4. Terminal fault: transient recovery voltage (TTR)

4.1 General

• Extinguishing a 10 or 30 kA arc is not a major problem, as it only needs to be cooled rapidly by means of a suitable blowing device. The difficulty in interrupting a current in a high-voltage network is due to the fact that, when the current is interrupted, the voltage applied to one terminal of the circuit-breaker joins that of the supply network, while the voltage on the other terminal remains zero (basic case of a single-phase earth fault illustrated in figure 9 ).