Current Interruption Transients Calculation, 2nd Edition

4Terminal Faults

4.1 General Considerations

To this point, we have explored the concepts of oscillatory circuits and pole factors. We will now relate these concepts to real transient recovery voltages (TRVs). The TRV requirements for a 245 kV circuit breaker, as specified in IEC 62271‐100, are given in Table 4.1.

The table is read as follows by column:

• Column 1: Circuit breaker rated voltage U_r which is always a maximum voltage.
• Column 2: Short‐circuit test duties to which the circuit breaker is type tested; T100 represents a test at the short‐circuit rating of the circuit breaker, T60 is a test at 60% of the above rating and so on for T30 and T10. As discussed in detail in 4.2, the varying percentage values represent different power system conditions with respect to fault current.
• Column 3: First‐pole‐to‐clear factor k_pp as calculated in Chapter 3 for circuit breakers applied on effectively earthed systems. Test duty T10, which represents the case of fault current fed through a transformer, is an exception from the 1.3 pu value. The reason for this is that the pole factor is now dependent on the sequence impedances of a typical power transformer.
• Column 4: Amplitude factors k_af as calculated in Chapter 2. The actual values are based on experience, studies and measurements over a long period of time. T10 is again an exception: the amplitude factor is dependent on the low‐loss damping RLC characteristics of power transformers. The reason for the 0.9 multiplier is that 90% of ...