TRENCH LIMITED Hi-Acc-ExtTM CT’s Extended Dynamic Range Current Transformers The IPP Problem: Many of today’s IPP plants are being built as peaking units which operate when power demand is high and energy costs are at a premium. When the plant is off line, it must draw auxiliary power from the utility for basic lighting and maintenance functions. Since the plant is connected at transmission voltages such as 123/138/230/345/500/765kV, the auxiliary power needed may amount to only a few amps of current. This current must be accurately metered through the current transformer as it can amount to substantial revenues annually and over the life of the plant. In addition to accurately metering a few amps, the current transformer must be designed to provide accurate metering outputs when the plant is running at perhaps a few thousand amps. Accurately metering a few amps to a few thousand ….this is the challenge. The TRENCH Solution: Trench Limited Hi-Acc-ExtTM Current Transformers and Combined Current / Voltage Transformers are designed to accurately transform primary currents from 0.05% to as high as 400% of rated current depending on current ratios and dynamic range required. Trench Hi-AccExtTM instrument transformers provide 0.15B1.8 or 0.3B1.8 revenue metering accuracy over wide dynamic ranges through the use of low loss nickel iron optimized cores, and in some cases, using higher thermal rating factor that work in harmony with electronic class 20 meters. The Hi-Acc-ExtTM line of current transformers is available in oil-filled or explosion proof SF6 designs from 36.5kV up to 765kV. Combined current / voltage transformers are also available for voltages from 36.5 up to 345kV. For details on unit construction and specifications, please refer to the Trench brochure number E217.11 (IOSK type current transformers) and E219.21 (N5/H combined metering units).

Typical Hi-Acc-ExtTM Current Ratings: Ratio 2000:5 1000:5 400:5 Accuracy 0.15B1.8 0.15B1.8 0.15B1.8 Rating Factor 2.0 2.0 2.0 Current Range 1A-4000A 0.5A-2000A 0.2A-800A Short time (1 sec) 90kA 63kA 50kA Secondary Current @ Lowest A rating* 2.5mA 2.5mA 2.5mA *Note: For typical electronic meters the minimum required pickup current is 10mA, therefore, the low end rating from the CT may not be within the meter’s accuracy range. We therefore also offer hi-accuracy units with current rating factor of up to 400% (see table below), which would allow to have lower CT ratio with higher minimum-secondary...