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phase and parallel to each other. This may be for example the typical operating principle of a three-phase time
overcurrent protection. When operating single-phase, the function employs either a phase's measured quan-
tity, which must be stated explicitly, (e.g. evaluating only the current in phase Ib), the measured ground
current In or the measured displacement voltage Vn. If the characteristic relates to the frequency or if
external trip commands are used, the operating principle is without (fixed) phase reference. Additional param-
eters can be set to specify the used MEAS. QUANTITY and the MEAS. METHOD. The MEAS. METHOD deter-
mines for current and voltage measured values whether the function uses the RMS value of the fundamental
component or the normal RMS value (true RMS) that evaluates also harmonics. All other characteristics use
always the rms value of the fundamental component. Parameter PICKUP WITH moreover specifies whether
the function picks up on exceeding the threshold (>-element) or on falling below the threshold (<-element).
Characteristic Curve
The function's characteristic curve is always "definite time"; this means that the time delay is not affected by
the measured quantity.
Function Logic
The following figure shows the logic diagram of a three-phase function. If the function operates on one phase
or without phase reference, phase selectivity and phase-specific indications are not relevant.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Functions
2.19 Flexible Protection Functions
325
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