5.3.1.a) Equation:
s
Sat
:
= 0.2 < s
ASA 10
/ 50
For the degauss process the output voltage U is set to a value below the saturation voltage U
Start
and is increased until the slope s is flatter than s
Sat
. Subsequently the voltage is stationary while the
CT under test is demagnetized.
90225-1.30 Instruction Manual CT-T1
Page 19 of 62
5.3.2. Knee Point / Excitation
Residual induction stored in the core of the CT under test must be eliminated before excitation test
(See chapter 5.3.1). This residual induction is caused by partial magnetization which induced by a
DC current or an incomplete shutdown cycle.
After the process of eliminating the remanence, the knee points detecting phase is started. (For a
thorough discussion about the three standard knee points see Chapter 5.4).
Figure 5 shows the measurement setup for the excitation measurement process.
At the beginning of the knee point detection phase, the voltage U
X
and the current I
X
are high for
the CT under test to be demagnetized. U
X
and thus I
X
are slowly decreased until the slope is steep
enough to allow the detection of the lowest (IEEE-45) knee point. The voltage U
X
is decreased
faster in the linear area to complete the graph.
90225-1.30 Instruction Manual CT-T1
Page 20 of 62
Figure 5: measurement setup for the excitation measurement process
WARNING !
WARNING !
If the voltage is applied to a section of the secondary winding, the voltage on
the full winding is proportionally higher due to the autotransformer
characteristics!
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