Reliability comparison between different 400 kV substation designs

This thesis examines how the unavailability for OKG will be affected by the planned replacement\nof the 400 kV substation at Simpevarp. The evaluation has been based on calculation of\nunavailability due to both faults and maintenance, fault and maintenance frequencies and\nestimated costs for the different substation designs. Four different variations of two-breaker\narrangement designs have been simulated and been compared to simulations of the existing\nsubstation.\nTo perform the calculations a program has been developed in java that simulates the different\nsubstation designs. The fault probabilities used in this study has primarily been taken from fault\nstatistics for the Swedish grid but has also been compared to the assumptions used in other\nsubstation reliability studies.\nThe results of this thesis show that the unavailability is likely to be higher for the proposed twobreaker\narrangement design without separate disconnectors compared to the existing substation.\nWhen the two-breaker arrangement simulation instead included separate disconnectors the\nunavailability was found to be lower for the two-breaker arrangement design compared to the\nexisting substation. The study also showed that the two-breaker arrangement designs had\nconsiderably lower fault frequencies compared to the existing substation. The thesis found that\nthe unavailability that will be caused by maintenance can be significant and are likely to be\nhigher than the unavailability caused by faults. The amount of unavailability caused by\nmaintenance was, however, found to be uncertain because a large part of it can be performed\nduring planned outage. Furthermore, it was found that the two-breaker arrangement design with\nand without disconnectors had similar expected present value of costs if the maintenance costs\nwere excluded. This indicates that the best substation option from an economic point of view is\ndetermined by the maintenance costs.