What are the applications of series resonance?

1) The analysis of the working principle of the LC series resonant circuit needs to be divided into three frequency points and frequency bands, that is, when resonant, the input signal frequency is higher than the resonant frequency and the input signal frequency is lower than the resonant frequency.

When the input signal frequency is equal to the resonant frequency, the circuit resonates, and the impedance of the LC series resonant circuit is in the minimum state, and can be equivalent to a pure resistor, and the signal current flowing through the entire resonant circuit is the largest. This is most important in in-circuit analysis.

2) When the input signal frequency is higher or lower than the resonant frequency, the LC series circuit is in a detuned state, and the impedance of the circuit is larger than that of the resonant frequency.

Series resonance is widely used in electric power, metallurgy, petroleum, chemical and other industries, and is suitable for the handover and preventive test of large-capacity and high-voltage capacitive samples.

Portable variable frequency series resonant device is mainly used in the following aspects:

AC withstand voltage test of KV-500KV high-voltage cross-linked cable.

2. AC withstand voltage test of generator.

3. AC withstand voltage test of GIS and SF6 switches.

Power frequency withstand voltage test of KV-500KV transformer.

5. AC withstand voltage test of other power high-voltage equipment such as busbar, casing and transformer.

GDTF-108 108 380 0-108 10831500KVA and below 35kV power transformer.

35kVA circuit breaker and closed busbar, insulator.

10kV (300 m) cable 2000m

35kV (300 m) cable 500m

1 set of 5kw variable frequency source.

1 set of 5kva excitation transformer.

4 reactors 27kV 1A

Voltage divider 100kV

Shi Jia, Shi Xiangyun, Cui Wei (Wei'er), Kwai Guan, Zhou's Nurse, Xue Jia, Aunt Xue, Tongxi, Tonggui.

The working principle of series resonant circuits and the analysis of series resonant circuits.

1. What is series resonance?

In a series resonant circuit, a frequency point occurs when the inductive reactance of the inductor is equal to the capacitive reactance of the capacitor. That is, x l = x c.

Series resonance. When x l = x c, this point is called the resonant frequency point (f r) of the circuit, and if it is on a series resonant circuit, this frequency will produce series resonance.

Series resonant circuits are one of the most important circuits in electrical and electronic circuits, and are often used in a variety of circuits, such as AC power filters, noise filters, radio and television tuning circuits, which produce selective tuning circuits for receiving different channels.

2. What is a series resonant circuit?

The diagram below shows a series resonant circuit.

Series resonant circuit.

The formula for calculating series resonant circuits is capacitive reactance and inductive reactance.

Capacitive and inductive reactance formulas for circuits.

When x l > x c, it is sensual.

When x l series resonant circuit is calculated: total reactance and total impedance.

The total reactance and total impedance formula of the circuit.

Series resonance. What is the role of the application?

The main function of the series resonance test device is to carry out the withstand voltage test for the high-voltage power cable and find the resonance point of the cable, because of the fast step-up and high precision, it is very popular in the power industry, and many power workers like to use series resonance when looking for the resonance point of the cable.

The series resonance test device adopts a multi-stage superposition method and multiple reactors.

It can be used in parallel and series, and the voltage divider is not only used to measure the test voltage, but also as a compensation capacitor for the small capacitance sample, so that the resonant frequency is reduced.

It can complete the AC withstand voltage test of a variety of power equipment in the range of 30 300Hz. The basic principle of frequency conversion series resonance is to use adjustable (30-300Hz) series resonance test equipment to generate AC test voltage with the capacitor of the tested product.

It is suitable for AC withstand voltage test of 10kV, 35kV and other cables, and the variable frequency series resonance withstand voltage test is to use the inductance of the reactor and the capacitance of the tested product to achieve capacitive resonance, and obtain high voltage and high current on the tested product. The cable AC withstand voltage test device is mainly composed of variable frequency power supply (host), excitation transformer, resonant reactor and capacitor voltage divider. It is widely used in electric power, metallurgy, petroleum, chemical and other industries, and is suitable for the handover and preventive test of capacitive test products with large capacity and high voltage.

1. The required power supply capacity is greatly reduced, and the power supply power required for the test is only 1 q of the test capacity.

2. Small size, light weight, generally 1 3-1 5 of ordinary test devices;

3. The series resonance test device uses excellent components imported from Japan for frequency modulation and power components of the resonant power supply, and the resonant filter circuit is designed.

It can improve the waveform distortion of the output voltage, obtain a good sine waveform, and effectively prevent harmonics.

False breakdown of the peak on the sample.

4. The variable frequency power supply has strong protection function and good stability; It has a variety of working modes with fully automatic (automatic tuning, automatic boosting), full manual (manual tuning, manual boosting) and semi-automatic (automatic tuning, manual boosting and manual tuning, automatic boosting), which can be switched at will and easy to operate; It adopts 220V or 380V single-phase power supply, which is convenient for on-site power supply.

5. Flexible configuration and strong expansion function. The resonant reactor adopts multiple ways and building block combinations, which can be connected or combined to meet the test requirements of a variety of samples and is more convenient for on-site use.

Variable frequency series resonance consists of a variable frequency power supply, an excitation transformer, a reactor and a capacitor divider. The capacitor of the tested product and the reactor form a series resonant connection mode; The voltage divider is connected in parallel on the test piece, which is used to measure the resonant voltage on the test product and is used as an overvoltage protection signal; The frequency modulation power output is coupled to the series resonant circuit through the excitation transformer to provide the excitation power of series resonance. The variable frequency series resonance test device uses the principle of series resonance, uses the excitation transformer to excite the series resonance loop, adjusts the output frequency of the frequency conversion controller, and makes the loop inductance L and the sample C resonate in series, and the resonant voltage is the voltage added to the sample.

