How to prevent fire and explosion of power transformer

Power transformers are the main equipment for power transmission and distribution in power systems. During operation, if an overload or short circuit occurs inside the transformer, the insulating material or insulating oil will decompose due to high temperature or electric sparks, expand and even vaporize, causing the internal pressure of the transformer to increase sharply, which may cause the transformer shell to explode and a large amount of insulating oil spray After burning, the oil flow will further expand the fire hazard. Therefore, pay attention to fire and explosion during operation:
(1) Overload operation is not allowed: Long-term overload operation will cause the coil to heat up, make the insulation aging gradually, and cause a short circuit.

(2) Frequent inspection of insulating oil quality: oil quality should be tested regularly, and unqualified oil should be replaced in time, or other measures should be taken.

(3) Prevent the insulation aging damage of the transformer core, and the insulation aging caused by the long-term heating of the core.

(4) Prevent the insulation from being damaged due to careless maintenance. If scratch damage is found, handle it in time.

(5) Ensure that the wire is in good contact, and poor contact will cause local overheating.

(6) To prevent lightning strikes, the transformer will burn out due to insulation breakdown.

(7) Short-circuit protection: If the transformer coil or load is short-circuited, if the protection system fails or the protection setting is too large, the transformer may be burned. For this, a reliable short-circuit protection should be installed.

(8) Well-protected grounding.

Controller selection guide

1. Product classification
1) Dimming module. The basic principle of the dimming module is that the microprocessor (CPU) controls the opening angle of the thyristor, thereby controlling the average amplitude of the output voltage to adjust the brightness of the light source

2) Switch module. The basic principle of the switch module is to control the switch of the power source by the relay output, thereby controlling the light source.

3) Input module. The basic principle of the input module is to accept passive contact signals

4) Sensor interface module. Used to connect sensors such as illuminance detection, presence detection, and motion detection

2 Design and selection points

1) Selection of switch module

(1) For lighting circuits that require switch control, a control module with the following functions should be used.

① AC power supply: incoming single-phase AC220V or three-phase AC380V, outgoing single-phase AC220V.

② The control function can be set through network software and self-learning function.

③ With system clock function.

④ It can set its network terminal function through software.

⑤ The logical relationship (AND, OR) can be set through software.

⑥ The interlock function of the relay can be set by software.

⑦ After the power is off, the relay status can be set when the call comes.

⑧ The microprocessor can also detect the operating temperature inside the switch module.

(2) The specifications (outgoing circuit and capacity) of the switch module should be determined according to the lighting circuit, capacity and control method in the controlled area.

2) Selection of dimming module

(1) For lighting circuits that require dimming control, a dimming module with the following functions should be used.

① AC power supply: incoming single-phase AC220V or three-phase AC380V, outgoing single-phase AC220V.

② The control function can be set through network software and self-learning function.

③ With system clock function.

④ It can set its network terminal function through software.

⑤ Each circuit has overload and overcurrent protection. The dimming module should be able to prevent damage to the light source due to the increase of the external main power supply voltage, and be able to control the input voltage value of the main power supply, thereby limiting the high voltage output.

⑥ It should be possible to ensure that the brightness of the light source is not changed abruptly, but is dimmed in a gradually increasing and decreasing manner.

⑦ Should be able to suppress the interference of higher harmonics.

⑧ Multiple dimming scene preset values ​​can be stored in the dimming module. All data to control the dimming of the lamps stored in the EEPROM memory will not be lost due to power failure, and the dimmer can still restore its original working state after the power failure returns to normal.

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⑨ The microprocessor can also detect the working temperature inside the dimming module.

⑩ Fluorescent lamp dimming module is used to dim the fluorescent lamp with high frequency dimmable electronic ballast

Coupling concept

Couplings belong to the category of general mechanical parts and are used to connect two shafts (active shaft and driven shaft) in different mechanisms to make them rotate together to transmit torque. In high-speed and heavy-load power transmission, some couplings also have the function of buffering, damping and improving the dynamic performance of the shafting. The coupling is composed of two halves, which are respectively connected with the driving shaft and the driven shaft.

