Expansion planning of substation capacity by considering service reliability

The expansion planning of substation capacity is a very critical issue for distribution system to maintain the service reliability. This paper proposes a methodology for capacity expansion planning of main transformers in substations by considering loss of load expectation (LOLE). To investigate the distribution system reliability, six service areas in Fengshan district of Taipower are selected for computer simulation. The forecasting of annual peak loadings of each area for the future 20 years is performed by the time series method based on the historical load data and load characteristics. By using the forced outage rate (FOR) of main transformers in the substations, the LOLE of each service area is solved. The capacity expansion planning of main transformers is therefore obtained by committing new main transformers at the year with LOLE exceeding the specified criterion. To further enhance system reliability, the capacity transfer capability of main transformers with constraint of tie line capacity between different areas is also considered. It is found that the expansion planning of main transformers by the proposed methodology can provide better-cost effectiveness of transformer investment to satisfy the service reliability as well as the system peak loading.