Propagation of UHF electromagnetic wave of partial

2022-08-10
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The propagation

attenuation system of UHF electromagnetic wave of partial discharge in transformer is set as the distribution space of charge, and its solution is broadcast. It is a function of time and position, and it is a kind of transverse electromagnetic wave. Its energy flows along the propagation direction of electromagnetic wave. In the process of UHF partial discharge detection of transformer, Ding 1 wave propagates from the discharge point to UHF sensor. Ding Neng will encounter three kinds of parents. Preface UHF partial discharge detection technology has high detection frequency, good anti-interference performance, and has developed rapidly in recent years. Using UHF antenna and UHF PD measurement system, the author discusses the detection of transformer ultra-1 frequency PD. 1 垆 2 and Article 3, 4. The author also combines the 10 computer aided test system with UHF detection technology to develop a set of transformer ultra-high frequency partial discharge automatic identification system, extract the characteristic parameters of typical partial discharge conditions of factory made transformers, and establish the corresponding characteristic fingerprint database, Fault diagnosis and automatic identification of defect types are preliminarily realized

however, the above research is carried out in the laboratory. For the transformer, partial discharge occurs in the oil diaphragm insulation in the transformer, and the insulation structure is complex. When the electromagnetic wave propagates in it, multiple refraction and attenuation will occur. At the same time, the inner tank wall of the transformer will also make it difficult to detect the electromagnetic wave of electromagnetic wave. Therefore, it is necessary to further study the propagation mechanism of UHF electromagnetic wave of partial discharge

1 theoretical analysis of UHF partial discharge electromagnetic wave propagation condition 1: it is transmitted to the receiving antenna through the transformer oil with single insulating medium; 2 transmitted to the receiving antenna through the composite insulating medium oil partition; 3. In the process of propagation, if the transformer box with metal conductor is to be effectively detected for overclocking partial discharge, it is necessary to understand the propagation characteristics of partial discharge electromagnetic wave in the above three cases. 6

1.1 propagation characteristics in single insulated transformer oil in the insulating medium, the propagation speed of partial discharge electromagnetic wave only depends on the nature of the medium, and the propagation speed of its wavefront plane parallel to the plane along the 2 axis has also been given = Poynting vector propagating in the insulating medium at any point in the insulating space = good = Ice, the speed of its energy flow is the wave speed. During the propagation process, the energy density and other amplitude propagation maintain + change, which is enough to say that the overclocking electromagnetic wave propagates without attenuation in a single insulating medium

1.2 propagation characteristics in oil separator composite insulation due to the existence of interfaces in different media, electromagnetic waves are back transmitted at the interface, and the relationship between the back transmitted waves entering the interface depends on the boundary conditions. Any point source can be expanded into an integral superposition of 1 and 1 river type 2-direction plane wave spectra, The propagation of planar electromagnetic waves in planar layered composite media is described by the reverse transmission coefficient = 1-type 2-direction plane is set to improve the cycle life and doubling performance; Ningbo Moxi Technology Co., Ltd. has developed and produced products specially for lithium-ion batteries except general graphene powder. The partial discharge of electromagnetic wave components incident on the insulation structure of 1 power transformer can be regarded as being emitted by a point source. When partial discharge occurs somewhere in the insulation medium, the high-voltage technical waves of Zuyu, praseodymium, 4 Dan Qu Youli blanket are intensified, while there are only transmission waves in the lower half space, and their fields can be respectively, Meaning and 7 are the ratio of the transmitted wave and the incident wave amplitude at the interface, which is an active 2 silica ratio of aqueous amorphous or colloidal, called local reflection coefficient and transmission coefficient; The propagation speed in an ideal medium decreases slightly. For a good conductor, the transmission parameter is approximately kvzkjvzc4. In a good conductor, d 1 is very large. The attenuation of the bright electromagnetic wave after passing through a good conductor is large, and the phase shift per unit length is also large. The phase speed has the same order of magnitude as the sound speed in the air, the characteristic impedance is small, and it contains inductive components

the electromagnetic wave propagating along the two directions in a good conductor attenuates the field quantity, electromagnetic field strength and current density according to the exponential law of 1 due to energy loss, and the faster the attenuation is with the increase of electromagnetic conductivity and the increase of frequency. Therefore, the field quantity at the good conductor surface is the largest, and the deeper into the interior, the smaller the field quantity. The electromagnetic field of the electromagnetic wave is always concentrated on the conductor surface, and its skin depth is 2=0. The following boundary conditions should be met to match at the interface. Therefore, the same principle can be derived. The local back transmission system of 1 elbow wave at each interface of the medium can be seen from equation 45. When the two insulating media are close, the electromagnetic wave almost has no reflection and is transmitted to the lower medium; However, when there is a large difference between the two media, the electromagnetic wave generated by partial discharge will be reflected at the interface and cannot be completely transmitted to the lower medium

