Zone Based Protection for Low Voltage Systems; Zone Selective Interlocking, Bus Differential and the Single Processor Concept

Time based coordination and protection is the normal basis for coordinating low voltage power distribution systems. Enhancements, such as zone selective interlocking and bus differential protection, may be used to accelerate protective devices. However, these improvements may be costly, difficult to implement, and may not function as expected using commonly available technology. Nevertheless, the potential benefit of fault clearing speed and selectivity are more valued in today´s arc-flash and reliability conscious environment than ever before. The writers shall discuss some issues associated with these traditional improvements, pitfalls to avoid and, more effective ways to implement zone-based protection to achieve fast fault protection while maintaining complete selectivity for a broad range of fault magnitudes, system configurations and load types.