Gary W. Scheer

Digital Communications Improve Contact I/O Reliability

This paper compares the reliability of traditional contact wiring to multiplexed IO via optical fiber and the resulting impacts on reliability. The paper also addresses adjustments to improve reliability, and summarizes the comparative reliability, costs, and other tradeoffs. Also presents an application example of a substation yard with IO at four locations, connected to a main station panel. It is important that system designers understand the reliability of the systems that they design. Manufacturers should be willing to provide MTBF data to help them analyze and compare their alternatives

Add trip security to arc-flash detection for safety and reliability

Arc-flash detection sensors provide a cost-effective way to reduce arc-flash energy by minimizing detection times. High-speed light detection and tripping can compromise protection security by misoperating during changing light conditions. Trip circuits using arc-flash light detection should be supervised using overcurrent protection with similar fast detection speeds. Combining arc-flash detection and high-speed overcurrent from a protective relay provides fast tripping and security, using both instantaneous overcurrent and light from the arc flash. The combination of relay and arc sensor provides independent fault detection with two separate technologies, thereby eliminating false trips from lighting and providing the fastest detection and tripping possible. Time coordination delays are eliminated when the arc is detected concurrently with an overcurrent. This paper presents the advantages of fast overcurrent detection combined with arc-flash measurement to produce a sensitive, fast, and secure tripping scheme.