Soul Returns to Hong Kong: From Tailor Shop to Richest Woman

The second semester of the new academic year for industrial automation graduate students saw a doubling of lab classes, while the number of theoretical classes decreased. Professor He's exact words were: "You laid a solid foundation last semester, so hone it this semester."

The first period on Monday afternoon is an analog and digital electronics technology experiment.

Lin Ying was able to manage the course fairly well; Tang Gong's soldering practice last semester hadn't been for nothing. She could now draw wiring diagrams for op-amp circuits, AD conversions, and logic gate combinations with her eyes closed; although she would occasionally make small mistakes when actually doing it, she could basically tune out the waveforms on the oscilloscope.

Sun Miaoshu remained in her group, responsible for recording data and handing over tools.

"Lin Ying, your hands have become much steadyer this semester," Sun Miaoshu remarked, watching her insert the chip into the breadboard.

"It's all from practice! Last semester, Teacher Tang had me desolder nearly three hundred points. It would be strange if it wasn't stable."

Teacher Zhou walked over to their table, looked at the output waveform on the oscilloscope, and nodded, a rare occurrence for him: "Lin Ying, not bad this time."

"Thank you, teacher."

"Don't get too excited yet." Teacher Zhou slammed the experiment schedule on the table. "Starting next week, we'll have the motor drive and speed regulation experiment, in groups of four. You'll gradually get to know this lesson."

Lin Ying glanced down at the experimental outline: Three-phase asynchronous motor starting characteristic measurement, DC motor speed control system design, PWM pulse width modulation experiment... She recognized every word, but when she put them together... ? ? ?

In theory, she has a concept of these things.

Sun Miaoshu leaned over and glanced at the schedule, her face immediately falling: "What is this? Three phases? Four quadrants? I don't even understand one phase!"

Lin Ying patted her on the shoulder: "It's okay, there are four of us in a group, someone will know how to do it eventually."

Next Wednesday afternoon, the motor experiment class will officially begin; Lin Ying, Sun Miaoshu, Liu Yang, and Chen Jian are grouped into teams of four. The laboratory is located on the first basement floor of the engineering building. It is a large space with two rows of motor sets and their corresponding control consoles. Each workstation has a metal-cased motor in front of it, with switches, frequency converters, and measuring instruments connected to it.

The teacher in charge of this course is Mr. Zhang, who is in his early fifties.

"Today we'll start with the starting characteristics of a three-phase asynchronous motor." Teacher Zhang stood on the podium and explained the experimental steps. "Be careful. The three-phase voltage is 380 volts. If you connect the wires incorrectly, it won't just blow the fuse, it will burn yourselves."

After saying that, he sat down in the back and went to drink tea.

Lin Ying and the other three stood in front of their workstations, looking at each other in bewilderment.

Liu Yang was the first to act. He picked up the wiring diagram and studied it for a long time, then looked up at the terminals on the control cabinet: "This... which is the U phase? Which is the V phase?"

Chen Jian pushed up his glasses: "Weren't you a graduate student recommended by this university? Didn't you do any electrical engineering experiments during your undergraduate studies?"

Liu Yang asserted confidently, "I did that in undergrad, but that motor was only the size of my palm! This one is as thick as my thigh! They're completely different!"

Lin Ying squatted down to look at the parameters on the motor nameplate, then looked up to compare them with the markings on the control cabinet. Theoretically, she could build the equivalent model of the entire circuit in her mind; however, the arrangement of the terminals on this control cabinet was completely different from the diagram in the textbook, and it didn't match up at all in actual operation.

"Connect the main circuit first." Lin Ying began to work. "Connect the three wires U1, V1, and W1 to the output terminal of the contactor, and then connect them to the three-phase power supply from the input terminal of the contactor."

Liu Yang picked up a cable and tried to screw it onto the terminal, but it wouldn't budge no matter how hard he tried: "This nut is way too tight! Who didn't loosen it last time they did this?"

Chen Jian went over to help, and the two of them twisted the wires together, finally managing to connect them; Sun Miaoshu stood by, checking the wiring diagram, muttering, "U1 to U1, V1 to V1...wait, is this blue wire V or W?"

"Blue is a V," Lin Ying said.

"Are you sure? I saw that the group next door received W."

Lin Ying turned her head and glanced at the wiring of the group next door: "The group next door connected it wrong."

Just as he finished speaking, a "bang" came from the next workstation, followed by a power outage, and all the lights in the row went out for a moment.

