Current Transformer
4 - 5
Three methods to determine I sec
The secondary current Isec can be determined either
1. by leading it directly via the 10A current input IAC (refer to Figure 2 on page
4-3), and let CPC 100 measure it.
2. by means of a current clamp that is connected, for example, to the V2AC low
level AC voltage measuring input (refer to ”Testing Ratio, Polarity (and
Burden) with a Current Clamp” on page 10 of this chapter).
3. by selecting the check box "Manual input". This option lets you enter the
value for Isec manually, for example, when Isec was measured with an
external current clamp that is not connected to CPC 100.
Measurements
Note: Select "Manual input" prior to starting the test. If the test card still
contains results, clear them by pressing C
LEAR RESULTS.
When "Manual input" is selected, there is no phase available.
Consequently, the polarity and cos
ϕ cannot be calculated.
Iprim: actual current output at the 800A AC output that is injected into
the CT’s primary side
Isec:
measured secondary current and phase angle
ϕ relative to
Iprim
Ratio:
ratio Iprim /Isec., here 200:5.0133
1
1. The value 5.0133 is calculated as follows:
Isec act x (Iprim nom / Iprim act); here: 5.013 A x (200A / 199.99A) = 5.0133
and deviation of current ratio in %.
((Kn x Isec - Iprim) / Iprim) x 100%
2
((200A / 5A * 5.013A - 199.99A) / 199.99A) x 100% = +0.265%
2. Kn = rated transformation value, here: 200A / 5A
Polarity: displays the status of the polarity
OK = phaseIsec - phaseIprim = -45°< 0° < +45°
NOT OK = all other cases
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