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The reliability evaluation process is divided in to two parts: the failure process and the recovery process. These two part will be discussed separately.
Failure process
The reliability module does not execute any short circuit calculations. All component failures are simulated by opening the protection deviced around the concerning group. Next the influence on the other groups is evaluated. The term 'group' is explained in Reliability: Concept.
The failure process is as follows:
•a component fails
•the relevant group is disconnected
•groups where components are in overload are also disconnected.
The reliability calculations are based on the methods from Billington.
Recovery process
The recovery process calculates the duration that the requested energy can not be served. The procedure is not developed to find out an optimal recovery strategy, but to calculate the expected duration for energy recovery by any topology changes, repair or back up generators. The recovered network can not be presented to the user.
All faults more or less lead to the same recovery process. The ultimate recovery method depends on the configuration. The process is, in general:
•signal a failure
•activate recovery and repair crew
•locate faulted component
•isolate faulted component
•recover energy service.
The duration for the first four activities will be summed up to the non availability duration. The last activity may take place in four different ways, called recovery phases. Each component may be recovered in any of the phases.
1.Switching on: The opened switches may be closed again. There may be no overload in any circuits. As many switches as possible are tried to close. Also double rail systems are treated in this phase by closing the double rail couplings.
Trecovery := Tsignal + Ttrouble-shooting team + Tlocate + Tisolate + Tswitch on
2.Topology change: All net openings around non available groups are tried to close, without causing any overload. As many net openings as possible are tried to close until the groups are recovered.
Trecovery := Tsignal + Ttrouble-shooting team + Tlocate + Tisolate + Ttopology change
3.Back up generator: If the back up generator duration is smaller than repair of maintenance cancellation the back up generator will be used for the groups still not recovered. Recovery is only possible if the total group requested power is smaller than the generator power.
Trecovery := Tsignal + Ttrouble-shooting team + Tlocate + Tisolate + Tback up generator
4.Repair or Maintenance cancellation: All other components will be recovered after repair or cancellation of maintenance. The assumption is that switching on or topology change always takes less time than back up generator, repair or maintenance cancellation.
Trecovery := Tsignal + Ttrouble-shooting team + Tlocate + Tisolate + min(Trepair ,Tmaint.cancel )
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