1. Distance protection directional function.2. Negative sequence based overcurrent function.6.4.7.4 Base quantities within the protectionThe base quantities are entered as global settings for all functions in the IED. Base current(IBase) shall be entered as rated phase current of the protected object in primary amperes.Base voltage (VBase) shall be entered as rated phase-to-phase voltage of the protectedobject in primary kV.6.4.7.5 Internal ground-fault protection structureThe protection is internally divided into the following parts:1. Four residual overcurrent steps.2. Directional supervision element for residual overcurrent steps with integrateddirectional comparison step for communication based ground-fault protectionschemes (permissive or blocking).3. Second harmonic blocking element with additional feature for sealed-in blockingduring switching of parallel transformers.Each part is described separately in the following sections.6.4.7.6 Four residual overcurrent stepsEach overcurrent step uses operating quantity Iop (residual current) as measuringquantity. Each of the four residual overcurrent steps has the following built-in facilities:• Directional mode can be set to Disabled/Non-directional/Forward/Reverse. By thisparameter setting the directional mode of the step is selected. It shall be noted that thedirectional decision (Forward/Reverse) is not made within each residual overcurrentstep itself. The direction of the fault is determined in a directional element commonfor all steps.• Residual current pickup value.• Type of operating characteristic. By this parameter setting it is possible to selectinverse or definitive time delay for step 1 and 4 separately. Step 2 and 3 are alwaysdefinite time delayed. All of the standard IEC and ANSI inverse characteristics areSection 6 1MRK 511 287-UUS ACurrent protection108Technical manual
