Bruce Bailey

Protection, metering, monitoring and control of medium voltage power systems

Traditional practices for industrial and commercial medium voltage power systems to provide protection, metering, monitoring, control, power quality analysis, disturbance recording and automation have changed. The introduction of new multifunction numerical protection relays using the processing power of the present generation of microprocessors, have very high functionality. Many functions can be integrated into one device, allowing new power system problem solving capabilities while permitting significant cost savings as compared with discrete protective relays, instruments, meters, recorders and transducers of the past. This paper describes the vast capabilities and enhancements of these devices, which are called intelligent electronic devices (IEDs) in this paper. Included are anecdotes obtained from an installation on a large industrial power system.

Risks From Utility Supply Disruption

This article elaborates on the properly required protection and how its operation will prevent the undesired consequences to the ICG owner, the utility, and the general public. This article also discusses actions that take place when the utility supply is disrupted, creating an islanding condition and states reasons why protection required by regulatory agencies, local utilities, and documents such as IEEE Standard 1547 IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems are required of an individual ICG. Consequences of not having the protection in place can damage the generator and/or its prime mover plus be a hazard to public safety. Examples of these consequences are given. This article will provide a clearer understanding to ICG owners of why they are required to have specified protective equipment in place.

Static relays permit enhanced protection

Multi-function multi-phase static overcurrent relays, using digital technology available today, provide basic time, (51) (51G) (51N) and instantaneous (50) (50G) (50N) three phase and ground overcurrent protection, and may offer some or all of the following additional functions: undervoltage (27); overvoltage (59); reverse phase sequence (47); negative phase sequence voltage (47N); directional overcurrent (67) (67N); frequency (81O/U); reverse interlocking trip coil monitoring; and battery monitoring. This article describes two applications that use some of the additional functions in such a relay: reverse interlocking, also using the directional overcurrent (67) function; and ground fault detection for systems utilizing high resistance grounding. The first application was installed on a 4160 volt power system which was supplied by two 5000 kVA transformers.

Static-digital overcurrent relays permit enhanced protection

Multi-function static overcurrent relays employing digital technology have functionality that permits improved and expanded protection in many applications. While a relay is normally selected for the required overcurrent and ground fault protection, effective utilization of additional available functions can provide added security without significant additional cost. This paper describes an application for an oil refinery power system that uses directional overcurrent elements and reverse interlocking between the main, tie and feeder relays for a dual source-normally closed tie system. This scheme provides fast tripping for bus faults, which has several advantages over traditional bus differential relaying. This paper also describes a ground fault protection scheme to detect feeder grounds on a high resistance grounded system.