Riding through the additional load

Our client’s substation has two transformers that are loaded near their n-1 load limit and a downstream industrial customer was planning to connect a large industrial load that would exceed this load limit. The obvious solution of installing new transformers with higher ratings did not fit within the industrial customer’s timeframes.


Tesla was engaged to carry out a detailed investigation and design a Special Protection Scheme (SPS) that utilised the smart features within modern protection devices to allow a large load to be carried when both transformers are in service.

Developing a Supply Transformer Overload Special Protection Scheme through Collaboration

Our challenge was to design an SPS scheme that could be installed, commissioned and fully tested as a complete scheme with minimal impact to the 11 kV supply.


Tesla worked collaboratively throughout the process with the Client and their maintenance technicians, using Tesla’s design and the Client’s protection test facilities to prove the design concepts, eliminate any issues, and to develop testing and commissioning procedures. This joint work enabled the scheme to be installed and commissioned on time while meeting the technical and operational performance objectives.


The scheme provides automatic overload protection for the transformers through a feeder load shedding scheme utilising communication between the transformer and feeder protection.


The SPS design was encompassed within a scheduled transformer protection replacement project and aligned with an RTU replacement, further widening the scope of the design works but resulting in economies and reduced outages for the project deployment.
The successful deployment of the SPS scheme has enabled a significant amount of expenditure to be deferred and now allows our Client some time to consider other options to manage the load increase in this area.


Tesla’s project team was lead by David Collins, with Maik Ufferhardt and Bevan Cooper. For further information contact David at david.collins@tesla.co.nz

Testing the scheme before deploying

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