Variable frequency resonance test device is widely used in electric power, metallurgy, petroleum, chemical and other industries, and is suitable for the handover and preventive test of large-capacity and high-voltage capacitive samples.

Series resonance is widely used in electric power, metallurgy, petroleum, chemical and other industries, and is suitable for the handover and preventive testing of large-capacity and high-voltage capacitive test products. Portable variable frequency series resonators are mainly used in the following aspects:

KV-500KV AC withstand voltage test of high-voltage cross-linked cable;

2. Generator AC withstand voltage test;

3. AC withstand voltage test of GIS and SF6 switches;

KV-500kV transformer is starting the power frequency withstand voltage test;

5. AC side service withstand voltage test of busbar, bushing, transformer and other power high-voltage equipment;

Series resonance. The series resonance test device is divided into frequency modulation type and inductance modulation type. It is generally composed of a variable frequency power supply, an excitation transformer, a reactor and a capacitor voltage divider.

The capacitor and reactor of the product under test form a series resonant connection; The voltage divider is connected in parallel with the product under test to measure the resonant voltage on the product under test and send out an overvoltage protection signal.

In a series circuit composed of resistors, inductors, and capacitors, when the capacitive reactance xc is equal to the inductive reactance xl, i.e., xc=xl, the voltage u and current i in the circuit are in phase, and the circuit appears resistive. This phenomenon is called tandem colifting. When the circuit is resonant in series, the circuit impedance z= r 2+(xc-xl) 2=r, the total impedance in the circuit is the smallest, and the current will reach the maximum value.

Series resonance refers to the resonance circuit in which inductance, capacitance and resistance are connected in series to form a resonant circuit.

Tandem resonance experimental setup.

It has the following characteristics:

Shared current: In a series resonant circuit, inductors, capacitors, and resistors are connected in series in sequence, so they share the same current. The current is continuous throughout the circuit, and the sum of inductance, capacitance, and resistance through it is constant.

Phase difference: The inductance and capacitance in a series resonant circuit can cause a phase difference between voltage and current. When the frequency is close to the resonant frequency, the impedance of the inductor and capacitor becomes equal, respectively, resulting in a phase difference between the current and the voltage approaching zero.

The law of the RLC series resonant circuit.

Resonant frequency: A series resonant circuit has a specific resonant frequency, that is, the circuit has the smallest blindness impedance at that frequency. At the resonant frequency, the impedance of the inductance and capacitor in the circuit is equal and cancel, and the circuit exhibits the characteristics of pure resistance.

Bandwidth: The bandwidth of a series resonant circuit is defined as the range in which the resonant frequency is reduced up and down to half of the resonant frequency. The narrower the bandwidth, the more selective the circuit is for frequency.

Impedance change: Above or below the resonant frequency, the impedance of the inductor and capacitor begins to increase, and the circuit exhibits high impedance. In the vicinity of the resonant frequency, the impedance of the inductor and capacitor is minimal, and the circuit exhibits low impedance.

Energy exchange: Near the resonant frequency, energy is exchanged between inductance and capacitance to achieve energy storage and release.

Series resonance has the selectivity of a specific frequency and the effect of signal amplification, and is widely used in many electronic and communication systems.

In the series circuit composed of resistance, inductance and capacitance, when the capacitive reactance xc and the inductive reactance xl are equal, that is, xc = xl, the phase of the voltage u and the current i in the circuit is the same, and the circuit presents pure resistance, this phenomenon is called series resonance. When the circuit is resonant in series, the impedance of the circuit Z = r 2 + (xc-xl) 2 = r, the total impedance in the circuit is the smallest, and the current will reach the maximum value. Advantages of spine deficiency products.

1.The required power supply capacity is greatly reduced. In the whole system, the power supply only needs to provide the active consumption part of the system, therefore, the power supply required for the test is only 1 Q times of the test capacity (q is the quality factor).

2.The weight and volume of the equipment are greatly reduced. In the series resonant power supply, not only the cumbersome high-power voltage regulating device and the ordinary high-power power frequency test transformer are omitted, but also the resonant excitation power supply only needs 1 q of the test capacity, so that the weight and volume of the system are greatly reduced, which is generally 1 5 1 10 of the ordinary test device.

3.Improved output voltage waveform. The resonant power supply is a resonant filter circuit, which can improve the waveform distortion of the output voltage and obtain a good sine wave, which effectively prevents the accidental breakdown of the tested product caused by the harmonic peak.

4.Prevent large short-circuit currents from burning the point of failure. In the resonant state, when the insulation weakness of the test product is broken down, the circuit is immediately detuned (the capacitance changes, and the resonance condition is not met), and the loop current rapidly drops to 1 q of the normal test current.

When the AC withstand voltage test is carried out by parallel resonance or traditional test transformer, the breakdown current immediately rises dozens of times, and the difference between the short-circuit current and the breakdown current is hundreds of times compared with the two. Therefore, series resonance can effectively find the insulation weakness, and there is no worry about the fault point of large short-circuit current burns.

5.There will be no recovery overvoltage. When the breakdown flashover occurs in the test piece, the high voltage disappears immediately due to the loss of resonance conditions, the arc is extinguished immediately, and the protection loop of the device is activated to cut off the output.