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The reason for the decrease in resonant frequency of series resonant circuit
2025-09-19A series resonance (also known as variable frequency resonance) circuit is composed of a series capacitor and a capacitor, with an inductive coil L and a resistor R.The ideal series resonant circuit consists only of an inductor (without its own resistance) and a capacitor (LC circuit). Then, in this system, the current in the circuit, the voltage across the capacitor, and the charge of the capacitor maintain continuous electromagnetic resonance. Let's take a look at the outline and consider the source of the vibration. Place the initially charged capacitor in the circuit we are describing.At the initial moment, all charges are concentrated on the capacitor and there is no current on the coil (Figure 1.1). Because there is no external electric field on the capacitor board, electrons from the board begin to "leave" into the circuit (the charge on the capacitor begins to decrease). In this case (due to the released electrons), the current in the circuit increases. In this case, the di
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Magnetic fluid in series resonant circuit
2025-09-19The influence of polarization voltage on the electrical properties of the magnetic fluid layer filling the inter electrode space of a planar parallel capacitor connected to a series resonant circuit. The formation, development, and self-organization of aggregates several millimeters in size have been recorded in the magnetic fluid layer, which affects its electrical and physical properties.The changes in the electrical and physical properties of magnetic fluids in the presence of structural formation in an electric field have been studied in many works. Structure formation under the influence of weak electric fields up to 400 kV/m. The average size of the formed structures was found to be no more than a few micrometers, and their appearance is related to the increase in dispersed phase concentration near the electrode and subsequent aggregation. The aggregation process was explained based on the thermodynamic concept of phase transition. As is well known, due to the strong influence of
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Resonance effects in series resonant and parallel resonant circuits
2025-09-19Series resonant circuitThe series resonant circuit is shown in the figure. When there is resonance in the circuit, the inductance reactance and capacitance reactance will completely cancel each other out, and only the resistance of the circuit will provide resistance to the current. In this circuit, the impedance is only equal to the value of R plus the DC resistance of the coil. The main characteristic of a series resonant circuit is that its impedance is minimized during resonance. When the frequency is adjusted above or below the resonant frequency, the impedance will increase.Due to the minimum impedance during resonance in a series resonant circuit, the current in the circuit rises to its peak. When this high current value is multiplied by the inductive and capacitive reactance, it will cause a very high voltage drop across the inductor and capacitor. In fact, the voltage drop between the two ends of the inductor and the capacitorUnder resonance conditions, the power supply voltag
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What is lightning impulse test? What is its function?
2025-09-19The lightning impulse voltage generator under UHV power can help many power workers conduct various power tests more conveniently.Lightning impulse test is a test used to evaluate the tolerance of electrical equipment and systems under lightning or surge conditions. Due to lightning being one of the strongest electrical phenomena in nature, its high voltage, high current, and rapidly rising electromagnetic waves can cause serious damage to electrical equipment. Therefore, conducting lightning impulse tests is crucial to ensure the safety and reliability of equipment.The basic principle of lightning impulseLightning impulse is an instantaneous high voltage phenomenon caused by lightning discharge. When lightning strikes, current flows rapidly in the air, forming strong electric and magnetic fields. This process generates voltages of up to millions of volts, instantly releasing enormous amounts of energy. When this voltage is applied to electrical equipment, it may cause insulation mater
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Why does the actual measured waveform of a lightning impulse voltage generator exhibit oscillations or overshoot?
