Development of a loss angle measurement technique for online monitoring of instrument transformers
Rautiainen, Kalle (2026)
2026
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2026-06-22
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202606197768
https://urn.fi/URN:NBN:fi:tuni-202606197768
Tiivistelmä
The energy transition, increasing electrification and the growing importance of security and reliability of electricity supply have created an increasing need for condition-based maintenance strategies in power systems. Loss angle measurement is a common method for assessing the insulation condition of high-voltage equipment. However, traditional loss angle measurements of instrument transformers require planned outages and extensive field work, which makes their implementation expensive and difficult to perform frequently. Therefore, an online loss angle measurement method could provide valuable information on long-term changes in insulation condition.
The objective of this thesis was to investigate whether an online loss angle measurement method tested at the substation could be developed into a reliable tool for continuous insulation condition monitoring of instrument transformers. The thesis is divided into two parts. The theoretical part presents instrument transformer technology, insulation aging mechanisms and loss angle measurement principles. The experimental part of the thesis includes laboratory measurements in which IoT-based measurement devices were tested with three different current sensing methods, including a split-core current transformer sensor, a solid-core current transformer sensor and a shunt resistor. The results were compared with reference measurements obtained using a traditional measuring bridge.
The results show that the proposed online measurement method can produce values
comparable with reference measurements when a suitable current sensing method is used. The solid-core and split-core current transformer sensors introduced considerable phase errors, which led to physically unrealistic negative loss angle values. In contrast, the shunt resistor provided loss angle values that corresponded well with the reference measurements. The determination of accurate absolute loss angle values remains challenging, and the method appears to be best suited for monitoring long-term trends. Further development is required especially in understanding earth current formation in substation environments, validating the results under field conditions and improving the signal processing methods.
The objective of this thesis was to investigate whether an online loss angle measurement method tested at the substation could be developed into a reliable tool for continuous insulation condition monitoring of instrument transformers. The thesis is divided into two parts. The theoretical part presents instrument transformer technology, insulation aging mechanisms and loss angle measurement principles. The experimental part of the thesis includes laboratory measurements in which IoT-based measurement devices were tested with three different current sensing methods, including a split-core current transformer sensor, a solid-core current transformer sensor and a shunt resistor. The results were compared with reference measurements obtained using a traditional measuring bridge.
The results show that the proposed online measurement method can produce values
comparable with reference measurements when a suitable current sensing method is used. The solid-core and split-core current transformer sensors introduced considerable phase errors, which led to physically unrealistic negative loss angle values. In contrast, the shunt resistor provided loss angle values that corresponded well with the reference measurements. The determination of accurate absolute loss angle values remains challenging, and the method appears to be best suited for monitoring long-term trends. Further development is required especially in understanding earth current formation in substation environments, validating the results under field conditions and improving the signal processing methods.