Pilot Project of the First Implementation of Optical Current Transformers at High Voltage

In early April 2024, optical current transformers at the 110 kV voltage level were commissioned for the first time in EMS, and consequently in the entire Serbian power system (EES), within an air-insulated substation. The advancement of modern technologies in the power sector in recent years has led to a strong focus on developing entirely new types of measuring transformers that operate on principles different from those of conventional transformers, which rely on electromagnetic induction. New technologies offer significant performance improvements but also introduce numerous challenges and requirements that need to be addressed. The advantages of optical current transformers primarily include higher accuracy, linearity of characteristics (eliminating the core saturation effect), significantly lower weight and material usage (no need for a magnetic core, copper for secondary windings, oil insulation, etc.), and reduced maintenance requirements. On the other hand, optical current transformers require coupling devices that, instead of analog signals, provide a so-called sampled values stream (SV), i.e., a digital format of the measured quantity. To utilize SV in substation automation, it is necessary to develop an appropriate interface – a process bus – and ultimately implement a digital substation. This paper presents the integration of new technology – optical current transformers – from the perspective of the practical implementation of the IEC 61850-9-2 standard in real conditions. The paper describes the system architecture, experiences gained during implementation, an analysis of results obtained under operational conditions, as well as the advantages and challenges of applying this concept.