2025-09-18The oscillation or overshoot of the waveform measured by the lightning impulse voltage generator is mainly due to the parasitic inductance and capacitance in the test circuit forming an unwanted resonant circuit.Core Reasons:1.Loop Stray Inductance (Primary Cause): Long high-voltage leads and the equipment itself have inherent inductance. The current changes extremely rapidly (very high di/dt). This inductance generates a back electromotive force (EMF), causing overshoot and subsequent oscillation.2.Stray Capacitance to Ground: The test object, voltage divider, and leads all have capacitance to ground. This forms unintentional LC resonant circuits with the loop inductance.3.Wave Reflection and Impedance Mismatch: If the high-voltage leads are too long, they act like transmission lines. If the generator's output impedance doesn't match the lead's characteristic impedance, voltage waves reflect back and forth, distorting the waveform and causing overshoot and ringing.Main Sol
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How to maintain and upkeep the impulse voltage generator
2025-09-18The impulse voltage generator is a high-voltage testing device that requires regular maintenance to ensure personal and equipment safety. Maintenance should pay attention to the following points:1. To avoid dust accumulation, the generator should be wiped regularly, especially the surface of the insulation rod should be kept clean. (Note: Do not wipe with liquids such as water or alcohol);2. After using the equipment for a period of time, lubricating oil or butter needs to be added to each mechanical transmission part. Suggest adding it once a month, depending on the actual situation;3. Ensure that the equipment has a good operating environment (condition);4. The semiconductor paint of the high-voltage rectifier transformer on the surface of the upper section porcelain sleeve near the central flange should be well protected; If wear or failure is found and strong corona occurs, semiconductor anti corona paint should be sprayed to make the corona disappear basically;5. If there is any a
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Working principle and application analysis of lightning impulse voltage generator
2025-09-18Lightning impulse voltage generator is a high-voltage testing equipment that simulates natural lightning impulse and is widely used in the insulation performance assessment of power equipment. It generates instantaneous high voltage pulses through special circuit design, providing important guarantees for the safe operation of the power system.1、 Working principle: Simulate lightning impulse waveformThe core of a lightning impulse voltage generator is to generate steep high-voltage pulses through capacitor energy storage and discharge circuits. The device first stores electrical energy in a high-voltage capacitor bank, and then releases the energy in a short period of time through a switching device, forming a surge voltage waveform with extremely fast rise time and short duration. This waveform simulates the instantaneous voltage characteristics when lightning strikes power equipment, and can truly reflect the insulation performance of the equipment under special conditions2、 Key tech
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Precautions for lightning impulse voltage generator of power transformer
2025-09-18A lightning impulse voltage generator is an experimental device that can generate high-voltage pulses that simulate natural lightning waves. It is mainly used to test whether the insulation performance of power equipment (such as transformers, lightning arresters, insulators, etc.) is reliable when struck by lightning.Precautions during the use of lightning impulse voltage generator1. All connecting wires should be as short as possible, and all grounding should be low impedance and properly connected to avoid interference.2. According to national standards and relevant technical provisions, confirm the test type and test voltage of each terminal, and determine the transformation ratio of the impulse voltage generator and voltage divider used based on the test voltage of different windings. For three-phase transformers with tap connections, lightning impulse tests are generally conducted at two limit tap connections and rated tap connections.3. The transformer assembly is intact, and qu
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Series resonance in RLC circuit
2025-09-18The basic relationship during resonanceIn the figure, a is a symbolic value model that includes series connected resistors, inductors, and capacitors. For the sake of certainty, let us assume that the complex number shown in the figure is a complex number of significant values.This type of chain is widely used in engineering practice, but it is considered separately.Series resonant circuit:A symbolic model of a chain; Vector diagram during b-resonanceDue to the series connection of components in a given circuit, only series resonance can be observed. The complex input resistance of the circuit relative to terminals "1" and "2" is equal toThe resonance condition is the equal BX of the imaginary part of zero Z, that isTherefore, during resonance, the reactance of inductance and capacitance are equal. Under the given parameters L and C, resonance occurs at frequencyThe symbol 0 for the resonant frequency ω used here will be used in the following text.The state of the chain is determined b
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Series resonant circuit
2025-09-18In a series resonant circuit, the generator is connected in series with the coil and capacitor. For example, in the case of inductive coupling, the resonant circuit is continuous because an electromotive force is induced in the coil, which is equivalent to connecting the generator in series with coil L and capacitor C. The figure shows the equivalent relationship of these transformations.During resonance, a series circuit has the following characteristics:1. The minimum loop resistance is equal to Rpot.2.The voltage across the capacitor (or coil) is Q times the voltage of the generator. Q is the quality factor of the circuit.3. The maximum and equal current flowing through the circuitThe diagram illustrates a specific example of a series resonant circuit, and Figure 9 shows its frequency characteristics, provided that the internal resistance of the generator is small.Therefore, voltage resonance occurs in a series resonant circuit. For undeveloped circuits containing series connected i
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Q factor of series resonant circuit
2025-09-18According to the definition, the quality factor of a series resonant (also known as frequency modulated series resonant) circuit is determined by the following expression:Among them, W max is the maximum energy stored in the circuit at the resonant frequency, and P is the active loss power under the same conditions.During voltage resonancesimultaneouslyTherefore, the expression for the circuit quality factor takes the following form:itReceived the name of the characteristic impedance of the circuit.According to the expression, this expression indicates that the quality factor exceeds the reactance W0L and 1/W0C is higher than the active resistance r.ConsideringAccording to the formula:From the above equation, it can be concluded that:That is to say, the quality factor of the considered circuit is determined by the ratio of the voltage across L or C at resonance to the voltage value applied to the circuit.The figure shows the frequency dependence of current for two consecutive series re
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What are the advantages of motor test benches in power systems?
