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Analysis of AC withstand voltage test using series resonance
2025-10-22For samples with good insulation, they will not be broken down in series resonant AC withstand voltage. To determine whether they have been broken down, the following phenomena can be analyzed.(1) Analyze according to the indications in the circuit access tableIn general, if the ammeter of a series resonant device suddenly rises, it indicates the breakdown of the tested product. But when the ratio of the capacitive reactance xc to the leakage reactance xl of the test transformer is equal to 2, although the test has been interrupted, the indicator light of the ammeter remains unchanged (because the circuit reactance x=xc xl, when the test short circuit xc=0, there is still xlt in the circuit, which is equal to the reactance before the test, so the indicator light of the ammeter will not change). When the ratio of xc to xl is less than 2, the reactance of the test circuit increases and the pointer of the ammeter decreases. Usually, XC>XL does not have the above situation. It can only occ
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What are the factors that affect the results of the variable frequency series resonance test?
2025-10-22Variable frequency series resonance adopts various protection measures, making the test convenient, safe, and reliable. The inherent filtering effect of the resonance circuit ensures that the test voltage waveform output by the system fully meets the requirements of the testing program. However, there are often some uncertain factors in the results of series resonance tests. So, what are these factors? 1) The impact of high-voltage leadsWhen conducting AC withstand voltage tests on a single electrical equipment, due to the small capacitance of the test product, the impact of high-voltage wires on the test is minimal. When conducting AC withstand voltage tests on outdoor distribution equipment as a whole, the installation height of the equipment increases with the increase of voltage level. The higher the voltage, the longer the high-voltage lead. Generally, the longer the high-voltage lead, the higher the corona loss and the equivalent resistance of the circuit. The stray capacitance
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Characteristics of series resonance and parallel resonance
2025-10-22Series resonancehas the following characteristics:(1) Due to inductance being equal to capacitive reactance, the impedance reaches its minimum and exhibits pure resistance characteristics.(2) When the voltage is constant, the current in the circuit reaches its maximum value, which is used as the resonant current.(3) Due to resonance, the capacitance reactance is equal to the inductance, and the voltage on the inductance is equal to the voltage on the capacitance. The voltage on the inductance and the voltage on the capacitance are related to the resistance. If the inductance and capacitance are much greater than the resistance, the voltage on the inductance and capacitance may be much greater than the power supply voltage. Therefore, resonance, also known as voltage resonance, is destructive.Parallel resonance has the following characteristics:(1) When parallel resonance occurs, the total current of the circuit is minimized and in phase with the voltage. When the total impedance of the
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The principle and advantages of series resonance withstand voltage test
2025-10-21The series resonance test device can utilize the inductance and capacitance of the resonant reactor to generate series resonance with the tested equipment, and obtain the required high voltage on the tested object. The basic principle of series resonance is shown in Figure 1.Figure 1 Schematic diagram of series resonanceWhen a series resonance occurs in the circuit, x1=xc，uc=u/rxc=u/rxl。 XL is the loop inductance, XC is the loop bending resistance, U is the excitation voltage, and UC is the receiving voltage of the test sample. If the quality factor of the resonant circuit is Q, then Uc=Qu, that is, the voltage obtained on the test sample is Q times the excitation voltage, and the capacity obtained on the test sample is Q times the capacity of the test power supply, thus achieving the purpose of conducting AC withstand voltage tests on low-voltage small capacity large capacity test transformers.The main method of tuning is to use adjustable iron core air gap reactors through modulation
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The following precautions should be taken during the operation of variable frequency series resonance
2025-10-211. Attention to wiring of excitation transformer: (1) For the withstand voltage device of 10 kV cable, the excitation transformer is generally connected to the low end; (2) The voltage withstand devices of 10 kV and 35 kV cables are connected to the low end of the 10 kV cable voltage withstand excitation transformer, and the high end of the 35 kV cable is connected to the high end; (3) 10 kV, 35 kV, and 110 kV cable voltage withstand devices: 10 kV and 35 kV cable voltage withstand excitation transformers are connected to the low end, and 110 kV cable voltage withstand excitation transformers are connected to the high end.2. Precautions for wiring reactors and capacitor dividers: For short cables, at least two reactors should be connected in series, regardless of voltage, to ensure that the circuit can resonate.3. Precautions for excitation transformer wiring: (1) The voltage withstand device of the motor is generally at the low end of the excitation transformer; (2) Voltage resistant
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Why is a series resonant circuit called a receiver circuit?
