ITR/ ALSTOM GRID
Digital Instrument Transformers
23616 N. 19th Ave., Suite 16 Phoenix, AZ 85085 Phone: 1 602 331 8000 www.alstom.com
March 31, 2011
Bushing Application of the NXCT-F3 Current Sensor
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The NXCT-F3 current sensor can be used in a number of field applications for the measurement of AC and DC currents. (See the attached product description and technical papers for more details.) The dielectric sensing cable can be placed around conductors of any shape and size, within a 100 m circumference. The sensor uses the Faraday effect with a closed optical path to measure the current encircled by the sensing cable. The sensor will measure only those currents encircled by the sensing cable. Currents flowing nearby, but not flowing inside sensing cable loop, are not measured. For applications of the NXCT-F3 measuring currents at cable terminations or on wall bushings the requirements for safe and accurate measurement are as follows: • The dielectric cable must be housed in an appropriate environment to prevent water ingression and UV damage. • The sensing cable can be housed inside a metal housing, however, the housing must have a dielectric break in it to prevent eddy currents in the housing walls that encircle the sensing cable and to prevent ground currents from flowing through the loop of sensing cable. • For bushing applications the sensing cable and housing must be below the metal flange of the bushing, at ground potential. Keeping the sensing cable and housing below the top of the metal flange prevents any electric field changes at this interface. (The sensing cable though dielectric, is not suited for pollution environments and its use at high voltages is not recommended.) • For bushing applications the sensing cable and housing must not interfere with the service ports of the bushing. (This is accomplished by using a large loop or housing that allows for access to the ports or a housing that can be opened for servicing the cable or...