Why is 50 hz, domestic motor instead of 60 hz?

by:J&T     2020-07-01
Motor is industrial production, the main electric rotating equipment of each equipment operation, domestic motor brand and use a lot of, so, do you know the why of the motor and other electrical equipment use is 50 hz alternating current (ac), rather than 60 hz? Some countries in the world, such as foreign use is 60 hz alternating current (ac), because the duodecimal, 12 constellations, 12 hours, 12 shilling to the pound, and so on. Later, the countries use the decimal, so frequency is 50 hz. So, why should we choose 50 hz alternating current (ac), rather than 5 hz or 400 hz? A, if the frequency is low? Low frequency is 0, that is, the dc. Also, under the current size of the human body resistance of ac dc time is longer than the tolerance time, related to ventricular fibrillation or something, also is an alternating current is more dangerous. The dc power is another problem is difficult to open circuit, until now the problem is still a problem. Dc transmission problem, like usual appliances pull bolt spark occurs, when the current is too big to a certain extent, the spark is unable to extinguish, we call & other; Arc & throughout; 。 For alternating current (ac), the current changes direction, it is current zero moment, use the small current point in time, we can through arc extinguishing device to cut off the line current. Dc current direction will not change, but don't have the zero point, we want the arcing is hard to. Second, the frequency of big? Such as set at 400 hz? Two problems, one is the line and equipment loss increase, the second is the generator speed too fast. 1, first loss, transmission lines, substation equipment, electrical equipment, are reactance, reactance is proportional to the frequency, the higher the frequency, the greater the reactance, the greater the consumption of reactive power, the less they can deliver the active power. The 50 hz transmission line reactance is about 0. 4 ohms, about 10 times that of resistance, if increased to 400 hz, the reactance is 3. 2 ohm resistance is about 80 times. For high voltage transmission lines, reduce reactance is the key to improve the transmission power. And corresponding reactance and capacitive reactance, capacitive reactance and is inversely proportional to the frequency, the higher the frequency, the smaller the capacitive reactance, the greater the leakage current of line. If the high frequency, the lines of the leakage current will increase. 2, another problem is that the speed of the generator. The generating set basic now is single stage machine, which is a pair of poles. In order to 50 hz power, rotor RPM to 3000 RPM. When the car engine speed to 3000 RPM, can obviously feel the engine in the vibration noises, turn to turn LiuQiQian, you will feel the engine is nearly jump out of the hood. Third, low-frequency alternating current (ac) what's the problem? 1, the efficiency of transformer is to rely on the edge of the original magnetic field changes, the induction to the edge of step-up or step-down. The frequency of the magnetic field changes the slower, induction is the less, extreme is dc, no induction, so the frequency is too low. 2, power electrical equipment problems, for example, the frequency of the automobile engine's speed is his, such as idle speed 500 r/min, accelerate the shift is 3000 r/min, when converted to frequency is 8, respectively. 3 hz and 50 hz. Watch out, the higher the speed, the greater the power of the engine. Similarly, under the same frequency, the engine, the greater the power output, the greater the this is why the cause of the diesel engine head is bigger than gasoline, bean big strength of the diesel engine to drive the bus truck and other heavy duty truck. By the same token, the motor ( Or all the rotating machinery) Both demands small, big output power, there is only one way to & ndash; — Improve the speed, which is why ac frequency can't too low, because we need small but the power of the motor. The same is true with frequency conversion air conditioning, by changing the frequency of the alternating current (ac), to control the output power of air conditioning compressor. In short, the power and frequency within a certain range are related. Four, the reasons for low frequency can't: transformer with high efficiency, the motor can be smaller power. The cause of the high frequency can't: lines and equipment can loss is small, the generator speed need not too high. So according to the experience and habits, our electricity was in the 50 or 60 hz.
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