A rotor open-phase imbalance protection for variable speed pumped storage unit based on rotation transformation fault component ratio

•The rotor open-phase imbalance protection method based on the rotation transformation fault component ratio (FCR) for variable speed pumped storage unit (VSPSU) is proposed.•The protection method uses the amplitude of the FCR as the action criterion, divides different protection action modes according to the amplitude, and gives the protection setting calculation method.•The proposed protection method has high sensitivity and fast action speed, and can meet the requirements for fast, real-time and high-reliability protection of large-capacity VSPSU.•The matching microcomputer protection algorithm is proposed, which can be directly embedded in the existing microcomputer protection device to meet the requirements of engineering application. Doubly-fed variable speed pumped storage unit (VSPSU) adopts slip ring injection AC excitation mode, and its rotor side structure is complex and prone to open-phase faults. It is very important to configure specific open-phase imbalance protection to ensure its safe operation. Traditional doubly-fed motors only stay in the state monitoring stage for rotor electrical imbalance, which cannot meet the requirements of large-capacity VSPSU for fast, real-time, and high-reliability protection. Therefore, this paper proposes a VSPSU rotor open-phase imbalance protection method based on the rotation transformation fault component ratio (FCR). The fundamental frequency component and fault characteristic component of the stator current space vector are extracted by rotation transformation and FCR is calculated, and then different protection action modes are divided according to the amplitude of FCR. To realize the engineering application, a microcomputer protection algorithm suitable for the proposed protection method is further proposed, and then a complete microcomputer protection scheme is formed. Simulation and experiment results show that the proposed protection scheme has high sensitivity and fast action speed. At the same time, the proposed algorithm can be directly embedded in the existing microcomputer protection device to meet the needs of engineering applications.