Grading ring for arrester 3

Grading Ring for Arrester with different shapes.

Eliminate the effects of equalizing rings
1. The simulation method eliminates the influence of the grading ring
ANSYS software is a large-scale, general-purpose finite element analysis software that integrates structural, fluid, electrical, magnetic and acoustic field analysis. Electromagnetic field problems encountered in power systems are also often solved using ANSYS. Therefore, by establishing a suitable finite element calculation model and selecting an appropriate dielectric constant, ANSYS was used to calculate the spatial discrete current generated when measuring the leakage current of the upper section unit at a DC voltage of 0.75U1mA of the 500kV porcelain-sleeved zinc oxide arrester.
During on-site measurement, due to the existence of this stray circuit, the test data will be incorrect, and some results may be greater than the attention value required by the test standard by 50μA. Therefore, when carrying out this test, the data read by the micro-ampere meter should be subtracted from the spatial discrete current, which is the leakage current of the upper section of the arrester.
However, the use of simulation methods to eliminate the influence of grading rings has the following disadvantages in field applications:
1) The size and parameters of the arrester of different manufacturers and batches are not the same, so if the method is used to eliminate the influence, it is necessary to re-simulate before each test, which increases the on-site workload;

2) The on-site environment is unpredictable, and it is difficult to establish a generalized simulation calculation model;
3) There may be a misunderstanding between the simulation calculation result and the actual value, which will affect the judgment of the final test result. Therefore, for tests with high accuracy requirements, such as preventive tests, it is not advisable to use simulation calculations to eliminate the influence of grading rings in the field.
2. The shielding cover eliminates the influence of the grading ring
Through the previous analysis, it can be seen that the space discrete current flows into the measurement micro-ampere meter through the lower end metal flange of the upper section arrester, so during on-site measurement, the lower end of the metal flange of the upper section arrester can be wrapped in multiple layers by using the heat shrinkable sleeve, cotton fabric, insulating paper and other wrappers that are easy to find on site, so as to ensure that the current value indicated by the DC micro-ampere meter is the leakage current flowing through the zinc oxide valve plate, so as to improve the accuracy of measurement.
With the addition of a shield, the effect of the grading ring on the spatial discrete current generated by the arrester has been virtually eliminated. However, the measured value is still slightly larger than the factory value, mainly because the simple shield is not custom-made, it is difficult to completely cover the flange as a whole, and a very small part of the spatial discrete current enters the measured value.
In short, when measuring the DC leakage current of the upper section of the 500 kV zinc oxide arrester, the installation of a shielding cover can eliminate the influence of the grading ring on the measurement results, and the field installation is simple and the effect is obvious, which can be vigorously promoted in the field test.