7SR224 Argus Description of Operation
3.3.3 Time Delayed Measured Earth Fault Protection (51G)
Four elements are provided e.g. giving the option of using two elements set to forward and two to reverse.
51G-n Setting
sets the pick-up current level.
A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is
selected from IEC and ANSI curves using
51G-n Char
. A time multiplier is applied to the characteristic curves
using the
51G-n Time Mult
setting. Alternatively, a definite time lag (DTL) can be chosen using
51G-n Char
.
When DTL is selected the time multiplier is not applied and the
51G-n Delay (DTL)
setting is used instead. The
full list of operating curves is given in section 2 – ‘Settings, Configuration and Instruments Guide’. Operating curve
characteristics are illustrated in section 3 – ‘Performance Specification’.
The
51G-n Reset
setting can apply a
definite time delayed
reset
,
or when configured as an ANSI characteristic
an
ANSI (DECAYING)
reset. If ANSI (DECAYING) reset is selected for an IEC characteristic, the reset will be
instantaneous. The reset mode is significant where the characteristic has reset before issuing a trip output – see
‘Applications Guide’.
A minimum operate time for the characteristic can be set using
51G-n Min. Operate Time
setting.
A fixed additional operate time can be added to the characteristic using
51G-n Follower DTL
setting.
For the directional elements the direction of operation can be set using
51G-n Dir. Control
setting. Directional
logic is provided independently for each 51G-n element.
Operation of the time delayed measured earth fault elements can be inhibited from:
Inhibit 51G-n
A binary or virtual input, or function key
79 E/F Inst Trips: 51G-n
When ‘delayed’ trips only are allowed in the autoreclose sequence
(
79 E/F Prot’n Trip n
=
Delayed
).
51G-n Inrush Action: Inhibit
Operation of the inrush current detector function.
51G-n VTSAction: Inhibit
Operation of the VT Supervision function.
Figure 3.3-3 Logic Diagram: Measured Time Delayed Earth Fault Element (51G)
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