Improving transformer´s utilization under customer reliability requirements

During the past two decades, utilities have increased transformer´s utilization by about 30% in North American power distribution systems. High utilization levels, for transformers in particular, make utility companies more financially efficient, and this is potentially beneficial to both stockholders and customers. However, reduced customer service reliability is often detected in highly-utilized distribution systems. This can be attributed to the incompatibility between a commonly used supply-side reliability planning approach and customer-side reliability requirements. For this reason, an improvement over the N - 1 methodology is sought to set the maximum utilization of transformers while assuring good customer service quality at the same time. This paper proposes a method to estimate the maximum transformer utilization level under a given customer reliability requirement. The method is formulated as a mixed-binary-integer optimization problem. Moreover, the formula enables the specification of customer reliability requirements at a system level and at designated localities. The proposed method can be applied to find the maximum utilization of transformers, and can be extended to other power delivery equipment, in distribution systems.