4 Protection Functions and Specifications
4-8
L-PRO 4000 User Manual
D02706R02.30
Relay Method of
Memory
Polarization
The 21P and 21N Mho/Quad elements use positive-sequence voltage, derived
from a memory voltage, as the polarizing quantity. No user settings are re-
quired for the memory polarization functionality. Sufficient positive-sequence
voltage should be available during all fault events. However, during certain
fault events, especially 3-phase bolted faults near the line VT location, the pos-
itive-sequence voltage may be insufficient for correct operation. To ensure ad-
equate positive-sequence voltage exists for all fault conditions, the relay uses
a ring filter, implemented in software, to provide memory voltage as the source
for the positive-sequence voltage. This memory voltage lasts for approximate-
ly 150 cycles, even if all voltage inputs from the line VTs go to zero. A practi-
cal effect of using a memorized voltage is to expand the Mho characteristic by
the magnitude of the source impedance see “Effect of using Memorized Volt-
age on a 3-phase forward fault condition” on page 4-8. This expansion of the
characteristic ensures correct operation for zero voltage faults at the relay lo-
cation, and for forward capacitive faults.
.
Figure 4.5: Effect of using Memorized Voltage on a 3-phase forward fault condition
Id Supervision (A second-
ary)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
Both
3I0 Supervision (A sec-
ondary)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
0.2 to 50.0
(5A) 0.04 to
10.00 (1A)
Both
Line Angle (degrees)
5.0 to 89.0
Setting is made in Line Parameters (Positive Sequence Angle)
Load Impedance (Ohms)
R (Ohms secondary)
-150.0 to 150.0
Both
X (Ohms secondary)
-150.0 to 150.0
Both
Table 4.2: 21N Ground Distance Element Settings
R
X
Li
ne
Z
So
u
rc
e
Z
No Memory
Voltage
Full
Memory
Voltage
Summary of Contents for L-PRO 4000
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