Polarising The Directional Decision; Psl Required To Activate Def Logic With An Independant Channel; Psl Required To Activate Def Logic With Shared Channel; Def Calculation - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-106
Figure 76: PSL required to activate DEF logic with an independant channel
Figure 77: PSL required to activate DEF logic with shared channel
Figure 78: DEF calculation
Note:
4.8.3.1

Polarising the Directional Decision

The relative advantages of zero sequence and negative sequence polarising are outlined in
the section 1.1.2. Note how the polarising chosen for aided DEF is independent of that
chosen for backup earth fault elements.
The V> threshold is set above the standing residual voltage on the protected system, to
avoid operation for typical power system imbalance and voltage transformer errors. In
practice, the typical zero sequence voltage on a healthy system can be as high as 1% (ie:
3% residual), and the VT error could be 1% per phase. This could equate to an overall error
of up to 5% of phase-neutral voltage, although a setting between 2% and 4% is typical. On
high resistance earthed and insulated neutral systems the settings might need to be as high
as 10% or 30% of phase-neutral voltage, respectively.
When negative sequence polarising is set, the V> threshold becomes a V2> negative
sequence voltage detector.
The characteristic angle for aided DEF protection (Figure 79) is fixed at –14°, suitable for
protecting all solidly earthed and resistance earthed systems.
V2
Negative
I2
Polarisation
VN
Residual
Polarisation
IN
Negative
V2
Polarisation
Residual
VN
Polarisation
IN>
IN
INRev = 0.6*INFwd
The DEF is blocked in case of VTS or CTS.
MiCOM P40 Agile P442, P444
Directionnal
Calculation
V>
Application Notes
DEF Fwd
DEF Rev
DEF V>
INRev>
INFwd>
P0545EN