Directional Sef Logic; Application Notes; Insulated Systems; Figure 48: Directional Sef With Vn Polarisation (Single Stage) - GE MiCOM P40 Agile Technical Manual

Chapter 6 - Current Protection Functions
8.4.3

DIRECTIONAL SEF LOGIC

SEF Options
ISEF
ISEFsin(phi)
ISEFcos(phi)
ISEF>1 Current
Inhibit SEF
I2H Any Start
ISEF> Blocking
2 H Blocks ISEF>1
ISEF>1 Direction
VN.ISEF.cos phi
PN> Setting
SEF Options
Wattmetric
VN
ISEF> VNpol Set
VTS Slow Block
ISEF> Blocking
VTS Blks ISEF>1
ISEF>1 CharAngle
ISEF>1 TripAngle
AR Blk Main Prot
ISEF> Blocking
AR Blks ISEF>3
AR blocking available for DT-only stages
ISEF>1 Timer Blk

Figure 48: Directional SEF with VN polarisation (single stage)

The sensitive earth fault protection can be set IN/OUT of service using the appropriate DDB inhibit signal, which
can be operated from an opto-input or control command. VT Supervision (VTS) selectively blocks the directional
protection or causes it to revert to non-directional operation. When selected to block the directional protection,
VTS blocking is applied to the directional checking which effectively blocks the start outputs as well.
The directional check criteria are given below for the standard directional sensitive earth fault element:
Directional forward: -90° < (angle(IN) - angle(VN + 180°) - RCA) < 90°
●
Directional reverse: -90° > (angle(IN) - angle(VN + 180°) - RCA) > 90°
●
Three possibilities exist for the type of protection element that you can use for sensitive earth fault detection:
A suitably sensitive directional earth fault protection element having a characteristic angle setting (RCA) of
●
zero degrees, with the possibility of fine adjustment about this threshold.
A sensitive directional zero sequence wattmetric protection element having a characteristic angle setting
●
(RCA) of zero degrees, with the possibility of fine adjustment about this threshold.
A sensitive directional earth fault protection element having Icosf and Isinf characteristics.
●
All stages of the sensitive earth fault element can be set down to 0.5% of rated current.
8.5

APPLICATION NOTES

8.5.1

INSULATED SYSTEMS

When insulated systems are used, it is not possible to detect faults using standard earth fault protection. It is
possible to use a residual overvoltage device to achieve this, but even with this method full discrimination is not
possible. Fully discriminative earth fault protection on this type of system can only be achieved by using a SEF
(Sensitive Earth Fault) element. This type of protection detects the resultant imbalance in the system charging
112
&
&
&
Directional
check
&
&
&
&
IDMT/DT
Timer Settings
Note: This diagram does not show all stages . Other stages follow
similar principles.
AR blocking is only available for stages 3 and 4
P14D
ISEF>1 Start
ISEF>1 Trip
V00746
P14D-TM-EN-8