ABB REB650, Technical Manual

Page: 95 / 504

• 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
0
from the first
three inputs into 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,
op
I 3 Io IA IB IC
= × = + +
EQUATION2011-ANSI V1 EN
(Equation 7)
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.
7.2.7.2 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 505 277-UUS C
Section 7
Current protection
89
Technical Manual