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    What is the difference between low voltage pulse and multiple pulse of cable fault detector
    Views:495    2021-01-26 17:17:37

    As the technology of the cable fault detector is constantly updated, the positioning of the cable fault detector of the equipment is getting higher and higher. At present, there are two commonly used detection techniques for cable tester equipment, low-voltage pulse method and multiple pulse method. So what is the difference between the low voltage pulse and the multiple pulse of the cable fault detector?

    Cable fault tester

    In the actual working process of the cable fault detection test, the cable faults are generally high-resistance faults and low-resistance faults. The low-voltage pulse method and the flash method in the pulse method solve the low-resistance and high-resistance cable faults with high accuracy. , Not affected by artificial factors. So it has become the main application method of power cable fault detection test. The working principle of the power cable fault low-voltage pulse method is that a low-voltage pulse wave is injected into the cable test end, and the pulse wave propagates along the cable to the fault point and is reflected and then sent back to the cable fault tester. The time of the transmitted pulse wave and the reflected pulse wave are recorded together interval. Knowing the propagation speed of the pulse wave in the cable, the distance to the cable fault point can be calculated.

    Cable fault tester

    The principle of multiple pulse testing is developed on the basis of low-voltage pulse detection technology. In addition to having all the advantages of the secondary pulse method cable fault tester, the point is: the fault waveform obtained by the field test allows the operator to have more choices In order to obtain an ideal secondary pulse waveform, the delay time of the test pulse is no longer adjusted continuously during the test, which reduces the technical and experience requirements of the operator. Improve the accuracy of judgment on site failures. Anyone can easily and accurately interpret the waveform, calibrate the distance to the fault, and achieve the purpose of quickly and accurately testing the cable fault.

    What is the difference between a traditional grounding resistance meter and a clamp-on grounding resistance meter
    Views:485    2021-01-26 17:16:22

    The measurement of grounding resistance testers is becoming more widespread and important. At present, there are two main methods for measuring grounding resistance: the traditional grounding resistance meter and the new clamp-on grounding resistance meter. The application of the two ground resistance measurement methods is analyzed below.

    1. Operation method:

    The grounding resistance meter must trip the grounding wire and hit the auxiliary grounding pin. The ground electrode to be measured is to be separated from the grounding system, and the voltage electrode and current electrode must be driven into the soil at a specified distance as an auxiliary electrode for measurement. The operation is more complicated and laborious.

    The clamp-type grounding resistance meter is a non-contact measurement. You only need to clamp the jaw of the clamp meter to the ground wire to be tested, and the ground resistance value can be read from the LCD screen of the clamp meter. The operation is very simple.

    2. Accuracy of measurement:

    The accuracy of the grounding resistance meter depends on the position between the auxiliary electrodes and the relative position between them and the grounding electrode. If the position of the auxiliary electrode is restricted and cannot meet the calculated value, it will cause the so-called distribution error. For the same ground electrode, different auxiliary electrode positions may cause the measurement results to have a certain degree of dispersion. And this dispersion will reduce the credibility of the measurement results.

    The Clamp-on Earth Resistance Tester does not need auxiliary electrodes, and there is no error in the arrangement of the poles. When repeated tests, the results have good consistency.

    3. Test environment:

    The grounding resistance meter adopts the voltage-current method, and two auxiliary grounding electrodes with relative position requirements must be inserted. Therefore, there must be soil that meets the position requirements near the test point.

    The clamp ground resistance tester measures the loop resistance value, so the ground electrode to be tested must form a loop, and it cannot be directly measured for single-point grounding.

    4. Other applications of clamp ground resistance tester:

    In many environments (such as computer rooms in basements or floors, lightning rods, elevators, gas stations, grounding bodies covered by concrete, and grounding bodies that cannot be separated from the system, etc.), use traditional grounding resistance meters to measure grounding resistance is very difficult. Although they are also single-point grounding, if there is a grounding body clamp meter available on site, their grounding resistance can be measured, and there is no need to disconnect the grounding electrode from the system during the test (see the instruction manual). The Fluke Clamp Ground Resistance Tester can measure ground faults that cannot be measured by traditional methods. For example, in a grounding system, the grounding resistance value of their grounding electrode is qualified, but the connecting wire between the grounding electrode and the lightning protection belt or the grounding overhead line may be used for a long time, and the contact resistance may be too large or even open. The grounding resistance of the pole is qualified, but the grounding system is unqualified.

