Hello, LZ, the first paper is about the basis of mechanical engineering; The second article talks about electricity, and the second article talks about electricity; Because there are many kinds of electricity, I don't know which one you are talking about, such as electricity; Architecture; Electrical automation; Cars; There are strong electricity and weak electricity, and so on ... the second article I used was cement technology; Because this is an inseparable one, simply put, it is widely used. "1" and "Fundamentals of Mechanical Engineering" are professional basic courses for mechanical majors, with many concepts, nouns and principles, abstract content and strong practicality. However, our vocational high school students have a poor learning foundation, and most schools lack teaching AIDS and equipment, which is easy to make students feel afraid of difficulties and neglect their studies. Through years of teaching practice, I have made some attempts on how to improve the teaching effect of mechanical engineering foundation, and achieved certain results. I'd like to take this opportunity to discuss with my colleagues. -Stimulate students' interest in learning and improve the effect of happy classroom teaching. Learning interest is a kind of positive cognition or consciousness tendency of students to learning activities or learning objects. When a student is interested in a subject, he always studies happily and actively acquires knowledge. In classroom teaching, it is the key to stimulate students' learning motivation to pay attention to cultivating students' interest in learning and create a relaxed and lively classroom atmosphere. In teaching, I focus on cultivating students' interest in learning from the following aspects. 1, stimulate interest with "strangeness". The strangeness in the classroom can stimulate students' interest in learning, and strangeness is the internal power source of learning. Students are curious about everything, which is called "potential interest" in psychology. Making full use of "potential interest" in teaching can stimulate students' interest in learning. Let it learn in happiness. When learning the transmission mechanism, introduce to the students that when driving a car, the driver often pulls the right pull rod with his right hand, so that the speed of the car is fast and slow according to the road conditions, and sometimes he has to reverse. Tell the students that the driver pulls the joystick to change the size and direction of the transmission ratio of a pair of gears, thus changing the speed and steering of the wheels. Let students feel very novel, thus stimulating students' interest in learning. 2. Use "doubt" to arouse interest. Doubt is difficult, and solving problems is the need of students' study. Asking questions and making students think is the key link in teaching. When learning ratchet mechanism, you can ask students: (1) When riding a bicycle, we walk forward with our feet on the pedal, but when we pedal backwards, why doesn't the bicycle reverse? (2) After the hoist lifts the goods, although the machine has stopped working, why does the goods not fall, but stay firmly in the air? A series of questions aroused students' thirst for knowledge. 3. Use "fun" to stimulate interest. "Fun" can not only enliven the classroom, but also stimulate students' interest in learning. Pay attention to the fun of teaching in teaching, and students must be immersed in joy. Geneva mechanism is a commonly used intermittent motion mechanism. In order to adapt to the persistence of human vision, the film winding mechanism on the film projector requires intermittent motion of the film. It adopts a four-groove pulley mechanism. When the transmission shaft drives the round pin to rotate once, the grooved wheel rotates 90 degrees correspondingly, so that the picture of the film can stay for a short time. Let the students get interested after listening. 4. Experience success and enjoy it. Suhomlinski once said: "The joy of success is a huge emotional force, which can make students want to study hard." Therefore, teachers should study teaching materials in depth and teach students in accordance with their aptitude, so that students at different levels can gain something and feel the joy of success. Contemporary vocational college students have a strong desire for self-expression, and the encouragement and praise of classmates, especially teachers, is an effective guarantee for them to realize continuous autonomous learning and improve their learning efficiency and interest. In a word, interest is a powerful catalyst and stabilizer, and it is the source of motivation for students to learn. Therefore, teachers should constantly change teaching methods, organically combine listening, speaking, reading and writing, and apply the laws and theories of pedagogy and psychology to keep students interested in learning, constantly improve their attention and often experience the joy of success, so as to truly master a low-cost and efficient learning method. Second, the use of multimedia-assisted teaching to improve the efficiency of classroom teaching. Many contents of this subject, such as teaching in various institutions, need dynamic demonstration. In the absence of teaching AIDS and equipment, the use of multimedia-assisted teaching can make boring content vivid and fully mobilize students' learning enthusiasm. This teaching method is very popular with students. When learning hinge four-bar mechanism, cam mechanism and intermittent motion mechanism, CAI courseware is used to vividly demonstrate the quick return characteristics, dead point position, motion law of cam mechanism follower and characteristics of intermittent motion mechanism. In the teaching process, strengthen the information exchange and feedback between teachers and students. Audio, video, text and pictures of teaching information enhance the artistic effect of teaching, enhance students' knowledge and understanding of learning content, and improve the efficiency of classroom teaching. Third, integrate theory with practice to cultivate students' practical ability. This course is developed from production practice and directly serves production practice. Therefore, it is a course closely related to production practice, which consciously guides students to integrate theory with practice in teaching and cultivates students' ability to analyze and solve problems. 1, combined with life and production practice, understand book knowledge. Book knowledge is often theoretical and abstract, which can be organically combined with daily life and practice, and can achieve twice the result with half the effort. When students learn the concepts of institutions and machines, they often just memorize them by rote, and the result is only a little knowledge. If we can combine the examples in daily life: bicycle is a kind of mechanism, motorcycle and battery car are both machines, motorcycle and battery car can realize energy conversion, motorcycle can convert chemical energy into mechanical energy, and battery car can convert electrical energy into mechanical energy. When learning the guide rod mechanism, we can explain the working principle of the moving guide rod mechanism by combining the manual water pump used in rural households, learn the crank-rocker mechanism by using the self-unloading principle of dump trucks, and explain the dead point position of the crank-rocker mechanism by using the pedal mechanism of sewing machines. 2, combined with classroom teaching, cultivate students' ability to make teaching AIDS. After learning the hinged four-bar mechanism, students will have a basic understanding of the motion law of the hinged four-bar mechanism, and will use their spare time to hold a small-scale production competition among students, and compare it with the works of previous students to see which students have done better, and the students' enthusiasm for participating in the competition is very high. After the small production is completed, please show your own works and compare them. Through small-scale production competition, students' practical ability is enhanced, theoretical knowledge is consolidated and deepened, and the existence conditions of crank-rocker mechanism, double crank-rocker mechanism and double rocker mechanism are deeply understood. 3. Conduct on-site visit teaching. Visiting teaching can make students contact with practical things, closely link teaching activities with production practice, enhance students' perceptual knowledge and deepen their understanding of theoretical knowledge of teaching materials. After learning the crank-rocker mechanism, organize students to visit the practice factory and carefully observe the working principles of shaper, reciprocating conveyor and slotting machine. Let the students observe the feeding action of the shaper, let them find that the feeding is slow and fast, and further understand the quick return characteristics of the crank-rocker mechanism. Such as cam mechanism, intermittent motion mechanism, clutch, coupling, brake, etc., please ask the master to operate on site after teaching. Teachers will visit and explain, which will make students have a deeper impression on what they have learned. At the same time, the visiting teaching method can also enable students to receive good professional ethics education such as love and dedication, which can be described as killing two birds with one stone.

