relay unit of the faulted bus section trips the breaker in approximately 250 ms (relaying
time), which becomes the total fault clearing time in this case.
A070980-ANSI V1 EN
Figure 57:
Numerical overcurrent protection functionality for a typical sub-
transmission/distribution substation (feeder protection not
shown).Blocking output = digital output signal from the pickup of a
protection stage, Blocking in = digital input signal to block the operation of
a protection stage
The operating times of the time selective stages are very short, because the grading
margins between successive protection stages can be kept short. This is mainly due to the
advanced measuring principle allowing a certain degree of CT saturation, good operating
accuracy and short retardation times of the numerical units. So, for example, a grading
margin of 150 ms in the DT mode of operation can be used, provided that the circuit
breaker interrupting time is shorter than 60 ms.
The sensitivity and speed of the current-selective stages become as good as possible due
to the fact that the transient overreach is very low. Also, the effects of switching inrush
currents on the setting values can be reduced by using the protection relay's logic, which
recognizes the transformer energizing inrush current and blocks the operation or
multiplies the current pickup value setting of the selected overcurrent stage with a
predefined multiplier setting.
Finally, a dependable trip of the overcurrent protection is secured by both a proper
selection of the settings and an adequate ability of the measuring transformers to
reproduce the fault current. This is important in order to maintain selectivity and also for
Section 4
1MRS240050-IB C
Protection functions
122
REF615R
Technical Manual
Содержание RELION REF615R
Страница 1: ... RELION PROTECTION AND CONTROL REF615R Technical Manual ...
Страница 2: ......
Страница 27: ...Section 18 Glossary 653 Table of contents REF615R 21 Technical Manual ...
Страница 28: ...22 ...
Страница 36: ...30 ...
Страница 46: ...40 ...
Страница 115: ...3 15 4 Settings 1MRS240050 IB C Section 3 Basic functions REF615R 109 Technical Manual ...
Страница 118: ...112 ...
Страница 318: ...312 ...
Страница 388: ...382 ...
Страница 456: ...450 ...
Страница 520: ...514 ...
Страница 652: ...646 ...
Страница 656: ...650 ...
Страница 658: ...652 ...
Страница 663: ...657 ...