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How to estimate the series resonant frequency?
2025-06-06A series resonant capacitor is simply the result of surface mount devices and pin leads. For a typical plug-in capacitor, its average equivalent series inductance is 2.5nH/2.54mm. The average equivalent series inductance of surface mounted capacitors is 1nH. Based on the above, it is important to consider the equivalent series inductance of capacitors when using decoupling capacitors. Surface mounted capacitors have better performance than plug-in capacitors at high frequencies because their equivalent series inductance is very low. Blocking network 2 is used to block f1=747KHZ, taking C2=1250pF, then:What is resonant frequencyA power of 1mW is applied on a 600 Ω load, and the voltage value on the load is at zero level. At this time, the AC voltage on the load is 0.775V.Definition of resonant frequencyThe impedance of an ideal capacitor decreases with increasing frequency, while the impedance of an actual capacitor exhibits capacitive characteristics at lower frequencies, where the im
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The function of AC series resonant reactor
2025-06-04As the name suggests, a reactor refers to a series connected inductor in a circuit. In the field of reactive power compensation and harmonic control, series reactors mainly refer to reactors connected in series with capacitors. The series connected reactor and capacitor form a resonant circuit. To eliminate or filter harmonics. Reduce the surge current multiplier and surge frequency of the capacitor bank, protect the capacitors, and facilitate the selection of supporting equipment. Form a complete resonant circuit together with the capacitor bank to filter out specific subharmonics. After the inductance of the series filter reactor and the capacitance of the capacitor are fully adjusted, an AC filter with characteristic subharmonics is formed to filter out the characteristic subharmonics, thereby reducing the voltage distortion of the harmonic on the bus and reducing the line. Harmonic current improves the power quality of the network and bus power supply. A bias that forms a resona
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The use and precautions of non partial discharge withstand voltage test device
2025-05-30In order to work in different usage environments and conditions, while adapting to different voltage levels and capacity requirements. Our company has designed a series of power frequency non partial discharge test transformers and their corresponding complete sets of equipment, including four models and over sixty specifications. Power frequency non partial discharge test transformers are divided into four types according to their structural types: single-phase iron shell type, single-phase iron shell cascade type, single-phase insulation cylinder shell type, and single-phase insulation cylinder external cascade type. Single phase iron shell is suitable for gas applications with low voltage capacity, easy portability, or high voltage capacity but low partial discharge requirements; Suitable for situations where the voltage is not too high and the use is relatively fixed. Users can choose single-phase insulated cylinder cascade products according to different needs. They are suitable
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What is the difference between the partial discharge high-voltage test system and the partial discharge test device?
2025-05-29What is the difference between high-voltage non partial discharge withstand voltage test kit and partial discharge withstand voltage test kit? This equipment is capable of conducting power frequency withstand voltage tests and partial discharge tests on power transformers, high-voltage circuit breakers, power cables, transformers, and insulation materials of 35kV and below, and belongs to the non partial discharge withstand voltage test equipment group. 1. Characteristics of the product. This device is fully functional, compact in size, lightweight, aesthetically pleasing, and easy to move. 2. All operations can be completed through the keyboard, all measurement and control data are digitized, and the entire workflow is intelligent.3. There are four display windows at the same time, which can display high and low voltage, current, and withstand voltage time. There are also multiple status indicator lights that make the workflow and status clear at a glance. 4. Enter automatic or ma
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The influence of operating parameters on the error of electric energy meters
2025-05-28The electric energy meters calibrated from the calibration room are all measured under normal conditions specified in the regulations. In fact, it is impossible for all electric energy meters to operate under the rated conditions specified in the regulations. Operating parameters such as voltage, load, waveform, etc. are subject to variation, which can cause additional errors in the energy meter. The reasons for the formation of additional errors in electric energy meters and their compensation measures will be discussed below. 1. The impact of voltage changes on errorsDue to the voltage variation of the power grid usually between 90% and 105% Ue, there is a voltage drop in each line, which causes the voltage U applied to the energy meter to be different from the rated voltage Ue. This will cause the voltage working flux to not change proportionally with the voltage, and destroy the original proportional relationship between the voltage suppression torque, compensation torque, and dri