"2" Water and Mud Technology

Science and leasing

1 overview

Case analysis of a transformer differential protection misoperation

Nicolas

(Hefei Cement Research and Design Institute 23005 1)

Chile Lafarge grinding 200,000 tons cement production line is the first in our hospital.

The relationship between success and failure of an EP project in the United States.

Whether our hospital can explore the American market is the implementation of our hospital's American development war.

Slightly critical. This project is from the initial design to the selection of equipment.

The most advanced technology in China. To this end, the work of our hospital

Cheng's technicians are working hard, but the electrical aspects of the site

There are still some technical problems. Our engineers and technicians are very

Pay attention to the problems, without any slack, and the technicians in Chile.

With the strong cooperation and efforts of our engineers and technicians, we require electricity.

The problem was finally solved satisfactorily and was well received by the owners.

Here, I only take the Transformers micro that appeared in Lafarge, Chile.

The misoperation of mechanical differential protection is listed and the technical analysis is made.

For your reference.

2 electrical fault phenomenon

The power supply for the 200,000-ton cement grinding production line in Lafarge, Chile is

Adopt 23/6.6 kV-23/0.4 kV bidirectional power supply mode, two main

See table 1 and table 2 for the technical parameters of the transformer.

Table 1 1# main transformer

Transformer model s11-Ⅳ b-3150/23.

On-load voltage regulation 23 2x2.5

Transformer connection mode Dynl 1

The transformer capacity is 3 150t.

The voltage ratio is 23/6.6 kV.

Table 2 2# Main Transformer

Transformer model Sl 1 MB 2000/23

On-load voltage regulation 23 2x2.5

Transformer connection mode Dynl 1

Transformer capacity is 2000 kilometers.

The voltage ratio is 23/0.4kv.

The main protection of main transformer is microcomputer differential protection (model:

R circle 1543), R 43 microcomputer comprehensive insurance is near ABB company.

A new type of comprehensive insurance is new to the world and has a very powerful function.

The self-programming of running software and programs provides convenience for users.

After half a year of installation, it was put into trial operation on June 20, 2008.

The two main transformers are running normally under no-load condition. But when two main transformers are in the band

After load production, the high voltage sides of two main transformers tripped one after another.

Like, ABB microcomputer comprehensive protection shows microcomputer differential protection action, obviously this

Samples will seriously affect the production of the whole factory, and this problem must be solved as soon as possible.

Solve.

3 Fault inspection steps and technical analysis

(1) First, check whether the phase sequences of the high and low voltage sides of the current transformer are the same.

Therefore, if the phase sequence of power supply is positive sequence, as long as the selection is reasonable.

The differential current flow through that variable ratio and the microcomputer phase compensation is very small, but

The situation of negative sequence is different, and the secondary side of current transformer on high voltage side loses power.

