How disruptions in DC power and communications circuits can affect protection

Modern microprocessor-based relays are designed to provide robust and reliable protection even with disruptions in the dc supply, dc control circuits, or interconnected communications system. Noisy battery voltage supplies, interruptions in the dc supply, and communications interference are just a few of the challenges that relays encounter. This paper provides field cases that investigate protection system performance when systems are subjected to unexpected switching or interruptions in dc or communications links. The discussion emphasizes the importance of environmental and design type testing, proper dc control circuit design and application, reliable and safe operating and maintenance practices with respect to dc control circuits and power supplies, and considerations for reliable communications design, installation, and testing. Some practical recommendations are made with regard to engineering design and operations interface with equipment to improve protection reliability and reduce the possibility of undesired operations.