Stating Duty Only Synchronous Transfer Systems

Synchronous transfer drive systems provide flexibility in pipeline and pumping applications. Within a pipeline, pressure to a system can be increased in stages, reducing mechanical shock to the pipeline. Pumping stations can closely regulate pumping capacity required by bringing pumps online and offline. By utilizing a single adjustable frequency drive (AFD), overall cost can be reduced, although control complexity increases depending on the specific system requirements.

In a pipeline system or gas compression facility, significant cost savings can be realized by sizing the drive for “starting duty only.” The drive is sized to start the motor under reduced load, synchronize the AFD output to the utility line, transfer the motor to the line, and only then is the compressor loaded. The same principle can be applied to soft or weak power systems that cannot support an across-the-line start and where continuous AFD speed regulation is not required. Pump or fan driven loads also benefit from this starting method. A drive size reduction of approximately 50% is obtained through a “starting duty only” rating with further reduction if exact motor and load parameters are known.

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