Application Notes; Setting Guidelines (Non-Directional); Figure 104: Directional Earth Fault Logic With Negative Phase Sequence Polarisation - GE P642 Technical Manual

Chapter 9 - Current Protection Functions
The directional criteria with negative sequence polarisation is given below:
Directional forward: -90° < (angle(I2) - angle(V2 + 180°) - RCA) < 90°
●
● Directional reverse : -90° > (angle(I2) - angle(V2 + 180°) - RCA) > 90°
6.4.2.1 DIRECTIONAL EARTH FAULT LOGIC WITH NPS POLARISATION
IN
IN>1 Current
CTS Block
EF1 IH2 Start
IN> Blocking
IN>1 2 H Block
IN> Direction
V2
IN> V 2pol Set
I2
IN> I2pol Set
VTS Slow Block
IN> Blocking
IN>1 2 H Block
EF 1 IN>1 TBlk
V00692
Figure 104: Directional Earth Fault logic with negative phase sequence polarisation (single stage)
Voltage Transformer 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 criteria with negative sequence polarisation is given below:
Directional forward: -90° < (angle(I2) - angle(V2 + 180°) - RCA) < 90°
●
Directional reverse : -90° > (angle(I2) - angle(V2 + 180°) - RCA) > 90°
●
6.5

APPLICATION NOTES

6.5.1

SETTING GUIDELINES (NON-DIRECTIONAL)

To provide backup protection for downstream equipment such as the power transformer and busbar, Standby
Earth Fault (SBEF) protection is commonly applied. This function is fulfilled by a separate earth fault current input,
fed from a single CT in the transformer earth connection. The earth fault elements may be used to provide the
SBEF function.
A Neutral Earthing Resistor (NER) is used to limit the earth fault level to a particular value. It is possible that under
an earth fault condition a flashover of the NER could occur, which could lead to a dramatic increase in the earth
fault current. For this reason, it may be appropriate to apply two-stage SBEF protection. The first stage should
have suitable current and time characteristics which coordinate with downstream earth fault protection. The
second stage may then be set with a higher current setting but with zero time delay, providing fast clearance of an
earth fault which gives rise to an NER flashover.
The remaining two stages are available for customer-specific applications.
220
&
&
Directional
check
&
This diagram does not show all stages . Other stages follow similar principles.
IDMT/DT
& &
P64x
EF1 IN>1 Start
EF1 IN>1 Trip
P64x-TM-EN-1.3