Negative Sequence Polarisation; Figure 38: Directional Ef Logic With Neutral Voltage Polarization (Single Stage) - GE P24DM Technical Manual

P24xM
7.4.1.1 DIRECTIONAL EARTH FAULT LOGIC WITH RESIDUAL VOLTAGE POLARISATION
IN1> DIRECTIONAL IN1> DIRECTIONAL
VN VN
IN1> VNpo l S et IN1> VNpo l S et
IN1 IN1
Lo w Curren t Th re shold Lo w Curren t Th re shold
IN1>1 Ch ar A ngle IN1>1 Ch ar A ngle
IN1>1 Trip Ang le IN1>1 Trip Ang le
VTS Slow Block VTS Slow Block
IN1> Blo cking IN1> Blo cking
VTS Blocks IN>1 VTS Blocks IN>1

Figure 38: Directional EF logic with neutral voltage polarization (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.
7.4.2

NEGATIVE SEQUENCE POLARISATION

In some applications, the use of residual voltage polarisation may be not possible to achieve, or at the very least,
problematic. For example, a suitable type of VT may be unavailable, or an HV/EHV parallel line application may
present problems with zero sequence mutual coupling.
In such situations, the problem may be solved by using Negative Phase Sequence (NPS) quantities for polarisation.
This method determines the fault direction by comparing the NPS voltage with the NPS current. The operating
quantity, however, is still residual current.
This can be used for both the derived and measured standard earth fault elements. It requires a suitable voltage
and current threshold to be set in cells IN> V2pol Set and IN> I2pol set respectively.
Negative phase sequence polarising is not recommended for impedance earthed systems regardless of the type
of VT feeding the relay. This is due to the reduced earth fault current limiting the voltage drop across the negative
sequence source impedance to negligible levels. If this voltage is less than 0.5 volts the device will stop providing
directionalisation.
The directional criteria with negative sequence polarisation is given below:
Directional forward
(Ð V2 + 180°) + RCA - 90° + (180° - tripping angle)/2 < Ð I2 < ( Ð V2 +180°) + RCA +90° - (180° -
tripping angle)/2
Directional reverse
(Ð V2 + 180°) + RCA - 90° - (180° - tripping angle)/2 > Ð I2 > ( Ð V2 +180°) + RCA +90° + (180° -
tripping angle)/2
This can be best visualised with reference to the following diagram:
P24xM-TM-EN-2.1
Directional
check
&
Chapter 6 - Current Protection Functions
To EF logic To EF logic
Note: This diagram shows the log ic fo r IN1 (me asure d ea rth fault). The logic for Note: This diagram shows the log ic fo r IN1 (me asure d ea rth fault). The logic for
IN2 (derived earth f ault) follo ws simila r p rinciples. IN2 (derived earth f ault) follo ws simila r p rinciples.
This diagram d oes no t show all st ages. Ot her stages f ollow simila r p rinciples. This diagram d oes no t show all st ages. Ot her stages f ollow simila r p rinciples.
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