Devices based on shape memory alloys for increasing reliability of bolted electrical contact connections

Abstract

Increasing reliability of bolted electrical contact connections is an important problem in power engineering. Such connections are very common and their damage can lead to serious consequences. One of the ways to increase reliability of bolted electrical connections is the use of special devices based on shape memory alloys (SMAs). This article contains an analysis of four devices that destroy films (oxides, sulfides etc.) which form on a contact surface of bolted electrical connections during operation. Destruction of such films slows down process of a contact connection degradation and, ac cordingly, extends its service life, thereby increasing reliability of a contact connection. The following devices were analyzed: a conical washer made of SMA, "Detachable connection of conductors with a contact crown nut", "Terminal lug" with shape memory effect (SME) element. These devices have SME elements which during activation increase a contact pressure in an electrical connection and, accordingly, destroy films on a contact surface. Another "Terminal lug" with SME element was also analyzed. This device has SME element which during activation displaces one contact rela tive to another. This motion cleans a contact surface from films without affecting a contact pressure. Analysis of these devices, in particular using the finite element method, which was implemented using Ansys 2020 R2 Academic software, showed the following disadvantages and features of the above-mentioned devices: the need to manufacture specially designed contact connection elements, the locality of a pressure increase on a contact surface, and the need to disassemble contact connections when installing SME elements. Based on the conducted analysis, a new design of a contact connection was proposed. This new design does not have indicated disadvantages and its principle of operation is based on a combined destruction of films on a contact surface by increasing a contact pressure and by the relative displacement of the contacts.