"It's not going to work." Below, hearing this question, even Zhao Guodong couldn't help but mumble in a low voice.

Don't look at Zhao Guodong is the director of the workshop, but the basic skills are also quite solid, and the hands-on ability is not weak.

He was very clear.

Three-phase electricity is very common in factories, and motors are also three-phase electricity, this kind of motor is simple to build and low cost, but there is a big disadvantage, that is, there is no way to adjust the speed!

If we talk about theoretical knowledge carefully, the speed formula of the motor N=(1-s)N0=(1-s)60f1/p, its speed is proportional to the power supply frequency f1, inversely proportional to the number of poles of the motor p, and also related to the slip rate.

Among them, the power supply frequency is fixed, can not change, the number of poles of the motor, in the manufacture of the time is done, can not be changed, as for the slip rate, that is also fixed, disassemble the motor to know, the rotor inside is a poured aluminum frame, can not be changed at all, if it must be changed, it has to become a copper wire, and then you can access a speed regulating resistor, this method is only suitable for wound rotor motors.

In the factory, the motor is used too much, but this kind of motor that can be adjusted is too few, and it is not economical, so, on the lathe, the reduction gearbox is often used to expand the speed range, that is, even if it is a gearbox, do not use the brain on the motor.

"Yes, this question is enough to be used as the physics finale of the college entrance examination." Wang Xiaoyu said.

If it is in the later generations, the physics of the college entrance examination, the finale is the compound field of the electromagnetic field, particle motion and other big questions, but now it is not, if you open the current high school physics textbook, you can find that the practical application of workers, peasants and soldiers is quite extensive, and the electric motor is specially explained as a chapter.

Just when the two whispered to each other, another master spoke: "In his model, the back 4 means that there are 4 magnetic poles, so that you can change it once, but if you change it directly, the speed can only be doubled, that is, the speed can only be doubled, from 1400 to 2800. ”

The only way to change this is the number of pole pairs, which can be changed by changing the connection method of each phase winding of the motor. The change of the number of pole pairs can change the synchronous speed of the motor, so as to achieve the purpose of changing the speed of the motor. But the number of pole pairs can only be multiplied, and according to that formula, it is no problem to get 2800, but to get 1800, it is impossible!

Even if the worker master doesn't know the formula, he can summarize it in practice, in short, it is impossible to get 1800.

Sure enough, Qin Zhenhua on the stage also spoke: "Are you sure that the problem with this question is to change the speed from 1400 to 1800, not 2800?" ”

Qin Zhenhua's rhetorical question made Niu Shilong stunned for a moment, could it be that there is a problem?

This time, he learned to be obedient, he didn't understand, others understood, so as soon as he beckoned, Song Weize came over, looked down, and sighed in his heart.

Who came up with this question? Can I use it as an exam question? This is simply the life of the master!

That's right, it's not 2800, if it's 2800, it's a matter of one sentence, just change the connection of the winding, but now, change it to 1800, it's complicated.

To be precise, it is to connect the starting winding and the running winding in a special way, the calculation is complicated, and even involves changing the magnetic resistance, this bunch of complex formula calculations is definitely not something that the group of boys under his command can come up with, it must have been copied from which book.

What is the reason for this kind of problem? When he saw the handwriting on it clearly and confirmed that it was Du Youwen, thinking about his and his own suggestions yesterday, the answer could be imagined.

just wants to rectify Qin Zhenhua and make Qin Zhenhua make a fool of himself in today's big competition, and deliberately asks people this kind of question that is impossible for people to answer.

Whose idea was it? Could it be Niu Shilong's meaning? Song Weize was embarrassed all of a sudden, and said that the question was wrong? Then it becomes the responsibility of the R&D room, after all, it is their problem, if it is too difficult to come out of the question, change the set, it still means that there is a problem here.

However, if the test continues like this, who will dare to play? Can a big competition where no one comes to the field achieve the purpose of the big competition?

Seeing Song Weize's embarrassed appearance, Qin Zhenhua also understood, and he said with a smile: "If the topic is 1800, then it doesn't matter, in fact, not only 1800, but also various other data, it's easy to say, a way can solve the problem." ”

Looking at Niu Shilong, Qin Zhenhua's mouth was close to the microphone and said his standard answer: "The second question, the answer I gave, is the upconversion governor." The speed can be changed at will, how much you want, our lathe is equipped with a set, even the reducer is saved, stepless speed regulation, the most suitable. After answering, let's move on to the next question. ”

Qin Zhenhua said very simply, what a big deal, if you want to change the speed of the motor, then go to the frequency conversion governor.

Changing the speed, the first power frequency, the country, even most countries in the world are the same, is 50 Hz, so, generally no one in this place to find a way, but now the technology in the West is developing rapidly, there is already a frequency converter such a device, referred to as the frequency converter.

That's right, if in a few decades, that advertising slogan is very smooth, a household name, to buy an air conditioner, you have to buy a frequency conversion, this frequency conversion is now the frequency conversion in Qin Zhenhua's mouth.

In terms of technical principle, the rectifier first converts the alternating current of 50 boxes into direct current with adjustable voltage, and then the direct current becomes three-phase alternating current with continuously adjustable frequency through the inverter. In this way, the frequency changes at any time, and the speed changes at any time.

What kind of complicated formula, and even what kind of coordinate value of the curve should be added, so that he will not be so complicated, Qin Zhenhua answered so easily and simply, and on the other side, Niu Shilong finally found an opportunity, and couldn't help but slap the table with one hand.

"Wrong, wrong answer, come, old Song, read the standard answer to him."

The second question, let you go, what kind of inverter governor you said, I opened my eyes wide, and I didn't see this standard answer, so, it must be the wrong answer, how much ability can you have as a hairy young man?

Hmph, you're continuing to be so crazy, young man, it's better to keep a low profile.

If you weren't afraid of making mistakes in reading the answers, you really wanted to read it yourself, and now, I'll leave it to Lao Song, hey, why does Lao Song have this expression?