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LLT is not recommended for three-terminal line due to difficulty in determining proper settings
(IL) and complicated infeed from the third terminal.
3.4.10 Current or Voltage Change Fault Detector ( ∆ I, ∆ V)
The REL300 relay normally operates in the Background mode, where it experiences phase cur-
rent or voltage disturbances. During background mode, the four input currents (I
and the three voltages (V
a phase disturbance (∆I or ∆V ) is detected, the relay enters a fault mode for several cycles or
longer, to perform phase and ground unit distance computation for each goal. The criteria for
determining a disturbance in the REL300 design are as follows:
1) Each phase ∆I :if [I
And [I
2) Each phase ∆V :if [V
and [V
Where n = 0,1, 2, 3, 4, 5, 6, 7 and
K = number of cycles
3.4.11 Selectable Ground Directional Unit (ZSEQ/NSEQ/DUAL)
The ground directional unit (DIRU) contains three selections (ZSEQ, NSEQ and DUAL), which
determine the operation of the forward directional overcurrent ground (FDOG) and reversed di-
rectional (RDOG). If the ZSEQ is selected, both FDOG and RDOG units will be operated as a
zero-sequence voltage polarizing directional element. Forward direction is identified by the
angle, if 3I
3V
>1.0 Vac. If NSEQ is selected, both FDOG and RDOG will be operated by negative se-
0
quence quantities. The maximum sensitivity for the forward directional unit is when I
by 98°, with V
If DUAL is selected, the FDOG and RDOG will be determined by either zero-sequence voltage
polarizing element, as the setting of ZSEQ or current polarizing directional element (I
is connected to 1FT-14, switch #12 and switch #11 is from power transformer neutral (ct). The
maximum torque angle between 3I
identified when 3I
I
>0.5 and I
0
3.4.12 Instantaneous Forward Directional Overcurrent Unit (FDOG) and Phase Unit (FDOP)
The instantaneous forward directional overcurrent ground function (FDOG) is a direc-
tional unit depending on the setting of DIRU as described in the preceding segment
(3.4.11). FDOG is supervised by the IOM setting and controls Zone 1, Zone 2 and Zone 3
ground units for security purposes and also for pilot high resistance ground fault trip
(FDOG/I
The phase directional unit (FDOP) is based on the angular relationship of a single-phase cur-
rent and the corresponding pre-fault phase-to-phase voltage phasors. The forward direction is
identified if the current phasor leads the voltage phasor. The pair of current and voltage pha-
, V
, V
A
B
- I
Kn
(K-1)n
- I
] / I
x 100% > 12.5%
Kn
(K-1)n
(K-1)n
- V
Kn
(K-1)n
- V
] / V
x 100% >12.5%
Kn
(K-1)n
(K-1)n
leads 3V
between 75° and 255°. The sensitivity of this element is 3I
0
0,
≥1.0 Vac and 3I
2
leads I
by 0° to 90° or lags by 0° to 90°. The sensitivity of this element is
0
P
>0.5 Amps.
P
).
OM
) are sampled at a rate of 8 per cycle to test a line fault. When
C
] > 1.0 amp.
] > 7.0 volts
≥ 0.5A.
2
and I
equals zero degrees, i.e., the forward direction is
0
P
I.L. 40-385.7
, I
, I
and I
)
A
B
C
P
> 0.5A and
0
leads V
2
2
), which
P
3-11
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