At present, the frequency conversion pump of pump industry or frequency conversion water supply equipment domain, in order to reduce the cost and consider the user's acceptance ability, basically is not to use specialized frequency conversion motor. But with the exception of the cooling fan, most of them have been modified. General such as industrial water, cooling water circulation, construction of secondary water supply, commercial buildings water supply, fire water supply, and other fields, the use of the modified ordinary three-phase asynchronous motor frequency conversion speed regulation operation is no problem. In fact, it's always been used that way. If your previous motor used for variable frequency speed regulation has frequent problems, it is likely to be a normal three-phase asynchronous motor without any modification. Now let's have a look at the common motor without any improvement in the variable frequency speed under the operation may occur what adverse phenomena:
1. Efficiency and temperature rise of the motor
Ordinary three-phase asynchronous motors operate in a 50Hz, standard sinusoidal cycle. Inverter in operation can produce different degree of harmonic voltage and current, make the motor run in non-sinusoidal voltage, power flow, which will cause a higher harmonic of motor rotor stator copper loss, copper loss, iron loss, and additional loss increases, the more significant is the rotor copper loss, the loss will make motor extra heat, low efficiency, output power decreases, and common motor temperature rise will increase 10% to 20%.
2. The insulation strength of the motor is tested
Frequency converter carrier frequency from thousands to tens of KHZ, so that the stator windings of the motor to withstand a very high rate of voltage rise, equivalent to the motor to apply a very steep impulse voltage so that the motor turn insulation bears a more serious test.
3. Harmonic electromagnetic noise and vibration
The vibration and noise caused by electromagnetic, mechanical, ventilation, and other factors will become more complicated when ordinary motors are powered by a frequency converter. Various harmonics in the frequency conversion power supply interfere with the inherent space harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces, thus increasing the noise. Due to the wide operating frequency range and wide rotation speed range of the motor, it is difficult for the frequencies of various electromagnetic waves to avoid the natural vibration frequency of each structural part of the motor.
4. Cooling problem at a low rotation speed.
As we know, the fan of the ordinary three-phase asynchronous motor rotates with the spindle. When the motor is regulated to slow down the running speed, the motor fan also slows down. If it works in the low-frequency range for a long time, the electric machine will face serious heat dissipation problems. This is also the general three-phase induction motor used as frequency control of the main problem. Especially most of the time when working in low frequency must choose a special frequency conversion motor or heat dissipation system to be improved, otherwise, the motor winding insulation is easy to breakdown and burn out the winding.
We currently used for variable frequency drive motor pump industry, basic it is for item 1, 2, 3, and improved the design of the ordinary three-phase asynchronous motor, if not most of the work in the low-frequency range, commonly used for building water supply and drainage and industrial water supply, heat cooling during low speed running basic problem, without using the special frequency conversion motor or design of the cooling system.