2025-10-21At resonance, the impedance of the inductor is equal to the impedance of the capacitorTherefore, ωL= 1 /ωC， Where w is angular frequency=2 π fω 2 LC = 1ω 2 = 1 / LCTherefore, during resonance, the impedance of the RLC circuit is equal to RDue to the fact that the current flowing through a series resonant circuit is the product of voltage and impedance, the impedance Z is at its minimum value (=R) during resonance. Therefore, the circuit current at this frequency will reach its maximum V/R value, as shown below.The frequency response curve of a series resonant (also known as a power frequency withstand voltage test equipment) circuit indicates that the magnitude of the current is a function of frequency. When plotted on a graph, it can be seen that the response starts from near zero, reaches its maximum value at the resonant frequency when I MAX=IR, and then decreases again to near zero as ƒ becomes infinite. The result is that even during resonance, the amplitude of the voltage C acros
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Charging Mode Control of Series Resonant Converter
2025-10-20In the technical field of devices and methods for converting power from power input to DC output voltage or current, a device and method for converting power from power input to DC output voltage or current, the device comprising a series resonant (also known as power frequency withstand voltage test equipment) converter, the series resonant converter comprising at least two semiconductor switches connected in series, the semiconductor switches having a common output terminal connected to at least one. The first coil may be part of a transformer, and the second winding of the transformer is connected to a rectifier device. The output of the rectifier device is connected to an output terminal, and the first feedback circuit is connected from the output terminal to an error amplifier. The error amplifier is connected to the input on the control circuit, and the output is connected to the input of the semiconductor switch through a driver device. The device further comprises a second feed
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Quality factor of series resonant circuit withstand voltage test
2025-10-201. IntroductionSeries resonant devices are widely used in on-site AC withstand voltage testing of large capacity test objects such as transformers and capacitors. Several factors affecting factor quality q in series resonant withstand voltage tests were analyzed to address common issues in practical applications.2. Capacity of the test objectThe q-value is the most important parameter for evaluating a series resonant circuit. It is proportional to the power frequency f and inductance L of the high-voltage capacitor, and inversely proportional to the impedance R, where R represents the active loss of the entire circuit. In the actual power frequency series resonance test circuit, according to the formula wl=l/wc, it can be concluded that the capacitance reactance determines the inductance reactance.However, Q = wL / R。 If the test object is GIS or equipment composed of independent components, voltage withstand testing can be carried out in sections to improve capacitance and obtain high
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Technical principle of frequency modulation series resonance test device
2025-10-20Power frequency withstand voltage test device. Composed of accessories such as 240 kVA/200 kV~400 kV variable frequency power supply, transformer, reactor, coupling capacitor, etc. The series resonance testing device has low waveform distortion, good stability, and functions such as frequency modulation, voltage regulation, operation, protection, and control. Provided assurance for on-site partial discharge testing. However, due to different testing items, the wiring method of the FM series resonance testing device is also different. For the possible problems of large transformers in partial discharge tests, we will take 220kV and 240 transformers as an example. By analyzing and calculating to select a reasonable wiring method, the testing work is completed, thereby improving the quality and efficiency of testing, and accumulating rich experience for future work.(1) Variable frequency power supplyVariable frequency power supply is the core of the equipment. It can change the input powe
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Why is a series resonant circuit called a receiver circuit
2025-10-17At resonance, the impedance of the inductor is equal to the impedance of the capacitorTherefore, ωL= 1 /ωC， Where w is angular frequency=2 π fω 2 LC = 1ω 2 = 1 / LCTherefore, during resonance, the impedance of the RLC circuit is equal to RDue to the fact that the current flowing through a series resonant circuit is the product of voltage and impedance, the impedance Z is at its minimum value (=R) during resonance. Therefore, the circuit current at this frequency will reach its maximum V/R value, as shown below.The frequency response curve of a series resonant circuit indicates that the magnitude of the current is a function of frequency. When plotted on the graph, it can be seen that the response starts from near zero, reaches its maximum at the resonant frequency when I MAX=IR, and then decreases again to near zero as ƒ becomes infinite. The result is that even during resonance. But the amplitude of the voltage C across the inductor L and capacitor C can be many times greater than the
