point and ground (current transformer located in the WYE point of a WYE
connected transformer winding).
• For some special line protection applications this dedicated IED CT input
can be connected to parallel connection of current transformers in all three
phases (Holm-Green connection).
2. calculated from three phase current input within the IED (when the fourth analog
input into the pre-processing block connected to EF4PTOC (51N/67N) function
analog input I3PPOL is NOT connected to a dedicated CT input of the IED in
PCM600). In such case the pre-processing block will calculate 3I
0
from the first
three inputs into the pre-processing block by using the following formula:
3= × = + +
Pol
I Io IA IB IC
EQUATION2019-ANSI V1 EN (Equation 15)
where:
IA, IB and IC are fundamental frequency phasors of three individual phase currents.
The Negative sequence current can be calculated from the three-phase current input
within the IED by using the pre-processing block. The pre-processing block will
calculate the negative sequence current from the three inputs into the pre-processing
block by using the following formula:
2
I2 = (IA+ IB+ IC)/3
a a
× ×
GUID-65EF3644-BDC6-4E4B-97B0-AA48929C4CAF V1 EN (Equation 16)
where:
IA, IB and IC are fundamental frequency phasors of three individual phase currents.
alpha is 1 with an angle of 120 degrees
This phasor is used together with the phasor of the polarizing quantity in order to
determine the direction of the ground fault (Forward/Reverse).
7.2.7.4 External polarizing for ground-fault function
The individual steps within the protection can be set as non-directional. When this
setting is selected it is then possible via function binary input BLKn(where x indicates
the relevant step within the protection) to provide external directional control (that is,
torque control) by for example using one of the following functions if available in the
IED:
1MRK 505 277-UUS C Section 7
Current protection
93
Technical Manual
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