Section 4
1MAC050144-MB C
Protection functions
362
615 series ANSI
Technical Manual
When injecting the currents in the high voltage winding, the angle values
I_ANGL_A1_B1, I_ANGL_B1_C1, I_ANGL_C1_A1, I_ANGL_A2_B2,
I_ANGL_B2_C2 and I_ANGL_C2_A2 have to show +120 deg. Otherwise the phase order
can be wrong or the polarity of a current transformer differs from the polarities of the other
current transformers on the same side.
If the angle values I_ANGL_A1_B1, I_ANGL_B1_C1 and I_ANGL_C1_A1 show -120
deg, the phase order is wrong on the high voltage side. If the angle values
I_ANGL_A2_B2, I_ANGL_B2_C2 and I_ANGL_C2_A2 show -120 deg, the phase order
is wrong on the low voltage side. If the angle values I_ANGL_A1_B1, I_ANGL_B1_C1
and I_ANGL_C1_A1 do not show the same value of +120, the polarity of one current
transformer can be wrong. For instance, if the polarity of the current transformer
measuring IL2 is wrong, I_ANGL_A1_B1 shows -60 deg, I_ANGL_B1_C1 shows -60
deg and I_ANGL_C1_A1 shows +120 deg.
When the phase order and the angle values are correct, the angle values I_ANGL_A1_A2,
I_ANGL_B1_B2 and I_ANGL_C1_C2 usually show 0 deg. There can be several reasons
if the angle values are not 0 deg. If the values are ±180 deg, the value given for CT
connection type is probably wrong. If the angle values are something else, the value for
Clock number can be wrong. Another reason is that the combination of Winding 1 type
and Winding 2 type does not match Clock number. This means that the resulting
connection group is not supported.
Example
IIf Winding 1 type is set to "Y", Winding 2 type is set to "y" and Clock number is set to
"Clk num 1", the resulting connection group "Yy1" is not a supported combination.
Similarly if Winding 1 type is set to "Y", Winding 2 type is set to "d" and Clock number
is set to "Clk num 0", the resulting connection group "Yd0" is not a supported
combination. All the non-supported combinations of Winding 1 type, Winding 2 type and
Clock number settings result in the default connection group compensation that is "Yy0".
Recommendations for current transformers
The more important the object to be protected, the more attention has to be paid to the
current transformers. It is not normally possible to dimension the current transformer so
that they repeat the currents with high DC components without saturating when the
residual flux of the current transformer is high. 87T operates reliably even though the
current transformers are partially saturated.
The accuracy class recommended for current transformers to be used with 87T is 5P, in
which the limit of the current error at the rated primary current is 1 percent and the limit
of the phase displacement is 60 minutes. The limit of the composite error at the rated
accuracy limit primary current is 5 percent.
The approximate value of the accuracy limit factor Fa corresponding to the actual current
transformer burden can be calculated on the basis of the rated accuracy limit factor Fn at
the rated burden, the rated burden Sn, the internal burden Sin and the actual burden Sa of
the current transformer.
Содержание 615 Series ANSI
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Страница 389: ...Section 4 1MAC050144 MB C Protection functions 382 615 series ANSI Technical Manual ...
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Страница 707: ...Section 15 1MAC050144 MB C Applicable standards and regulations 700 615 series ANSI Technical Manual ...
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