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Rubber plastic series resonant AC withstand voltage test
2025-10-17Years of operational experience both domestically and internationally have shown that DC withstand voltage testing is not suitable for the handover or preventive testing of rubber plastic power wires. Instead, AC withstand voltage testing (frequency range 30-300hz) should be used to ensure safe movement. Cable. This is a groundbreaking change in the development history of preventive testing for power equipment. However, the DC withstand voltage test is still effective for oil immersed paper insulated power wires and should continue to be used. Due to the large capacity of the wires, it is not suitable to use high-capacity power frequency test transformers on site. The advantages of frequency modulation series resonance high-voltage testing equipment are light weight and small power capacity (only 1/30~1/80 of the power capacity of the testing transformer)This testing equipment is specifically designed and manufactured for on-site AC withstand voltage testing of rubber and plastic power
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What should I do if there is a series resonance mismatch
2025-10-17First of all, let me briefly explain the function and role of series resonance devices. Series resonance is applied in power systems for insulation testing of high voltage and large capacity electrical equipment. In practical use, series resonance requires matching of capacitors and inductors. Only when the matching is good can resonance voltage be generated. So, what should be done if series resonance loses its resonance?I believe that a small number of customers may encounter such problems, and we cannot do so now. To understand the series resonance detuning, we first need to know the composition and structure of the series resonance testing device. Under a certain capacitance, the circuit can produce a resonant state by adjusting the inductance and frequency. There must be a certain parameter generation method for series resonance detuning. The common detuning phenomenon is when the cable fails during the series resonance test, and the series resonance will inevitably detune and the
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Series resonant system
2025-10-16A series resonant device is a system designed primarily for testing capacitive loads using reactive voltage and reactive power. It draws very little power from the mains, only enough to meet the losses of the testing circuit.This series of resonance testing systems is designed for high-voltage testing of capacitance testing objects. For example, power cables, generators, bushings, capacitors, transformers, and SF6 gas insulated equipment.Working Principle:The practical series resonance testing system consists of a voltage regulator, excitation transformer, high-voltage variable reactor, and capacitor testing object. The voltage regulator is connected to the power supply through a main circuit breaker, and this component provides a variable voltage to the excitation transformer, allowing the output voltage to be adjusted to a value suitable for testing.The excitation transformer provides necessary power to the high-voltage circuit composed of HV variable reactors and test objects. The e
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Series resonance of series LCR circuit
2025-10-16When the reactants are equal, series resonance occurs. The inductance reactance (XL) of frequency and inductance is:The capacitance reactance (XC) is composed of:The reactance frequency is directly proportional, and its graph is plotted as a straight line with the frequency (ƒ). The capacitive reactance is inversely proportional to frequency, as shown in the graph where ƒ is the curve. These two quantities indicate that, R, By planning together for the ƒ plot, it can be seen that the intersection of XC and XL is equal, so the graph of (XL-XC) must be on the frequency axis, which is zero.The characteristics of series resonance in LCR circuits.The LCR series circuit is designed to respond to the situation where the resistance (R) and impedance (Z) occur when the frequency of the power source (VS) changes from 0Hz to XC. Firstly, the circuit behaves as a capacitor, and the total impedance (Z) of the circuit falls on a very similar curve to XL-XC.The relationship between individual compone
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What makes the variable frequency series resonance test device powerful?