The output current is in phase with the secondary output current of the low-voltage side current transformer.

The bit difference is 60. , so it will cause differential protection misoperation, but

Carefully check whether the phase sequence of the power supply is correct on site.

(2) Comprehensively check the transformation ratio at both ends of the current transformer.

Ensure that the protection values match, recheck and calculate the protection settings.

A 35—

2008.N93

Cement slurry technology

Science and logic OFC

Value, did not find any problems.

(3) Check whether the secondary side of the current transformer is damaged, because

When the transformer has a certain load, if the secondary circuit of the current transformer is disconnected

Line, is likely to cause differential protection starting element, differential element action,

Thus lead to misoperation of differential protection. The inspection result was not found.

Describe the problem.

(4) Then, all technicians began to suspect that the transformer was inside.

Whether there is a fault or not, it has been tested by two main transformers and the factory.

Value verification, the detected data is almost the same as that of the transformer when it leaves the factory.

(5) According to ABB's technical data of microcomputer integrated protection (RKI'543),

Check ABB (RY43) microcomputer integrated protection terminal (transformer)

Whether the current terminals of current transformers on both sides are connected to comprehensive protection.

Correct), found that the transformer on both sides of the current transformer and comprehensive protection wiring are

The manufacturer mistakenly placed the current transformer on the high voltage side and the low voltage side of the transformer.

The current signal of the current transformer is reversely connected to the position of comprehensive protection, and

After the wiring adjustment is correct, the differential protection tripping phenomenon is still found.

Existence.

At this point, the problem at the scene seems confusing, but both China and Chile

Engineers and technicians are not discouraged. They looked at the drawings and looked up the information, and finally found it.

The chronic disease of the problem It turned out to be the same polarity terminal on the secondary side of the transformer.

Wrong wiring will lead to differential protection misoperation, because this wiring mode will

Lead out the secondary current direction of current transformers on both sides in the differential circuit.

Similarly, the current flowing through the microcomputer comprehensive protection is the sum of two-phase currents, which is a changing voltage.

Faults during no-load operation are generally not easy to reflect, only when

When the transformer has a certain load, the differential protection will act. Reconnect

The two transformers behind the line are running normally with load.

Figure 1

In this way, with the efforts of technicians from both sides, this situation will change together.

A 36 one

The misoperation of differential protection of voltage transformer finally came to the bottom, and the fault was rounded.

Full solution, but in the hearts of engineers and technicians for a long time lingering.

The distant fog gradually melted away and became the joy of the smooth completion of the project.

It is raining. Figure 1 shows the correct and wrong wiring of differential protection.

4 experience and suggestions

4. 1 Fault analysis and elimination

Through the analysis and elimination of differential protection misoperation fault

The whole process, elaborated some normal operation (system trouble-free and no

Influence) differential protection misoperation, but in addition to the above reasons.

There are also some factors that may lead to time difference dynamic protection of transformers in normal operation.

The main phenomena of misoperation protection in the secondary circuit of current transformer are: (1).

The terminal screw is loose, resulting in poor connection or short circuit of the secondary circuit.

Open the way. (2) The primary phase contact in the secondary circuit of the current transformer is poor,

The arc generated at the poor contact causes single-phase grounding or grounding between two phases.

Grounding (short circuit in secondary circuit of current transformer). (3) Current transformer

The outer insulation of the cable core of the secondary loop is damaged or damaged, and it is running.

Vibration causes short circuit to ground. (4) Secondary differential current transformer

The loop is grounded at multiple points, and the grounding point is not in one place, resulting in a grounding point.

The potential difference between them is too large, which leads to differential current and differential error.

Action (thunderstorm season).

4.2 Suggestions

In order to improve the reliability of differential protection, the following work should be done.

Operation: (1) Strictly check the polarity of current transformer; Intermediate frequency current mutual inductance

If the polarity of the device is wrong when wiring, it is used in the protection circuit.

This will cause misoperation of protection. If it is use in that measuring circuit of an instrument,

Will affect the accuracy of measurement. (2) Be careful of the secondary circuit of the current transformer.

Poor road contact and open circuit; Strengthening differential current transmission of differential circuit

Maintenance of line monitoring and protection devices. In transformers and protective equipment

After installation and debugging, carefully check the secondary circuit of current transformer.

Road, tighten the secondary circuit terminal screw and use the spring pad.

Reinforcement. (3) Strictly implement the specification requirements; All electrical connections

The secondary circuit of differential current transformer can only have one male * * * grounding point.

The location of the grounding point should be on the protection disk. (4) ensure differential electricity

The secondary cable cores of the current transformer are insulated from each other, and the cores are insulated from the ground; correct

It is necessary for the initial operation of the transformer and the operation of the high-voltage equipment after maintenance.

Measure the secondary cable core of current transformer with 1000V insulation resistance meter.

Insulation between conductor and ground to meet the requirements of electrical regulations; in addition

The cross section of the secondary cable of the externally selected current transformer shall be no less than 4 mm.