Directional Sef Logic; Figure 60: Directional Sef With Vn Polarisation (Single Stage) - GE P24DM Technical Manual

Chapter 6 - Current Protection Functions
The diagram illustrates the method of discrimination when the real (cosf ) component is considered. Faults close to
the polarising voltage will have a higher magnitude than those close to the operating boundary. In the diagram,
we assume that the current magnitude I is in both the faulted and non-faulted feeders.
For the active component Icos, the criterion for operation is: Icosf > ISEF>(n) current
●
● For the reactive component Isin, the criterion for operation is: Isinf > ISEF>(n) current
Where ISEF>(n) current is the sensitive earth fault current setting for the stage in question
If any stage is set to non-directional, the element reverts back to normal operation based on current magnitude I
with no directional decision. In this case, correct discrimination is achieved by means of an Icos characteristic as
the faulted feeder will have a large active component of residual current, whilst the healthy feeder will have a
small value.
For insulated earth applications, it is common to use the Isin characteristic.
All of the relevant settings can be found under the SEF PROTECTION column.
8.4.3

DIRECTIONAL SEF LOGIC

SEF Opti o ns
ISEF
ISEFsin(phi)
ISEFcos(phi)
ISEF>1 Current
Inhibit SEF
I2H Any Start
ISEF> Blocking
2H Blocks ISEF>1
ISEF>1 Direction
VN.ISEF.cos phi
PN> Setting
SEF Opti o ns
Wat tmetric
VN
ISEF> VNpol Set
VTS Slow Block
ISEF> Blocking
VTS Blks ISEF>1
ISEF>1 CharAngle
ISEF>1 TripAngle
ISEF>1 Timer Blk

Figure 60: 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°
●
134
&
&
&
Directional
check
&
&
&
IDMT/DT
Timer Settings
Note: Thi s diagram does not show all stages. Other
stages fol l ow simil a r principles.
P24xM
ISEF>1 Start
ISEF>1 Trip
V04005
P24xM-TM-EN-2.1