Cascaded Stalling of Induction Motors in Fault-Induced Delayed Voltage Recovery (FIDVR)
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In recent years, the phenomenon of Fault-Induced Delayed Voltage Recovery (FIDVR) has increasingly been observed. Air conditioner (A/C) motor stalling is considered as one of the main reasons for the occurrence of delayed voltage recovery events . This thesis studies the possibility that the stalling of a small percentage of induction motors could precipitate FIDVR events. A 12.5kV distribution network model with A/C motor load is used to construct certain bifurcation diagrams. Continuation methods based on the predictorcorrector technique are used to arrive at system steady-state solutions tracing the curves of motor behavior while the system bus voltage is varied. The stable and unstable operating points of induction machines are obtained and analyzed. Results show that a small percentage of induction motors stalling could exacerbate the stalling of additional motors. There could be either no stable solutions for the system with a partial number of A/C motors stalled or stable solutions with a certain number of A/C motors stalled, depending on the percentage of integrated motor loads. We conclude that a small percentage of stalled induction motors in practice could precipitate the stalling of additional motors, or even all motors in a distribution network. Thus, a mitigation strategy of replacing a number of ?prone to stall? motors to ?robust? ones may not effective. This information is crucial in developing mitigation plans to avoid a FIDVR event.