    5. For the same ground electrode, when the measurement results of the two instruments are quite different, please pay attention to the following issues:

    1) When testing with a traditional grounding resistance meter, whether the ground down conductor is tripped (that is, whether the tested ground electrode is separated from the grounding system). If it is not tripped, the resistance value measured by the shaker is the parallel value of all grounding resistances of the grounding system. This parallel value is much smaller than the grounding resistance of the grounding electrode, and it is meaningless.

    2) The national standard GL/T621-1997 "Grounding of AC Electrical Devices" stipulates: "The sum of the ground resistance of the grounding electrode or natural grounding electrode and the resistance of the grounding wire is called the grounding resistance of the grounding device." Generally, traditional grounding The resistance meter can only measure the resistance of the ground electrode to the ground, but cannot measure the resistance of the ground wire. The ground resistance measured by the clamp meter is the sum of the ground resistance of the ground electrode and the ground wire resistance, which fully meets the requirements of the national standard.

    3) If the grounding system has only a few grounding electrodes, there will be some errors in the measurement with a clamp meter, which are generally larger. If you want to get an accurate grounding resistance value, you can use the "Solution Program for Finite Point Grounding System" to solve it.

    In summary, the two measuring methods of universal grounding resistance are conditionally restricted, and each has advantages and disadvantages that cannot be replaced by each other. The user should determine the measurement method according to the system structure and environment of the ground electrode to be tested in order to obtain credible measurement results.

    What are the reasons for the error of the cable fault detector equipment
    Views:484    2021-01-26 17:10:55

    Although the cable fault detector equipment brings certain convenience in the cable fault detection. However, in practice, the cable fault detector equipment will cause deviations in the detection results due to various uncertain factors. So what are the reasons for the error of the cable fault detector?

    Cable fault detector

    Human error

    At present, the cable fault detector developed on the principle of traveling wave method is mainly used by testers to judge and calculate the distance position of the fault point after analyzing the fault detection waveform. The interpretation error produced by the user is sometimes the detection error, which is usually related to the work experience of the detection point personnel, mainly in the application of detection methods, the test voltage level during the detection process, the connection details, and the judgment of the inflection point of the detection waveform. . This is also one of the main reasons why cable fault detection is more difficult than other electrical equipment fault detection. Due to the irregularity and complexity of the cable fault detection waveforms, it is currently difficult to achieve true automatic calculation and judgment of the location of the fault point.

    Cable fault detector

    Cable error

    It is mainly the error caused by the transmission speed V of the electric wave on the cable under test. From the formula L=(U*T)/2, it can be seen that the cable fault detection distance L is proportional to V. In the cable fault detection, we say that V is a constant, it is a relative concept, not an absolute fixed value. The actual measurement and related data show that the transmission speed V can generally produce a relative error of ±2%. For example, the transmission speed V of the XLEP cable is about 172.3m/靤, and there are two reasons for the error of the transmission speed V: First, the same type of cables produced by different manufacturers may cause errors due to the production process and ingredients. Second, the aging of the cable insulation causes a change in V, and there is no accurate data to explain this trend. Note: There are inconsistencies among the marked length, actual length and detected length of the tested cable.

    Cable fault detector

    Environmental error

    When the rough measurement of the cable fault is completed, the distance measurement is usually carried out according to the detection distance data along the direction of the cable. However, due to poor environmental conditions (such as rivers, trenches, buildings, etc.) and the winding of the buried cable, it is accurate. It is very difficult to measure, and a lot of time can only be a very rough and approximate designated location. This error is also called measurement error, and in many cases is a source of error that cannot be estimated. Therefore, it is very important to establish and improve the detailed files of power cables, and the digital management of pipe network GIS will be more indispensable in the future.

