• 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 systemWYE point and ground (that is, current transformer located in the neutralgrounding of a WYE connected transformer winding).• one single current instrument transformer located between two parts of aprotected object (that is, current transformer located between two WYEpoints of double WYE shunt capacitor bank).2. calculated from three-phase current input within the IED (when the fourth analoginput into the pre-processing block connected to EF4PTOC (51N/67N) functionAnalog Input I3P is not connected to a dedicated CT input of the IED inPCM600). In such case the pre-processing block will calculate 3I0 from the firstthree inputs into the pre-processing block by using the following formula (willtake I2 from same SMAI AI3P connected to I3PDIR input (same SMAI AI3Pconnected to I3P input)):If zero sequence current is selected,opI 3 Io IA IB IC= × = + +EQUATION2011-ANSI V1 EN (Equation 39)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 thefundamental frequency component of the residual current is derived. The phasormagnitude is used within the EF4PTOC (51N/67N) protection to compare it with theset operation current value of the four steps (Pickup1, Pickup2, Pickup3 or Pickup4). Ifthe 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 signalwill, without delay, activate the output signal PU_STx (x=step 1-4) for this step and acommon PICKUP signal.8.2.7.2 Internal polarizingA polarizing quantity is used within the protection in order to determine the directionto the ground fault (Forward/Reverse).The function can be set to use voltage polarizing, current polarizing or dual polarizing.1MRK 502 043-UUS B Section 8Current protection183Technical Manual
