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Newcastle Electricity and Steam Company (NESCO)
Connection and grid impact studies for 20MW co-generation power plant

South Africa

Client:

Independent Power South Africa (IPSA)
PSD sub-contracted to Thabile Engineering (Main Contractor)

Project Status: Completed in 2007

temane Project Outline
PSD was commissioned to perform the requisite studies for connecting the NESCO 20MW co-generation power plant into the existing Karbochem electrical plant network.

Services to Client

•	Data collection and system modeling
•	Load flow and fault level studies
•	Machine transient stability studies
•	Load impact and motor starting studies
•	Advised the client on the best grid connection point
•	Connection cost estimation

Project Detail
The study included:

•	Data collection. A model of the complete electrical plant network was built using the PSS/E simulation program.
•	Grid connection studies for the NESCO 20MW co-generation plant. The plant is connected to the Karbochem electrical plant via a high voltage 11kV cable system over a distance of about 1.5km. The co-generation plant comprised two gas-fired turbine units (7.3MVA each) and one steam-turbine unit (8.25MVA).
•	Extensive load flow and fault level studies were performed. This was done to (1) dimension the new infrastructure components that were to be installed and to (2) to ascertain the impact of increased loading stresses on existing electrical plant components.
•	Machine transient stability studies determine critical fault clearing times along the length of the connected power system. The results of this study, together with the fault level study results, were given as input into the system protection applications and settings.
•	Electrical load impact studies confirmed that the generators could remain stable and that voltage profiles were within acceptable limits during load switching operations, e.g. large motor starting or energisation of a block of load.
•	One of the advantages of embedded generation is that it can assist in making the chemical/industrial plant immune to voltage dips, especially against voltage dips induced by faults on the connecting utility networks. A study was done to assess the improvements in dip performance that could be expected.
•	PSD also assisted with a technical and economic evaluation of two possible, alternate grid connection points. The one option was to connect the co-generation plant into the municipal 11kV network with overhead power line over a distance of approximately 2km. The other option, which was eventually implemented, was to connect into the Karbochem plant 11kV switchboard.

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