    Cable fault detector

    In addition to the above, the reasons for the error of the cable fault detector are other than the above, but other factors, such as equipment failure, etc., are also excluded. In order to avoid errors in the detection of the cable fault detector, we need to carefully analyze the data in the detection.

    How to use ground resistance tester
    Views:486    2021-01-26 17:10:28

    When an abnormal situation occurs, if there is no grounding wire, the product will be damaged due to leakage and excessive voltage, which will endanger personal safety. In order to prevent such problems from occurring and ensure safety, a grounding wire is required. Metal electrical products The metal rod with the shell connected to the ground can discharge electricity. In order to prevent danger and ensure safety, grounding construction should be carried out and grounding resistance testing should be carried out.

    The grounding resistance is measured by inserting two grounding rods into the ground, adding an AC voltage between the grounding rods E and C to generate a current I, and the grounding resistance can be detected by the voltage generated between the EC. The relationship between the current I and the voltage V As shown below, the ground resistance value can be calculated from this. However, the ground resistance value R calculated by the above method includes not only the ground resistance of the ground electrode E, but also the ground resistance of the ground electrode C, so it needs to be at the ground level of the EC A third ground electrode is established between EP and the value of the ground resistance RE of the ground electrode E can be calculated from the voltage Vp and the current I between EP. *The ground electrode P also has a resistance area, but the AC constant current impedance of the power supply is relatively high , Has no effect on detection.

    Ground rod configuration method:

    3-electrode method:

    The distance between E (grounding wire) and auxiliary grounding rods P and C should be about 5-10M, and should be in a straight line. When there are obstacles that cannot be set in a straight line, a suitable angle can be used between EP and EC, generally Within 30 degrees.

    2-electrode method:

    It is already known that the grounding resistance point E (grounding wire) is nearby, it can be used to detect the unknown grounding resistance. The E terminal and E point of the grounding resistance meter are connected with a wire, and the P and C terminals are used as 1 terminal. The resistance value can be detected between;

    The displayed value contains the resistance value of point E. The true effective value should be calculated. The grounding resistance value of point E must be subtracted;

    Sand, sand grains, frozen soil, need to expose the soil surface;

    Concrete requires the use of auxiliary nets. The auxiliary nets should be fully sprinkled with water to make it contact the earth as much as possible for accurate detection;

    Asphalt, cannot be detected;

    The Method and Necessity of Testing and Testing the Mechanical Characteristics of High Voltage Switches
    Views:474    2021-01-26 17:07:25

    Only by ensuring proper opening and closing speeds can the high-voltage switch give full play to its ability to break current, reduce the electrical wear of the contacts caused by the pre-breakdown during the closing process, and avoid contact burnout, fuel injection, and even explosion occurs. The decrease of the just-closing speed, if the closing is in a short-circuit fault, due to the effect of blocking the electrical power of the contact closing and closing, it will cause the contact to vibrate or put it in a stagnant state, which is also prone to explosion, especially when the automatic reclosing is not This is especially true in the case of success. On the contrary, if the speed is too high, the motion mechanism will be subjected to excessive mechanical stress, causing damage to individual components or shortening the service life. At the same time, due to strong mechanical shock and vibration, the contact bounce time will be lengthened. The situation is similar for vacuum and SF6 circuit breakers.

       The opening and closing of the high-voltage switch are severely different in different periods, which will cause the non-full-phase connection or cut-off of the line or transformer, which may cause overvoltage that may harm the insulation. Some aspects of the mechanical characteristics of high-voltage switches are represented by contact action time and movement speed as characteristic parameters. In the mechanical characteristic test, the main ones are just opening speed, just closing speed, opening speed, opening time, closing Opening time, closing-opening time, opening-closing time, opening and closing synchronicity, etc.

