•
I-Setting: current enabling level
•
MeasBwd: fault in backwards direction including Transient blocking
•
MeasBwd': fault in backwards direction
•
MeasFwd: fault in forwards direction
•
Rx: receive
•
T: trip
•
t TransBlk: blocking time
•
TB: transient blocking
•
t
Basic
: basic time
•
t
Wait
: waiting time
•
Tx: send
•
V-setting: reference voltage
5.9.6.4
Setting the enabling pick-up levels
GUID-E1B70D52-C69A-43A2-AA45-C8502F086DE2 v1
The setting of the current enabling
I-dir must take account of the zero-sequence component in
normal operation arising from system asymmetries.
The pick-up setting for the voltage enabling signal
V-Setting is determined by the level of
asymmetries on the secondary side (VT tolerances, asymmetrical burdens etc.).
The ability to read voltage and current values on the relay is a useful aid for determining these
settings.
For example, if the enabling current setting
I-Setting is too low, the pick-up signal lights
continuously (current circuit enabled).
Since a ground fault causes asymmetrical voltages in the vicinity of the fault, the current
flowing via the system capacitances also has a zero-sequence component. A capacitive current
of this kind on a long line lies within the setting range of the sensitive ground fault protection
function.
The pick-up level
I-dir of the current circuit for the directional measurement has a fixed setting
of 0.7 ×
I-Setting to take account of influences, such as CT errors and the capacitive charging
currents of the line.
The following procedure is recommended for setting the pick-up levels:
•
The enabling current for the directional measurement must be set to at least twice the
maximum possible asymmetrical current, which can occur in normal operation.
-Setting
2.0
asymm
N
I
I
I
•
The voltage pick-up must be set to 1.6 times the level of the spurious voltages, which can
occur due to asymmetries in the VT secondary circuit.
-
sec.asymm
N
U
V Setting
1.6
U
where:
•
I
asymm
: current component 3I
0
caused by asymmetrical load currents
•
I
N
: primary CT rated current
•
I-Setting: setting of the enabling current
1MRK 505 406-UEN B
Section 5
Bay protection functions
Bay protection functions REB500
165
Technical manual
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