Earth Fault Protection Logic; Application Notes; Residual Voltage Polarisation Setting Guidelines; Setting Guidelines (Directional Element) - GE P4A Technical Manual

P54A/B/C/E
4.4

EARTH FAULT PROTECTION LOGIC

IN
IN>1 Current Set
928
CTS Block
467
Inhibit IN >1
IN>1 Directional
VN
IN> VNpol Set
IN
Low Current
Residual voltage polarisation
833
VTS Slow Block
IN> Blocking
VTS Blocks IN>1
405
IN>1 Timer Blk
V2
IN> V2pol Set
I2
IN> I2pol Set
Negative Sequence Polarisation
V00737

Figure 101: Earth Fault Protection logic diagram

4.5

APPLICATION NOTES

4.5.1

RESIDUAL VOLTAGE POLARISATION SETTING GUIDELINES

It is possible that small levels of residual voltage will be present under normal system conditions due to system
imbalances, VT inaccuracies, IED tolerances etc. Hence, the IED includes a user settable threshold (IN> VNPol Set)
which must be exceeded in order for the DEF function to be operational. In practice, the typical zero sequence
voltage on a healthy system can be as high as 1% (i.e. 3% residual), and the VT error could be 1% per phase. A
setting between 1% and 4% is therefore typical. The residual voltage measurement may assist in determining the
required threshold setting during commissioning, as this will indicate the level of standing residual voltage present.
4.5.2

SETTING GUIDELINES (DIRECTIONAL ELEMENT)

With directional earth faults, the residual current under fault conditions lies at an angle lagging the polarising
voltage. Hence, negative RCA settings are required for DEF applications. This is set in the cell I> Char Angle in the
relevant earth fault menu.
P54xMED-TM-EN-1
&
Directional
check
&
Chapter 9 - Current Protection Functions
IDMT/ DT
& &
Note: For the purpose of clarity, this diagram shows the first
relevant stage number for each signal and setting name .
777
IN>1 Start
671
IN>1 Trip
205