The general power machine is mostly connected with the working machine by means of a coupling, which is the most commonly used coupling component for shaft transmission of mechanical products. In the late 20th century, coupling products at home and abroad developed rapidly. In product design, how to choose a coupling that can meet the requirements of the machine from a variety of couplings with different performances? For most designers, It is always a troublesome problem. Commonly used couplings include diaphragm couplings, drum gear couplings, universal couplings, safety couplings, elastic couplings and serpentine spring couplings.

Testing Machine

A testing machine, in a broad sense, is an instrument that verifies the quality or performance of a product or material according to the design requirements before it is put into use. It can be seen from the definition that any instrument that verifies quality or performance can be called a testing machine, but it is sometimes also called a tester, a tester, a tensile tester, a tester, a tester, etc. In the textile industry it is customary to call it a powerful machine, which is actually a tensile testing machine. The testing machine is mainly used to measure the physical properties of materials or products, such as the yield strength and tensile strength of steel, the hydrostatic time determination of pipes, and the fatigue life of doors and windows. The one used to measure the chemical properties of materials is also the chemical composition, which is generally called an analyzer, not a testing machine.

The concept and use of the testing machine The testing machine is a precision test to determine the mechanical properties, process performance, internal defects, and check the dynamic imbalance of rotating parts under various conditions and environments, such as metal materials, non-metal materials, mechanical parts, engineering structures, etc. instrument. In the process of researching and exploring new materials, new processes, new technologies and new structures, the testing machine is an indispensable important testing instrument. It is widely used in machinery, metallurgy, petroleum, chemical industry, building materials, construction, aerospace, shipbuilding, transportation, and other industrial departments, as well as related laboratories in universities and research institutes. It plays an important role in effectively using materials, improving processes, improving product quality, reducing costs, and ensuring product safety and reliability.

The testing machine industry mainly produces the following eight types of products: 1. Metal material testing machine; 2. Non-metal material testing machine; 3. Force and deformation testing equipment (force sensor, dynamometer, displacement sensor, extensometer, accelerometer, etc.) ); 4. Packaging and process performance testing machines (including packaging drop testing machines, packaging impact testing machines, friction and wear testing machines, bending testing machines, straightening machines, etc.); 5. Balancing machines (including on-site balancers) ); 6. Vibration table (including impact table and collision test table); 7. Non-destructive testing equipment (magnetic particle flaw detector, X-ray flaw detector, gamma ray flaw detector, ultrasonic flaw detector, eddy current flaw detector, acoustic emission detector, etc.) ; 8. Testing machine functional accessories and testing equipment and equipment related to the testing machine.

Diesel engine maintenance and maintenance

After a diesel engine is used for a period of time, due to the influence of various factors, the working capacity of the parts will gradually decrease, and the technical state of the whole machine will gradually deteriorate, which will affect the normal use of the diesel engine. For this reason, regular inspection and maintenance are required. Maintenance adopts maintenance technical measures such as cleaning, tightening, adjustment, replacement, and addition to maintain the normal working capacity of the parts and the normal working state of the diesel engine. In addition, the purification of diesel engines is also very important.
1. Fuel net. There are three ways to purify diesel. The first is to let the purchased diesel stand and settle for more than 96 hours, and then add a filter to the funnel and add a layer of silk cloth when refueling. When taking oil from the oil drum, take the filter and wrap it with a layer of silk cloth, and it should be cleaned or replaced regularly.

2. Clean air. When the engine is running, the cylinder draws in air 2 to 4 cubic meters per minute. In order to ensure that the air entering the cylinder is clean, the air filter must be inspected and cleaned regularly.

3. Lubricating oil is net. Always pay attention to the use of clean lubricants that meet the standards of this machine. The filter element of the oil filter should be cleaned regularly. The rotor-type filter pastes a layer of kraft paper of appropriate width and length on the inner wall of the rotor to facilitate the adsorption of dirt under the action of centrifugation. When cleaning the dirt adsorbed on the filter element, it is best to inflate it with an inflator, blow from the inside to the outside, and scrub with a brush. Never wipe it with your hands. Use clean calcium-based grease for butter, and do not inject other lubricants casually.

