1. Distance protection directional function.
2. Negative sequence based overcurrent function.
7.2.7.5 Base quantities within the protection
The 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 protected object in primary kV.
7.2.7.6 Internal ground-fault protection structure
The protection is internally divided into the following parts:
1. Four residual overcurrent steps.
2. Directional supervision element for residual overcurrent steps with integrated
directional comparison step for communication based ground-fault protection
schemes (permissive or blocking).
3. Second harmonic blocking element with additional feature for sealed-in blocking
during switching of parallel transformers.
Each part is described separately in the following sections.
7.2.7.7 Four residual overcurrent steps
Each overcurrent step uses operating quantity Iop (residual current) as measuring
quantity. 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
this parameter setting the directional mode of the step is selected. It shall be noted
that the directional decision (Forward/Reverse) is not made within each residual
overcurrent step itself. The direction of the fault is determined in a directional
element common for all steps.
• Residual current pickup value.
• Type of operating characteristic. By this parameter setting it is possible to select
inverse or definitive time delay for step 1 and 4 separately. Step 2 and 3 are always
definite time delayed. All of the standard IEC and ANSI inverse characteristics are
Section 7 1MRK 505 277-UUS C
Current protection
94
Technical Manual
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