Abstract: A method and a device are for power supply switchover in a power system, including two power supplies, each being connected to a bus through an incoming line. The power supply currently in operation is used as the main power supply and the other power supply is used as a backup power supply. Both the incoming line and the bus have three phases, and the lines are connected by their phases. In an embodiment, the method includes: determining whether there is at least one sound phase among the three phases after identifying a fault in the power system; and if there is, obtaining a power data on the sound phase before the main power supply is disconnected. The power data is usable to determine whether the backup power supply meets the condition for connecting in the quick mode after the main power supply is disconnected.

Abstract: A method and a device are for power supply switchover in a power system, including two power supplies, each being connected to a bus through an incoming line. The power supply currently in operation is used as the main power supply and the other power supply is used as a backup power supply. Both the incoming line and the bus have three phases, and the lines are connected by their phases. In an embodiment, the method includes: determining whether there is at least one sound phase among the three phases after identifying a fault in the power system; and if there is, obtaining a power data on the sound phase before the main power supply is disconnected. The power data is usable to determine whether the backup power supply meets the condition for connecting in the quick mode after the main power supply is disconnected.

Abstract: A method for detecting a magnetizing inrush current of a transformer includes the steps of obtaining a difference current for each AC phase of a transformer and calculating, for each AC phase, at least two factors for waveform symmetry recognition, on the basis of the difference currents obtained within one period. For each type of factor, one obtains the maximum value of the three factors corresponding to the three AC phases, to serve as a maximum phase factor of that factor. Based on the maximum phase factor obtained, a waveform symmetry recognition algorithm is used to calculate a corresponding waveform symmetry parameter, and if the waveform symmetry parameter meets a requirement for waveform asymmetry, then it is determined that a magnetizing inrush current has occurred. A device for protecting the transformer is further provided.

Abstract: A fast bus transfer method and a device reduce the impact on a load connected to a bus caused by a power cut. The method includes calculating the amplitude of the voltage vector difference between the bus and the backup power supply and the phase angle difference between the bus and the backup power supply; and transferring the load on the bus to the backup power supply only when the amplitude is less than its limit value and the phase angle difference is less than 90°. The device contains a detection module, a calculation module, a comparison module, and a transfer module. By calculating the real-time residual voltage, it is unnecessary for a user to know all the details of the residual voltage characteristic, and can achieve fast transfer simply by setting the limit of the voltage difference when a circuit breaker of the backup power supply is closed.