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Analysis of Grounding Line Selection and Criteria for Small Current Grounding Systems
2025-05-271. IntroductionIn China's 35kV and 10kV power systems, the neutral point of transformers is often non directly grounded (for small grounding current systems). When a single-phase grounding fault occurs in the line, the value of the fault current is often much smaller than the load current. The fault phase voltage drops to zero, and the non fault phase voltage rises to times the phase voltage. However, the line voltage between the three phases still remains symmetrical and has no impact on the power supply load. Therefore, the regulations allow for continuous operation for 1-2 hours. However, in actual operation, accidents such as power cable explosions, TV fuse melting or even burning, and bus short circuits may occur due to overvoltage. Therefore, quickly determining the system grounding point and eliminating single-phase grounding faults is of great significance for the safe operation of the system. The traditional method of finding grounding fault lines is to sequentially discon
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Classification and protection of oil immersed transformers
2025-05-26According to the number of phases of a single transformer, it can be divided into three-phase transformers and single-phase transformers. In three-phase power systems, three-phase transformers are generally used. When the capacity is too large and limited by transportation conditions, three single-phase transformers can also be used to form a transformer group in three-phase power systems. According to the number of windings, it can be divided into double winding transformers and three winding transformers. Typical transformers are double winding transformers, which have two windings on the iron core, one as the primary winding and one as the secondary winding. A three winding transformer is a transformer with a larger capacity (above 5600 kVA) used to connect three different voltage transmission lines. In special cases, there are also transformers that use more windings. According to the structural form, it can be classified into iron core transformers and iron shell transformers. I
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Advantages of series resonant power supply in power system applications
2025-05-221. The required power capacity is greatly reduced. Series resonant power supply generates high voltage and high current through resonance between resonant reactor and tested capacitor. In the entire system, the power supply only needs to provide the active consumption part of the system. Therefore, the required power supply for the test is only 1/Q of the test capacity2. The weight and volume of the equipment have been greatly reduced. In a series resonant power supply, not only is the bulky high-power voltage regulating device and ordinary high-power power frequency test transformer eliminated, but the resonant excitation power supply only requires 1/Q of the test capacity, greatly reducing the weight and volume of the system, usually 1/3-1/5 of ordinary test devices 3. Improve the waveform of the output voltage. A resonant power supply is a resonant filtering circuit that can improve the waveform distortion of the output voltage, obtain a good sine waveform, and effectively prevent
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Research on anti-interference methods for digital time relays
2025-05-21Abstract: Through the analysis of the causes of misoperation of digital time relays under electromagnetic interference conditions, this paper preliminarily discusses the anti-interference measures of digital time relays under such interference conditions, and provides reference for further improving the anti-interference performance and reliability of digital time relays. Keywords: Digital time relay, anti-interference filteringIntroductionWith the continuous development of digital technology and related professions, relay protection technology has also made great progress, such as the application of static relays in power systems. Among them, digital time relays, as basic components, have been widely used in various relay protection and automatic control circuits, enabling the controlled equipment or circuit to obtain the required delay and achieve selective coordination between main protection and backup protection. Digital time relays are used for relay protection, primarily to repl
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The advantages of conducting AC withstand voltage tests on cables
2025-05-20With the development of the national economy and the improvement of the voltage level of urban power supply, cross-linked polyethylene insulated power cables (XLPE) have been increasingly widely used at home and abroad due to their reasonable process and structure, excellent electrical performance, and safe and reliable operating characteristics. Especially in the field of high-voltage transmission, significant progress has been made. Compared with oil filled cables, cross-linked cables are easy to lay and install, have simple operation and maintenance, and do not have oil leakage problems. However, recent operations and research have shown that the insulation of cross-linked polyethylene cables is prone to dendritic discharge during operation, causing insulation aging and damage, seriously affecting the service life of cross-linked polyethylene insulated power cables. Therefore, fully understanding the insulation characteristics of cross-linked cables, timely and effectively discoveri
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Why use high current to measure the circuit resistance of a circuit breaker?
