Eskom’s power transmission development plan

November 13th, 2015, Published in Articles: Energize


The Eskom transmission development plan (TDP) represents the transmission network infrastructure investment requirements and covers a ten year window. The plan is adapted and modified on an annual basis to accommodate changes in both generation and load requirements. The latest version of the plan was made public recently and this article summarises the main points of the plan as presented by Eskom.

Eskom, as the national transmission company (NTC), is responsible for providing and maintaining the national transmission network. The TDP is one of the largest infrastructure development programmes in South Africa and is intended to create grid capacity to integrate the generation envisaged in the 2010 IRP.

The key plans driving the expansion of the transmission network are:

  • Integrated resource plan (IRP). The Department of Energy (DoE) is accountable for the IRP 2010-2030, which is intended to drive all new generation capacity development. NERSA licences new generators according to this determination. The IRP covers total resources only and does not give any spatial information.
  • The Eskom strategic grid plan (SGP) formulates long term strategic transmission corridor requirements, and is based on a range of generation scenarios and associated strategic network analysis. The horizon is 20 years and the plan is updated every two to three years.
  • The TDP represents the transmission network infrastructure investment requirements and covers a ten year window. The plan is updated annually and indicates financial commitments required in the short to medium term.

Although the plan is based on the IRP, other growth and demand projections and customer applications are taken into account in the preparation of the TDP.

The present plans and demand projections are affected by a constrained generation network. There is no point in installing capacity that will not be used and could end up as stranded assets. The plan needs to provide a balance between accommodating existing generation capacity and demand, and providing for future growth in generation and demand. The Renewable Energy Independent Power Producers Procurement Programme (REIPPPP) and the resultant renewable energy generation are changing the power flow patterns in the network, and any network growth needs to accommodate this. The existing energy flow is from the north of the country to the south, but this could change in future with the south becoming a net producer of electricity and the power flow changing to south to north. Renewable energy is also variable and a future network will have to accommodate bi-direction flow of energy.

Fig. 1: Major projects undertaken recently (Eskom).

Fig. 1: Major projects undertaken recently (Eskom).

Major projects undertaken recently

2142 MW of renewables have been connected to the grid underpinned by a R 2,4-billion Eskom network investment. Fig. 1 shows other major projects completed recently.

Major features of the programme

Fig. 2 shows the major projects included in the plan and Table 1 shows the extent of network growth.

Fig. 2: Changing generation footprint based on 2040 study (Eskom).

Fig. 2: Changing generation footprint based on 2040 study (Eskom).

Capital plan

The total transmission capital plan amounts to R213 billion over the TDP period 2016 to 2025 of which:

  • R151-billion is required for reliability (N-1) projects, integration of committed generation (Medupi, Kusile, Ingula, IPPs up to Bid Window 3) and connection of new load onto the system.
  • R30-billion is required to integrate new IPPs (i.e. RE, gas, coal, co-gen) beyond bid window 3 of the DoE’s IPP programme.

Transmission capital expenditure drivers

Table 1: Transmission infrastructure requirements over the TDP period (Eskom).
Transmission assets New assets expected in 2016 – 2020 New assets expected in 2021 – 2025 Total new assets
Total km of lines 2958 7011 9969
765 kV lines (km) 350 1760 2110
400 kV lines (km) 2589 4915 7504
275 kV lines (km) 19 336 355
Total transformer MVA 29 240 46 155 75 395
Transformers 71 94 165
Capacitors 15 6 21
Reactors 6 15 21

Capacity expansion and network strengthening:

  • Connection of new and anticipated customer loads and generation
  • N-1 reliability investments
  • Mitigation of fault-level exceedances (existing and anticipated)
  • Resolution of quality of supply excursions
  • Securing of servitudes and environmental authorisations
  • Compliance (regulatory, OHSAct, environmental etc.)

Refurbishment (i.e. extension of life of existing assets):

  • Refurbishment based on asset condition (CTs, VTs, surge arresters, HV circuit breakers and power transformers)
  • Replacement of substation batteries and electronic components for protection and control systems, corroded conductors, etc., (i.e. those not repairable)
  • Targeted asset performance improvements (lines and substation equipment)
  • Physical security improvements and surveillance and monitoring at our key assets and sites
  • Strategic and operational spares holding (to reduce SML <1 and MI risk)
  • Compliance (regulatory, OHSAct, NKP Act, environmental, etc.)

Asset purchases:

  • Specialised equipment for: live-line work; fault location systems, and online condition monitoring, etc.

Allocation of capital

Table 2 gives the total allocation of capital to the plan.