       1. Definition of time parameter

      1, opening time

       refers to the time interval from the moment when the circuit breaker is opened (the moment when the opening command is received) to the moment when the contacts of all poles are separated. The opening time must be within the specified time range. If the opening time is too short, the DC component will be too large when the system is short-circuited, which may cause difficulty in opening; if the opening time is too long, the stability of the system will be affected.

      2, closing time

       refers to the time interval from the moment when the closing circuit is energized to the moment when all pole contacts are in contact with the circuit breaker in the off position. It should have a short closing time, reduce the energy of the arc when closing, and prevent the arc from welding the contacts.

      3, opening-closing time

       is the time interval from the moment when all the pole contacts are separated to the moment when the pole contacts first when the circuit breaker is auto-reclosing.

      4, close-minute time

       is the time interval from the moment when the contacts of the first contact pole are contacted to the moment when all pole contacts are separated during the subsequent opening operation during the closing and opening process of unsuccessful reclosing or during the separate closing and opening operation of the circuit breaker.

      5. Synchronization of opening and closing operations

    It refers to the time difference between the three-phase breaking and contact instants of the circuit breaker during the opening and closing operations, and the time difference between the contact breaking and contact instants of the arc extinguishing units in the same phase. The former is called phase-to-phase synchronism, and the latter is called the same-phase fractures. Inter-synchronism.

       2. Definition of speed parameter

      1, the contact speed

       refers to the movement speed at the moment when the moving contact is separated from the static contact during the opening of the switch. When the technical conditions are not specified, the national standard recommends to take the average speed within 0.01s just after the minute as the instantaneous speed of the just split point, and use the nominal overtravel calculation point as the just split point.

      2, contact just closing speed

       refers to the instantaneous movement speed of the moving contact and the static contact during the closing process of the switch. When the technical conditions are not specified, the national standard generally recommends taking the average speed within 0.01s before just closing as the instantaneous speed of the just closing point, and the nominal overtravel calculation point as the just closing calculation point.

      3, opening speed

       refers to the MAX of the average speed of the section during the opening of the switch, but the section length should be specified in accordance with the technical conditions, if not specified, it is calculated as 0.01s.

       The speed parameter of the circuit breaker is expressed by its opening and closing speed. Since the speed of the circuit breaker is different at each moment in the process of movement, the general concern is just opening, just closing speed and speed.

       Three, the method of measuring the time parameter of the circuit breaker

      In the field test of the circuit breaker, the opening time, closing time, opening and closing synchronicity measurement should generally be carried out. For circuit breakers with reclosing operation, the opening-closing time and closing-opening time should also be measured.

       is measured by a high-voltage switch mechanical characteristic tester. It has the advantages of intelligence, multiple functions, accurate data, strong anti-interference, simple operation, small size, light weight, and beautiful appearance. It is suitable for various indoor, multi-oil switches, vacuum switches, and sulfur hexafluoride switches. Characteristic test. Main test items and functions: inherent opening and closing time of 12 fractures; reclosing time; different periods of opening and closing; just opening and closing speed; bounce time and amplitude; switch opening distance and switch overtravel ( Vacuum switch, preset switch stroke); average speed of opening and closing.

    Six factors that need attention to prevent pressure sensor problems
    Views:454    2020-12-26 17:17:59

    [Guide] If the pressure sensor is exposed to a manufacturing environment that exceeds the limits specified by the supplier during storage or assembly, the sensor will have problems. The following six factors are worth noting.

    If the pressure sensor is exposed to a manufacturing environment that exceeds the limits specified by the supplier during storage or assembly, the sensor will have problems. The following six factors are worth noting:

    1. Temperature

    Excessive temperature is one of the common causes of many problems with pressure sensors, because pressure sensors have many components that can only work normally within the specified temperature range. During assembly, if the sensor is exposed to an environment outside these temperature ranges, it may be negatively affected.

    For example, if the pressure sensor is installed close to the steam pipe that generates steam, the dynamic performance will be affected. The correct and simple solution is to move the sensor to a location far away from the steam line.

