Abstract
This paper aims to develop a multi-phase under voltage load shedding (MUVLS) strategy that effectively sheds the load to mitigate delayed voltage recovery (DVR). The major cause of the DVR phenomenon is related to the dynamic characteristics of induction motor (IM) loads. The deaccelerating and stalling of the IM load during disturbances is the main driving force of short-term voltage instability, resulting in an amount of reactive power consumption and excessive current draw. With the economic efficiency of energy use, the proportion of IM loads is gradually increasing, and this trend might deteriorate system stability. This paper focuses on the impact of IM loads in the Korean power system and analyzes the parameter sensitivity of IM loads and the proportion of appropriate IM loads. The proposed procedure for under voltage load shedding (UVLS) applies voltage stability criteria to decide the most efficient load shedding scheme. The determined MUVLS scheme can offer new and more effective remedial actions to maintain voltage stability, considering the characteristics of IM loads. Case studies on the Korean power system have validated the performance of the proposed MUVLS scheme under severe contingency scenarios, showing that the proposed strategy effectively mitigates DVR.
Highlights
The increased use of electronically controlled loads and the increasing induction motor (IM) loads make modern power systems more complex in terms of dynamic stability
The increase in active power flow via the interface lines due to the economical purpose inevitably leads to voltage instability in cases where reactive power is not adequately supported in the metropolitan area
The Korean power system has a critical constraint with the interface flow, which is mainly determined by voltage stability
Summary
The increased use of electronically controlled loads and the increasing induction motor (IM) loads make modern power systems more complex in terms of dynamic stability. Systems with a large portion of inductive (IM) loads might face delayed voltage recovery (DVR) after the fault. The phenomenon is basically caused by stalling of IM loads, and it could in turn potentially result in the cascading effect on other IMs in the same feeder or in their vicinity. As dynamic reactive power consumption by the IM loads stalling increases during disturbances, the imbalance between the reactive power supply and demand is aggravated. This might eventually cause voltage collapse in the power system
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