Overview

Winding vibration originating from a transformer is a vibration phenomenon that uses Lorentz force as the vibration force, which occurs when flux leakage from the winding works on the current inside the winding. A large scale power transformer usually operates with the commercial frequency and the iron core size can be a few meters.
So its eigen frequency also becomes the same order of the operating frequency, which means that dominant components of the excitation force directly concern the vibration of windings.
This case study examines a power transformer running at 50Hz with three-phase cylindrical windings, and vibrations and noise caused by the windings are analyzed using JMAG. For a winding vibration analysis, a vibration analysis should be performed with the windings with Lorenz force as the vibration source. Since Lorentz force on the windings is largely affected by leakage flux distribution, an electromagnetic field analysis is needed to estimate leakage flux distribution which does not flow through the main magnetic path. Therefore, a electromagnetic field – vibration coupling analysis is inevitable for analyzing winding vibration precisely.
The analysis model is shown in the left of figure 1. Since the winding is composed of a group of multiple conductors with insulating paper inserted between them, it must be handled as anisotropic materials with different stiffness for the circumferential direction, radial direction, and height direction of the winding respectively in the case it is modelled as a bulk in an eigenvalue analysis / vibration analysis.