High x/r ratio on transmission network

[Chunky12345]

Good morning all,

I've conducted a fault level study on PSSe on a 400kV and 275kV network and though the fault levels are within the ratings of relevant switchgear, the 3ph RMS x/r ratio is above 14 (close to 25). The initial peak current isn't over the make rating of the circuit breaker so no issues there. Am I right in thinking the only issue with a high x/r ratio is that the peak current might be higher than the make rating of the circuit breaker? Is there anything else I should be worried about?

 

[RRaghunath]

Circuit breakers also need to be selected appropriate to the higher X/R, as the standard circuit breakers are designed for X/R of 14 only.

Good morning all,

I've conducted a fault level study on PSSe on a 400kV and 275kV network and though the fault levels are within the ratings of relevant switchgear, the 3ph RMS x/r ratio is above 14 (close to 25). The initial peak current isn't over the make rating of the circuit breaker so no issues there. Am I right in thinking the only issue with a high x/r ratio is that the peak current might be higher than the make rating of the circuit breaker? Is there anything else I should be worried about?

 

[dpc]

Depending on the type of breaker and the test standard used by the manufacturer, the interrupting rating may need to be checked (or derated) as well depending on your actual X/R vs the test value. IEC and ANSI standards and calculation methods are a little different.