4. Cooling water is clean. Engine cooling water is best to use soft water, that is, rainwater or treated tap water and clean well water. When cleaning the cooling system, add 1% caustic soda and 0.5% kerosene in proportion to the water volume.

Anticorrosion technology of magnesium alloy

1. Chemical conversion treatment
The chemical conversion coating of magnesium alloy can be divided into chromate series, organic acid series, phosphate series, KMnO4 series, rare earth element series and stannate series according to the solution.

The traditional chromate film has a dense structure with Cr as the framework, while Cr containing structured water has a good self-repair function and strong corrosion resistance. However, Cr is highly toxic and the cost of wastewater treatment is high. Therefore, it is imperative to develop chromium-free conversion treatment. The magnesium alloy is treated in KMnO4 solution to obtain a chemical conversion coating of amorphous structure, and its corrosion resistance is equivalent to that of chromate coating.

The chemical conversion treatment of alkaline stannate can be used as a pretreatment for electroless nickel plating of magnesium alloys, replacing traditional processes containing harmful ions such as Cr, F, or CN. The porous structure of the chemical conversion coating shows good adsorption during the activation before plating, and can change the bonding force and corrosion resistance of the nickel plating layer.

The conversion coating obtained by organic acid treatment can simultaneously possess comprehensive properties such as corrosion protection, optics and electronics, and it occupies a very important position in the new development of chemical conversion treatment.

The chemical conversion film is thin, soft, and weak in protection. It is generally only used as a decorative or intermediate layer of protection.

2 . Anodizing

Anodizing can obtain a better wear-resistant and corrosion-resistant coating base coating than chemical conversion, and has good bonding force, electrical insulation and thermal shock resistance. It is one of the commonly used surface treatment technologies for magnesium alloys. .

The electrolyte of traditional magnesium alloy anodic oxidation generally contains chromium, fluorine, phosphorus and other elements, which not only pollutes the environment, but also harms human health. In recent years, the corrosion resistance of the oxide film obtained by the environmentally-friendly process researched and developed is greatly improved compared to the classic process Dow17 and HAE. The excellent corrosion resistance comes from the uniform distribution of Al, Si and other elements on the surface after anodic oxidation, so that the formed oxide film has good compactness and integrity.

It is generally believed that the pores in the oxide film are the main factor affecting the corrosion resistance of magnesium alloys. Studies have found that adding an appropriate amount of silicon-aluminum sol to the anodic oxidation solution can improve the thickness and density of the oxide film to a certain extent, and reduce the porosity. In addition, the sol component will cause the film formation rate to increase rapidly and slowly in stages, but basically does not affect the X-ray diffraction phase structure of the film.

However, the anodic oxide film is brittle and porous, and it is difficult to obtain a uniform oxide film on complex workpieces.

3. Metal coating

Magnesium and magnesium alloys are the most difficult metals to plate. The reasons are as follows:

(1) Magnesium oxide, which is easily formed on the surface of magnesium alloy, is not easy to clean, and seriously affects the adhesion of the coating;

(2) The electrochemical activity of magnesium is too high. All acidic plating solutions will cause rapid corrosion of the magnesium matrix, or the substitution reaction with other metal ions is very strong, and the coating bonding after substitution is very loose;

(3) The second phase (such as rare earth phase, γ equal) has different electrochemical characteristics, which may cause uneven deposition;

(4) The standard potential of the coating is much higher than that of the magnesium alloy substrate. Any through hole will increase the corrosion current and cause serious electrochemical corrosion. However, the electrode potential of magnesium is very negative. It is difficult to avoid hydrogen evolution caused by pinholes during plating. ;

(5) The compactness of magnesium alloy castings is not very high, and there are impurities on the surface, which may become the source of pores in the coating.

Therefore, the chemical conversion coating method is generally used to first dip zinc or manganese, then plate copper, and then perform other electroplating or electroless plating treatments to increase the bonding force of the coating. Magnesium alloy electroplating layer has coatings such as Zn, Ni, Cu-Ni-Cr, Zn-Ni, etc. The electroless plating layer is mainly Ni-P, Ni-W-P and other coatings.

