Internal Polarizing - ABB Relion Technical Manual

Section 8
Current protection
8.2.7.2
210
• parallel connection of current instrument transformers in all three phases
(Holm-Green connection).
• one single core balance, current instrument transformer (cable CT).
• one single current instrument transformer located between power system WYE
point and ground (that is, current transformer located in the neutral grounding
of a WYE connected transformer winding).
• one single current instrument transformer located between two parts of a
protected object (that is, current transformer located between two WYE points
of double WYE shunt capacitor bank).
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 I3P is not connected to a dedicated CT input of the IED in PCM600).
In such case the pre-processing block will calculate 3I
the pre-processing block by using the following formula (will take I2 from same
SMAI AI3P connected to I3PDIR input (same SMAI AI3P connected to I3P input)):
If zero sequence current is selected,
= × = + +
I 3 Io IA IB IC
op
EQUATION2011-ANSI V1 EN
where:
IA, IB, IC are fundamental frequency phasors of three individual phase currents.
The residual current is pre-processed by a discrete Fourier filter. Thus the phasor of the
fundamental frequency component of the residual current is derived. The phasor
magnitude is used within the EF4PTOC (51N/67N) protection to compare it with the set
operation current value of the four steps (Pickup1, Pickup2, Pickup3 or Pickup4). If the
residual current is larger than the set operation current and the step is used in non-
directional mode a signal from the comparator for this step is set to true. This signal will,
without delay, activate the output signal PU_STx (x=step 1-4) for this step and a common
PICKUP signal.

Internal polarizing

A polarizing quantity is used within the protection in order to determine the direction to
the ground fault (Forward/Reverse).
The function can be set to use voltage polarizing, current polarizing or dual polarizing.
1MRK 502 048-UUS A
from the first three inputs into
0
(Equation 47)
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