What is the function of transformer bushing? What performance do we need?
The bushing of a transformer is a common accessory, and whether it is an oil immersed transformer or a dry-type transformer, you will see such a component on the outside of the transformer. Today, we will mainly introduce its performance and function, and make some corresponding extensions: about the bushing,
There are two common types: capacitive and non capacitive. The bushing with a rated voltage of not less than 35kV is generally a capacitive bushing. Why is it divided like this? Mainly because their materials are different and they can withstand different voltages,
So this extends to our introduction of the role of transformer bushings:
1. Function
The reason why the bushing needs to withstand voltage is that the winding needs to rely on the bushing to pass through the transformer oil tank. Therefore, if the bushing fails, the transformer cannot operate directly, and the fault may also be caused by fire, etc.
Let's explain in detail below: The oil tank of an oil immersed transformer is made of steel and grounded. The lead wire of the winding can only be connected to the power grid through the oil tank; And the winding lead must rely on a sleeve to pass through the oil tank. The bushing is a part of the winding lead wire and is a component of the winding circuit.
2. Introduction to Performance:
The performance of the bushing that most oil immersed transformer manufacturers are concerned about mainly includes insulation and thermal performance. These two properties can determine the stability of its operation and ensure its normal functioning. Below, we will introduce these two points:
A. Insulation performance A, key performance of internal insulation. The key insulation performance requirements for capacitive sleeves are: good sealing performance and no leakage; Local discharge level is less than 10pC; Tan is stable.
B. The key performance of external insulation. The external insulation of the casing refers to the insulation of the outer surface of the casing in contact with the atmosphere, and with oil or SF. The outer surface in contact with gas does not belong to external insulation. The key performance of porcelain bushing external insulation is that the creepage distance of the bushing is suitable for the pollution level of the application, and there is a margin left.
(2) Thermal performance
A. Thermal performance of current carrying conductors. The thermal performance of current carrying conductors is used to determine whether electrical poles, cables, and their wiring terminals may overheat when subjected to rated operating current for a long period of time or overcurrent for a short period of time. The temperature rise of the cable or conductive rod is related to the current density used, and no faults have occurred when used at the rated current. The temperature rise of terminal blocks is related to various factors such as apparent current density, coating quality (including tin plating, silver plating, etc.), and fastening force. The overheating fault of the wiring terminal is generally not caused by improper connection, but by the operation during connection
B. Thermal performance of casing core insulation. The thermal performance test of casing core insulation is called the thermal stability performance test in the national standard. During the experiment, immerse the bushing in transformer oil at (90 ± 2) ℃ and measure the qualified condition relationship between the insulation of the bushing core and the water content of the applied voltage.
From the above, it can be seen that the performance of each major point can be divided into two small points, both inside and outside. Therefore, the position of transformer bushing in transformers is still very important. Therefore, a transformer manufacturer needs to better select materials and conduct factory tests on important components in order to produce more high-quality transformers.
