Description

The collapse of a high power circuit breaker determined by earthquake has determinant implications in breaking the power supply for large territorial areas. So, the design of the circuit breaker structure must include the simulations of the earthquakes, made by experiments and by Finite Elements Methods programs. The challenge is to determine the behaviour of the SF6 circuit breaker during three types of earthquake using ANSYS program and some FEM models validated with experimental results in modal analysis.

SOLUTION

For a complete test of the seismic capability it is necessary to perform an experimental study combined with a numerical simulation because the experiment is expensive and not so flexible regarding the simulation of all types of limit conditions of earthquakes. The numerical simulation of the seism is made using FEM and ANSYS program which permit to perform a spectrum analysis on the FEM model of the circuit breaker.
The seism simulation using FEM is a two step analysis. First we have made a modal analysis of the SF6 circuit breaker FEM model and we have compared the results with the experiment in order to validate the FEM model. Then it must be done the spectrum analysis on the validated FEM model for different seism types.

A spectrum analysis is one in which the results of a modal analysis are used with a known spectrum to calculate displacements and stresses in the model.
The FEM spectrum analysis was performed on the validated FEM model of the SF6 circuit breaker. The following results were obtained for three type of earthquake:
- earthquake type AF2 (<5.5 degrees Richter)
- earthquake type AF3 (5.5…7 degrees Richter)
- earthquake type AF5 (> 7 degrees Richter)

The results of this research study are the final step of the entire process of earthquake simulation and consist in determination of displacements and stresses values achieved during three types of earthquake (AF2, AF3, AF5).
Analyzing the computed values we can see that in the case of the circuit breaker the most vulnerable parts are the isolator columns made by ceramics for which the admissible stress is  = 40 MPa.
During earthquake type AF2 the stress value over the isolator parts are smaller then 40 MPa, so all three poles (A, B and C) stand out to a AF2 seism.
By comparing with the value of 40,3 MPa determined by FEA for the lower part of the isolator column of the pole “C” it can be considered that the pole “C” stand out to a seism type AF3 corresponding to a 7 degrees seism on Richter scale. Similar conclusions can be made for pole “A”. Some problems are with the pole “B”, because of the rigid connections with poles “A” and “C” and looseness of the shrinkages.
For seism type AF5 the stresses obtained are superior to the admissible value of the stress for ceramics material so, the base isolator of the pole C and B will collapse. The conclusion is that the resistance structure of the SF6 circuit breaker is not performing well during AF5 seism, and is necessary to optimize the structure. The optimization can be done using the Finite Element model used in this study.

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