Aurora is delighted to have been approached by the IET to prepare a technical paper for a new Engineering & Technology and Reference (ETR) service. Aurora have proposed to prepare a technical paper that discusses the complexities associated with circuit breaker asymmetrical switching duties, due to electrical networks that have a high system X/R ratios and high percentage of DC component in the fault level.

We have chosen to prepare a paper on this phenomena of asymmetrical switching duties on circuit breakers, as it is not always understood by many engineers, who often believe (incorrectly) that the problem is simply associated with large power plants and generators. Aurora’s paper will show that this problem can be associated even for relatively small 30MVA DNO substations, or industrial plants with a lot of motor load of standby / embedded generators and give practical advice for identify the problem, and explain the appropriate corrective actions to deal with the issue.