2025-05-16Many high current electrical equipment in the power system require accurate measurement of circuit resistance values during preventive and handover tests. Circuit breakers are important electrical equipment in power systems. The national standards GB763 and GB50150, as well as the power industry standard DL/T596, stipulate that the measurement of the conductive circuit resistance of circuit breakers should be carried out using the DC voltage drop method, with a current not less than 100A.The resistance of the conductive circuit of a circuit breaker mainly depends on the contact resistance between the moving and stationary contacts of the circuit breaker. The existence of contact resistance increases the loss of the conductor when it is energized, causing the temperature at the contact to rise. The magnitude of its value directly affects the current carrying capacity during normal operation and to some extent affects the ability to cut off short-circuit current. Therefore, the resistanc
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Method for measuring transformer resistance exceeding the standard using a DC resistance tester
2025-05-14The DC resistance tester under UHV power can help many power workers conduct various power tests more conveniently.The measurement of DC resistance is to check the welding quality of the winding and the short-circuit situation between the windings; Whether the position of the tap changer is good and whether the actual position is consistent with the indication; Whether the wire is broken or loose; And the winding of the strands did not break. Stocks and so on. The measurement of DC resistance is an essential inspection item for transformers after major repairs, pre tests, and changes in tap changer positions. It is also an important inspection item after faults.In general, measuring the DC winding of transformer windings and high-power inductive devices using conventional methods (bridge method and voltage drop method) is a time-consuming and labor-intensive task. In order to change this situation, shorten measurement time, and reduce the workload of testers, Wuhan Hezhong Electric has
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The usage steps and diagnosis of cable fault testing
2025-05-14The cable fault tester under UHV power can help many power workers conduct various power tests more conveniently.1. Fault diagnosis:The nature of cable faults can be simply divided into the following categories:1) Breakage: One or more core wires of a cable are disconnected, causing a signal interruption. This type of fault is detected using the pulse method.2) Mixed wire: There are three types: grounding, self mixing, and other mixed wires, which refer to insulation layer damage between core wires and leads, between the same pair of core wires, and between core wires. The insulation resistance of different pairs of wires drops to a very low level (several hundred to several thousand ohms), and even short circuits, seriously affecting signal quality. This type of fault can be tested using the pulse method first, and when the waveform of the cable fault tester is difficult to recognize, the bridge method can be used for side measurement.3) Poor insulation: The insulation material of the
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Comparison of advantages between clamp type grounding resistance tester and traditional grounding resistance tester
2025-05-13The clamp type grounding resistance tester under UHV power can help many power workers conduct various power tests more conveniently.Clamp type grounding resistance tester, also known as clamp type grounding resistance tester or grounding resistance tester. Widely used for measuring grounding resistance of electrical equipment in power, telecommunications, meteorology, oil fields, buildings, and industry. The clamp type grounding resistance meter does not require disconnecting the grounding wire and auxiliary electrode when measuring a grounding system with a circuit, making it safe, fast, and easy to use. The clamp type grounding resistance meter can measure grounding faults that cannot be measured by traditional methods, and can be applied in situations where traditional methods cannot measure them, because the clamp type grounding resistance meter measures the combined value of grounding body resistance and grounding body resistance. The resistance of the ground wire. The clamp type
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Testing method of commonly used transformer DC resistance rapid tester
2025-05-13The DC resistance tester under UHV power can help many power workers conduct various power tests more conveniently.1. The accuracy level of a general transformer DC resistance tester should be (0.2): the output current of transformers below 120MVA should be greater than 10A, the output current of transformers above 120MVA should be greater than 20A, the output current of transformers above 180 MVA should be greater than 40A, and the output voltage should be as high as possible. The output voltage of the 10A transformer DC resistance tester shall not be less than 18V, and the output voltage of the 20A transformer DC resistance tester shall not be less than 25V.The output current of the instrument determines the measurement accuracy, and the output voltage of the instrument determines the measurement speed. Therefore, when choosing an instrument, it is important to understand the output voltage of the selected instrument. The instrument should have the function of directly converting the
