ABB Relion 670 series, Technical Manual

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8.4.7.6 Internal ground-fault protection structure
M13941-157 v3
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.
4. Switch on to fault feature with integrated Under-Time logic for detection of breaker problems
during breaker opening or closing sequence.
8.4.7.7 Four residual overcurrent steps
M13941-166 v7
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 the residual overcurrent step itself. The
direction of the fault is determined in common “directional supervision element”.
• Residual current pickup value.
• Type of operating characteristic (inverse or definite time). By this parameter setting it is
possible to select inverse or definite time delay for the ground-fault protection. Most of the
standard IEC and ANSI inverse characteristics are available. For the complete list of available
inverse curves please refer to section "Inverse characteristics" .
• Type of reset characteristic ( Instantaneous / IEC Reset / ANSI Reset). By this parameter
setting it is possible to select the reset characteristic of the step. For the complete list of
available reset curves please refer to section "" .
• Time delay related settings. By these parameter settings the properties like definite time
delay, minimum operating time for inverse curves, reset time delay and parameters to define
user programmable inverse curve are defined.
• Supervision by second harmonic blocking feature (
Enabled/Disabled). By this parameter
setting it is possible to prevent operation of the step if the second harmonic content in the
residual current exceeds the preset level.
• Multiplier for scaling of the set residual current pickup value by external binary signal. By this
parameter setting it is possible to increase residual current pickup value when function binary
input MULTPUx has logical value 1.
Simplified logic diagram for one residual overcurrent step is shown in figure 254 .
1MRK 502 066-UUS B Section 8
Current protection
483
Technical manual