1MAC050144-MB C
Section 4
Protection functions
615 series ANSI
171
Technical Manual
Figure 75:
Definition of the relay characteristic angle, RCA=–90 degrees in an
isolated network
Directional ground-fault protection in an isolated neutral network
In isolated networks, there is no intentional connection between the system neutral point
and ground. The only connection is through the line-to-ground capacitances (C
0
) of phases
and leakage resistances (R
0
). This means that the zero sequence current is mainly
capacitive and has a phase shift of –90 degrees compared to the residual voltage (-V
0
).
Consequently, the relay characteristic angle (RCA) should be set to -90 degrees and the
operation criteria to I
0
sin(
φ
) or phase angle. The width of the operating sector in the phase
angle criteria can be selected with the settings
Min forward angle
,
Max forward angle
,
Min
reverse angle
or
Max reverse angle
. The figure below describes how ground fault current
is defined in isolated neutral networks.
For definitions of different directional ground-fault characteristics, see
Directional ground-fault principles
.
maximum torque line
Min forward angle
Min reverse angle
Min operate
current
Max forward angle
Max reverse angle
zero torque line
Non-operatin
g area
Characteristic angle
= -90 deg
(operating quantity)
-
(polarizing quantity)
0
V
0
I
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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