Outputs Terms of Reference Background

Given the technological progress in the fields of digital components and Information Technology within substations, new generations of instrument transformers with digital output, known as Non Conventional Instrument Transformers (NCIT) and/or Electronic Instrument transformers (EIT) are now becoming attractive for large scale application. These devices (both primary sensors & digital interfaces), which are typically very compact, have already been analysed & described by a WG of SC A3 (publication imminent). However, even though digital communication methods are being used more often for new substations and for the modernisation of existing installations, the interface between high voltage equipment and low voltage equipment (so called "0/1 interface") remains predominantly classical (100 V/√3, 1 or 5 A). To promote digital communication for this "0/1 interface " and to obtain all the advantages of Information Technology, the development of a "Stand Alone Merging Unit " (SAMU) is under widespread consideration. This new equipment is an essential tool to enable the use of classical magnetic ITs alongside NCITs in the same substation; an essential consideration for the refurbishment of existing substations. The ability to mix conventional & non-conventional devices will also tend to accelerate the development of EITs with digital interfaces. The use of digital output for ITs (magnetic or electronic) requires development & adaptation of the accuracy testing procedures and the development of appropriate methods for in-factory and on-site calibration which may become more frequent with the deregulation of electric power companies. The redundancy of various equipment and links will also need to be considered to achieve the high reliability and availability levels required for a modern electrical network. This accuracy testing & calibration activity is the main focus of thi