What is the working principle of the variable frequency series resonance test kit?

Power cords and electrical equipment are well insulated. The live parts of lamp heads, sockets, and switches shall not be exposed to prevent electric shock.

It is strictly forbidden to randomly connect the wires to avoid electric shock or **.

Do not stand on wet ground and move live objects to prevent electric shock.

The choice of fuse should be fair. It is strictly forbidden to replace it with copper wire, aluminum wire or iron wire to prevent fire.

Household appliances such as refrigerators, refrigerators, washing machines, etc. It should be equipped with a socket with a grounding wire that meets the requirements of the product.

Check or replace the lamp head. Even if the switch is off, do not touch it directly with your hands to avoid electric shock.

In the event of a fire in an electrical appliance, the power supply should be blocked first, and it is strictly forbidden to use water directly to prevent electric shock. 8. In case of electric shock, the power supply should be disconnected first (such as electric shock from a height, and measures should be taken to prevent the electric shock from falling), and then first aid should be carried out.

1. Introduction to the series resonance test device system.

The variable frequency series resonance test equipment is based on the principle of the inductor and the capacitance of the cable to generate high voltage. The simplified circuit of a typical series resonant test device system is shown in Figure 2a, where the adjustable autotransformer T1 provides a variable operating voltage for the excitation transformer T2, and T2 provides the resonant circuit power supply and isolates the test circuit from the power supply circuit. Capacitor C represents the test capacitor and its parallel capacitance, such as voltage divider capacitor, bushing capacitor, etc.

Inductance l is a variable reactor in which the capacitance of capacitor c is adjusted to the resonant state of the circuit when the capacitance reactance of capacitor c is shifted.

Analysis of the working principle of the complete set of frequency conversion series resonance test device.

in a resonant state.

For high-quality capacitive loads, the Q value of a typical system is between 50-80, and in the resonant state, the current i in the resonant loop is in phase with the voltage u of the excitation transformer, so the input power is the stored power p, i.e., cos = 1, p = ui cos = ui.

In the resonant state, the reactive power wc on the capacitive load c is .

wc=uci=qui=qp

Therefore, the rated capacity of electrical components such as circuit breakers, voltage regulators, and contactors is reduced to 1 q of the required power, which greatly reduces the requirements of the power supply system.

2. Series resonance distortion.

Assuming that the input voltage is distorted at steady state, the ratio of the voltage gain function uc to u can be expressed as.

Analysis of the working principle of the variable frequency series resonance test device.

This function can be simplified into:

where: is the harmonic (n>l) of the input power supply frequency

Therefore, when the series resonant circuit is tuned at the input power frequency (n=1), a large voltage gain will be generated, thereby reducing the influence of the input power frequency harmonics on the system. The typical harmonic distortion levels of the resonant circuits in this series are completely below.

3. Transient calculation of the series resonance test device system.

In series resonant circuits, the output voltage recovery rate caused by arc suppression caused by flashover is slow. The recovery voltage can be expressed as follows.

Analysis of the working principle of the series resonance test system.

In Eq. (5), the time t can be calculated from the moment when the arc goes out, and the exponent t 2q can be rewritten as a variable of the flashover frequency number n.

t/2q=nπ/q

When n q 3 or n q, the voltage uc(t) given in the equation will return 96% of the original value. Therefore, after a flashover, the power supply needs about q cycles to charge the load capacitor to full voltage. In general, the overload protection of the test setup is put into operation before this value is reached.

4. Tuning of the series resonance test device system.

By adjusting the air gap of the core, the inductance at a fully closed core is continuously changed from the maximum to the minimum when the core is fully open (typically, the reactor can be tuned in the 4% 90% core air gap range). When the reactor inductance is equal to the circuit capacitance, the system reaches resonance. Over here.

l=1/ωc

where: l is the reactor inductance; c is the load capacitance; is the angular frequency (=2 f, where f is the input power frequency).

Respondent: Huatian Power.

How it works:

The working principle of the frequency modulation series resonance test device is wired, the AC 220V power frequency power supply, the voltage adjustable at the frequency conversion control unit is output at 30 200Hz, and it is sent to the excitation transformer, and the voltage is boosted to 0 1000V, and the resonant reactor L and the tested product CX form a high-voltage main harmonic circuit, and the capacitor voltage divider is a pure capacitive type, which is used to measure the test voltage. First, a lower voltage UE is sent to the main resonant circuit by the frequency conversion control unit through the excitation transformer, and the output frequency of the frequency conversion control unit is adjusted, and when the frequency meets the condition l=1 c, the circuit reaches the resonant state. At this time, under a small excitation voltage UE, a voltage UCX dozens of times that of UE can be generated on the CX of the test product.

