Do you know why our country chooses 50Hz AC? And listen to the big blue motor Xiaobian slowly come.
Do you know why our country chooses 50Hz AC? And listen to the big blue motor Xiaobian slowly come.
The lowest frequency is 0HZ, which is DC. The problem of direct current transmission is the same as the electric spark that occurs when the electrical plug is pulled out. When the current is large enough, the electric spark cannot be extinguished. We call it "arc". The direction of the DC current does not change. Without this zero crossing, we want to extinguish the arc.
AC power beats DC by virtue of its ability to change voltage levels. When the transmission power is the same, the voltage is increased, the power transmission current is reduced, and the energy consumed on the line is also reduced.
For AC power, the current will change direction, so there is a moment when the current crosses zero. With this small current time point, we can cut off the line current through the arc extinguishing device.
The problems caused by low frequency AC are as follows:
1. The problem of transformer efficiency.
1 Transformer is changed by the magnetic field of the primary side, and the secondary side is induced to step up or step down.
2 The slower the frequency of the magnetic field changes, the weaker the induction is. The extreme case is DC, there is no induction at all, so the frequency is too low.
2. Power problems with electrical equipment.
1 At the same frequency, the larger the engine, the greater the output power.
2 The motor requires both a small head and a large output power. There is only one way to increase the speed, which is why the AC frequency cannot be too low, because we need a small but powerful motor.
The same is true for the 3 inverter air conditioner, which controls the output power of the air conditioner compressor by changing the frequency of the alternating current. In short, power and frequency are positively correlated within a certain range.
The problems caused by high frequency alternating current are as follows:
1. The loss of lines and equipment increases.
1 Transmission lines, substation equipment, and electrical equipment are all reactive. The reactance is proportional to the frequency. The higher the frequency, the larger the reactance, the more unused work is consumed, and the less useful power can be transmitted.
2 Corresponding to the reactance, there is capacitive reactance, and the capacitive reactance is inversely proportional to the frequency. The higher the frequency, the smaller the capacitive reactance, and the larger the leakage current of the line. If the frequency is high, the leakage current of the line will also increase.
2. The second is that the generator speed is too fast.
1 The generator set is basically a single-stage machine, that is, a pair of magnetic poles. In order to emit 50 Hz, the rotor should reach 3000 rpm. When the engine speed reaches 3000 rpm, it will be obvious that the engine is vibrating. When you turn to six or seven thousand turns, you will feel that the engine is jumping out of the hood.
2 Such a heavy rotor has considerable inertia, which is also a prerequisite for the power system to be called an inertial system, which can maintain safe and stable operation. It is also the reason why intermittent power supplies such as wind and solar power pose challenges to traditional power supplies.
So in summary:
1, the frequency can not be too low: the transformer can be high efficiency, the motor can be small and small.
2, the frequency can not be too high: the line and equipment can be small loss, the generator speed does not have to be too high.
3, so according to experience and habits, our power is set at 50Hz.
----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant
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