The dissertation is devoted to the solution of an actual scientific and technical problem in the sphere of fire safety – revealing the relations between transformer oil temperature decrease and parameters of oil receiver gravel backfill as a scientific basis for the improving of the efficiency of fire prevention system of oil-filled transformer substations under fire conditions.
The purpose of the dissertation is to reveal the laws of cooling and stopping the burning of transformer oil depending on the parameters of the gravel backfill of the fire protection system of the transformer substation, as a basis for improving existing structural solutions during the design of oil receivers of transformer substations, which should perform the function of stopping burning and ensuring oil cooling below the flash point.
The scientific novelty of the obtained results is in the revelation of the trends of cooling and cessation of the combustion of the transformer oil depending on the parameters of gravel backfill of the fire prevention system of the transformer substation which is a sound theoretical basis for creating prerequisites for improving methods for predicting efficiency of such systems. At that:
- it was established for the first time that the relationship between the cooling temperature of the burning transformer oil contained in the oil receiver and width (d) and height (h) of the gravel backfill and slope (i);
- it was established that the decrease in the temperature of burning transformer oil, depending on the distance (width d), which it travels from the entrance to the gravel filling of the oil receiver to the oil collector, is described by a polynomial dependence of the 3rd order, which has the form;
- the geometric parameters of the gravel backfill of the fire protection system of the transformer substation, under which the temperature of the transformer oil decreases to a safe value (from 250 °С to 150 °С), are substantiated, namely: the minimum dimensions of the gravel backfill: width 1500 mm, height 250 mm, the effective slope of the oil receiver in oil sump side 0,05 m/m;
- improved theoretical approaches for evaluating the conditions of the cooling and cessation of burning of the transformer oil in the gravel backfill of the fire prevention system of the transformer substations were improved;
- the parametric methods of normalization in construction in terms of reducing the temperature of transformer oil from the parameters of the gravel filling of the fire protection system of oil-filled transformer substations have been further developed in order to increase its efficiency in fire conditions.
The practical value of the research lies in the development of a methodical and experimental basis for the method of predicting the effectiveness of the fire prevention system of oil-filled transformer substations under fire conditions, as a scientific basis for their design.
During the execution of the work, an experimental stand was created to study the process of heat and mass transfer of transformer oil in the gravel backfill of the fire protection system of the oil-filled transformer substation.
During the work, a mathematical model of research of heat and mass transfer processes of transformer oil and regularities of its temperature decrease from parameters of the gravel backfill of oil receiver is developed.
Using the proposed mathematical models, a complete factor computational experiment was performed for predetermined parameters resulting in the derivation of the dependency of the decrease in the temperature of transformer oil in the oil receiver upon its slope, width and height of gravel backfill.
Based on the identified patterns of cooling and cessation of burning of the transformer oil, the parameters of gravel backfill of the fire prevention system of the transformer substation were substantiated; it is established that the cessation of combustion and lowering the temperature of transformer oil provide the minimum dimensions of gravel backfill with a width of 1500 mm and a height of 250 mm; at the same time, the effective inclination of the oil receiver towards the oil collector should be 0,05 m/m.
Proposals are developed to improve the existing design solutions to limit the spread of fire in the event of accidents at oil-filled transformer substations. Based on the obtained research results, a methodological basis has been developed which is the basis for creating regulations to determine the minimum parameters of gravel backfill oil receiver, in particular, formulated proposals for amendments to the Rules of Arrangement of Electrical Installations.
Economic effect of the proposed technical solutions compared to existing approaches based on feasibility study of gravel backfill parameters in oil receivers of oil-filled transformer substations on the example of long-term operation, for the city of Kyiv, taking into account reduction of the gravel amount and operational costs up to 72 %.
