ABB RED615 Technical Manual page 174

Section 4
Protection functions
168
PH3LPTOC
MF
PH3HPTOC
PH3IPTOC
CCBRBRF
HV-side
INRPHAR
PH3LPTOC
LV-side
PH3HPTOC
PH3IPTOC
CCBRBRF
MF
MEASUREMENT O U T G O N I G O U T G
INCOMING
MF MF
Blocking output
(Outgoing feeder
PH3HPTOC START)
GUID-F7E5C2F1-FDF4-490D-B69D-6535FCEDBDE4 V1 EN
Figure 81: Numerical overcurrent protection functionality for a typical sub-
transmission/distribution substation (feeder protection not shown).
Blocking output = digital output signal from the start 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 practically zero. Also, the
effects of switching inrush currents on the setting values can be reduced using the
IED logic which recognizes the transformer-energizing inrush current and blocks
the operation or multiplies the current start 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 maintaining selectivity and also for
the protection to operate without additional time delays. Additional information
about available measuring modes and current transformer requirements can be
found in the General function block features
Blocking output Blocking output
(PH3HPTOC (PH3HPTOC
START) START)
O N I G B U S T - E I
PH3LPTOC
PH3HPTOC
MF
PH3IPTOC
CCBRBRF
section in this manual.
1YHT530004D05 D
PH3LPTOC
MF
PH3HPTOC
PH3IPTOC
CCBRBRF
HV-side
INRPHAR
PH3LPTOC
LV-side
PH3HPTOC
PH3IPTOC
CCBRBRF
MF
B U S _ T E I O U T G O N I G O U T G O N I G
INCOMING
MF MF
Blocking output
(Outgoing feeder
PH3HPTOC START)
Technical Manual
MEASUREMENT
615 series