Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 86/220 MiCOM P441/P442 & P444
DIST. CR
DEF. CR
Opto label 01
Opto Label 02
DEF CS
DIST CS
P0534ENa
Relay Label 02
Relay Label 01
FIGURE 48 - PSL REQUIRED TO ACTIVATE DEF LOGIC WITH AN INDEPENDANT CHANNEL
DIST. CR
DEF. CR
Opto label 01
DEF CS
DIST CS
P0544ENa
>1
Relay label 01
FIGURE 49 - PSL REQUIRED TO ACTIVATE DEF LOGIC WITH SHARED CHANNEL
Directionnal
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>
P0545ENa
INFwd>
DEF V>
FIGURE 50 - DEF CALCULATION
NOTE: The DEF is blocked in case of VTS or CTS
2.18.1 Polarising the Directional Decision
The relative advantages of zero sequence and negative sequence polarising are outlined on
the previous page. Note how the polarising chosen for aided DEF is independent of that
chosen for backup earth fault elements.
The relay has a V> threshold which defines the minimum residual voltage required to enable
an aided DEF directional decision to be made. A residual voltage measured below this
setting would block the directional decision, and hence there would be no tripping from the
scheme. 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 20% 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 is fixed at –14°, suitable for protecting all
solidly-earthed and resistance earthed systems.