Chapter 29. Recommended practices for mounting buses and
making bus joints
Precautions in mounting insulators and
Types of joints
Making a joint
Bending of busbars
Precautions in mounting insulators and conductors
Often a failure on a fault may be due not to the inadequate size of busbars, fasteners or insulators but to poor alignment of the insulators or to too large a gap between the busbar and the insulator slots. It may be a consequence of an inappropriate mounting or unequal width of the busbars or insulator slots. In such cases, load sharing will be uneven and the weakest section may fail. This can be illustrated as follows:
1. As shown in Figure 29.1(a) as a result of loose fit of busbars with an unequal gap, the insulators (shaded in the figure) may fail for the following reasons:
• Misalignment of insulators may cause an unequal distribution of forces.
• A loose fit of busbars inside the slots may cause excessive vibrations on a fault and may lead to loosening of the fasteners and shearing of the wedges and/or the edges and the fingers of the insulators. Even the insulator mounting section X – X¢ may become vulnerable to failure.
2. When one or all of the busbars are shorter in width as shown in Figure 29.1(b) the upper insulator may fail at the shaded parts through the wedges or the edges, as they will now encounter relatively higher cantilever forces.