"This is simply impossible." Below, upon hearing this question, even Zhao Guodong couldn't help but muttered in a low voice.
Although Zhao Guodong is the workshop director, he still has solid basic skills, and his hands-on ability is not weak. He is definitely a popular and professional model in the factory. If he hadn't always offended people, he would have been the deputy director long ago.
He is very clear.
Three-phase electricity is commonly used in factories, and motors are also three-phase. This type of motor is simple in structure and low in cost. However, it has a big disadvantage, that is, it cannot adjust the speed!
If we talk about the theoretical knowledge carefully, the speed formula of the motor is N=(1-s)N0=(1-s)60f1/p. Its speed is proportional to the power frequency f1, inversely proportional to the motor magnetic pole logarithm p, and also to the rotation speed.
Depends on the margin.
Among them, the power frequency is fixed and cannot be changed. The number of pairs of magnetic poles of the motor is prepared during manufacturing and cannot be changed. As for the slip rate, it is also fixed. You can know it by disassembling the motor. The rotor inside
It is just a poured aluminum frame, which cannot be changed at all. If it must be changed, it must be changed into copper wire, and then a speed regulating resistor can be connected. This method is only suitable for wound rotor motors.
In factories, too many electric motors are used, but these adjustable motors are too few and uneconomical. Therefore, on lathes, reduction gearboxes are often used to expand the speed range, that is to say,
Even if you use a gearbox, don't use your brain on the electric motor.
"Yes, this question is enough to be the final physics question in the college entrance examination." Wang Xiaoyu said.
If it were in later generations, the final questions in physics in the college entrance examination would be big questions such as the composite field of electromagnetic fields and particle motion. But it is not the case now. If you look at the current high school physics textbooks, you can find that it has a wide range of practical applications with workers, peasants and soldiers.
, the electric motor is explained in a dedicated chapter.
Just as the two were talking quietly, another old master spoke: "In his model, the 4 at the end means that there are 4 magnetic poles. This can make a change. However, if it is changed directly, the rotation speed can only be
Double change, that is to say, the rotation speed can only be doubled, from 1400 to 2800. He now said that it has become 1800. Isn't this another mistake? "
The only way to change is the number of magnetic pole pairs. The number of magnetic pole pairs can be changed by changing the connection method of each phase winding of the motor. Changing the number of magnetic pole pairs can change the synchronous speed of the motor, thereby achieving the purpose of changing the motor speed. But the magnetic pole pairs
Numbers can only change exponentially. According to that formula, it is no problem to get 2800, but getting 1800 is impossible!
Even if the master worker doesn't know the formula, he can sum it up in practice. In short, it is impossible to get 1800.
Sure enough, Qin Zhenhua on the stage also spoke: "Are you sure that the question in this question is to change the speed from 1400 to 1800, not 2800?"
Qin Zhenhua's rhetorical question made Niu Shilong stunned. Is there another problem?
This time, he learned the lesson. He didn't understand, but others did. So he waved and Song Weize came over. When he lowered his head and looked down, his heart skipped a beat.
Who came up with this question? Can it be used as a test question? This is simply going to kill the master!
That's right, it's not 2800. If it were 2800, it would be a matter of just one sentence. Just change the winding connection. But now, if it is changed to 1800, it will be complicated.
To be precise, it means connecting the start winding and the running winding in a special way. The calculation is complicated and even involves changing the reluctance. This bunch of complex formula calculations are definitely not something that the group of boys under me can think of.
It must have been copied from some book.
Why did this kind of question arise? When he saw the handwriting clearly and confirmed that it was Du Youwen, he thought about his and his own suggestions yesterday, and the answer was obvious.
He just wanted to rectify Qin Zhenhua and make Qin Zhenhua look embarrassed in today's competition. He deliberately asked people questions like this that were impossible to answer.
Whose idea was it? Did Niu Shilong mean it? Song Weize was suddenly in a dilemma, saying that the question was wrong? Then it becomes the responsibility of the research and development room. After all, it is they who came up with the question. If it is said that the question is too difficult,
If you change the set, it still means there is something wrong here.
However, if the exam continues like this, who will dare to come to the competition? Can a competition with no one come to the competition achieve the purpose of the competition?
Seeing Song Weize's embarrassed look, Qin Zhenhua understood. He said with a smile: "If the question is 1800, that's okay. In fact, it's not just 1800, but also various other data. That's all easy to explain. A
There is a way to solve the problem.”
Looking at Niu Shilong, Qin Zhenhua put his mouth close to the microphone and said his standard answer: "The answer I gave to the second question is an up-conversion speed regulator. The speed can be changed at will. You can have as many as you want. Our lathe is equipped with
One set, even the reducer is omitted, and stepless speed regulation is the most suitable. After answering, let’s move on to the next question.”
Qin Zhenhua said it very simply. What a big deal. If you want to change the speed of the motor, then use a variable frequency speed regulator.
When changing the speed, the first power frequency is the same across the country, and even in most countries in the world, which is 50 Hz. Therefore, generally no one thinks of a solution in this place, but now Western technology is developing rapidly.
There is already a device like a variable frequency speed regulator, referred to as a frequency converter.
That's right, if in a few decades, that advertising slogan goes smoothly and becomes a household name, if you want to buy an air conditioner, you must buy a frequency converter. This frequency converter is what Qin Zhenhua is talking about now.
The technical principle is to first convert the AC power of the 50 box into DC power with adjustable voltage through a rectifier, and then the DC power is converted into three-phase AC power with continuously adjustable frequency through the inverter. In this way, the frequency changes at any time, and the speed also changes at any time.
.
What kind of complicated formulas, or even what coordinates should be added to the curve, would not be so complicated. Qin Zhenhua answered so easily and simply. On the other hand, Niu Shilong finally found an opportunity and couldn't help but slap the table with one hand.
.
"Wrong, the answer is wrong. Come on, Old Song, and read the standard answer to him."
The second question, let me put you down. What kind of variable frequency speed regulator you are talking about? I opened my eyes wide and did not see this standard answer. Therefore, it must be the wrong answer. How big can you, a young boy, have?
ability?
Humph, you continue to be so crazy. Young man, it's better to keep a low profile.
If I were not afraid of making mistakes when reading the answers, I would really want to read them myself. Now, I would leave it to Lao Song. Hey, why is Lao Song looking like this?