A single electroless nickel layer is sometimes insufficient to protect magnesium alloys. It has been studied that by combining the electroless Ni layer and the alkaline electroplating Zn-Ni coating, the coating with a thickness of about 35μm can withstand 800-1000h neutral salt spray corrosion after passivation. Some people also use electroless nickel plating as the bottom layer, and then use DC electroplating nickel to obtain a microcrystalline nickel coating. The average crystal grain size is 40nm. Due to the refinement of the crystal grains, the porosity of the coating is greatly reduced and the structure is more compact.

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Electroplating or electroless plating is a surface treatment method that simultaneously obtains superior corrosion resistance and electrical, electromagnetic and decorative properties. The disadvantage is that the Cr, F and the plating solution in the pretreatment cause serious environmental pollution; most of the plating layer contains heavy metal elements, which increases the difficulty and cost of recovery. Due to the characteristics of the magnesium matrix, the binding force needs to be improved.

4. Laser processing

Laser treatment mainly includes laser surface heat treatment and laser surface alloying.

Laser surface heat treatment is also called laser annealing, which is actually a rapid surface solidification treatment method. The laser surface alloying is a new technology based on laser surface heat treatment. Laser surface alloying can obtain alloy layers with different hardnesses and have metallurgical bonding interfaces. Single-layer and multi-layer alloying layers can also be prepared on high-purity magnesium alloy by using the cladding action of laser radiation source.

When a broadband laser is used to prepare Cu-Zr-Al alloy cladding coating on the surface of magnesium alloy, the alloy coating has high hardness, elastic modulus and wear resistance due to the enhancement effect of various intermetallic compounds formed in the coating Resistance and corrosion resistance. However, due to the presence of the rare earth element Nd, the laser multi-layer coating obtained after the laser rapid melting treatment can significantly refine the crystal grains, which can improve the compactness and integrity of the cladding layer.

Laser processing can process surfaces with complex geometries, but magnesium alloys are prone to oxidation, evaporation, vaporization, pores, and thermal stress during laser processing. It is important to design the correct processing technology.

5. Other surface treatment technologies

Ion implantation is a method in which accelerated high-energy ions (Al, Cr, Cu, etc.) impact the surface to be processed at a high speed under the action of an electrostatic field with a voltage of ten to hundreds of KV in a high vacuum state and are injected into the sample. The injected ions are neutralized and left in the vacancies or gaps of the sample solid solution, forming an unbalanced surface layer.

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Some studies believe that the improvement of corrosion resistance is due to the densification of natural oxides, the radiation of implanted ions, and the formation of magnesium nitrides. The performance of the modified layer obtained is related to the amount of implanted ions and the thickness of the modified layer, and the MgO on the surface of the substrate also has a certain promotion effect on the improvement of the corrosion resistance of the modified layer.

Vapor deposition is the vapor deposition of coatings. There are physical vapor deposition (PVD) and chemical vapor deposition (CVD). It is used to greatly reduce the content of impurities such as Fe, Mo, and Ni in the magnesium alloy, and at the same time, the coating is used to cover various defects of the substrate to avoid the formation of local corrosion cells, thereby achieving the purpose of improving the corrosion resistance.

Diagnosis and elimination of common faults of transmission shaft

The damage, wear, deformation, and loss of dynamic balance of the drive shaft components will cause abnormal noise and vibration when the car is driving, and will cause damage to related components in severe cases. When the car is running, it makes a “Gerdon” sound when it starts or accelerates rapidly, and it clearly shows the feeling of loose parts. If it is not the loosening of the drive axle transmission gear, it is obviously that the transmission shaft is loose. The loose parts are nothing more than universal joint cross bearings or steel bowl and flange fork, the spline shaft and spline sleeve of the telescopic sleeve. Generally speaking, the cross shaft diameter and the bearing openness should not exceed 0.13mm, and the meshing gap between the telescopic spline shaft and the spline sleeve should not exceed 0.3mm. The service limit should be repaired or replaced.
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If the chassis makes a “humming” sound while the car is driving, and the higher the running speed, the louder the sound. This is generally caused by the wear and tear of the universal joint cross shaft and the bearing, the middle bearing of the transmission shaft, the damage of the intermediate rubber support or the loose hanger, or the fixed position of the hanger.