2025-10-16In the high-voltage withstand voltage test device, the variable frequency series resonance test device is an ideal choice,. Due to the many advantages of variable frequency series resonance over traditional voltage withstand test devices, series resonance voltage withstand test devices are also highly welcomed by power workers. What makes the variable frequency series resonance withstand voltage test device powerful?The variable frequency series resonance test device has powerful protection functions and is safer than traditional high-voltage withstand voltage testing methods, such as overvoltage, overcurrent, system flashover, zero position start and other protection functions. In addition, the overvoltage and overcurrent protection functions can be adjusted according to user needs. During flashover protection, in addition to the flashover action, the flashover voltage value can also be recorded, making it convenient for users to conduct test analysis. The variable frequency series r
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The complete set of equipment for frequency conversion series resonance test is used to conduct AC withstand voltage test on the generator
2025-10-15To evaluate the insulation strength of a generator, the frequency conversion series resonance test equipment and the power frequency AC withstand voltage test are the most effective and direct ways, because the waveform frequencies of the voltage and working voltage in the power frequency AC withstand voltage test are the same, which will have important decisive significance for determining whether the generator can be used. Therefore, the power frequency AC withstand voltage test is a very important test in the generator insulation test.It should be noted that before conducting the AC withstand voltage test, it is necessary to comprehensively analyze and judge other non-destructive testing results such as insulation resistance, absorption ratio, leakage current, etc., and then decide whether the generator can undergo the withstand voltage test to avoid excessive insulation breakdown during the test.How to conduct AC withstand voltage test for series resonant generator, the specific op
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How to use the complete set of frequency conversion series resonance test equipment to quickly find the resonance point?
2025-10-15In practical work, power workers often need to conduct resonance tests on high-voltage power cables to find the resonance point of the cable. Therefore, a complete set of frequency conversion series resonance test equipment is needed. Many people often cannot quickly find the resonance point during use, and sometimes they cannot find it at all, which wastes a lot of time and energy on the test site. So, how to use the frequency conversion series resonance test equipment to quickly find the resonance point? The complete set of frequency conversion series resonance test equipment is preferred for quickly finding the resonance point. Depending on the voltage level of the tested cable, different types of series resonance test equipment need to be selected. The voltage level of the series resonance test equipment generally needs to cover the voltage level of the cable. If the voltage of the equipment is not as high as that of the cable, it is impossible to find the resonance point of the c
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Calculation formula for the complete set of frequency conversion series resonance test equipment
2025-10-15The complete set of frequency conversion series resonance test equipment mainly refers to the voltage and current of the series circuit reaching the same phase, that is, the inductance reactance of the inductor and the capacitance reactance of the capacitor in the circuit are equal, making the circuit exhibit pure resistance characteristics. Under the given terminal voltage, a large current will occur in the circuit, and the active power consumed in the circuit will also be large. This article introduces the formula for the complete set of variable frequency series resonance test equipment.The imaginary part of the impedance of the frequency conversion series resonance testing device circuit is equal to 0. So Z=R+jX, X=0, Z=R, so I=U/Z=U/R.1. Resonance definition: The energy of components L and C in a circuit is equal. When one reactive element in the circuit releases energy, the other reactive element must absorb the same energy. In other words, resonance occurs between the two reacti
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Power equipment testing often uses a complete set of frequency conversion series resonance testing equipment
2025-10-14The complete set of frequency conversion series resonance test equipment is used to change the inductance and test frequency of the testing system, so that the circuit is in a resonant state, and most of the capacitance current on the testing circuit is cancelled out by the induced current on the reactor. The energy provided by the power supply is only a small part of the resonance multiple consumed in the circuit, that is, a part of the resonance multiple of the capacity of the test piece; Therefore, the capacity of the test power supply slowly decreases, and the weight is greatly reduced. The complete set of frequency conversion series resonance test equipment system can be divided into two types according to the adjustment method: regulating type and frequency modulation type.Belonging to the resonant current filtering circuit, it can improve the waveform distortion of the power supply, obtain a better sine voltage waveform, and effectively prevent harmonic peaks from causing false
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Protection function of the complete set of frequency conversion series resonance test equipment
2025-10-14Before using power cables, a series resonance test must be conducted. At the same time, the complete set of variable frequency series resonance test equipment also has corresponding protection functions. What is the protection function of the complete set of variable frequency series resonance test equipment?Flashover protection: When the tested object experiences a discharge fault, the device will quickly cut off the output voltage and disconnect the power supply. The load of the high-voltage circuit will be released through the intermediate boosting transformer, without causing overvoltage or affecting other equipment. The 'flashover fault' will be displayed on the screen of the console. Overvoltage protection: The complete set of frequency conversion series resonance test equipment can set the test voltage to prevent the test voltage from rising due to external reasons; When the test voltage exceeds the set value, the console will automatically cut off the cycle and prompt
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