8.4.7 Operation principleThis function has the following three “Analog Inputs” on its function block in theconfiguration tool:1. I3P, input used for “Operating Quantity”. Supply the zero-sequence magnitudemeasuring functionality.2. U3P, input used for “Voltage Polarizing Quantity”. Supply either zero ornegative sequence voltage to the directional functionality3. I3PPOL, input used for “Current Polarizing Quantity”. Provide polarizingcurrent to the directional functionality. This current is normally taken from thegrounding of a power transformer.4. I3PDIR, input used for “Directional detection”. Supply either zero or negativesequence current to the directional functionality.These inputs are connected from the corresponding pre-processing function blocks inthe Configuration Tool within PCM600.8.4.7.1 Operating quantity within the functionThe function always uses Residual Current (3I0) for its operating quantity. Theresidual current can be:1. directly measured (when a dedicated CT input of the IED is connected inPCM600 to the fourth analog input of the pre-processing block connected toEF4PTOC function input I3P). This dedicated IED CT input can be for example,connected to:• 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 systemstar point and earth (that is, current transformer located in the star point of astar connected transformer winding).• one single current instrument transformer located between two parts of aprotected object (that is, current transformer located between two starpoints of double star 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 function AnalogInput I3P is not connected to a dedicated CT input of the IED in PCM600). In suchcase the pre-processing block will calculate 3I0 from the first three inputs into thepre-processing block by using the following formula (will take I2 from SMAIAI3P connected to I3PDIR input which was connected to I3P input also):If zero sequence current is selected,Iop 3I IL1 IL2 IL30= = + +EQUATION1874 V2 EN (Equation 63)Section 8 1MRK502052-UEN BCurrent protection362Technical manual
