254 – Vibration Analysis of Oil-Immersed Large Transformer

Model Data

Overview

Large power transformers are used to transform high voltage power generated in power stations into power that can be transmitted. In recent years, regulations concerning vibrations in particular are becoming gradually more strict in instances where install locations are near residences and urban areas. Trial productions are also difficult because of the lack of ease in producing mass-produced products in general, and it is this that makes trial productions difficult to evaluate.
By using the finite element method, an evaluation of vibrations is possible without the need for any trial productions. It is additionally possible to handle a multitude of complicated phenomena that would be otherwise difficult via manual calculations, such as tank vibrations due to magnetix flux leakage, etc.
This document introduces a case example of evaluating the vibrations of a large transformer. Parts that are usually the source of vibrations are the core, tank, and windings, but this case example focuses on the core and tank.

Excitation Force Distribution

Core electromagnetic force distribution is displayed in Fig. 1, core magnetostrictive force distribution is displayed in Fig. 2, and tank electromagnetic force distribution is displayed in Fig. 3. Tank magnetic flux leakage and eddy current is additionally displayed in Fig. 4.
It is understood that magnetostrictive force is dominant as the magnitude of the excitation force, as indicated Fig. 1 to 3.
From Fig. 4, it can be seen that a generation of eddy currents follows the linkage of tank magnetic flux leakage. The electromagnetic force acting on these eddy currents is the tank’s main source of vibration.

Acceleration Distribution

Core acceleration distribution is displayed in Fig. 5, and tank acceleration distribution is displayed in Fig. 6.
Core magnetostrictive force dominated excitation force, but it is understood that vibration is larger for the tank than it is for the core. It is thought that the cause may be that tank rigidity is low. Because vibrations are additionally large on the side not fitted with a shielding plate, provisions are being considered to add a shielding plate to this side also, reducing both excitation and vibration.

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