Effective Protection Distances of SPDs for Household Electrical Appliances

The installation of surge protective devices (SPDs) is important for the protection of today's household appliances against in-rushing surge. The effective protection distance should be taken into account for the installation to avoid the influence of oscillation phenomenon. For household appliances, their port impedance characteristics are more complex and frequency dependent, and for some appliances, the impedance characteristics are different in operating state and nonoperating state. With the method proposed in this paper, operating state impedance characteristics of 16 different kinds of appliances are measured and the equivalent circuits are obtained by vector fitting and circuit synthesis. The protection effect of SPDs is simulated by electromagnetic transient analysis software using a practical distribution system model, and the effective protection distances of SPDs with different protection level for these appliances are obtained. Several analyses are made about relationships between the protection distance and factors such as the type of appliance, operating condition, and protection level. A case of protection for multiappliance is also analyzed.