GE P444 User Manual

P
44x/EN AP/Hb6
Application Notes
(AP) 5
-106 MiCOM P40 Agile
P442, P444
Figure 76: PSL required to activate DEF logic with an independant channel
Figure 77: PSL required to activate DEF logic with shared channel
D
irectionnal
Calculation
Negative
Polarisation
Residual
Polarisation
VN
V2
I2
IN
V2
VN
Negative
Polarisation
Residual
Polarisation
V>
IN
IN>
INRev = 0.6*INFwd
DEF Fwd
DEF Rev
INRev>
P0545EN
INFwd>
DEF V>
Figure 78: DEF calculation
Note: The DEF is blocked in case of VTS or CTS.
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.

GE P444 Specifications

General

Brand	GE
Model	P444
Category	Protection Device
Language	English