In the sinusoidal balanced system, the definition of reactive power without any doubt. However, in the three-phase non-sinusoidal unbalanced system, there is a great debate about this definition. The paper firstly describes the representative and widely recognized power theory in detail, in principle, compares their differences in the definition of reactive power. Then select a typical unbalanced distortion load, electrified railway, use the measured signal for simulation calculation. Based on considering reactive power compensation, monitoring, management and billing, the paper finally selects the power theory that IEEE 1459 standard states as the reactive power definition in typical non-sinusoidal unbalanced system. This theory suggests that the usage efficiency of energy can be evaluated by measuring parameters such as fundamental positive sequence reactive power, non-fundamental equivalent apparent power and unbalanced apparent power, so as to help the power companies and enterprises to implement electricity management more scientifically and reasonably.