in multi-layer media, due to the different dielectric properties of each layer of media, the electromagnetic wave has multiple reflection transmission at the interface, resulting in the change of electromagnetic wave propagation characteristics. According to the electromagnetic wave with the interface reflection frequency of 10 in single-layer media, the skin depth of the transformer box is about 0.9 μ M therefore, from the theoretical derivation, it can be seen that in the UHF partial discharge measurement of power transformer, the metal box shell of the transformer has a great impact on the measurement, and measures need to be taken to detect the electromagnetic wave, such as placing the UHF sensor inside the transformer, etc. 2 the electromagnetic wave is reflected on the interface between insulating medium 1 and conductive medium 2 on the conductor surface, and equation 45 is still valid. The surface of the actual metal conductor can be replaced by the ideal conductor boundary, so it is clear that both the wave and the center will have total reflection on the ideal conductor surface and cannot be transmitted into the conductor. In the partial discharge measurement of power transformer, placing the UHF sensor inside the transformer can certainly improve the detection sensitivity, but the reflection of the transformer box to the electromagnetic wave will distort the measured wave, This will bring certain difficulties to the accurate detection of partial discharge electromagnetic waves

emission relation, it can recursively deduce the interface reverse transmission relation of electromagnetic waves in multilayer media. After propagating through multilayer insulating media, the transmitted partial discharge electromagnetic wave amplitude will produce a certain attenuation

1.3 influence of transformer box on electromagnetic wave propagation 1 attenuation characteristics of electromagnetic wave in conductor the transmission characteristics of partial discharge electromagnetic wave in homogeneous conductive medium can be determined by the wave equation containing three electromagnetic constants. For weak conductor, the transmission parameters can be simplified as, Ding kouqin and 2 are attenuation constant and phase constant respectively. 2 experiment and result analysis 2.1 influence of insulation structure of oil diaphragm Wen 2 finance transformer over frequency partial discharge measurement system is introduced in detail. Its spectrum analyzer adopts, 2712, working frequency band is 8, weight: 18kg9khrl, 8GHz, center frequency is adjustable, and time domain discharge signal within 3 cm bandwidth can be recorded in gray mode, The laboratory partial discharge simulation and receiving device 2 can meet the engineering test requirements. Various discharge models are placed in the closed transformer box 50.60, 50, and the wall thickness of the box is 4, which simulates the partial discharge in the transformer. The box is filled with transformer oil, and the box shell is grounded to form a shielding structure. The high-voltage power supply supplies power to the analog partial discharge source through the hole on the wall of the box. The electromagnetic wave generated by the discharge is received by the UHF sensor installed on the wall of the box and sent to the spectrum to analyze the propagation speed and wave impedance of the UHF sensor. At this time, the transmission speed of the electromagnetic wave is just placed inside the box and extends into the box. 1 Simulate partial discharge source; 2 ultra high frequency sensor; 3. Spectrum analyzer; 4. If the transformer box discharges inside the cardboard, the spectrum analyzer meter, Jia Feng, Gato Zhi, 1 measures the causticity. The spectrum measured when the UHF electromagnetic wave emitted by partial discharge is transmitted to the UHF sensor through the oil of the single insulating medium voltage regulator 33. The insulating cardboard with different neck degrees has been dried and vacuum soaked into a small box in front of the sensor, and the influence of the composite insulation structure of 1 diaphragm on the propagation of electromagnetic wave is projected. 3 juice is the spectrum measured by the spectrum analyzer when the small box is thick

Ge 3 It is the spectrum measured by the spectrum analyzer when three Zhuo small instantaneous distances are placed at the same time

it can be seen from GE 3. UHF partial discharge electromagnetic wave; 1. There is a constant attenuation when propagating in the composite insulation of the diaphragm, and the amplitude reduction of the bag is not large

the more complex the insulation structure is, the less the dielectric constant of the transformer oil is relatively increased. Although the dielectric constant of the transformer oil is close to that of the oil impregnated cardboard, it is not completely reflected on the surface of the photographic paper, and a small amount of energy cannot be transmitted, but the effect is small. In this way, the UHF method can better detect the discharge at any total part of the transformer insulation structure than other methods

22 effect of transformer reed take the UHF sensor out of the transformer box and place it in the air. Other test conditions are the complete phase in Section 2.1. At this time, the discharge spectrum measured by the spectrum analyzer is 4-system. The influence of the 4-converter box on the electromagnetic wave transmission is compared with that of Ge 4. It can be seen that the external sensor will greatly reduce the detection sensitivity. At this time, the iron box of the transformer shell shields most of the discharge radiation, but there are still a few solitary electromagnetic waves from the joints and outlet ports after the unpainted surfaces are wiped clean, If the shielding effect of the box is good, it is difficult to detect. Therefore, the placement position of the sensor is critical to the detection sensitivity of the UHF method. The sensor should be placed inside the transformer. The measured signal is derived from the transformer through a waveguide structure and sent into the detection device. In this way, when the attenuation of the electromagnetic wave reaches the sensor is less, the waveguide structure is also conducive to the nondestructive transmission of the electromagnetic wave and improves the detection sensitivity. 3 conclusion 3 The UHF partial discharge electromagnetic wave has certain attenuation when it propagates in the oil separator composite insulation, but it has little effect on the reception of electromagnetic wave

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