    2. Voltage spikes

    Voltage spikes refer to short-term voltage transients. Although this high-energy surge voltage lasts only a few milliseconds, it can still cause damage to the sensor. Unless the source of the voltage spike is very obvious, such as from lightning, it is extremely difficult to find. OEM engineers pay attention to potential failure risks in the entire manufacturing environment and surrounding areas. Timely communication with us helps to identify and eliminate such problems.


    3. Fluorescent lighting

    Fluorescent lamps require high-pressure arcs to break down argon and mercury when starting, so that the mercury is heated into a gaseous state. This starting voltage spike may pose a potential hazard to the pressure sensor. In addition, the magnetic field generated by the fluorescent lighting may also induce a voltage to act on the sensor wire, so that the control system may mistake it for the actual output signal. Therefore, the sensor must not be placed under or near the fluorescent lighting device.


    4. EMI/RFI

    Pressure sensors are used to convert pressure into electrical signals, so they are susceptible to electromagnetic radiation or electrical interference. Although sensor manufacturers have tried their best to ensure that the sensor is protected from the adverse effects of external interference, some specific sensor designs should reduce or avoid EMI/RFI (Electromagnetic Interference/Radio Frequency Interference) effects.


    Other sources of EMI/RFI to avoid include contactors, power cords, computers, walkie-talkies, cell phones, and large machinery that generate varying magnetic fields. Common methods to reduce EMI/RFI interference include shielding, filtering and suppression. You can consult us for the correct precautions.


    5. Shock and vibration

    Shock and vibration can cause a variety of problems, such as dents in the housing, broken wires, cracked circuit boards, signal errors, intermittent failures, and shortened lifespan. In order to avoid shock and vibration in the assembly process, OEM manufacturers must first consider this potential problem in the designer, and then take measures to eliminate it.

    The simple method is to install the sensor as far away as possible from obvious shock and vibration sources. Another possible solution is to use a vibro-isolator, depending on the installation method.


    6. Overpressure

    Whether it is at its own manufacturing site or at the user's place, once the OEM has completed the machine assembly, care should be taken to avoid overvoltage problems. There are many reasons for overvoltage, including water hammer effect, accidental heating of the system, and voltage stabilizer failure.


    If the pressure value occasionally reaches the upper limit of the withstand pressure, the pressure sensor can still withstand and restore the original state. But when the pressure value reaches the burst pressure, this will cause the sensor diaphragm or housing to rupture, causing leakage. The pressure value between the upper limit of the withstand pressure and the rupture pressure may cause the diaphragm to deform, thereby causing output drift.


    To avoid overvoltage, OEM engineers understand the dynamic performance of the system and the limits of the sensor. When designing, they need to grasp the interrelationships among system components such as pumps, control valves, balance valves, check valves, pressure switches, motors, compressors, and storage tanks.

    Sensor + cloud monitoring makes uninterrupted production possible
    Views:497    2020-12-26 17:17:41

    Foreign R&D institutions have launched cloud monitoring software and SensoNODE sensors to allow users to access machine status data through a Web browser, so as to achieve the purpose of identifying operations and improving performance. Industry 4.0 and the Internet of Things are bringing huge benefits to industry, and innovative solutions fill the gap between modern technology and traditional manufacturing.

    R&D technology is a cloud-based continuous monitoring solution that reverses the chaos of traditional asset monitoring, enabling users to centrally access asset information, whether on site or miles away.

    The remote continuous monitoring system allows factory employees to access asset data from any place connected to the Internet, monitor and solve machine health problems, analyze production or manufacturing potentially dangerous situations, and receive alarm notifications of problems through email, text and system messages. In addition, it also supports exporting data for analysis and reporting, and multiple users can monitor the data at the same time.

    David Shannon, the R&D worker, said that continuous monitoring means that the system always pays attention to problems and reminds users when there are problems. He said this allows employees to "manage by exception" and focus on those assets and/or processes that require their attention, instead of spending unnecessary man-hours to manually check and collect data on assets/processes that are correctly operated. Check out the Reconnaissance Cloud Software product page for more details.

