Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 82
2.11.1 Substation Shielding
ОглавлениеThe switchyard design for over voltage protection in addition to employing the protective equipment should also be shielded (protection coverage) to force the lightning strikes to hit the masts or shielding wires strung between the shielding masts, and not the operating equipment. Utilities typically have an area charted for flash density as Zones 1 and 2, which generally corresponds to the isokeraunic levels of the region and which can be applied on this project (see Chapter 10). Substations in Zone 2 area must be shielded with overhead shield wires or lightning masts.
Based on the criteria (Chapter 10) and the method of grounding, the equipment shall be protected by the lightning arresters having the following ratings (see Table 2.5):
Table 2.5 System lightning arresters.
| Grid | 13 kV Transformer | O/H lines | 4.16 kV Switchgear | |
| Voltage (kV) | 230 | 13.8 | 13.8 | 4.16 |
| Highest voltage (kV) | 245 | 15 | 15 | 5 |
| Grounding | Solid | Resistance | Resistance | Resistance |
| BIL (kV) | 900 | 95 | 110 | 60 |
| MCOVa) (kV) | 150 | 15 | 15 | — |
| Vr rating (kV) | 188 | 18 | 18 | — |
| Type (class) | Station | Line | Distr. | Not Req. b) |
| Discharge current (kA) | 10 | 5 | 5 | — |
a) It is the maximum continuous operating voltage r.m.s. (root mean square) voltage that can be continuously applied to the arrester terminals. The selection must consider the voltage regulation that may be applicable to the operating system.
b) The 5 kV switchgear is fed from a transformer which in turn is connected to a 13.8 kV O/H line. The line is protected by lightning arresters on both ends of the line. This protection coverage is considered satisfactory for the 5 kV switchgear.