Table 2:  Capital allocation to the TDP (Eskom).
Totals: (FY 2016 – 2025)
Capital expansion 151 152
Capital expansion for IPPs 30 305
Refurbishment 16 948
Capital spares 2531
Telecoms 4019
Aviation 669
Production equipment 630
Other 1831
Land and rights 4940
213 026

Potential risks to the TDP

The liquidity position of Eskom may have an impact on execution. The IPP programme may also trigger extensive network reinforcements. The time taken to acquire servitudes and secure water use licenses continues to be a challenge to the roll out. Under-investment in transmission infrastructure threatens network reliability and load growth in the country. The ability to execute projects to accomplish the plan also remains a challenge.

Maintenance of existing plant

The plan also has to accommodate maintenance and upgrades of existing plant. The South African grid code (SAGC) stipulates that the NTC is responsible for the renewal, optimisation, reconfiguration and decommissioning of existing assets to ensure sustainability of the network. The development of the transmission refurbishment plan is based on an asset management (AM) framework The AM approach involves asset condition assessment and asset risk assessment, to support the compilation of refurbishment plans. The AM approach seeks to sustain a reliable and quality of supply, by managing the delicate balance between network performance, network risks and capital constraints .

The AM is based on condition monitoring rather than age, and the condition of all the approximately 40 000 assets in the transmission network is monitored on a regular basis. The annual programme is focused on the approximately 5000 items that are considered to be in need of attention each year. Action is based on a prioritisation matrix. As a starting point assets are identified at bay level and based on condition rolled up per bay. The bay items are rolled up into the substation level, and phased using criticality, importance and impact.

Generated projects to cost and enter into plan

In spite of monitoring, assets do fail, and it is necessary to establish and maintain a stock of spares, which also forms part of the program. The current ten-year transmission refurbishment plan is based on asset condition assessments, asset criticality and network risks and embodies the requirements and stipulations of the SAGC.

Transmission strategic grid planning: integrating future IPPs

Planning is part of a process framework to deliver transmission infrastructure and is based on the transmission load demand forecast and the IRP. The TDP is based on spatial assumptions made by Eskom for the 2010 IRP. The grid access plan (GAP) is the agreement with stakeholders on the physical location and associated timing of the future generation capacity.

Change in generation spatial footprint irrespective of generation scenario

The IRP 2010 sketches several scenarios of future generation and demand but gives no indication of spatial distribution of these quantities. This is an important factor as major changes in spatial distribution will require major changes in the transmission network.

Fig. 2 illustrates the changing spatial generation distribution as forecast by Eskom.

Strategic investment is needed to be able to adapt to the uncertainty of future. The  need to identify and invest in critical power corridors for the future transmission network and unlock and create a flexible and robust grid, to be able to respond to the changing future, has been identified.

The Eskom long term grid assessment (2040 transmission study) was based on the projected 2040 spatial generation and load requirements, and the results have been used to project future transmission corridor requirements and potential. The study showed that although there was a significant change in the generation spatial footprint, the load spatial footprint did not change much, with 75% of the load remaining in northern sector of the country and 25% in the southern. The generation footprint changes however, with a predicted flow from south to north in excess of  8 GW by 2030. From Fig. 3 it can be seen that the generation in the southern region is wide spread and dilute, compared to the centralised concentration of generation in the north. This adds to the complexity of the network as generation density may vary with time from place to place within the southern network due to the variability of renewable energy sources.

Fig. 3: Major projects included in the TDP (Eskom).

Fig. 3: Major projects included in the TDP (Eskom).

Change in generation diversity has a major impact on the future transmission network. The change of generation footprint into areas with limited demand requires additional transmission capacity and increased connection capacity will be needed in new areas with shorter delivery times. Smaller IPP generation plant can be constructed faster, with delivery time of less than five years, and at locations as yet unknown.

Parties involved in the development program have undertaken projects to identify and establish the groundwork for future strategic transmission corridors, to accommodate future generation scenarios. One of the main projects is the SEA strategic electrical grid infrastructure project coordinated by the DEA and involving Eskom, the CSIR and SANBI.

The main objectives of the programme are to:

  • Identify strategic corridors which support electricity transmission needs up to 2040.
  • Refine the corridors based on high level suitability from an environmental, economic and social perspective.
  • Facilitate streamlined environmental authorisation for transmission infrastructure development within the corridors.
  • Promote collaborative governance between authorising authorities.
  • Develop a site specific development protocol.
  • Enable Eskom greater flexibility when undertaking land negotiation.
  • Support upfront strategic investment.

These projects involve IEA work on potential routes, and acquiring wayleaves, well in advance of any firm plans. Corridors are based on 100 km wide strips which can be subjected to IEA processes and which allow considerable leeway in obtaining wayleaves within the boundaries of the corridor. Final planning will then proceed at a much faster pace, and more flexibility will result. This exercise is being done in conjunction with the renewable energy development zone (REDZ) initiative, which is aimed at identifying and developing areas where renewable energy generation will bring the greatest overall benefit, and have the greatest potential for implementation, taking all factors including technical, social, etc., into account. The project has identified five strategic corridors, as shown in Fig. 4.

Fig. 4: Initial strategic transmission corridors identified by the project (Eskom).

Fig. 4: Initial strategic transmission corridors identified by the project (Eskom).

The 2040 network study findings and supporting studies enabled the five power corridors to be further refined. The plan is to gazette both corridors and the process by March 2016.

N-1 reliability upgrade projects

Eskom is licenced by NERSA to be the national transmission company (NTC), and as such has to comply with the SAGC). The N-1 reliability conditions of the SAGC require that for any section of the network, with one line or transformer or reactive compensation device out of service, it shall be possible to supply the entire load under all credible system operating conditions. A number of sections of the existing transmission network do not meet this criterion and Eskom has been granted a concession to operate the network in this condition until a fixed date in the future, with the proviso that a network upgrade program is in place to meet the requirements for the whole network. This upgrade programme forms an important part of the TDP, but financial constraints will affect the ability of Eskom to meet the required target date. Some 40 transmission lines and 30 substations are considered to be vulnerable and do not meet the requirements. The largest impact here seems to be the network connecting renewable energy sites, as upgrades that were required have been delayed or postponed due to financial restraints. Fig. 5 illustrates the impact on the N-1 reliability project.

Fig. 5: N-1 compliance program (Eskom).

Fig. 5: N-1 compliance program (Eskom).

Provincial plans


Load demand is 4800 MW (2014) growing to 5500 by 2025.The following transmission projects are included in the TDP:

  • Mafikeng MTS: 2 x 500 MVA transformers
  • Mookodi MTS: 2 x 250 MVA transformers
  • Watershed extension: first 250 transformers, 2 x 30 Mvar 88 kV CVs;2 x 30 Mvar 132 kV CVs
  • Kimberly strengthening phase 3: in progress
  • Ngwedi MTS: 2 x 500 MVA transformers; third 500 MVA transformer
  • Rustenburg strengthening phase 3
  • Dineldi MTS: third 500 MVA transformer
  • Trident, Ararat, Marang network optimisation
  • Bighorn extension: 2 x 500 MVA transformers
  • Marang extension: 2 x 500 MVA transformers


The following transmission projects are included in the TDP:

  • Construct Kusile-Lulamisa 400 kV line
  • Establish Demeter 400/88 kV substation
  • Establish Donatello 275/88 kV substation
  • Establish Kyalami 400/132 kV substation in the Leeukop area
  • Construct Apollo-Lepini 275 kV line
  • Establish 400 kV at Westgate substation
  • Construct Hera-Westgate 400 kV line
  • Establish 400 kV at Etna and Taunus substation
  • Establish new Quattro substation 275/88 kV transformation to City Power, and 275/132 kV transformation to Eskom
  • Etna to Quattro 400 kV lines (to be operated at 275 kV)
  • Etna to Glockner 400 kV lines (to be operated at 275 kV)
  • Establish North Rand 275/132 kV substation
  • City Power to establish Sebenza 275/88 kV substation
  • Establish Jupiter B substation
  • Establish Siluma 275/88 kV substation
  • Construct Matla-Jupiter 2 x 400 kV lines (to be operated at 275 kV
  • Energise Diphororo to Pelly 275 kV line
  • Establish Diphororo 400/275 kV substation
  • Construct Diphororo to Kwagga 275 kV line
  • Loop in and out Wildebees-Dinaledi 400 kV line into Diphororo (Phoebus) 400/132 kV substation
  • Loop in and out Apollo-Dinaledi 400 kV line into Wildebees 400/132 kV substation

Limpopo province

Load demand is 2807 MW. A major recent project was the integration of the Medupi power station with new 400 kV and 765 kV corridors.

The following transmission projects are included in the TDP:

  • New Nzhelele substation and a new 400 kV corridor
  • Borutho to Silimela: first 400 kV line
  • Medupi to Witkop: first 400 kV line
  • Witkop to Senakangwedi B: first 400 kV line
  • Merensky-Foskor: first 400 kV line
  • Foskor-Spencer:first 400 kV line
  • New 400/275 kV and 400/132 kVtransformation at the new Senakangwedi B substation


Load demand is 3750 MW (2014) growing to 4750 MW (2025). The following transmission projects are included in the TDP:

  • Kusile power station integration
  • Coal IPP integration
  • Highveld south reinforcement
  • Lowveld strengthening schemes two and three
  • Shunt compensation at Khanyazwe


Load demand is 6799 MW (2014) growing to 8045 MW (2025). A major project is the 765 kV strengthening to increase power transfer from the power pool into KwaZulu-Natal to cater for load growth in the province. The project involves the Umfolozi-Mbewu 765 kV line, Emapangaeni and Pinetown 765 kV strengthening. The following transmission projects are included in the TDP:

  • Lambda 765/400 kV subsation and associated 400 kV lines to integrate to Majuba and Tutuka substation
  • Lambda-Isundu 765 kV line
  • Ingula Power Station integration
  • Ariadne-Venus 400 kV line
  • Shongweni 400/132 kV substation
  • Eros-St Faiths 400 kV line
  • St Faiths 400/132 kV substation
  • Aiadne-St Faiths 400/132 kV line
  • Inyaninga 400/132 kV substation
  • 2 x Isundu-Mbewu 400 kV lines
  • Mbewu 765/400 kV substation and associated 400 kV lines to integrate to Athene and Invubu substation
  • Lambda-Mbewu 765 kV line
  • Duma-Candover 400 kV line
  • Candover 400/132 kV substation


Load demand is 2357 MW (2014) growing to 2706 MW (2025). There is 124 MW of solar PV at present. Major projects include strengthening the Everest-Merapi 400 kV and Beta-Harvard-Merapi 400 kV lines and integration of 400 kV at Harvard and Merapi substations. The following transmission projects are included in the TDP:
l    Makalu B 275/88 kV substation and associated 275 kV lines
l    Sorata 275/132 kV substation (extension)
l    Everest-Merapi 400 kV line
l    Merapi 400/132 kV substation
l    Harvard-Merapi 400 kV line
l    Harvard 400/132 kV substation
l    2 x Beta-Harvard 400 kV lines

Western Cape

Load demand is 3800 MW (2014) growing to 4960 MW in 2025.

The deficit between Koeberg generation and the greater Cape load is offset by the generation pool in the Highveld via the Cape corridor which comprises 400 kV and 765 kV lines originating from Zeus substation (near Bethal) and Alpha substation (near Standerton) in the Mpumalanga province to Hydra substation (near De Aar) in the Northern Cape. It then extends into the Western Cape and terminates at Muldersvlei substation (near Klapmuts).

There is an expected 1008 MW from REIPPPP windows 1 to 4. The following transmission projects are included in the TDP:

  • Ankerlig-Sterrekus: first and second 400 kV lines
  • Koeberg-Acacia second 400 kV line
  • Erica integration: 400 kV lines
  • Cape Corridor: first and second 765 kV lines
  • Blouwater integration 400 kV lines (operated at 132kV)
  • Droerivier-Narina-Gourikwa 400 kV line

Eastern Cape

Load demand is 1445 MW. There is an expected 1423 MW from IPP windows 1 to 4, and 4500 MW from nuclear. The following transmission projects are included in the TDP:

  • East London network
    – Neptune-Pembroke 400 kV line
    – Pembroke-Poseidon 400 kV line
    – Pembroke B conversion to 400 kV
    – Delphi 100 Mvar shunt capacitor
    – Delphi third transformer
    – Pembroke and Buffalo transformer normalisation
  • Port Elizabeth network
    – Grassridge – Dedisa 132 kV line
    – Grassridge third 400/132 kV transformer
    – Dedisa third 400/132 kV transformer
    – Gamma – Grassridge 765 kV lines
    – Poseidon, Grassridge, Dedisa first 100 Mvar shunt caps
    – Poseidon 400/132 kV transformer (renewables)
    – Poseidon 220/66kV 80 MVA transformer
    – Strategic IPP integration plans
    – Thyspunt integration

Northern Cape

Load demand is 742 MW (2014) growing to 1671 MW in 2025. There is an expected 3569 MW from IPPs windows 1 to 4. The following transmission projects are included in the TDP

  • Aggeneis-Paulputs second 220 kV line and transformation upgrade
  • Upington substation and 4 x 400 kV lines
  • Aries-Nieuwehoop-Ferrum 400 kV line
  • Second Oranjemond-Gromis 400 kV line
  • Juno-Gromis 400 kV line
  • Transformers at Nama, Paulputs, Helios, Aries, Kronos and Hydra.

Some of the 400 kV lines will be operated at a lower voltage (220 kV) until 400 kV is available.

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