Comparison and extension of IEC thermal models for dynamic rating of distribution transformers

Unison Networks Ltd (UNL) in Hastings, New Zealand is in the process of implementing the smart grid initiative, as part of advancing Life Cycle Asset Management (LCAM) practices. As a part of that initiative, ETEL Transformers Ltd, a subsidy of UNL has been assigned the task of developing a smart transformer kiosk. As condition monitoring and diagnosis are now an essential part of a transformer management system, ETEL is developing an intelligent framework for dynamically measuring and assessing the condition of the transformer. ETEL has developed a unique low cost fibre optics based transformer oil and winding temperature monitoring system. ETEL in collaboration with Robinson Research Institute is also developing the Distribution Transformer Dynamic Rating (DT-DR) algorithm. The extension of the two IEC thermal models for the DT-DR algorithm is proposed in this paper under unbalanced loading with different harmonic distortions in each phase.

I. Introduction

Unison Networks Limited (UNL) is the fourth largest electricity distribution company in New Zealand. UNL owns, maintains and operates electricity distribution assets that supply more than 100,000 consumers in Hawkes Bay, Rotorua and Taupo region. The implementation of smart grid became a company focus for UNL in 2009 with the definition of smart grid being adopted as “The application of real time data, communications technologies and emerging trends in electricity distribution to improve capacity utilization, enhance life-cycle asset management and provide additional services on the modern network, thereby optimizing network investment to the benefit of all stakeholder” [1].