Planning of OLTC Transformers in LV Systems under Conservation Voltage Reduction Strategy

The wide voltage control capacity of on-load tap changers (OLTCs) forces them into the list of reinforcement alternatives in the expansion planning of distribution systems. Their high investment and operation cost, however, is a downside. The voltage dependent nature of loads can be deemed as an opportunity to reduce the system demand and operation cost by managing the voltage at substation level (referred to as conservation voltage reduction strategy). Here, it is shown that consideration of this strategy justifies the investment on OLTCs against the other options even for LV systems. Both short-term and long-term variations of the system parameters are taken into account, since as it will be shown, the rate of system variations affects the decision on replacing the available transformers with OLTC transformers. The proposed method embodies a prognosis of long-term future by modeling the operating conditions in a set of daily scenarios with hourly time resolution to include the cost of tap changing operations in the objective function. The oltcs' control strategy in this daily scenarios matches the industry common practice.