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GE P444

GE P444
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Application Notes
P44x/EN AP/Hb
6
MiCOM P40 Agile P442, P444
(AP) 5-
103
When protecting solidly-earthed transmission systems, a -60° RCA setting should be
set.
4.7.2.2 Application of Negative Sequence Polarising
In certain applications, the use of residual voltage polarisation of DEF may either be not
possible to achieve, or problematic. An example of the former case would be where a
suitable type of VT was unavailable, for example if only a three limb VT were fitted. An
example of the latter case would be an HV/EHV parallel line application where problems with
zero sequence mutual coupling may exist. In either of these situations, the problem may be
solved by the use of negative sequence quantities for polarisation. This method determines
the fault direction by comparison of negative sequence voltage with negative sequence
current. The operate quantity, however, is still residual current.
When negative sequence polarising is used, the relay requires that the Characteristic Angle
is set. The Application Notes section for the Negative Sequence Overcurrent Protection
better describes how the angle is calculated - typically set at - 45°
(I
2
lags (-V
2
)).
4.8 Aided Directional Earth Fault (DEF)
4.8.1 DEF Protection Against High Resistance Earth Faults
Protection against high-resistance earth faults, also called DEF (Directional Earth Fault), is
used to protect the network against highly resistive faults. High resistance faults may not be
detected by distance protection. DEF Protection can be applied in one of the two following
modes: faults using the following:
The main operating mode, directional comparison protection uses the signalling
channel and is a communication-aided scheme.
In backup-operating mode SBEF (Stand-By Earth Fault), an inverse/definite time earth
overcurrent element with 4 stages is selectable.
Both the main and backup mode can use different methods for fault detection and directional
determination (negative or zero sequence polarisation, RCA angle settable for backup SBEF
protection, etc.)
The use of Aided-Trip logic in conjunction with the DEF element allows faster trip times, and
can facilitate single-phase tripping if single-phase tripping is applied to the breaker.
The DEF directional comparison protection may be applied on the same signal channel as
the distance protection, or it may be applied on an independent channel (ability to use two
different aided-trip logics for the distance and DEF elements).
When used on the same signalling channel (shared scheme selected by MiCOM S1 Agile)
as the distance protection, if the distance protection picks up, it has priority (the output from
the DEF element is blocked from asserting the Carrier Send common output).
The use of directional comparison protection with an independent signalling channel allows
the distance functions and DEF function to operate in parallel. Each function is routed to its
own Carrier Send output. If an earth fault is present where both the distance and DEF
elements pick up, the faster of the two functions will perform the trip.
4.8.1.1 High Resistance Earth Fault Detection
A high resistance fault is detected when residual or zero sequence voltage (3V0) and current
thresholds are exceeded or using the high speed algorithms:
I 0.05 In
V 0.1 Vn (Ph-N)
A fault is confirmed if these thresholds are exceeded for more than 1 ½ cycles.
4.8.1.2 Directional determination
The fault direction is determined by measuring the angle between the residual voltage and
the residual current derivative. The fault is forward if the angle is between 14
° and +166°.
A negative or zero-sequence polarisation is selectable to determinate the earth fault
direction.

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