The system level electricity distribution reliability indices are calculated accord-ing to Chapter 2.2.4. The charts in Figure 33 present the effect of the different feeder automation schemes on the electricity distribution reliability indices of the different generic feeders.
Figure 33. The calculated percentage T–SAIFI (a), T–MAIFI (b) and T–SAIDI (c) of the different generic feeders as a function of the different FA schemes. The comparison level is the generic ohl model feeder with only manually operated line switches. The present expected average rural/sub-urban performance level is marked with a red circle.
Since the reliability indices are influenced by the feeder line total length the indi-ces are presented as a percentage of the indiindi-ces of the generic ohl model feeder with only manually operated line switches. The average Finnish standard, which corresponds to one remote controlled line switch group, is marked in the charts.
Because line reclosing has not yet widely been used the improvement potential of T–SAIFI and T–MAIFI is high. Due to a high implementation of remote operation of line switches T–SAIDI has improved with about 50 %. Still there are
im-provement possibilities by using more reliable network feeders than overhead line feeders or/and using different line reclosing schemes. In Figure 34 the improve-ment potential by using line reclosing for the different generic model feeders compared to remote control of line switch groups is presented. As can be seen there is a substantial improvement potential for the three reliability indices by using line reclosing. This can also be seen from the expressions of the reliability indices of long feeders in Table 2 (page 51) by comparing the expressions of feeders with and without line sectionalisation. When the number of sectionalisa-tion zones grows the expression for the reliability indices goes towards a half of the expression of the indices without sectionalisation.
Figure 34. The improvement potential of the distribution substation level relia-bility indices of the different generic model feeders compared to the same model feeder with remote operated line switches halfway downstream of the feeder (rc scheme).
3.8 Summary
To be able to compare the performance and economy of different network types and feeder automation schemes and the interaction and influence of these on dif-ferent investment strategies six difdif-ferent generic model distribution systems have been designed. In the design of the primary distribution substation distribution area statistics from both Finnish geodesy and distribution company annual aver-age data have been analysed and applied.
Different feeder automation schemes have been designed to be applied to all the designed model feeders. While the protection of the feeders in Finnish medium voltage distribution systems mainly is concentrated to the primary distribution substation the designed feeder automation schemes also include remote operated line reclosers along the second part of the model feeders both on the trunk line and the lateral lines. In the different line reclosing schemes the number and loca-tion of line reclosers are varied. The effects of the secloca-tionalisaloca-tion schemes on the reliability indices of the designed generic model feeders are compared. It has been shown that by using remote control of line switches the improvement of the aver-age T–SAIDI of the Finnish sub-urban and rural distribution system has been in the order of 50 %, while average T–SAIFI and T–MAIFI have not improved. It has also been shown that by using different line reclosing schemes there is yet another improvement potential of about 50 %. A question is how cost-effective the use of the whole improvement potential is. This will be developed further in the next chapters.
4 THE ANNUAL COST OF ELECTRICITY
DISTRIBUTION OF THE GENERIC FEEDERS
To benefit from the incentives in the Finnish regulation model, adapted since 2008, the distribution companies could optimize their cost of investment, opera-tion and maintenance. In this chapter, calculaopera-tions of the costs that are significant-ly influenced by the feeder type and automation scheme are calculated and pre-sented. With regard to the operational costs, only the cost of losses is taken into consideration, while the costs of maintenance and repair are considered to be in the same order of size for the different generic distribution systems and are there-fore omitted from this work. The costs are studied on an annual basis. The elec-tricity distribution annual total cost can be given by the following equation:
INT
CINV = the annual investment cost COPE = the annual operation cost CINT = the annual total outage cost The total outage cost is:
DIP
Ccom = the cost for compensation to customers due to the outage CNDE = the cost for non-delivered energy
CAR = the cost of auto-reclosing CDIP = the cost of voltage dips
The cost of fault repairing and customer compensation depend mainly on the dis-tribution system category (rural, urban, city) and are not in the scope of this re-search. Because the number of voltage dips cannot be reduced by the use of feed-er automation the cost of voltage dips are not included in the study.