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Gas chromatography detection method and judgment criteria
2025-05-12The oil chromatography analyzer under UHV power can help many power workers conduct various power tests more conveniently.Gas chromatography is a technique for separating and analyzing multi-component mixtures. It mainly utilizes the differences in boiling point, polarity, and adsorption coefficient of each component in the sample to separate the components inside the column, and conducts qualitative and quantitative analysis on the separated components.Chromatography analyzers use gas as the mobile phase (carrier gas). When the sample is sent to the injector and vaporized, it is carried by the carrier gas into the packed column or capillary column. The differences between components cause them to be separated in the chromatographic column, and then the detector behind the column sequentially detects the components based on their physical and chemical properties. After the conversion, the electrical signal is sent to the chromatograph. workstation. The chromatographic workstation recor
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Characteristics of on load tap changer tester for transformers
2025-05-09The on load tap changer tester under UHV power can help many power workers conduct various power tests more conveniently.1. Strong comprehensive measurement ability. One instrument can measure various quantities of on load tap changers. Such as switch selection, whether there is a breakpoint, transition waveform, transition time, transition resistance, three-phase synchronization, etc.2. More comprehensive analysis of measurement results. Users can analyze the resistance values and time of each point in the waveform, the time of each time period, and the three-phase of different phases through the large screen LCD display and function buttons. Through visual analysis, it is possible to understand the changes in various parameters of the three-phase switch at every moment during the switching process, and to analyze and compare waveform printing, storage, and historical waveforms.3. Print it out. The instrument is equipped with a front panel paper exchange printer, which can be directly
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Reasons and solutions for inaccurate grounding resistance testing in lightning protection detection
2025-05-09The grounding resistance tester under UHV power can help many power workers conduct various power tests more conveniently.In electrical lightning protection testing, many factors can lead to inaccurate readings of grounding resistance. In summary, there are generally several reasons.1. When inspecting high-rise buildings, using excessively long or thick wires can increase line resistance and induced voltage, resulting in measurement errors. At this time, wires with relatively low resistance should be used to minimize measurement errors as much as possible.2. The insertion depth of the iron drill should be greater than 1/4 of the length of the iron drill. Otherwise, testing errors may occur. So. During testing, the iron should be deepened as much as possible.3. In the case where the tested grounding electrode is "common ground", due to poor insulation or short circuit of the equipment, the grounding device generates a certain grounding voltage to the ground, making the reading unstable.
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Troubleshooting of Karl Fischer Titimeter
2025-05-08The trace moisture analyzer under UHV power can help many power workers conduct various power tests more conveniently.1、 Open circuit measurementWhen measuring an open circuit, the measurement status display and electrolysis status display will show the maximum. Excessive iodine is generated in the electrolyte of the anode chamber of the LED digital display meter, causing the color to darken. At this point, the following situations should be checked:1. Measure whether the plug and socket are in good contact.2. Measure whether the electrode leads are open and whether the plug is well soldered.2、 Open electrolysisWhen the electrolysis is turned on, the measurement status indicator light indicates, but the electrolysis status indicator light only lights up two green lights, and the "LED" digital tube does not count. At this point, the following conditions should be checked:1. Is the electrolytic plug in good contact with the socket.2. Whether the electrolytic leads on the cathode chamber
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Specific operating methods and test procedures for partial discharge test
2025-05-08The specialized production of partial discharge testers for UHV power can help many power workers conduct various power tests more conveniently.Partial discharge test is a non-destructive testing project. From the perspective of testing sequence, it should be placed after all insulation tests. Generally, the power frequency withstand voltage is used as the pre applied voltage for a few seconds, and then reduced to the partial discharge measurement voltage (usually a multiple of Um/√ 3, 1.5 times for transformers, and 1.1 to 1.2 times for transformers), with a duration of a few minutes. Measure partial discharge; Pre applied voltage refers to the overvoltage (such as lightning strikes) during simulated operation. The amount of partial discharge excited by pre applied voltage should not be continued by the partial discharge test voltage, that is, the amount of partial discharge excited when the system experiences overvoltage will not be prolonged by long-term operating voltageSpecific di
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