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Insulation Coordination Study: Transient and Harmonic Studies for the Planned Cape 765 kV Transmission System Expansions

South Africa

Client:

Eskom (Transmission)

Project Status: Completed in 2008

Eskom Transmission Insulation Coordination Study Project Outline
Eskom Transmission plan to strengthen the 400 kV back-bone Transmission System spanning from the strong generation pool in the north of the country to the load centres in the southern parts of the country. This strengthening / expansion projects comprised 765 kV lines, substations and series capacitors.

Services to Client

•	Built PSCAD / EMTDC model of the network
•	Frequency scans
•	Line reactor optimization study
•	Temporary over-voltage (TOV) studies
•	Line energization studies
•	Auto re-close (ARC) and neutral reactor studies
•	Transient Studies

Project Detail
The study included:

•	The Main Transmission System was modeled in PSCAD using frequency dependant line models, SVC’s, Shunt reactors, Shunt Capacitors.
•	Frequency Scans were done at various points in the Transmission System to determine if any resonance conditions exist.
•	Studies were done to determine the optimal sizing of the line reactors taking into account power transfer and voltage control issues (e.g. Ferranti voltage rise).
•	The TOV studies included load rejections and single phase line faults.
•	The impact of transformer and line energisation on the network were studied.
•	Auto Re-close (ARC) and neutral reactor studies
•	Auto Re-close (ARC) and neutral reactor studies were done to size the neutral reactors in order to increase the possibility of a successful single-phase auto re-closing (ARC) event.
•	Transient studies were done to investigate the need and effect of pre-insertion resistors on breakers, the optimal size of the surge arrestors, effect of controlled switching etc. Included here will were deterministic switching studies on all line sections and statistical switching study on one line section.
•	Alternatives were considered for sections where the lines were too long resulting in an inoperable system. The options included:
	o Additional Switching Stations in the middle of the long line sections.
	o Series Compensation on the lines.
	o SVCs at strategic substations

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