Teacher Zhang placed the enamel mug on the table, got up, and went to inspect it; three minutes later, his booming voice rang out: "Who told you to short-circuit the motor windings?! This isn't the way to die!"

The four boys in the next group were being scolded with their heads down.

Lin Ying looked away: "Alright, let's test the power switch."

Liu Yang placed his hand on the power button, hesitated, and looked at everyone: "Really going to power on?"

"Yes." Lin Ying took a step back.

Liu Yang pressed the button, and the motor roared to life, vibrating the entire workstation. Sun Miaoshu instinctively jumped back a step; Chen Jian stared intently at the ammeter, rapidly counting down: "Starting current... 80 amps! 90! And it's still rising!"

"Normal." Lin Ying looked at the data. "The starting current of an asynchronous motor is five to seven times the rated current. It will decrease after it finishes accelerating."

The data did indeed decrease, and the motor is running stably.

The problem is that they need to measure more than just one set of data; the entire experiment requires four different starting methods: full-voltage starting, reduced-voltage starting, star-delta starting, soft starting... and each one requires disconnecting and reconnecting the wires.

Every time a different starting method was used, the four people had to completely disconnect and reconnect all the previous wiring. The three-phase power wires were thick cables, heavy and stiff, and they had to be inserted into the terminals and nuts tightened. The four people took turns working, connecting and disconnecting the wires repeatedly throughout the afternoon.

After three hours, only two of the four starting methods were completed; the data for the remaining two methods was incorrect, and after checking, Teacher Zhang pointed out that their star-delta switching circuit was connected in reverse.

"Tear it down and start over."

Liu Yang rubbed his palms together vigorously: "Teacher! My hands are all blistered!"

"Blistering means you're applying force in the wrong direction! Continue next week."

After class, the four of them collapsed on a bench in the corridor outside the laboratory.

Sun Miaoshu laid her hands flat on her knees, her palms covered in red marks: "Lin Ying, this experiment is more difficult than all the classes last semester combined."

Liu Yang stared at the ceiling and muttered to himself, "Now I finally understand why the experienced workers in the factory earn such high monthly wages."

Chen Jian took off his glasses and wiped them: "Lin Ying, didn't you minor in electronic engineering at Cambridge? You've never done something like this before?"

"No." Lin Ying rubbed her aching wrists. "The electrical engineering experiments at Cambridge are small-scale, mainly for teaching and demonstration, and the professors connect all the wires first, so students just press buttons and look at the data; they would never let you connect a 380-volt three-phase cable by hand."

"Your professor is really nice."

"It's not that they're kind people, it's that they're afraid the students will blow up the school and they won't be able to afford the compensation."

In the second week of the electrical engineering class, we switched to a DC motor speed control experiment! The excitation circuit, armature circuit, and speed controller parameter settings of the DC motor... every link can go wrong, and the consequences of the error are particularly obvious: the motor may directly jam and not turn, or it may turn at high speed until sparks are produced, or even an overcurrent trip may occur.

Lin Ying's group experienced six power outages in one afternoon, and Teacher Zhang gave them a hard time whenever she saw them.

"This is the sixth time." Teacher Zhang walked over and checked their wiring, pointing to one of the wires. "Where did you connect this feedback signal?"

All four of them looked down at the same time.

"...It's connected to the positive terminal of the power supply." Chen Jian's voice was very soft.

Teacher Zhang turned off the power switch: "Take it all apart, start from scratch."

That night, Lin Ying returned to her dormitory, sat at her desk, and stared blankly at her Apple laptop for a full five minutes; then she opened the drawer and took out letter paper and a fountain pen.

Recipient: Matthew Smith.

"Matthew, are you still alive? If so, please reply immediately! I'm having a major problem with the motor speed control system. I can deduce the theory, but I can't figure out the pattern for parameter tuning in actual operation! Professor Zhang said it depends on feel, but I don't have feel, I only have math! Please tell me how someone with a physics background understands this kind of intuitive system response? Reply immediately, Lin Ying."

At the end, Lin Ying added one more line:

"P.S.: If you can travel abroad again next time, I'll treat you to authentic Peking duck and hot pot, all you can eat; and I swear I'll never argue with you again about whether math or physics is more fundamental! Whatever you say, I'll listen to you."

After writing that sentence, Lin Ying put down her pen. Looking at the line of writing, she felt it lacked any backbone. There was nothing she could do; this thing was genuinely difficult.

Lin Ying put the letter in an envelope, affixed the stamp, and went directly to the post office to have it sent by express mail; international mail takes about two weeks to reach England, and another two weeks for a reply, so it takes a month for the whole trip.