor. The motor completely abandons the slip ring brush, cable and resistor on the rotor circuit (the appearance is exactly the same as that of the squirrel-cage motor), and adopts the technical scheme of direct starting with pole changing and full voltage. For example, when the motor runs at 6 poles (synchronous speed is 1000 rpm), it starts at 8 poles (synchronous speed is 750 rpm), and then the motor automatically switches to 6 poles for normal operation. The startup time is generally about 6 seconds.
After more than a year of industrial operation, the new motor has obvious energy-saving effect. Generally speaking, the energy saving rate of the towed equipment is 8%, the lowest is 5%, and the highest is over 10%. This is because different production sites have different energy-saving effects. If the resistance cabinet connected in series on the rotor of the original winding motor is far away from the motor (the cable is long), the energy-saving effect will be more obvious after replacing it with a new motor. But even if the resistance cabinet is more than ten meters away from the motor, the power saving effect can only be 5% after replacing the ordinary winding motor with a new motor. Under normal circumstances, users only need 1 year or so to recover their investment.
What is said here is only the energy saving of the motor itself. In fact, because the power factor of the new motor itself can reach 0.9 1, there is no need to add reactive power compensation devices (such as cameras). ) or add a fan to forcibly cool the slip ring. Only this can save about 10kwh/ hour (compared with 380kW motor).
Because the slip ring brush is removed, the new motor is actually a maintenance-free motor, which can run continuously and safely for a long time, just adding butter to maintain the bearings as usual.
So far, the new motor is very mature in both technology and manufacturing process. Slip-free wound rotor induction motors with capacity of 90 ~ 5000 kW can be manufactured, and new motors with voltage classes of 380V, 6000V and 10000V are put into industrial operation. Practice has proved that our new motor can completely replace the existing ordinary wound motors of various specifications, and the motors of the same specifications are completely interchangeable. It can be said that it is the replacement product of ordinary YR and JR series wound motors. If the new motor can be popularized and applied in all relevant units in the country, according to the most conservative 5% power saving rate, its annual power saving is also an astronomical figure. Among the ten key energy-saving projects, the electromechanical industry is required to develop and manufacture energy-saving motors. YBWR and JBWR series new rotor induction motors with pole-changing starting without slip ring should belong to this kind of energy-saving motors.
Whether the variable frequency governor can save electricity is determined by the speed regulation characteristics of its load. For centrifugal fans, centrifugal pumps and other loads, torque is directly proportional to the square of rotational speed, and power is directly proportional to the cube of rotational speed. As long as the valve is used to control the flow, and it is not working at full load, it can save electricity by changing the speed regulation. When the speed is reduced to 80%, the power is only 5 1.2%. It can be seen that the application of frequency conversion governor in this kind of load has the most obvious energy-saving effect. For roots blower and other loads, torque has nothing to do with speed, that is, constant torque load. If the original method of adjusting the air volume by releasing excess air volume through the bleeder valve is changed to speed regulation operation, power saving can also be realized. When the speed drops to 80%, the power is 80%. Compared with centrifugal fans and centrifugal pumps, the energy-saving effect is much smaller. For a constant power load, power is independent of speed. Constant power load of cement plant, such as batching belt scale, slows down the belt speed when the material layer is thick under the condition of set flow; When the material layer is thin, the belt speed increases. The application of frequency conversion governor in this kind of load can't save electricity.
In addition, the variable frequency governor has soft start function, which can reduce the high starting current when starting repeatedly and save energy. But it can't save energy for the equipment running continuously at full load.