Teridian 71M65XX Using DC-Tolerant CTs by J&D Electronics

Teridian 71M65XX Using DC-Tolerant CTs by J&D Electronics

IntroducTIon

DC-tolerant CTs are gaining importance in the metering marketplace.  As compared to general-purpose CTs, DC-

tolerant CTs have a much larger phase angle and can also be less linear than general-purpose CTs at low cur-

rents.  J&D Electronics Co Ltd, Korea, has introduced a series of DC-tolerant CTs that can be successfully used

in accurate electricity meters when combined with the excellent compensaTIon features of the Teridian family of

metering ICs.  Regardless whether the 71M6511, 71M6513, 71M6521, 71M6523, 71M6531/32, 71M6533/34, or

the latest 71M6541/42 or 71M6543 is used, linearizaTIon of the CT output over current and over temperature can

be implemented easily and in a straight forward manner.

The J&D Electronics CTs

J&D Electronics provided samples of several advanced CTs to Teridian for tesTIng.  The model JDTN100W was

selected for testing in a poly-phase meter setup.  The data sheet of the JDTN100W (see Figure 1) indicates that it

is a CT that has a narrowly contained magnitude error and large phase shift, which itself has a strong temperature

dependency. At 60° load angle, we would expect the phase error shift from 3.1° (-40°C) to 5.2° (+85°C) to cause

an error component for the Wh measurement of 5.8%.  Even at constant temperature, the phase angle varies by

as much as 0.3% over current, resulting in a Wh error of 0.54%.  This means that compensation has to be intro-

duced for the phase error over temperature and over current at the least.