reliability improving investments
5.1.1 The annual economic benefit of feeder automation
The annual benefit or cost saving of feeder automation is calculated by comparing the annual total outage cost of the reliability improving investment to the total outage cost of the feeder before the investment. The annual benefit of the reliabil-ity improving investment i is:
INTi INT
i C C
B , (56)
where
CINT = the annual total outage cost without the investment i CINTi = the annual total outage cost with the investment i
In Figure 41 the influence of the different line reclosing schemes on the annual cost saving of the different generic feeders is presented when the comparison lev-el is no existing feeder automation (a) and a remote controlled line switch group halfway downstream the feeder (b). The annual total outage cost saving potential for the mixed generic model feeders with line reclosing is about twice in (a)
com-pared to (b). The highest annual cost saving is achieved with the generic ohl feed-er and the line reclosing scheme TR1+LR.
Figure 41. The annual total outage cost saving of the remote controlled line recloser schemes of the different generic feeders when the compari-son level is no FA (a) and a remote controlled line switch group halfway downstream of the feeder trunk line (b).
5.1.2 The benefit/cost of the different automation schemes
The benefit per cost ratio is used for various efficiency or cost-reduction pro-grams where spending on optional projects is justified only when benefits out-weigh costs. Here the annual total outage cost saving of an investment is com-pared to the annual total outage cost without the investment. The benefit/cost is:
INVi INTi INTi
C C C C
B 1 , (57) where
CINTi-1 = the annual total outage cost without the investment CINTi = the annual total outage cost with investment i
CINVi = the annual cost of investment i
The cost of the investment includes the total equipment investment cost including installation while the annual benefit is the annual total outage cost saving achieved by the use of the investment in question. In Figure 42 the annual bene-fit/cost of the different feeder automation schemes is presented.
Figure 42. Annual benefit/investment cost of remote control related FA schemes when the comparison level is no FA (a) and remote con-trolled line recloser schemes when the comparison level is a remote controlled line switch group halfway downstream of the feeder trunk line (b).
5.1.3 The incremental benefit/cost of the different automation schemes When the investment with the highest annual benefit/cost is found a second in-vestment may also be cost-effective. This is calculated by assuming that the first investment is already performed. When changing from one line reclosing scheme to another, available equipment needed are reused when possible, and only the cost of new automation equipment is included. The incremental benefit/cost is thus:
1 1 INVi
INTi INTi
C C C C
incB , (58) where
CINTi+1 = the annual total outage cost of investment i+1 CINV+1 = the additional cost of investment i+1
The incremental benefit/cost expresses how cost-effective it is to change the feed-er automation scheme from one scheme to anothfeed-er scheme. Because TR1 was the most cost-effective feeder automation scheme Figure 43 shows that changing the feeder automation system from this scheme to another scheme is not very cost-effective. As only a few (1–2) automation schemes are cost-effective it is ex-tremely important to find the most cost-effective automation scheme in the first place because also the investment order influences the cost/benefit results. There-fore the calculation of the cost-efficiency of different investment strategies has to
be done one step at a time so that the cost-efficiency of each single investment is known.
Figure 43. The incremental benefit/cost of different FA schemes.
5.1.4 The payback time of the different feeder automation schemes
When comparing different alternative investment strategies the payback time of the different alternatives is of great importance. The payback time TPBi of the in-vestment i is:
INTi INVtoti
PBi B
T C , (59) where
CINVtoti = the total cost of investment i
BINTi = the annual total outage cost saving of investment i
The results show that the network type highly influences the payback time of the different feeder automation schemes (Figure 44). Because the overhead line feed-er has the highest annual total outage cost, it has also the shortest payback times of the different feeder automation schemes. For the remote control related feeder automation schemes the comparison level is the basic distribution system with no feeder automation (a) and for the line reclosing schemes a remote controlled line switch group (b). As can be seen the payback time for the line reclosing schemes are more scattered than those for the remote control related schemes. Fault indica-tion is a low-cost fault locaindica-tion system and has therefore a short payback time,
while remote control of line switches is more expensive with a payback time of a few years in overhead line networks. The payback time of the most cost-effective line reclosing scheme (TR1) is around two years in overhead line networks. From the calculations not presented here it can be concluded that the payback times of the line reclosing schemes are typically reduced by about 50 % if there is no ex-isting feeder automation in the network.
Figure 44. The payback time of different remote control related FA schemes when the comparison level is no present FA (a) and a remote con-trolled line switch group halfway downstream of the feeder trunk line (b).
5.1.5 The feeder automation scheme impact on the regional annual total outage cost level
The regional impact of the different feeder automation schemes differs in terms of both the different generic feeder models and feeder automation schemes. In Fig-ure 45 the regional impact of feeder automation scheme on the ohl generic feeder is presented. In Figure (a) the comparison level is no feeder automation. Remote control of a line switch group reduces the annual total outage cost in all the feeder regions while a remote controlled trunk line recloser further reduces the outage cost of the first part of the feeder. Increasing the number of line reclosers reduces the annual outage cost of the lateral area of the second halve of the feeder. In (b) the ratio of the annual total outage cost between the first/second half and lat-eral/trunk line of the feeder is presented. The latter ratio differs substantially de-pending on the implemented feeder automation scheme. The feeder automation scheme is thus a means for optimising the outage cost for different customer groups with regard to regional location.
Figure 45. Annual total outage cost share of the different regions of the ohl ge-neric feeder (a), feeder lateral/trunk line and first/second part of the line (b). A = feeder first part, B = feeder second part, T = trunk line, L = lateral lines.