Zero Energy Sag Correctors - Optimizing Dynamic Voltage Restorers for Industrial Applications

Plants and processes with a high level of industrial automation are most severely affected by short duration power disturbances. Such plants are most frequently fed from highly reliable utility grids, with measured reliability levels that are consistently in excess of 3 - 5 nines, yet face hours of unscheduled downtime resulting from short duration voltage sags. Extensive data confirms that such plants experience, on an average 30 power disturbances annually, of which over 95% are short duration disturbances lasting on an average no more than 6 cycles. Data also confirms that over 90% of these disturbances are asymmetrical faults. This paper shows a new approach to protecting industrial plants from power disturbances by building on the fact that it is prohibitively expensive to protect against all possible power disturbances, and that cost-effective protection is based on a statistical assessment of disturbances recorded and equipment susceptibility. This paper shows that it is possible to use a new family of zero energy sag correctors to realize protection against over 96-98% of all power disturbances. The paper also develops the design guidelines for such sag correctors, and shows simulation and experimental results for the new DVR system.