About halfway of its length, feeder F1 is divided into two branches forming a T-branch which is significant regarding both line length and average power (Figure 63). Because the payback time of R3 was the shortest of the studied individual alternative line reclosers it is assumed that it is installed first. According to the additional calculations the second line recloser to be added to the feeder is R1 with a payback time of 2.6 years. Adding a third line recloser R2 is not so profita-ble because its payback time is 8 years.
Figure 63. Alternative FA schemes of the T-branch in feeder F1 (left) and pay-back time of the first, second and third remote controlled line reclos-er (right).
The profitability of each single investment depends on the annual cost saving and the payback time of the investment, which are presented in Table 24. Depending on the higher fault rate and average power the profitability of remote controlled line recloser investments are higher in feeder F1 than in feeder F2.
The most cost-effective line reclosers are R3 and R1 upstream of the T-branch in feeder F1. The payback time of these line reclosers is 1.2 and 1.4 years respec-tively. The highest annual cost saving of a line recloser in feeder F1 is about twice the highest annual cost saving of a recloser in feeder F2. According to the results, line reclosing is especially effective in long overhead line feeders with a high av-erage power and little or no remote control.
Table 24. The cost-efficiency of the line reclosers when compared to the situation in year 2009 with remote control of line switch groups.
R1(3) = Installing of recloser R1 in the feeder already containing recloser R3.
Feeder Recloser Annual saving [k€]
The second supervisory period that took effect from the beginning of 2008 has introduced new elements into the investments on the reliability of electricity dis-tribution. When the reliability goals set by the EMA are exceeded the distribution company gets a price bonus and vice versa. This enables the distribution compa-nies to calculate in advance the cost efficiency of alternative reliability improving investments. Here the cost-efficiency of using remote controlled line reclosers in two real feeders has been studied. The annual total outage cost is calculated for
the basic feeders without feeder automation, with the feeder automation scheme used in year 2009, usually remote controlled line switch groups, and also with different remote controlled line recloser schemes. Thus the annual economic ben-efit, benefit/cost and payback time of different automation scheme investments have been calculated.
According to the results the distribution company Vaasan Sähköverkko Oy has improved T–SAIDI of the two feeders to about the half of the value of the original feeders and reduced the outage related cost with about a third compared to the original feeders with no remote control. What can then be achieved by the use of remote controlled line reclosers? According to the calculations, the payback time of the first remote controlled line recloser in feeder F1, depending on the location, is 1.2–2.3 years. In feeder F2, the payback time of the first alternative line reclos-er varies from 2.4 to 4.4 years. In these two studied feedreclos-ers the saving potential obtained by using remote controlled line reclosers is of the same order as the sav-ing already achieved with remote control of line switch groups or another third of the annual total outage cost. As a result of these studies Vaasan Sähköverkko Oy has now a total of 17 line reclosers of which most are remote controlled. A GPRS modem handles the communication between the primary distribution substation and the line recloser. In this way all the three electricity distribution reliability indices T–SAIFI, T–MAIFI and T–SAIDI are improved, because line reclosing limits the influence of a fault to the nearest upstream recloser.
Regarding the location of line reclosers the starting-point is the actual feeder con-figuration including present remote controlled line switches/line switch groups and normally open points. If the network is homogenous, that is both load density and configuration are uniform, the line reclosers can be located evenly along the feeder according to the even distance principle. In case the network is not homog-enous, natural and cost-effective locations of line reclosers are downstream of load centres and upstream of long branches.
The cost-effective number of line reclosers also depends on the extent of present remote controlled line switches. In this aspect feeder F2 is not typical although it is cost effective to install one line recloser also into this feeder. In feeder F1 with no remote control at present it is cost-effective to install a line recloser even if the fault frequency of the feeder is only a half of the actual fault frequency. A rough estimate of the potential number of cost-effective line reclosers for the studied distribution company would be about 15, the total number of feeders being 95.
This means that about 16 % of the feeders of this distribution company have cost-effective locations for remote-controlled line reclosers. This estimate is made ac-cording to the results of the calculations and the fault frequency statistics so it is only an estimate but still indicative.