The variability of renewable power means that flexible grid-support plants are increasinglyneeded to balance power fluctuations. Together with the current development towardsreal-time energy markets, this evolution implies changed operational profiles forgenerators. In this new environment generators have to cater for frequent starts andstops, and rapid load cycling.A typical set of requirements could include multiple starts and stops per day, rapidreadiness for synchronization, and continuous load cycling. This involves the need toramp up from standstill to full load in a few minutes and ramp down from full load to stopin even less time.Generator designs have to be modified to ensure that these tough new requirements aremet. Based on experience with alternators and motors in applications with similaroperating profiles, the key factor that must be taken into account is the increased numberof thermal and speed loading cycles. This is confirmed by studies of real-life loadingcycles in grid support duty.Thermal and speed cycles create stresses at various points in the alternator structure,and a number of methods for managing these stresses effectively are described. Inparticular, the thermal cycles must be considered in insulation design, and the speedcycles in fatigue design. In addition, the implications for the design of major components- stator core, winding, frame, rotor, and bearings, as well as the cooling arrangements –are considered in detail.The age of variable generation means that generators are subject to even greaterstresses than before, but with the right designs they can deliver high reliability over verylong lifetimes.
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