Wednesday, 26 July 2017

Comparison of four methods for detecting faulty insulators on line

According to the working principle of high voltage insulator and the development of electric power industry , we explore new methods of detecting faulty insulators in recent years. Some people who have developed and used the methods for the new insulator tester scene. Some are still at the experimental stage. There are four main types of these methods. This paper introduce the advantages and disadvantages of four kinds of test methods for convenient power industry flexible to choice.
Insulator

1.Self-climbing type poor insulation detector
The self-climbing poor insulator detector used in 500kV EHV line is mainly composed of self-climbing driving mechanism and insulation resistance measuring device. The capacitor is used to bypass the AC voltage component of the insulator under test, and the insulation resistance of the insulator is measured in the live state. Judging whether the insulator is good according to the size of DC insulation resistance. When the insulation resistance insulator value is lower than the predetermined resistance value, we can determine by monitoring a poor insulator, but also can clearly see that part of the waveform reproduction device defect of insulator in automatic recording from the cassette. When the V type string and the suspension string are detected, the weight of the insulator can be moved down along the insulator without any special drive mechanism.
2.Corona pulse detector
The utility model is a detector specially used on the ground, which can be used for detecting the lines in the plain area and also for detecting the routes in the mountain areas:
(1) Light weight, small size, power supply is battery of number 1, easy to use and safe.
(2)You can detect on the ground without using a pole.
(3) The first tower unit coarse, determine if the tower has a poor insulator, then the insulator fine test one by one.
(4) the microcomputer system is used for logical analysis and processing, and the detection efficiency is higher.
In the transmission line operation, the insulator string of the insulator will produce corona, and form a corona pulse current flowing through the tower into the ground. The corona current corresponds to each phase voltage and occurs only in a certain phase range. If you separate the positive and negative polarity of current , the polarity of each phase current pulse width phase range is smaller than the phase voltage of each phase. With proper phase selection method, each phase pulse current,iaibic can be observed.
Each phase corona pulse is counted respectively, and the maximum and minimum values are selected, and the ratio (maximum / minimum) of them is different index, which is used as the basis of discrimination. When the same three-phase insulator tower on poor insulator, the corona pulse is in equilibrium, the ratio is close to 1; when there is a poor insulator, each phase of corona pulses in an unbalanced state, the ratio will have a large deviation with the 1 pulse corona detector is developed according to this principle.
It consistes of four parts:
(1) the formation of the circuit of corona pulse signal;
(2) periodic signal forming circuit;
(3) each phase counting circuit of corona pulse;
(4) calculation and display circuit of different indexes of iron towers. 
3.Electron optical detector
The motion of the electron optical detector of electrons and ions in the electromagnetic field, the concept and principle and light propagation in an optical medium similarity that charged particles (electrons and ions) in electromagnetic field (electromagnetic lens) capable of focusing and imaging and deflection] manufacture.
The voltage distribution of each insulator in an insulator string of an overhead transmission line is uneven, and the voltage drop is the largest on the insulator nearest to the conductor. When the zero value insulator, redistribution along the insulator string voltage, voltage from the conductor insulator on the recent sharp rise will cause partial discharge. Partial discharge surface or increase the strength of the surface. According to the intensity of light radiation produced by partial discharge on the surface, the insulation performance of insulator string can be known.
By monitoring the insulator partial discharge, corona discharge and insulator surface light image by the lens input light brightness intensifier cathode; electronic form electronic current from the photo cathode to escape, according to the planar distribution of the electron current density can show the original image brightness distribution. The focal length adjustment system causes electrons to accelerate so that the brightness intensifier screen is lit. In this way, the original light and shadow, like midway through an electronic image, is again transformed into light and shadow. In the process of image transmission, the magnetic field system accelerates the electrons, increasing the brightness of the original image of light and shade (up to a hundred times). The luminance intensifier can measure the weak light of partial discharge on the suspended insulator string of transmission line from the ground distance (5 -50m).
When detecting at night, in order to distinguish the partial discharge of the insulation porcelain surface and the interference of other external light sources (moonlight and illumination), and improve the signal-to-noise ratio, the pulse power supply can be used to power the brightness intensifier. Because the surface partial discharge occurs near the maximum value of AC voltage applied by insulators, the frequency is 100Hz, while the external luminous intensity is independent of the frequency of the grid. When the insulating porcelain in the instrument surface partial discharge (1-6ms), press close to 100Hz frequency brightness intensifier input, will make the background light and weak interference light weakened. On the screen of the electron optical detector, the bright region pulsation of the surface partial discharge in line with the grid frequency and brightness intensifier will be observed. The pulse can distinguish the light intensity of the partial discharge of the surface with the attenuation of the non pulsation and the external interference. In actual test, the radiation of partial discharge on the faulty insulator string exceeds the average intensity of radiation.
To evaluate the difference of light radiation intensity from the partial discharge of conductor surface recently on the first insulator and the average radiation intensity is the use of electronic optical detectors, analyze the relationship between the sensitivity threshold of the optical detector Ø0 electronic and optical input system parameters and its relationship to
Ø0τD/F2AL2
Τ - Transmission coefficient of input system;
D/F - measure the light intensity (relative aperture, aperture) of the input eyepiece;
A - constant;
L -- the distance from the emitter.
Reduce Ø0 (turn off the small input aperture). When the D is reduced to a certain value, the average light intensity no longer occurs on the screen of the electron optical detector, and the screen will only show partial discharge on the surface of the defective insulator. Then, further light radiation intensity on the first insulator surface discharge near the wire and the average radiation are compared, if the light radiation intensity than light radiation intensity in the presence of faulty insulators, according to voltage relationship curve of light radiation intensity and insulator partial discharge on the surface of the first insulator to find the voltage distribution on the wire. According to the difference between the distribution voltage value and the normal distribution voltage value of the first insulator of the good insulator string, the bad insulator can be judged. This method of detection is efficient.
However, the electronic optical detector can only determine whether there is a zero value insulator in the insulator string, and it is not sure how many pieces of zero value insulators and their positions are in the end.
4.Detecting poor insulators with infrared thermal imager
infrared thermal image

There is a difference in the surface temperature between the poor insulators and the good insulators, but this difference is very small, so it is difficult to distinguish them with the general method of temperature measurement. In recent years, infrared thermal imager has been widely used to convert the temperature distribution of the insulator surface into an image, which is displayed by an intuitive and vivid thermal image, and then the poor insulators are detected according to the thermal image.
To detect faulty insulators by infrared imaging method, simple and convenient, fast speed, high efficiency, and even census every string insulators can also be combined with detection of transmission line,which is the direction of detection of poor insulator HV and EHV and UHV transmission line. However, at present, two problems widely exist: one is the thermal infrared imager is expensive, each about hundreds of thousands of RMB; second is to be the instrument used for mountain or both line, should be equipped with aerial aircraft, these are general and not the unit force. Of course, it is beneficial to organize the research in this field at present, sum up experience and grope for the law.

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