Influence of Oil-Filled Transformers Overload Capacity on the Throughput Capacity of the Electrical Network

During the operation of the electric power system, there is often a need to overload its individual elements (generators, power transformers, overhead and cable power lines, switching electric devices) for a period lasting from several dozens of minutes to a day. The overloads can be caused by intentional disconnection of parallel elements of the system because of scheduled preventive repairs, post-accident disconnections, as well as an unexpected increase in electricity consumption due to the impact of various factors. The overload capacity of the system elements makes it possible to increase operational reliability of power supply to consumers without additional expenditures while maintaining, in most cases, the almost normal service life of electrical equipment. Oil-filled transformers have the greatest potential overload capacity power, which makes it possible to consider them as a significant source of increasing the capacity of the transmission and distribution networks of the electric power system. Excessive over-current of power oil-filled transformers significantly reduces reliability and reduces their normal service life. This is due to the accelerated process of wear of the insulation material of the transfer windings as a result of overheating of the transformer oil, that causes structural changes and, as a consequence, to mechanical damage to the insulation of the windings; the latter can cause an electrical puncture. On the other hand, underestimation of the permissible overload of transformers might result in economic losses due to under-produced products when the functioning of the part of the transformers connected in parallel are ceased for scheduled preventive maintenance or as a result of forced emergency shutdowns. Therefore, there is a need to assess the potential of reasonable increase in the throughput capacity of the electrical network and, accordingly, the reliability of the power supply system, taking into account the requirements for the permissible loads of transformers when the electrical network and various operating modes are being designed.

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