16.1 Importance of Busbars

Busbars are the most important component in a distribution network. They can be open busbars in an outdoor switch yard, up to several hundred volts, or inside a metal clad cubicle restricted within a limited enclosure with minimum phase-to-phase and phase-to-ground clearances. We come across busbars, which are insulated as well as those, which are open and are normally in small length sections interconnected by hardware.

They form an electrical 'node' where many circuits come together, feeding in and sending out power (see Figure 16.1).

Figure 16.1: Schematic illustrating area of busbar zone

From the above diagram, it is very clear that for any reason the busbars fails, it could lead to shutdown of all distribution loads connected through them, even if the power generation is normal and the feeders are normal.

The important issues of switchgear protection can be summarized as:

• Loss very serious and sometimes catastrophic

• Switchgear damaged beyond repair

• Multi-panel boards not available 'off-the-shelf'

• Numerous joints

• Air enclosure

• Dust build-up

• Insect nesting

• Ageing of insulation

• Frequency of stress impulses

• Long earth fault protection tripping times.

16.2 Busbar Protection

Busbars are frequently left without protection because:

• Low susceptibility to faults - especially metal clad switchgear

• Rely on system back-up protection

• Too expensive and expensive CT's

• Problems with accidental operation - greater than infrequent busbar faults

• Majority of faults are earth faults - limited earth fault current - fast protection not required.

However, busbar faults do occur.

16.3 The Requirements for Good Protection

The successful...