Banca de DEFESA: Douglas Guimarães Braga

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Douglas Guimarães Braga
DATE: 12/12/2023
TIME: 14:30
LOCAL: Microsoft TEAMS
TITLE:

ASSESSMENT OF FAILURES DUE TO SLIPPING OF PREFORMED SPLICES

KEY WORDS:

Preformed splices, overhead conductors, failure analysis, transmission lines.

PAGES: 78
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

The aim of this work is to carry out a detailed and systematic study to evaluate the causes of failures due to slippage of several preformed joints used in various 500 kV transmission lines in different regions of Brazil. All slippages always involved the same model of preformed joint (made of 13 rods, each with a diameter of 7.34 mm, a length of 3.5 m, and a pitch of 244 mm) mounted on a 838 MCM (diameter 26.78 mm) aluminum alloy conductor (AAAC-1120). To assess the reasons for slippage, one investigated the material composition, the mechanical propertes and dimensions of both, the conductor and the preformed splice. After confirming that these components met the specifications for material, properties and nominal dimensions, an analysis of the joint's design, its operating principle, and the installation and assembly procedures of these joints in the field was carried out.
The studies and analyses conducted demonstrated that the design of the joint was changed from 12 rods (7.87 mm) to 13 rods (7.34 mm) during the executive design phase of these lines. With this new joint design, the total gap between the rods (total GAP) was calculated. It was concluded that, considering the worst combination of allowable dimensional tolerances for the rods and the conductor, the preformed splice could have a negative total GAP. This means that all combinations of conductor and splice dimensions whose total GAP falls within a range between 0 and this negative value would behave like a "tube." In this way, these joints were compromised in terms of their operating principle. The tube effect can reduce the pressure of the joint should the conductor tension increases (for example due to stronger winds) or the conductor’s cross-sectional area experiences a reduction (for example, due to creep, Poisson's effect, or plastic deformations resulting from the assembly process). Thus, the lack of total GAP when the worst geometric combinations between the conductor and the splice occurs was one of the reasons for these slippages.
After detailed field inspections and the use of digital radiography, it was also discovered that there were gross assembly errors in the splices. These errors were likely exacerbated by the lack of GAP between the rods, which greatly hindered their installation process by the installers. Therefore, the reasons that led to the slippage of these joints are associated with bad installing and mounting pratices and to the design concept of the joint, which could lead the assembly to have a null or even a negative total GAP. Last, but not least, wind vibration tests of the assembly were conducted in this work with severe levels of displacement. The results of these tests ruled out the possibility that wind vibration could be the primary cause of joint slippage.

 

COMMITTEE MEMBERS:
Externo à Instituição - ANDRÉ LUIS PINTO - IFB
Interno - 1523261 - COSME ROBERTO MOREIRA DA SILVA
Interno - 1249764 - JORGE LUIZ DE ALMEIDA FERREIRA
Presidente - 1345908 - JOSE ALEXANDER ARAUJO