ERL L-PRO 4000, Руководство пользователя

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4 Protection Functions and Specifications
D02706R02.30 L-PRO 4000 User Manual 4-13
The settings for the negative-sequence voltage sensitivity and negative-se-
quence current sensitivity should be normally higher than the maximum nega-
tive sequence quantities generated by unbalanced load. These settings should
also be low enough to maintain sensitivity for the minimum unbalanced fault,
in terms of negative sequence quantities.
The zero-sequence directional element can be used in many applications. How-
ever, where strong mutual coupling between parallel lines exist, the zero-se-
quence calculation must be disabled to prevent an incorrect directional
determination. The sensitivity settings should be low enough to permit opera-
tion during the lowest expected ground fault in terms of zero-sequence quanti-
ties expected during a fault, and high enough to allow for normal load
imbalance.
.
21P and 21N
Phase Selector
The phase selector algorithm for the relay ensures that:
• 21N only trips on single-phase-to-ground fault, so as to prevent 21N from
false tripping for phase-to-phase-to-ground faults with arc resistance
• Supervise 21P for low Source Impedance Ratio (SIR) ratios and single-
phase-to-ground faults at 20% of line reach or below.
Algorithm Details
The phase selector uses a combination of positive, negative and zero sequence
current phasors to correctly determine the faulty phase. No user settings are re-
quired for the phase selector functionality. An OR function with angle checks
between
I
1
and I
2
as well as the angle between I
2
and I
0
. The OR function al-
lows the algorithm to adapt to various fault conditions and provide the correct
fault type. When energizing a line with a T-tapped load, the user may have sys-
tem conditions where no pre-trigger load current is available. Using positive
and negative sequence currents alone may cause an incorrect fault determina-
tion if the load current is significantly large enough to affect the total positive
sequence current, which includes both load and fault current. Our algorithm
overcomes this problem.
Table 4.3: Directional Element Settings
Override Enabled Enable/Disable
Negative-Sequence Enable/Disable
V2 Sensitivity Level (V secondary) 0.5 to 5.0
I2 Sensitivity Level (A secondary) 0.1 to 1.0 (5 A)
0.02 to 0.20 (1 A)
Zero Sequence Enable/Disable
3V0 Sensitivity Level (V secondary) 1.0 to 10.0
3I0 Sensitivity Level (A secondary) 0.2 to 2.0 (5 A)
0.04 to 0.40 (1 A)