Mathematical simulation of thermal state of digital current and voltage transformer in unfavourable weather conditions

Elena E Gotovkina,Vladimir V Tyutikov,Nikolay N Smirnov,Vladimir D Lebedev,Grigory I Parfenov,G.V Kuznetsov,D Feoktistov,E Bulba

doi:10.1051/matecconf/201819401021

Elena E Gotovkina, Vladimir V Tyutikov + Show 6 more

Open Access

https://doi.org/10.1051/matecconf/201819401021

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Abstract

This study examines issues relating to heat exchange between an innovative 6(10) kV current and voltage transformer (and its components) and its environment in unfavourable weather conditions. Existing designs of digital current and voltage transformers are featured in systems of commercial and technical electric power accounting, and also relay protection and automation. We have presented the results of mathematical simulation of the thermal state of both a single resistor included in our measuring device, and the digital transformer as a whole. Simulation was performed using the finite element method. We have taken into account the impact of such factors as direct and diffused solar radiation, high ambient temperatures and various voltage levels on the thermal state of the functioning equipment. To verify the developed mathematical model we have presented the results of a series of experiments conducted in a high-voltage environmental chamber. Our study conclusively shows that voltage, insolation and ambient temperature significantly affect the thermal state of a functioning current and voltage transformer.

Highlights

The digital instrument transformer [1] consists of a resistive voltage divider and current transformer
The electrical processes occurring in resistive voltage dividers comprising a group of resistors entail heat emission
Heat emissions from precision resistors in the voltage transformer were calculated according to the Joule-Lenz law and set with the aid of a function depending on electric grid mode, simulating various values of voltage and current

Summary

Introduction

The digital instrument transformer [1] consists of a resistive voltage divider and current transformer (see Figure 1). Thermal tests during operation of power transformers, and even more so in the case of current and voltage instrument transformers (especially new types) are often performed according to maintenance schedules [3], which negatively impacts the reliability of such electrical equipment [4]. Mathematical simulation of heat exchange was performed both for the entire digital current and voltage transformer and for the cylindrical measuring resistor with R1 resistance, placed in insulation material identical to the one used in the transformer. Since the transformer is intended to operate in the open air and exposed to insolation (see Figure 2), with surface temperatures tsurf exceeding ambient temperature tamb, the thermal balance for this model may be written as follows: Qel

Qdiff ins

Conclusion