The frequency conversion test system works on the principle of series resonant circuit. The resonance point is achieved by adjusting the frequency of the frequency converter to the natural frequency of the series resonant circuit. After the loop is resonated, the output voltage waveform is a pure sine wave, and the frequency of the system depends on the L-C parameters of the loop.

The reactance value of the reactor is adjustable, and the frequency of the system depends on the size of the load capacitance, as shown in the above formula. According to the size of CX, the inductance L value of the reactor can be adjusted appropriately, so that the resonant frequency is fixed within a required range, so as to meet the experiment of the sample that must be tested under the power frequency condition.

According to the principle of series resonance, Wuhan Sanxin Electric Power has designed a lightweight and easy-to-operate test equipment.

The complete set of variable frequency series resonance test device is to use the principle of series resonance, use the excitation transformer to excite the series resonance loop, adjust the output frequency of the frequency conversion controller, make the loop inductance L and the test product C resonate in series, and the resonant voltage is the voltage added to the test product. 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.

Baoying high-power power equipment factory.

The variable frequency series resonant complete test device is composed of a variable frequency power supply, an excitation transformer, a high-voltage reactor and a capacitor voltage 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, is used to measure the resonant voltage on the test piece, 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.

Variable frequency series resonance test complete set of device is an indispensable test method for the daily debugging of electrical equipment, and the circuit of the complete set of frequency conversion series resonance test is well used in the withstand voltage test of electrical equipment such as transformers and power cables. This paper mainly introduces the physical application of the circuit of the complete set of variable frequency series resonance test.

1) AC withstand voltage test of power cable, at present, there are more and more XLPE-XLPE insulated power cables at home and abroad to replace the original oil-filled paper insulated power cables. However, there are many problems in the DC withstand voltage test of traditional XLPE cables; Because the cross-linked cable is a large capacitance test, the use of series resonance test method is simple and convenient, and good AC voltage frequency and waveform can be obtained, which has become an ideal test method in the AC withstand voltage test of cross-linked cable.

2) AC withstand voltage test of power transformer, reactor and transformer, the world clearly stipulates that the AC withstand voltage test of power transformer, reactor and transformer can be used to use power frequency voltage test or induced voltage test method, and the test voltage waveform should be as close to sinusoidal as possible. According to this standard, the circuit of the complete set of variable frequency series resonance test device can be tested under any conditions. The device has a wide frequency and voltage range, is highly adaptable to the test object, and can be used with a wide range of voltage levels of test objects.

3) AC withstand voltage test of SF6 closed combiner, AC withstand voltage test is an important method to check the GIS main insulation when SF6 is closed. In most cases, a series resonant test setup is used.

4) AC withstand voltage test of other equipment, for circuit breakers, bushings and other equipment, it is generally required that the withstand voltage test is a power frequency voltage test. If the power frequency test device cannot meet the on-site requirements, the resonant withstand voltage test method can also be used instead. When the resonance withstand voltage test is adopted, the test frequency is higher due to the small capacitance of the device, but the series resonance test device can also use appropriate compensation capacitance to reduce the test frequency, so that the instrument can reach the test frequency close to the power frequency.

Respondent: Huatian Power.

The variable frequency series resonance test device is composed of a variable frequency power supply, an excitation transformer, a high-voltage reactor and a capacitance voltage divider.

1.Variable frequency power supply: the power supply of 220V, 380V, 50Hz is changed to adjustable frequency and continuously adjustable voltage, and at the same time, it integrates operation, protection, control and monitoring functions.

2.Excitation transformer: Voltage boost the output voltage of the variable frequency power supply, and isolate the high voltage and low voltage at the same time.

3.High-voltage reactor: series resonance with capacitive specimen.

4.Voltage divider: Measure the high voltage value and low voltage on the regulator.

The series resonant withstand voltage test device has five major structural components:

Variable frequency voltage regulation power supply: it can not only change the frequency of the output, but also change the voltage of its output;

Excitation transformer: plays the role of coupling signal and voltage conversion, and increases the voltage according to its own transformation ratio;

Reactor: It is connected in series with the test product to form an LC loop;

Voltage divider: used to measure the voltage on the test product, and at the same time as a sampling signal feedback to the instrument;

Compensation capacitor: used to adjust the frequency of the test product;

1. Main components.

The complete set of variable frequency series resonance test device is composed of variable frequency power supply, excitation transformer, reactor and capacitor voltage divider, as shown in the following figure

2. Resonance accessories.

Reactor equalizing ball, voltage divider equalizing ball, insulating base, air duct, power inlet, high-voltage short wiring, excitation variable incoming line, discharge rod and other accessories, as shown in the following figure: