Efficiency analysis – Southern African 420 kV transmission line

This article presents an investigative case study and efficiency analysis of the 405 km, 420 kV transmission line between Insukamini substation in Bulawayo, Zimbabwe and the Matimba thermal power station in South Africa (which is routed through Botswana).

An analysis was done on the energy efficiency of the load with respect to three scenarios by means of a simulation model, the development of which is explained in detail. The simulation model was slightly adapted in order to simulate series compensation on the network. From the results obtained from the simulation model it can be seen that the energy efficiency decreases for all three scenarios.


Summary of scenarios and results

Line to ground fault occurred on the secondary bus: The available power on the load drastically decreased the moment the fault was induced. The available power restored to its initial value the moment the fault cleared. During this fault almost no power was transferred to the load. It was therefore decided not to calculate the efficiency loss for this scenario and the scenario was only used for investigative purposes.

Impedance fault occurred on the two transmission lines: The energy efficiency of the load followed a curve with respect to the impedance of the transmission line. The load efficiency decreased when the transmission line impedance increased. A more than 1% efficiency loss on the load was calculated for an impedance increase of only 10% (resistance increase of 1,1 mΩ/km and inductance increase of 87,6 μH/km).

Combination of the above two faults: The available load current, load voltage and load power decreased, the moment the two faults were induced. Almost no power was transferred to the load the moment the line to ground fault (fault from scenario 1) was induced.


Take note

  • Transmission line compensation can affect efficiency.
  • The benefits of either series at parallel compensation should be considered from an efficiency point of view.
  • Simulation can play an important role in better understanding the performance of a transmission line.


Published as:

Investigation and efficiency analysis: 405 km transmission line with series compensation

By R Gouws, North-West University

Electricity+Control, April 2012 (pgs 42 – 46)

Email: Rupert.Gouws@nwu.ac.za