    David Shannon said that continuous monitoring means that the system will constantly monitor equipment and alert users when there are problems, so that employees can manage exceptionally and focus on assets or processes that need their attention without spending unnecessary manual time. To manually check and collect asset or process data for correct operation.

    Wireless sensor networks are maturing and have broad application prospects in the industrial field
    Views:285    2020-12-26 17:12:35

    With the continuous maturity of industrial wireless sensor network technology and the continuous improvement of market demand, the effect of industrial wireless sensor network products on the replacement of traditional industrial sensors has been continuously improved.
       In 2015, my country's industrial wireless sensor network products accounted for about 4.9% of the industrial sensor market, with a scale of 780 million yuan. By 2020, my country's industrial wireless sensor network products will account for 11.7% of the industrial sensor market, and the market size is expected to reach 3.6 billion yuan, with a compound annual growth rate of as high as 35.8%. The market prospect is broad.
    To
      working principle
    To
    The component modules of the wireless sensor are encapsulated in a shell. When it is working, it will be powered by a battery or a vibration generator to form a wireless sensor network node. It consists of randomly distributed micro nodes integrated with sensors, data processing units and communication modules. The way of organization constitutes a network.
    To
       It can collect the digital signal of the device and transmit it to the wireless gateway of the monitoring center through the wireless sensor network, and send it directly to the computer for analysis and processing. If necessary, the wireless sensor can also transmit the entire time history signal collected in real time. The monitoring center can also wirelessly transmit information such as control and parameter settings to the nodes through the gateway. The data conditioning, acquisition and processing module amplifies and filters the weak signal output by the sensor, then sends it to the analog-to-digital converter, converts it into a digital signal, and sends it to the main processor for digital signal processing to calculate the effective value and displacement of the sensor. Value etc.
    To
       three advantages
    To
       With the development and maturity of wireless sensor network technology, wireless sensor network products have begun to gradually replace traditional wired sensor products with their own unique advantages, and have penetrated into all aspects of the industrial field, becoming an emerging hot spot in the market. Compared with traditional wired sensors, wireless sensors exist, and their advantages are mainly reflected in the following aspects:
    To
       Higher flexibility. It is suitable for situations with mobile requirements but inconvenient wiring, such as cranes, mobile bottling equipment, transportation industry, automatic guided vehicle systems and monorail conveyors.
    To
      Higher reliability. The wireless sensor can avoid the damage caused by movement, such as the bending of the wire caused by the long drag chain, the twisting and breaking of the cable caused by the rotating movement, and so on. At the same time, the fault factor caused by the connector in the wired network is eliminated.
    To
      Higher security. With the development of technology and the continuous emergence of new threats, the ability to upgrade security maintenance is essential. The new encryption strategy and covert data transmission indicate that wireless security levels will exceed wired systems. In addition, in some dangerous extreme environments, such as blasting occasions where wiring is inconvenient, wireless sensors can ensure the safety of personnel.
    To
      Application area
    To
       The advantages of wireless sensor network make it have a wide range of market applications, almost involving all areas of social and economic activities.
    To
       One is the field of pipeline and trench monitoring, such as the monitoring of temperature, pressure, and flow parameters of pipelines such as water supply and drainage, heating, gas supply, and oil supply. The second is the field of warehouse monitoring, such as the monitoring of temperature and humidity, temperature, flammable and explosive gases, and toxic and harmful gases in grain warehouses, drug warehouses, food warehouses, and factory hazardous chemical warehouses. The third is the monitoring field of manhole covers and fire hydrants, such as the monitoring of the operation status of urban manhole covers and fire hydrants. The fourth is the field of liquid level and water level monitoring, such as the parameter monitoring of water level and liquid level in rivers, dams, reservoirs, and oil tanks. Fifth is the field of greenhouse monitoring, such as the monitoring of temperature, humidity, light, gas...parameters such as vegetables, flowers, breeding (chicken, duck, pig house, etc.). Sixth is the field of aquaculture monitoring, such as the monitoring of water quality and gas parameters such as fish ponds and cages. Seven is the field of atmospheric environmental monitoring, such as the monitoring of toxic and hazardous gases in public places such as parks, schools, and communities. In addition to the above 7 main application areas, there are other applications, such as military, scientific research and so on.
    To
       One of the key technologies in the Internet of Things is sensor technology. The wireless sensor network plays a pivotal role in the application process of the industrial Internet of Things. It is responsible for connecting independent sensor units through a wireless network, and collecting the data collected by each sensor, so as to realize the physical or environmental conditions in the scattered range of the space. Collaborative monitoring, and then perform corresponding analysis and processing based on this information. Nowadays, modern industrial production is developing in the direction of large-scale, rapid and low-consumption. The wireless sensor network will play a special role in the future intelligent production of enterprises by virtue of its advantages of flexibility, safety, reliability, convenience and low cost.

