The latest reform phase in the Chinese power market will result in a prolonged period of coexistence between the plan and the market. In this context, the operation of the electricity market gives rise to imbalanced costs because of discrepancies between the planned scale of priority power generation and consumption, inconsistencies in priority power generation and consumption curves, and deviations between forecasts of priority power purchases and actual power consumption. To accurately assess the scale of imbalanced power and the associated costs, this study analyses the formation mechanisms...