2025-09-17A motor test bench is an integrated testing platform that combines power sources, loads, measurement systems, controls, and data acquisition. It is primarily used for type tests, factory acceptance tests, commissioning tests, and performance verification of rotating electrical machines such as generators and motors after maintenance.Its advantages in power systems can be elaborated from multiple perspectives, centering on ensuring system safety, improving economic efficiency, and driving technological progress.1. Advantages for Power System Safety and StabilityThis is the most critical and essential value of motor test benches.1）Fault Prediction and Prevention: Before a motor is connected to the grid, rigorous tests (such as temperature rise tests, overload tests, insulation withstand voltage tests, and short-circuit characteristic tests) can identify potential design, material, manufacturing, or installation defects and weaknesses. This prevents "operating with hidden faults," avoidin
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What should be noted when using a motor test bench
2025-09-17Using a motor test bench is a highly cautious and professional task that involves three core aspects: personal safety, equipment protection, and data accuracy. The following are key points that require special attention.1、 Safety First: Core Security Standards1. Electrical safety:Grounding protection: Ensure that all equipment on the test bench (power supply, dynamometer, frequency converter, electrical parameter meter, etc.) have good and reliable grounding wires. This is the lifeline to prevent electric shock accidents.Insulation inspection: Before connecting the tested motor, check the insulation resistance of its winding to the casing (using a megohmmeter) to ensure good insulation and prevent leakage or short circuit.Anti electric shock: All high-voltage wiring and exposed terminals must be covered with insulation shields. When wiring, disconnecting or changing the circuit, the power must be completely cut off and a "Do not close" warning sign must be hung. Operate after dischargi
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Safety operating procedures for motor test bench
2025-09-17As a key equipment for motor performance testing, the safe operation of the motor test bench is a prerequisite for ensuring the safety of laboratory personnel and equipment. This article will provide a detailed explanation of the safety operating procedures for the motor testing bench, in order to enhance the safety awareness of operators and reduce the possibility of accidents.1、 Equipment inspectionBefore conducting any experiments, operators should conduct equipment checks on the motor test bench to ensure that all equipment is in good condition. Specifically, it includes:1) Power systemEnsure that the power cord is securely connected and there are no worn or exposed cables. Check if the power switch and emergency stop button are flexible and reliable.2) Mechanical structureCheck whether the transmission system, bearings, and connecting components are loose or worn. Ensure sufficient lubrication of the mechanical parts.3) Control systemCheck if the buttons, switches, and indicator l
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Working principle of fully automatic motor test bench
2025-09-17The motor test bench is an important equipment in the field of motor manufacturing and testing. It can comprehensively and accurately evaluate motors by integrating various testing functions. This article will delve into the working principle of the motor test bench.1. Structure and compositionMotor architectureThe basic architecture of the fully automatic motor comprehensive test bench includes mechanical structure, electrical system, and automatic control system. Mechanical structures are usually composed of motor brackets, rotors, sensors, measuring instruments, etc. The electrical system includes motor windings, power supply, frequency converter, etc., while the automatic control system is the brain of the entire test bench, responsible for coordinating and monitoring the operation of each part.Sensors and measuring instrumentsThe test bench is equipped with various sensors to monitor the operating status of the motor. These sensors include but are not limited to temperature sensor
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What are the contents usually included in the test report of the motor test bench
2025-09-17The motor test bench test report is a comprehensive and structured document used to record the performance, quality, and compliance of the motor under specific testing conditions. It is not only the final output of testing work, but also the key basis for product acceptance, quality traceability, and problem analysis.A professional motor testing report typically includes the following core contents:1. Report informationReport number, product model, serial numberTest date and testing criteria2. Test objectKey parameters such as motor model, rated power, rated voltage, and rated speed.3. Main testing equipmentList key instruments (such as dynamometers, power analyzers) along with their identification numbers and calibration status.4. Test items and resultsNo load characteristics: No load current, No load loss.Load characteristics: efficiency, power factor, speed vs torque curve.Locking test: starting torque, starting current.Temperature rise test: winding temperature rise (Δ T).Insulatio