    The principle and application of high current temperature rise test using simulated load method
    Views:499    2020-12-26 16:50:03

    The high current temperature rise test is an important indicator to measure the performance of electrical equipment, especially in the factory inspection test of transformers and circuit breakers. Although there are many types of transformers and circuit breakers and their functions are very different, the process of temperature rise test is basically the same. The following explains the principle and application of the large current temperature rise test system using the simulated load method for the large current temperature rise test.

    The temperature rise test of dry-type transformers with simulated load method needs to be carried out step by step. Carry out a no-load test, let the exciter core heat up, wait until the temperature is stable, and then perform a short-circuit test until its temperature is stable, and measure the temperature rise of the winding under the no-load test and the temperature rise of the winding under the short-circuit state respectively. According to the temperature rise in the two stages, the total temperature rise is calculated.

    The no-load temperature rise test uses an open circuit on one side and a rated voltage on the other side. Place the thermometer at the point that needs to be measured, and then let the iron core generate heat due to no-load loss until the temperature is stable. Since the winding does not generate heat during the no-load test, the heat exchange process between the iron core and the winding cannot be effectively displayed. The measured value is only a reference value and cannot be evaluated as the actual temperature rise. When the temperature of the iron core stabilizes, the temperature rise of the winding is measured.

    The measured temperature rise is obtained indirectly by measuring the change of the winding resistivity, and belongs to the average temperature rise. After cutting off the power, it will first measure a value, and then measure a value every 30 seconds, continuously measure ten times, and then measure once every 10 minutes. The measured value needs to use a semi-logarithmic coordinate to make a curve, and then measure its instantaneous thermal resistance value according to the extrapolation method. The short-circuit temperature rise test is carried out after the no-load temperature rise test. The connection method of the short-circuit temperature rise transformer is the same as the no-load temperature rise test. The low-voltage side is short-circuited and the high-voltage side is used for power supply. After the testing of the test circuit is completed, the rated current is applied to the high-voltage side, and the transformer generates heat due to the short-circuit of the winding. After the temperature rise is stable, the thermal resistance of the high- and low-voltage windings is tested.

    The short-circuit temperature rise of the high and low voltage windings is calculated. The test method and calculation method are the same as the no-load temperature rise test. The actual temperature rise of the windings is calculated according to the temperature rise of the high and low voltage windings measured during no-load and short-circuit conditions.

    The mutual load method uses an auxiliary transformer with the same test voltage ratio and connection group. One winding is used for rated excitation, and the other winding is connected in parallel through the auxiliary transformer and the end of the test product with the same name. By adjusting the input voltage of the load auxiliary transformer, Adjust the load current to reach the rated value. The power supply of the auxiliary transformer can be the same as or different from the rated excitation power supply, but no matter what kind of power supply, it should be ensured that the phase and frequency of the power supply are exactly the same, so as to ensure the smooth progress of the test.

    Since in the actual test process, there are often many factors that affect the test results, it is necessary for the tester to take these factors into consideration. Under the existing conditions, effective measures should be taken to reduce the interference of external factors. Obtain more accurate data.

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