SUMATRA SYSTEM
CHAPTER 9 SELECTION OF PROJECTS FOR PRE F/S
9.7 ACCESS ROAD AND TRANSMISSION LINE
9.7.1 ACCESS ROAD
Required lengths of permanent access road to intake weir and powerhouse site are reviewed and roughly re-estimated as shown in Table 9.7.1 based on the available topographic map as well as site reconnaissance result.
Table 9.7.1 Access Road Plan of Candidate Projects for Pre F/S Project Length to
Intake Weir (km)
Length to P/H (km)
Total Length (km)
Sirahar 5 5 10
Simanggo-2 4 4 8
Gumanti-1 1 1 2
Anai-1 0 1 1
Endikat-2 2 2 4 Cibareno-1 5 3 8
Cimandiri-1 2 0 2
Masang-2 1 2 3 Source: JICA Study Team
9.7.2 TRANSMISSION LINE
In a strict sense, development of transmission lines (power source lines) needs multidisciplinary studies on the prospective construction routes with coverage of items including the selection of route zones, capacity of accessing power transmission facilities, and other technical issues, as well as economic merit, environmental and social considerations, and apprehensions in the aspect of
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meteorological conditions. This section, however, presents the results of a summary screening based on estimates of the access to the nearest power facilities (substations or transmission lines) in the next few years, and with respect to the degree of impact (transmission loss sensitivity), which depends greatly on the distances involved in transmission line construction..
This sort of simple screening method was utilized this time for the following reasons: 1) factors of uncertainty are too large for an in-depth study at the present time; and 2) construction of the station proper generally accounts for the majority of the total cost of hydropower station construction; the share occupied by construction of transmission facilities such as transformers, switching units, and transmission lines is small (no more than about 10 percent). Because of the latter factor in particular, it was judged that it would be unadvisable to make detailed estimates and comparisons of costs for construction of transmission facilities at this point, and that the important thing was to make a decision based on the outline.
(1) Estimate of Type of System Access
The sites with hydropower potential will presumably be connected to the system access points offered by the nearest ends of existing and future transmission and transformation facilities. Strictly speaking, selection of system access points to existing transformation facilities (substation: GI) must be preceded by studies of factors such as the availability of space for installation of additional facilities at the GI. This study does not include the examination of such details.
There are two major alternative options for access to system access points, as noted below. The following section also notes the prerequisites common to both.
- Extension - Branching
(Common prerequisites)
- The extension of transmission lines to the system access point will consist of two parallel circuits1.
- A selection is made of the proper voltage class for the access system based on comparison of the anticipated generation rated capacity of the hydropower potential and the transmission capacity of the standard transmission lines in each voltage class. As noted in RUPTL, however, access to 70-kV transmission lines is to be excluded from consideration because such lines are to be phased out of the Jamali system eventually.
1) Extension
If the nearest power transmission facility from the hydropower potential site is a substation (GI), the GI is accessed by extension of a transmission line from the site. In this case, the requisite transmission facilities are as follows.
1 This is because the standard transmission line facilities in Indonesia consist of two parallel circuits.
JICA Project for the Master Plan Study of 9-20 August, 2011 Hydropower Development in Indonesia
- Selected voltage class IBT + Trf.B: 2 units (determination of transformer capacity based on the rated capacity of the generator)
- Selected voltage class LB: 2 units x 2 locations
- Selected voltage class transmission line: 2 circuits from the hydropower potential site to the nearest substation
2) Branching2
If the nearest power transmission facility from the hydropower potential site is a transmission line, the line is connected to the site by pi feeder. In this case, the requisite transmission facilities are as follows.
- Selected voltage class IBT + Trf.B: 2 units (determination of transformer capacity based on the rated capacity of the generator)
- Selected voltage class LB: 4 units
- Selected voltage class transmission line: 4 circuits from the hydropower potential site to the nearest transmission line branching location
GI ’A GI ’B
Extension
Branching Figure 9.7.1 Types of System Access
Comparing the aforementioned requisite facilities, the difference in transmission line distance in the case of different hydropower potential sites with a generator rated capacity on the same scale appears as a cost difference. Because a difference in transmission line length may be equated with a difference of transmission loss, assessment of transmission loss may be equated with assessment of the cost level.
(2) Impact (degree of transmission loss sensitivity)
A sensitivity analysis was made for transmission loss on the transmission lines posited in Section (1).
The loss sensitivity was sought for the types of transmission wire with a high frequency of use in the
2 A T-type feeder is another option, but it was decided to use the pi-type feeder in the study because there are few locations in the Indonesia power system where T-type feeders are employed in operation of other terminal systems.
9-21 Java3 system at present, in each voltage class.
Class Kind RAC(effective level/km)
500kV Dove×4 0.104
275kV Zebra×2 0.071
150kV Zebra×2 0.071
Here, transmission loss was calculated by obtaining the value for I2 x RAC from the current flowing through each type of transmission line. The impact was judged to be "normal" (problem-free) if the loss rate did not exceed about 0.5 percent4, "big" at higher rates, and "small" at very low rates.
(3) Estimated Length of Transmission Line
Required lengths of transmission line are reviewed and roughly re-estimated as shown in Table 9.6.2 based on the existing or planned transmission line system as well as site reconnaissance result.
Table 9.7.2 Transmission Line Plan of Candidate Projects for Pre F/S Project Grade (kV) Length (km) Connection Point
Sirahar 150 58 PLTP Pumuk Bukit
Simanggo-2 150 40 Dolok Sanggul
Gumanti-1 150 80 Solok
Anai-1 150 40 Singkara
Endikat-2 150 32 Pagar Alam
Cibareno-1 150 50 Bunar
Cimandiri-1 150 18 Sukabumi
Masang-2 150 36 Simpan Empat, Maninjau
Source: JICA Study Team