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Four types of voltages that the series resonance test device can withstand
2025-09-17The insulation structure of electrical equipment can withstand the following four voltages during operation:1. The insulation structure of electrical equipment must be able to withstand the maximum working voltage of the power frequency for a long time throughout the entire operation process. Usually referred to as the maximum operating voltage of the system, it is usually 1.15 times the rated voltage.2. Transient overvoltage, including rising frequency voltage and resonant overvoltage, is caused by the capacitance effect, load shedding, and asymmetric grounding of the no-load line in the resonant AC power frequency voltage of the series resonance test device. When the load suddenly unloads, due to the fact that there is only one unloaded transmission line in the power supply, and the grounding reactance of the transmission line can be represented by X0, the current flowing through the internal resistance of the power supply becomes a capacitive current. This current flows through the
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Precautions for the use of variable frequency series resonant devices
2025-09-17Precautions for the use of variable frequency series resonant devices:1. Before conducting a voltage withstand test using a variable frequency series resonant device. Please measure the insulation resistance of the test sample according to the test procedure and confirm that it meets the relevant insulation requirements before proceeding to the next step of the voltage withstand test.2. Before conducting a voltage withstand test and starting the frequency converter series resonant device, please recheck if the wiring is correct. For example, the voltage output terminal of the excitation transformer should be connected to the lower end of the lowest level reactor using a grounding cable. The high-voltage output line at the upper end of the upper level reactor should be suspended as much as possible from the ground or surrounding objects to prevent the high-voltage line from discharging to the ground or objects. Every small mistake you make can cause irreparable damage to equipment and p
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Working principle of variable frequency series resonance test device
2025-09-17The variable frequency series resonance test device applies the working principle of knowledge series resonance. The excitation transformer can excite the series resonance control circuit, adjust the output signal frequency of the variable frequency controller, and make the circuit inductance L and the test sample C resonate in series. The resonance voltage is the voltage applied to the test sample. During the operation of power equipment, insulation materials gradually degrade under the action of temperature, electric field, and mechanical vibration for a long time, including overall and local degradation, resulting in defects. For example, due to the concentration of local electric fields or weak local insulation, there are local defects. Various preventive testing methods can detect some defects and reflect the condition of insulation materials. However, the test voltage of the testing method is often lower than the working voltage of the power equipment, which is not enough to ens
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Safety measures and operating precautions for transformer test bench
2025-09-16The transformer comprehensive test bench under UHV power can help many power workers conduct various power tests more conveniently.Safety measures for transformer test bench1. Before using this instrument, it is necessary to carefully read this manual.2. The operator of the instrument should have general electrical knowledge.3. The transformer comprehensive test bench should be used in places that are not exposed to rain, corrosive gases, excessive dust, high temperatures, direct sunlight, etc.4. Instruments should avoid severe vibrations.5. After the test is completed, be sure to wait for the discharge alarm to stop before turning off the power and removing the test line.6. When measuring an unloaded voltage regulating transformer, be sure to wait for the discharge indicator alarm sound to stop before switching gears.7. During the testing process, it is prohibited to move the test clamp and power supply line.Precautions for transformer characteristics comprehensive test bench1. It is
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