Design of a High-Speed Motor Bus Transfer System

This paper addresses the design of a high-speed motor bus transfer system for power-generating plants and industrial facilities where motor loads require comprehensive source transfer strategies during transfer of the load from one source to another. Motor bus transfer schemes are needed not only to maintain process continuity but also to transfer sources in such a manner to prevent damage to the motors and connected loads. The motor bus frequency and voltage decay rapidly upon disconnection from the main source. This paper proposes a digital signal processing algorithm that can measure the magnitude and phase angle of the decaying bus voltage accurately while measuring the auxiliary-source voltage magnitude and phase angle at rated frequency. This paper details an algorithm to predict the phase coincidence between the motor bus voltage and the auxiliary-source voltage. The algorithm uses delta frequency, the rate of change of delta frequency, and breaker closing time to predict the phase coincidence. This paper also details the implementation of the motor bus transfer scheme that includes fast, in-phase, and residual transfer methods. The results of some real-time transfer cases are also included.