• An isolated phase bus (IPB) system
• Constructional features
• Special features of an IPB system
• Enclosure heating
• Natural cooling of enclosures
• Continuous rating
• Forced cooling
• Influence of a space field on the metallic structures
• Fault level
• Voltage drop
• Forming of sections for IPB systems
• Determining the section and size of conductor and enclosure
• Sample calculations
Isolated phase bus (IPB) system
In this construction the conductors of each phase are housed in a separate non-magnetic metallic enclosure to isolate them completely from each other with the following objectives:
1. It eliminates phase-to-phase faults.
2. It eliminates the proximity effect (extra forces and heating) by providing a magnetic shielding to the supporting and metallic structures in the vicinity.
3. It reduces the proximity effects between the main current-carrying conductors of the adjacent phases to almost zero due to magnetic shielding and large centre spacing.
4. It provides complete protection for operating personnel from high touch or step voltages (for details see Section 22.9) across the enclosure and the metallic structures caused by parasitic (electromagnetic) currents.
5. The bus system is easy to handle, bend and instal.
This is used for HV systems of very large ratings. Since it is a more expensive arrangement it is normally preferred only for critical installations such as a power generating station, where it has to carry large to very large currents due to high ratings of the generating units. In a thermal power plant it is used between the generating unit (G) and the generator transformer (GT) and the unit auxiliary transformers (UATs) and sometimes between the UAT and the unit HV switchgear as illustrated in Figure 13.21 (redrawn in Figure 31.1 for more clarity). A typical layout of such a bus system in a thermal power plant is illustrated in Figure 31.2(a) and (b). It may comprise sections noted in Section 31.1.1.Gas insulated busbars (GIB) The above features would be easily possible in an SF6 bus systems also but that being a costlier arrangement is usually not adopted. However, when required at locations having space constraints or other hindrances such as within a power generating station, such bus systems are an immediate solution. Also see Section 19.10.