FUNCTION CHARACTERISTICS
65
NG10 - Manual - 04 - 2022
Additional stabilization on through current by means of saturation detector
To stabilize at current loops with long time constants (eg short circuit outside the differential protec-
tion of generator starting current of motors with direct start), the differential protection (with the
exception of the second threshold I
d
>>) can be blocked by a CT’s saturation detector as additional
security to the double slope percentage operating characteristic.
In the first quarter of power cycle after the zero crossing of the instantaneous values of stabiliza-
tion current in a phase, the level of instantaneous values of the differential current at that phase is
controlled by the relay.
In the case of internal fault differential current appears along with the stabilization current after
the zero crossing, with the differential current instantaneous value of twice the actual value of the
stabilization current.
In the case of external fault however, the differential current does not appear until the beginning of
the CT saturation.
The saturation condition of in one phase (87SatDet or 87SatDet-L1-L2-L3 or 87SatDet) is detected if
all the following conditions are met:
1) the saturation detector is enabled (SatDet parameter set ON inside the Set \ Profile A (o B) \ Dif-
ferential - 87G-M-L \ CT saturation detector menu),
2) the value of the differential current, in absolute value, inside the first quarter of each power cycle
after the zero crossing of the stabilization current is, at that phase, less than 1.6 times the absolute
value of instantaneous value of the stabilization current in (corresponding to 80 % of the operating
characteristic for internal fault),
3) the operating point at that phase is above the first three sections of the double slope percent
operating characteristic and below the second threshold I
d
>>.
An adjustable recovery time tSatDet-RES detector saturation is adjustable.
The saturation detector does not block the second threshold of the differential protection I
d
>>.
The saturation detector can be enabled or disabled by selecting ON or OFF the STSatDet param-
eter, available, together with the tSatDet-RESreset time delay, within the menu Set \ Profile A (o B)
\ Differential - 87G-M-L \ CT saturation detector menu.
The start of an output relay can be controlled by programming the STSatDet-K parameter inside the
Set \ Profile A (o B) \ Differential - 87T \ CT saturation detector menu and similarly the programming
state can be viewed on LED (STSatDet-L).
The differential locking at the saturation detector activation is independent for each of the three
phases.
To Next Page
Loading...
Need help?
General
