Considerations for differential protection in LV buses

Current-differential principles are well known and commonly used for protection of medium and large size transformers, large motors, medium voltage (MV) generators, medium and high voltage buses, and any type of important power equipment with measurable input and output currents. However, is it practical to protect low voltage distribution buses using differential protection? This paper will describe bus differential protection principles as well as interlocking principles for overcurrent protection. It will discuss specific issues in applying differential protection in LV systems. It will present a concept of partial differential protection, which can be used in conjunction with Zone-Selective-Interlocking (ZSI), or as backup to traditional overcurrent protection to achieve high-speed and selective fault clearance. Additional concepts for implementation of bus differential protection using networked data in low voltage systems will be introduced.