Introduction to the Significance and Methods of Dielectric Loss Measurement< p>

1. The significance of measuring the tangent value of the dielectric loss angle

The tangent value of the dielectric loss angle is also known as the dielectric loss factor or dielectric loss.

. The measurement of dielectric loss factor by pilot holding is a highly sensitive experimental project, which can detect the overall moisture, deterioration, and local defects of the insulation of power equipment, as well as the connection and non connection of small volume test equipment. For example:

For example, for the bushing of a certain transformer, the normal tg value is 0.5%, but when it is damp, the tg value is 3.5%, and the difference between the two data is 7 times; When measuring insulation resistance for detection, the difference in values before and after being damp is not significant Due to the high sensitivity of measuring the dielectric loss factor to reflect the aforementioned defects, it has been widely used in electrical manufacturing, power equipment handover, and preventive testing. The "Regulations" for dielectric loss testing of electrical equipment such as transformers, generators, and circuit breakers are all specified

Secondly, the current status and difficulties of dielectric loss testers in China

The technology of dielectric loss testers has developed rapidly. The QS1 Xilin bridge, which was previously widely used in the power system, is being replaced by intelligent dielectric loss testers. The new generation of pilot holding dielectric loss testers are equipped with built-in voltage boosting equipment and standard capacitors, and have features such as simple operation, accurate data, and convenient reading of test results.

. Although dielectric loss testing technology is currently developing rapidly, there is still a significant gap compared to the international level in many aspects, mainly manifested in the following aspects:

(1) anti-interference ability

Due to the high sensitivity of dielectric loss testing, the test data is also highly susceptible to external electric field interference. Currently, the anti-interference methods adopted by dielectric loss testers mainly include: phase inversion method, phase shift method, frequency difference method, etc. Although these methods can solve the problem of interference to a certain extent, they still produce significant deviations when external interference is strong

(2) Testing accuracy issues with reverse connection method

Many power equipment on site have been grounded, so reverse connection method must be used for testing. However, when reverse connection is used, there are many factors that affect the test data, and there is often a large deviation in the data, especially when the capacity of the test object is small (such as sleeve) and the high-voltage wire is dragged to the ground for testing (some dielectric loss testers are equipped with high-voltage wires that can be dragged to the ground, but have a large leakage current to the ground), It will seriously affect the accuracy of testing

Thirdly, "fully automatic anti-interference source" and its unique advantages compared to other anti-interference methods

The so-called "fully automatic anti-interference source" refers to a set of detection devices inside the instrument that can detect the amplitude and phase of external interference signals, transmit relevant information to the CPU, and the CPU outputs instructions to the "anti-interference source control device".

, This device will generate an "anti-interference signal" with the same amplitude but opposite phase as the interference signal inside the instrument, which will be superimposed and cancelled with the "interference signal" to achieve the purpose of anti-interference. Due to the automatic generation of "anti interference sources" throughout the entire testing process, users do not need to intervene, and we call them "fully automatic anti interference sources"

The anti-interference methods and working principles of the fourth system are as follows:

1. The instrument's working power supply undergoes two reverse phase tests, and the results of the two tests are analyzed and processed to achieve anti-interference purposes. This method has a certain effect in situations where external interference is weak.

2. Phase shifting method

The idea is derived from the "phase inversion method", which only changes the phase inversion of the working power supply to the same phase as the interference signal to weaken the interference effect. Practice has shown that even in cases of strong interference, the data still deviates significantly.