When a 6×4 car is under heavy load, especially when driving bumps, it occasionally makes a knocking sound. Pay attention to check whether the balance shaft of the middle and rear axle is displaced and interferes with the transmission shaft. If the noise increases with the increase of the vehicle speed during the operation of the car, and accompanied by jitter, this is generally caused by the loss of balance of the transmission shaft. This vibration is most noticeable in the cab. The unbalance of the dynamic balance of the drive shaft should be less than 100g.cm.

Serious failure of the dynamic balance of the drive shaft will cause damage to related parts. The most common are the clutch shell cracks and the fatigue damage of the middle rubber support

Turbine flowmeter

Turbine flowmeter is a speed type instrument. It has the characteristics of small pressure loss, high accuracy, low starting flow, good shock resistance and anti-pulsation fluidity, wide range and easy maintenance. Turbine flowmeter places the turbine under test. In the fluid, when the gas enters the flowmeter, it is rectified and accelerated under the action of the special structure rectifier. Within a certain flow range, the angular velocity of the turbine is proportional to the flow rate. The electromagnetic induction principle is used to induce a pulse signal proportional to the volume flow of the fluid. After the signal is shaped by the preamplifier, the actual flow rate is obtained and displayed on the LCD screen. If the signal detected by the temperature and pressure sensor is input into the intelligent flow calculator for calculation processing, the flow rate under standard conditions will be obtained, and Displayed on the LCD screen.

Turbine flowmeter is a kind of impeller type instrument, its working principle is relatively simple. A turbine is placed in the center of the pipeline of the turbine flowmeter body, and both ends are supported by bearings. When the fluid passes through the pipeline, it impacts the turbine blades and generates a driving torque to the turbine, so that the turbine overcomes the friction torque and the fluid resistance torque to generate rotation. In a certain flow range Inside, for a certain fluid medium viscosity, the rotational angular velocity of the turbine is proportional to the fluid flow rate. Therefore, the fluid velocity can be obtained from the rotational angular velocity of the turbine, so that the fluid flow through the pipeline can be calculated.

At the same time, the turbine rotation speed is installed on the machine. The sensor coil outside the shell detects. When the turbine blade cuts the magnetic field lines generated by the permanent magnet steel in the shell, it will cause the magnetic flux in the sensor coil to change. The sensor coil sends the detected magnetic flux periodic change signal into The preamplifier amplifies and reshapes the signal, generates a pulse signal proportional to the flow rate, and sends it to the unit conversion and flow integration circuit to obtain and display the cumulative flow value; at the same time, it also sends the pulse signal to the frequency current conversion circuit to convert the pulse The signal is converted into an analog current quantity, which then indicates the instantaneous flow value.

Turbine flowmeter is a kind of speed-type flow meter. According to its transliteration, it is also called turbine flowmeter in China. Turbine flowmeters are divided into gas turbine flowmeters and liquid turbine flowmeters according to their different measuring media. Among various flow meters, the turbine flowmeter is the product with high repeatability and the best accuracy. Such as simple structure, fewer parts to be processed, light weight, convenient maintenance, large flow capacity (large flow through the same caliber) and adaptability to high parameters (high temperature, high pressure and low temperature).

Turbine flowmeters are widely used in the following measurement objects: petroleum, organic liquids, inorganic liquids, liquefied gas, natural gas, coal gas and cryogenic fluids. It is widely used in the transfer and gathering stations of foreign liquefied petroleum gas, refined oil and light crude oil, and the first and last stations of large crude oil pipelines for trade settlement.

Causes of quenching cracks in steel parts

There are many reasons why steel parts produce scrap during the production process or fail during use, but the appearance of quenching cracks is an important reason.
Since the cooling rate of the surface and the core of the part is different during the quenching process, the sequence of forming martensite is also different. When martensite is formed on the surface of the part first, the core part that is still in austenite state is given tension. At this time, due to the good plasticity of austenite, this stress can be relaxed by plastic deformation of austenite .

