Time Delayed Measured Earth Fault Protection (51G); Figure 3.3-3 Logic Diagram: Measured Time Delayed Earth Fault Element (51G) - Siemens 7SR224 Description & Operation

(1) Description of Operation 7SR224

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
79 E/F Inst Trips: 51G-n
51G-n Inrush Action: Inhibit
51G-n VTSAction: Inhibit
Figure 3.3-3
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A binary or virtual input, or function key
When 'delayed' trips only are allowed in the auto-reclose
sequence (79 E/F Prot'n Trip n = Delayed).
Operation of the inrush current detector function.
Operation of the VT Supervision function.
Logic Diagram: Measured Time Delayed Earth Fault Element (51G)
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