Extended Range Current Transformers0 pages

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).