7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 30 of 52
3.4.2 Time Delayed Measured Earth Fault Protection (51G)
Optionally two time delayed measured earth fault elements are provided, each can be selected to either winding 1
or winding 2.
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, ANSI or user defined 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 51G-n Reset setting can apply a definite time delayed or ANSI (DECAYING) reset. 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.
Operation of the time delayed measured earth fault elements can be inhibited from:
Inhibit 51G-n A binary or virtual input.
51G-n Inrush Action: Inhibit Operation of the inrush detector function.
General Pickup
51G-nIG
n
51G/50G Measurement
51G-n Setting
51G-n Charact
51G-n Time Mult
51G-n Min Operate Time
c
51G-n Delay (DTL)
51G-n Follower DTL
c
Pickup
trip
51G-n Reset
Inhibit 51G-n
&
51G-n Element
Enabled
Disabled
81HBL2
51G-n Inrush
Action
Off
Inhibit
&
Figure 3-10 Logic Diagram: Time Delayed Measured Earth Fault Element (51G)
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