ISA T 2000 - CT Tests: Excitation Curve

DOC. MIE11110 Rev. 5
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1 .1.5. CT tests : excitation curve
When this test is selected, the following menu is displayed.
For the first parameter, standard, we have three choices: ANSI1
(no gap); ANSI2 (gap) or IEC, as they have the following
definitions of the knee point (see std. C.57.13, paragraph 6.10.2).
. ANSI1: In a log-log diagram, the knee point is the one where the
curve has a tangent at 45°. This refers to gapless CT’s.
. ANSI2: In a log-log diagram, the knee point is the one where the
curve has a tangent at 30°. This refers to gapped CT’s.
. IEC: the knee is the point of the curve where a 10% increase of
the voltage causes a 50% increase of the current.
Input the other parameters of the CT under test. From these
data, the test set computes and displays the nominal knee voltage
and current, according to the selected standard definition. Now, in
order to define the voltage output to be used, you should
compute:
VSM = VA * KN / IS
The test voltage range is the following.
VSM < 40 V 50 TO 125 V > 125 V
V RANGE 90 V 250 V 3000 V