The use of AC contactors and inverters can improve the efficiency of motors, and when I saw this statement, I was not only a little dumbfounded, do you believe this is true? I don't believe it anyway! According to Yifan's more than 20 years of experience in inverter, servo and inverter and servo harmonic control, if the inverter can improve the efficiency of the motor, this possibility exists, but there is absolutely no AC contactor in it, what do you think?
Can an AC contactor change motor efficiency? This also needs to start from the working principle and function of the AC contactor. Let's talk about the working principle of the AC contactor first, when the AC contactor coil is energized, the coil current will produce a magnetic field, which makes the static iron core produce enough electromagnetic attraction to attract the moving core, and drive the contact action of the AC contactor, the normally open contact is engaged, and the normally closed contact is disconnected, and the two are linked; When the coil of the AC contactor is de-energized, the electromagnetic attraction of the static iron core disappears, and the armature is released under the action of the release spring, so that the contact of the AC contactor is restored, the normally open contact is disconnected, and the normally closed contact is closed.
After talking about the working principle of the AC contactor, let's talk about the role of the AC contactor. The function of the AC contactor is actually very simple, and it can be explained in one sentence, that is, it can be used as an actuator to turn on or off the line.
According to the formula for calculating the rated current of the three-phase motor: p 1732 u i cos, in order to change the input power of the motor, you need to change the voltage, current or power factor of the three-phase motor, and the AC contactor can only be used for the on-off of the line, that is, the AC contactor can not change the current on the input side of the motor, nor can it change the voltage on the input side of the motor, let alone change the power factor on the input side of the motor, that is, the AC contactor can not change the power on the input side of the motor at all.
According to the formula for calculating the efficiency of the motor: =(P2 P1) 100% (where P2 is the output power of the motor and P1 is the input power of the motor). Since the AC contactor cannot change the input power of the motor, it is even more impossible to change the output power of the motor, from this, we can conclude that:It is simply not possible for an AC contactor to change the efficiency of a motor
Can a frequency converter change the efficiency of a motor? Let's start with the working principle of the inverter. When the inverter works, it first converts the alternating current into direct current, and then combs and filters the direct current, and finally, the inverter converts the direct current after combing and filtering back to alternating current with controllable frequency.
According to the formula for calculating the speed of the motor: n=60f p (wherein, n is the speed, f is the frequency of the power supply, and p is the number of pole pairs of the motor), it can be concluded that the frequency converter can change the frequency of the power supply, that is, the speed of the motor can be changed.
According to the formula for calculating the motor power: p t n 9550 (where p is the motor power, t is the motor torque, n is the motor speed), it can be concluded that the inverter changes the motor speed at the same time, but also changes the power of the motor. At the same time, there is another very important conclusion, that is: in the case of the actual operating frequency of the inverter 50Hz, the input power of the motor increases with the increase of the actual operating frequency of the inverter, of course, the actual output power of the motor also increases with the increase of the actual operating frequency of the inverter.
Then according to the motor efficiency calculation formula: =(P2 P1) 100% (where P2 is the output power of the motor, P1 is the input power of the motor). In the case that no inverter is installed, the actual input power P1 of the motor has been a fixed value, but, after the installation of inverter, in the case of the actual operating frequency of inverter 50Hz, the actual input power P1 of the motor begins to change with the change of the output frequency of the inverter, and the actual power after the installation of inverter must be the actual power before the inverter is not installed (under the ideal condition of not considering various losses). At this point, we can easily draw a conclusion:When the inverter runs at a frequency of 50Hz, the inverter can effectively improve the efficiency of the motor.
In the case of the actual operating frequency of the inverter 50Hz, the efficiency of the motor can be effectively improved, but at the same time, the inverter will inevitably bring some damage, and the common injuries are:
1. Problems such as vibration, whine, and overheating of the motor.
I believe that many customers have already encountered, before the optional inverter, the motor is good, but after the optional inverter, the motor has undergone some changes, for example, the motor began to vibrate, whistling, abnormal noise, overheating and other problems emerged.
2. The motor bearing is broken.
Optional frequency converter, after a period of operation, when dismantling the motor, you will find that the motor bearing has pits, cracks, cracks and other problems, this phenomenon is relatively rare, but there have been customers to confirm to a fan, it is indeed actually possible.
3. The output shaft of the motor is overheated.
After the optional inverter, there will be problems such as overheating of the motor output shaft. Let's say Ichifan personally went to handle a customer who had a compressor. When there is no inverter, the output shaft of the motor is stable at about 70, but, after the optional inverter, the temperature of the motor output shaft easily exceeds 90, resulting in the compressor alarm, and can not work normally.
4. The insulation of the motor is frequently broken down.
After installing the inverter for a period of time, the motor is broken, and after finding a professional master who repairs the motor, or the motor manufacturer disassembles it, it is found that the insulation inside the motor has been broken down.
5. The life of the motor is significantly reduced.
In the case of not being driven by an inverter, the life of the motor may be 8 to 10 years, or even longer, but the motor driven by the inverter may only be used for a few months.
In general, the above problems can be solved by selecting the output filter of the inverter, the output reactor of the MLAD-VR-SC inverter, the DU DT filter, the sine wave filter, etc.