However, when this part of austenite cools down and transforms into martensite, because the martensite formed earlier has high hardness, high brittleness, and extremely small plasticity, the tensile stress generated by the later formed martensite will increase rapidly. Big. Once the strength limit of the material is exceeded, it will cause cracking. In addition, even if the tensile stress does not exceed the strength limit of the material, the strength is reduced due to the internal defects of the material, which can also cause cracks. This is the physical mechanism that causes quenching cracking. In the actual production process, it manifests itself in 8 forms.

Quench cracks caused by defects in raw materials

If there are cracks on the surface and inside of the raw material, which are not found before heat treatment, quenching cracks may form. Observed under a metallurgical microscope, there are decarburized layers on both sides of the crack, and the ferrite grains in the decarburized layer are coarse.

2 Quenching caused by inclusions

If the inclusions in the parts are serious, it is easy to cause stress concentration, and cracks may occur during quenching.

3 Quench cracks caused by poor original organization

(1) If the steel microstructure has severe band segregation or severe chemical composition segregation, it will cause a great structural transformation stress during quenching. In addition, over-burning is prone to occur where carbides accumulate, which makes parts prone to cracking.

(2) If the residual internal stress of the steel is large before quenching, it is easy to cause cracking during quenching. Parts with this condition often have coarse grains and Widmanstatten structure.

(3) If the parts need to be repaired after a quenching, and the structural stress is not eliminated before the second quenching, cracks may occur in the second quenching, and the cracks are often distributed along the first hardened layer .

4 Two kinds of quenching cracks caused by improper quenching temperature

(1) The indicated temperature of the instrument is lower than the actual temperature of the furnace, which makes the actual quenching temperature too high, causing overheating and quenching, resulting in cracking of the parts. All the microstructures cracked by overheating and quenching have coarse grains and coarse martensite, and the cracks produced mainly exist in the form of intergranular.

(2) The actual carbon content of steel parts is higher than the content specified by the steel grade. If the normal process is quenched according to the original grade, the quenching temperature of the steel is increased, so it is easy to cause overheating of the parts and grain growth, which will cause the quenching The increase in stress may cause quenching cracks.

5 Quenching cracks caused by improper cooling during quenching

Due to improper cooling during quenching, quenching cracks will also occur in parts. For example, No. 45 steel has a tendency to form quenching cracks during quenching. Especially when the carbon content is at the upper limit and the part diameter is 7-8mm, it is easy to crack. Therefore, it is extremely important to select a suitable cooling medium during quenching. In addition, the structure of some parts is more complicated, and the cross-sectional dimension changes greatly. If the coolant is not selected properly, the thin wall parts are likely to cause stress concentration and cause quenching cracks.

6 Quenching cracks caused by machining defects

Due to poor mechanical processing, deep and thick knife marks are left on the surface of the parts. During quenching and cooling, stress concentration in this place causes cracks.

7 The influence of parts shape on quenching cracks

Part geometry is unreasonable or the thickness of the cross-section transition zone is very different, and it is easy to crack due to stress concentration during quenching. In addition, if the forging streamline of the part is poorly distributed, it may also cause quenching cracks during quenching.

8 Cracking caused by not timely tempering

If the tempering cannot be performed in time after quenching, so that the structural stress cannot be eliminated in time, it may cause cracks due to excessive quenching residual stress. Especially for large-sized workpieces, although the surface has been cooled to room temperature after quenching, the core has not yet been completely cooled, and the core austenite structure is still transforming to martensite, and the stress is increasing, that is, the quenching process It is still going on inside the part, so that after a period of time at room temperature, the part cracks.

The importance of springs and shock absorbers

The two major components of the suspension system include springs and shock absorbers. The main function of the spring is to play a supporting role. The function of the shock absorber is to reduce the vibration of the spring. It can ensure that the car is driving smoothly at all times.
However, the shock absorber is easy to wear. As long as you drive 60,000km on the side, the shock absorber has to be replaced. How do you know that it is time to replace the shock absorber? In fact, the clearest signal is the feeling of dizziness while driving. In addition, it is another sign that the car will bump for a while after driving through a roadblock before returning to its stability.

When encountering this kind of problem, the car owner can do the following tests:

(1) Press down firmly on the car shell (the part above the wheel).

(2) Then let go. If the car keeps shaking, the shock absorber is worn out.