Thermal-fluid characterization of alternative liquids of power transformers: A numerical approach

Abstract

The transformers lifespan depends importantly on its refrigeration. Mineral oils perform this work in the majority of the power transformers. However, this type of coolant has two main drawbacks: low biodegradability and low ignition point. Several alternative liquids are being developed in order to overcome these drawbacks. This paper compares their thermal-fluid behavior with a mineral oil by means of several parameters, such as temperature, flow rate, fluids velocity, convective heat transfer coefficient (h) and the cooling criterion (P). These are calculated using the numerical results of the simulation of a 3D-model of a Low Voltage Winding that belongs to a power transformer with ONAN cooling. The software COMSOL Multiphysics has allowed the simulation of the geometry using a physical model in which buoyancies and viscous forces are the only considered establishing the natural convection. As a result of the comparison, it is clear that the mineral oil is the best coolant liquid. Among the alternative liquids, silicone oil would be the second best coolant fluid, followed by the synthetic and natural esters, respectively. On the other hand, it seems to be clear that the 3D simulations can be used to compare properly the cooling capacities of the liquids.

Numerical analysis of the hot-spot temperature of a power transformer with alternative dielectric liquids

“…In 2015 Park et al [17] employed a 2D CFD model in order to obtain temperature and velocity profiles of some alternative liquids used in a distribution transformer of 2.3 MVA and a power transformer of 16.5 MVA. In the same year, Lecuna et al [18] carried out a 3D CFD simulation of an ONAN distribution transformer comparing a natural ester, a synthetic ester, a high kinematic viscosity silicone oil and a low kinematic viscosity silicone oil with a mineral oil. These works conclude that alternative liquids produce higher temperatures in the transformer windings designed for mineral oil.…”

Thermal Modelling of Electrical Insulation System in Power Transformers

“…In 2015, Park et al employed a 2D-CFD model to obtain temperature and velocity profiles of some alternative liquids used in a distribution transformer of 2.3 MVA and a power transformer of 16.5 MVA [15]. In the same year, Lecuna et al carried out a 3D-CFD simulation of an ONAN distribution transformer comparing a natural ester, a synthetic ester, a high kinematic viscosity silicone oil and a low kinematic viscosity silicone oil with a mineral oil [16]. These works conclude that alternative liquids produce higher temperatures in the transformer windings designed for mineral oil.…”

“…With these two equations, Eqs. (16) and (17), there are three variables that are volume oil flow Q o , bottom-oil temperature T Ob and top-oil temperature T Ot . Eq.…”

Numerical and Experimental Analysis of the Aging Impact on the Cooling Capacity of a Natural Ester-Based Oil Used in Power Transformers

“…Several works have studied the cooling capacity of alternative dielectric liquids in comparison with that of mineral oil, [1][2][3]. However, the authors of this work have not found many articles in the scientific literature in which the impact of the insulation system aging on the cooling capacity of the liquid have been studied.…”