SELECTION OF CURRENT TRANSFORMERS …（电流互感器的选择u2026）.pdfVIP

SELECTION OF CURRENT TRANSFORMERS WIRE SIZING IN SUBSTATIONS Sethuraman Ganesan ABB Inc. Allentown, PA ABSTRACT More and more sub-stations are retrofitted with numerical relays, meters and monitoring devices. Most often, the older relay gets replaced with a newer relay with the rest of the installation such as Current Transformer (CT) and lead remaining undisturbed. Utilities have standardized on their older current transformers and want to maintain the same current transformer specifications throughout their system even in their newer installation. An extension of the above approach is that even the cable leads and panel wiring sizes are over-specified resulting in totally unjustified cost of installations as well as difficulty in terminating such wires in the modern panels and equipment. On the other end of the spectrum, in rare cases, the existing CT sizes and lead sizes of electromechanical relays may not be adequate for the latest protective relays which might demand a different current transformer performance. A careful evaluation of current transformer size and their leads is recommended, either to save an appreciable cost of installation or to avoid costly protection mis-operation or non-operation. This paper systematically lists and analyses such requirements for various modern protective relays. This work is expected to be a good reference source for the new generation utility protection engineers in selecting the CTs and wire sizes and understanding impact of various connections in determinin