This study examines the results of thermal tests on a 6(10) kV digital combined current and voltage transformer conducted in an environmental chamber. This measuring instrument consists of current and voltage transformers, featuring a resistive divider, and is used for commercial and technical electric power accounting. Ambient temperatures and levels of insolation on the transformer surface were set for the environmental chamber, with simulation of voltage transformer functioning in normal and emergency modes. We determined the time needed for the thermodynamic system to move to steady heat exchange mode, and also the final temperatures in the lower resistors and on the surface of the voltage transformer insulation cover. The results of our study have been used in developing algorithms for self-diagnostics of the thermal state of a digital combined transformer.

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Physical simulation of heat exchange between 6(10) kV voltage instrument transformer and its environment with natural convection and insolation

The use of capacitive dividers (CDs) in medium-voltage (MV) networks started as simple voltage detectors and as rough voltage measurement instruments for protective purposes. Now, with the spread of intelligent electronic devices and renewable energy sources at the distribution level, capacitive dividers are designed and installed to perform accurate voltage measurements. Such a requirement is mandatory when the power quality has to be assessed. Therefore, CDs are currently being used either for power frequency or for high-frequency (supraharmonic- or partial-discharge-level) measurements. In this paper, typical off-the-shelf CDs are studied and modeled to understand how they behave in a wide range of frequencies and when the temperature varies. To this purpose, specific setups and tests have been developed and performed. From the results, it is clear that with proper modeling of CDs, it is possible to exploit them for measuring phenomena in a wide range of frequencies, including the effects due to temperature variations and self-resonances.

Modeling Capacitive Low-Power Voltage Transformer Behavior over Temperature and Frequency.

In July 1986, reports surfaced of widespread moisture damage in walls of manufactured single-family homes in Wisconsin. The homes were manufactured by a company that declared bankruptcy and was liquidated justbefore the reports ofmoisture damage surfaced. This paper presents information about the nature and extent of the damage and summarizes the results of a health study of residents of the homes and air quality measurements of the homes. Site visits and a home inspection program revealed decayin fewer than halfthe homes. Mostdecay was in the sheathing, with far less damage to the wall framing. A survey of homeowners and airtightness measurements further confirmed that the damage was primarily due to excessively high indoor humidities, which led to conden­ sation in the walls during winter: Thehomes were veryair­ tight, leading to verylowventilationratesduring winter. In­ sufficient ventilation, combined with a relatively large number of occupants, appeared to have led to highhumidify conditions; the authors found a direct relation­ ship between occupant density and the incidence of moisture problems. Other features, such as the type of heating system, were nor found to have a significant influence. Medical evaluation showed that the residents of these homes suffered more often from respiratory pro­ blems than residents of similar site-built homes included in the study. This appears to be related more to the high level of several pollutants in the homes than to the presence offungal spores. However; no single individual contaminant couldbe identified as responsible for the irri­ tanteffect.

https://www.fpl.fs.fed.us/documnts/pdf1989/merri89a.pdf

Overview of Moisture-Related Damage inOne Group of Wisconsin Manufactured Homes

The article considers issues related to providing dynamic heating and ventilation of transformer substation buildings featuring designed digital voltage transformers demanding particular ambient temperatures. We have shown the efficiency of using heat reflecting screens in windows with lower transmission heat losses from the transformer substation buildings concerned.

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Dynamic heating and ventilation of transformer substation buildings with adjustable resistance to heat transfer in windows

The article presents a study on low-power voltage transformers (LPVTs). Considering their increasing spread among Smart Grids, it is fundamental to assess their accuracy behavior in as realistic conditions as possible. Therefore, this article presents a detailed calibration procedure to test LPVTs’ accuracy when various external influence quantities are simultaneously acting on them. In the calibration procedure, the considered quantities are frequency, air temperature, and external electric field. Afterwards, the designed procedure is applied on three different off-the-shelf LPVTs using a measurement setup developed in a laboratory environment. The presented results (i) confirm the easy applicability of the designed calibration procedure; (ii) highlight the various effects of the influence quantities on the accuracy of different types of LPVTs; (iii) confirm the need to include more realistic tests, like the type-tests presented, into the standards to appreciate a wider set of possible in-field behaviors.

Calibration Procedure to Test the Effects of Multiple Influence Quantities on Low-Power Voltage Transformers.

This study examines the results of thermal and aerodynamic tests of a digital combined current and voltage transformer conducted in an environmental chamber. This measuring instruments consist of current and voltage transformers, featuring a resistive divider, and are used for commercial and technical electric power accounting. Different ambient temperatures, airflow rates and levels of insolation were set for the environmental chamber, with simulation of transformer functioning in emergency modes. It was established that heat release at transformer outer surface with natural convection depends to a larger extent on the difference between the temperature at the transformer surface and ambient temperature, while with forced convection this heat release depends more on air mass speed, with greater heat release on the surface of an upward facing rib than on the surface of a downward facing rib. The results of our study have been used in developing algorithms for diagnostics of the thermal state of digital combined transformers.

/pdf/thermal-and-aerodynamic-tests-of-a-digital-combined-current-57j9kbnud4.pdf

Thermal and aerodynamic tests of a digital combined current and voltage transformer

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.

/pdf/mathematical-simulation-of-thermal-state-of-digital-current-jm2x8nal1c.pdf

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

A mathematical model describing the process of heat transfer through windows with heat-reflecting screens, taking into account physical and geometrical parameters of the building construction, was developed. The computer program for the calculation of heat transfer through the window has been developed and results of numerical heat transfer simulation for different parameters of indoor and outdoor air are given. Expressions to determine the thermal resistance for the specific types of glazing with a heat-reflecting screens installed outside were derived on the basis of the developed method. The adequacy of the suggested mathematical model was confirmed by experimental data.

/pdf/mathematical-and-physical-modeling-of-heat-transfer-through-5afn4phglz.pdf

Mathematical and physical modeling of heat transfer through window with heat-reflecting screens to determine the potential of reducing thermal costs for microclimate parameters maintaining

Vladimir Tyutikov

Papers

Physical simulation of heat exchange between 6(10) kV voltage instrument transformer and its environment with natural convection and insolation

Dynamic heating and ventilation of transformer substation buildings with adjustable resistance to heat transfer in windows

Thermal and aerodynamic tests of a digital combined current and voltage transformer

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

Mathematical and physical modeling of heat transfer through window with heat-reflecting screens to determine the potential of reducing thermal costs for microclimate parameters maintaining