5.4 Standard Knee Points The CT-T1 is able to fully automatically determine three different knee points which are listed
below and described.
The listed knee-points above are defined in 5.6.3). They both appear in 5.6.2) as well:
1. Definition 3.11(A) for Class C transformers (described in 5.6.4).
They are described in (5.4.1 IEEE 45°) and (5.4.2 IEEE 30°).
2. Definition 3.11(B) derived from 5.6.1) (described in 5.6.2)).
The ASA 10/50 knee-point is described in (5.4.3. ASA 10/50).
5.4.1. IEEE 45° IEEE 45° The knee point of a CT with a non-gapped core as defined by the Institute of Electrical
and Electronics Engineers (IEEE). The tangents slope is 45° in the log-log-graph with square
decades (see Definition 3.11(A) of 5.6.3).
The IEEE knee point of a Class C transformers with non-gapped cores is makes an angle α IEEE 45°
of 45 to the abscissa (horizontal I-axis). Using Equation 5.2.c) leads to the slope m IEEE 45°
.
5.4.1.a) Equation: s IEEE 45° =tan α
IEEE 45 ° =tan 45 ° 5.4.1.b) Equation: s IEEE 45° =1
5.4.1.c) Equation: σ IEEE 45 ° =45° 5.4.2. IEEE 30° IEEE 30° The knee point of a CT with a gapped core as defined by the Institute of Electrical and
Electronics Engineers (IEEE). The tangents slope is 30° in the log-log-graph with square
decades.
IEEE defines the knee point for Class C transformers with gapped cores as the point in the square
log-log graph which tangent makes an angle α IEEE 30°
of 30° to the abscissa (horizontal I-axis). Using
Equation 5.2.c) leads to the slope m IEEE 30°
.
5.4.2.a) Equation: s IEEE 30 ° =tan α
IEEE 30 ° =tan30°
