In the industrial and mining enterprises abundantly is using fan, water pump, mixer, compressor to wait, these machine are average with AC motor drive. Among them major electromotor all is not the job in rated power, and the 50% ～ that often have rated power only 70% , a few lower even (20% ～ 70%) . But electromotor runs state at constant speed for the most part, undertake the adjustment of discharge or pressure with plate washer, valve or the way that put empty circumfluence, thereby for nothing the electric energy with much loss, power jumps over big fan, water pump, losing electric energy is more.

To water pump and fan, convey its characteristic parameter to have: Condyle? wind force) Q, lift (wind pressure) H, power P. Turn into from N1 when rotate speed when N2, q, h, p changes roughly the relation is:

Q2=Q1(n2 / N1)

H2=H1(n2 / N1)2

P2=P1(n2 / N1)3

Namely: Couple of  of condyle hole Guang burns the square of  ? lift and rotate speed to become direct ratio, the cubic metre of axial power and rotate speed becomes direct ratio.

The wind force of the discharge that is like water pump or fan adjust, need to adjust only the rotate speed of electric machinery can come true, and consume what reduce electric machinery greatly power at the same time, managing electric energy.

According to the fundamental that electrician learns, the rotate speed N of electromotor expresses by the following formula:

In type: N---The rotate speed of electromotor

F1---Power supply source | Manostat frequency

S---Turn poor rate

P---Of electromotor extremely logarithm

Because this wants to change the rotate speed of electromotor, should change the frequency of power supply source to perhaps change electromotor only extremely logarithm perhaps turns the rotate speed that poor rate can change electromotor.

Change pole logarithm undertakes timing from theoretic stress efficiency highest, because it does not have additional loss, but tall to the production requirement of electromotor, rigid structure is relatively complex, and belong to timing having class, not agile, use lesser accordingly. The change turns poor rate, ever had used slippery poor electric machinery before, but as a result of electric machinery structure complex, fault rate is higher, maintenance is difficult, also use rarely now. Change frequency undertakes timing, can achieve stepless speed regulation, in 20 centuries 80 time initial stage is used in our country not much still, the reason is the limitation of itself of frequency conversion device, reach the rapid development of IGBT power parts of an apparatus as microelectronics technology later, frequency control technology also got unprecedented development, press at present technical level, not only timing precision was achieved very tall, and loss can decrease the smallest (transducer efficiency can be as high as 99%) . Frequency control can apply in the electromotor of all sorts of norms now.
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