Knowledge about the thermal conductivity of dielectric liquids/oils is essential to understanding and predicting the heat transfer in a liquid-filled transformer. Transformer oils perform two crucial functions. First, they electrically insulate the windings and coils to prevent electrical shorting and leaks. Second, they dissipate heat through convection and conduction to protect from overheating the transformer. These functions demand thermal stability in a temperature range of transformer operation, a high temperature dielectric breakdown point, low viscosity, high thermal conductivity (TC) and high heat capacity (HC). HC reflects how much heat can be absorbed by the liquid, whereas TC characterizes the rate of heat transfer through the liquid (given it does not flow). Together TC and HC measure the liquid’s ability to carry heat away from the transformer core by means of thermal conductance and convection flow.

The emergence of new dielectric liquids, including such exotic materials as nanofluids, emphasizes the need for accurate TC measurements which can be performed on a wide variety of complex test systems.
Various approaches to TC measurement di¬ffer in sensor construction and sample geometry requirements, and thus time and complexity involved in running a TC measurement varies. The modi¬fied transient plain source (MTPS) technique used by TCi sensor of C-Therm has many advantages. TCi can be employed to obtain high accuracy TC data, and to help identify more efficient transformer liquid with improved TC properties. The technology of TCi allows for TC measurements of solids, liquids, powders and pastes without special sample preparations. The method does not require samples to conform to the geometry of a test cell, and is a reliable and fast way of measuring TC particularly on relatively small amounts of liquid samples.

 

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C-Therm TCi Thermal Conductivity Analyzer with Modified Transient Plane Source