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I.L. 40-385.1B
The application of "close-into-fault" and "stub-bus
protection" are selected by setting the value field of
CIF to CIFT/STUB/BOTH/NO.
3.4.8 Unequal-Pole-Closing Load Pickup Logic
The ground units may pick up on a condition of load
pickup with unequal breaker pole closing. The high
speed ground units (Z1G, FDOG and RDOG and
PLTG) should be supervised under this condition.
This can be achieved (as shown in Figure 3-16) by
inserting a 0/20 ms timer (controlled by the 52b sig-
nal) to supervise the Z1G trip AND-3. It should be
noted that the 20 ms time delay will have no effect on
a normal fault clearing.
3.4.9 Selectable Loss-of-Load Accelerated Trip
Logic (LLT)
The load-loss speedup Zone 2 trip logic senses re-
mote 3-pole clearing on all faults except 3φF to com-
plement or substitute for the action of the pilot
channel, to speed up trip at the slow terminal. Logic
includes AND-24, AND-25, OR-13, 0/32, and 10/0
ms timers (as shown in Figure 3-17). Under normal
system conditions, 3-phase load currents are bal-
anced, the low set overcurrent units (IAL, IBL, ICL
satisfy both AND-24 and OR-13). On remote internal
faults, Z2P or Z2G picks-up and satisfies the third in-
put to AND-25 via OR-6. However, the signal from
AND-24 is negated to AND-25, therefore, AND-25
should have no output until the remote end 3-pole
trips. At this time, the local end current will lose one
or two phases, depending on the type of fault (except
for the 3-phase fault). The AND-24 output signal
changes from "1" to "0" and satisfies AND-25. After
10 ms, this output by-passes the T2 timer, and pro-
vides speedup Zone 2 trip. The (10/0 ms) time delay
is for coordination on external faults with unequal
pole clearing. The 0/32 ms timer is needed for secu-
rity on external faults without load current condition.
Target LLT will turn on after a LLT trip. The LLT func-
tion is selected by setting "YES, FDOG, NO", where
YES = LLT with Z2 supervision; FDOG = LLT with
both Z2 and (FDOG/I
OM
function is not used.
3.4.10 Current or Voltage Change Fault Detector
(∆I, ∆V) and GS
The MDAR relay normally operates in the Back-
ground mode, where it experiences phase current or
3-6
) supervision; the NO = LLT
voltage disturbances. During background mode, the
four input currents (I
, I
A
voltages (V
, V
, V
) are sampled at a rate of 8 per
A
B
C
cycle to test a line fault. When 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 MDAR
design are as follows:
Each phase ∆ I: if [I
1)
And [I
- I
] / I
Kn
(K-1)n
Each phase ∆ V: if [V
2)
and [V
- V
] / V
Kn
(K-1)n
∆I
3)
if [(3I
)
- (3I
)
0:
0
Kn
0
Where n = 1, 2, 3, 4, 5, 6, 7, 8 and
K = number of cycles
For every voltage or current disturbence, the Gener-
al Start (GS) relay will pick up for 3 cycles for starting
external (fault) recorder.
3.4.11 Selectable Ground Directional Unit
(ZSEQ/NSEQ/DUAL)
The ground directional unit (DIRU) contains three
selections (ZSEQ, NSEQ and DUAL), which deter-
mine the operation of the forward directional over-
current ground (FDOG) and reversed directional
(RDOG). If the ZSEQ is selected, both FDOG and
RDOG units will be operated as a zero-sequence
voltage polarizing element. Forward direction is
identified by the angle, if 3I
and 210°. The sensitivity of this element is 3I
and 3V
>1.0 Vac. If NSEQ is selected, both FDOG
0
and RDOG will be operated by negative sequence
quantities. The maximum sensitivity for the forward
directional unit is when I
≥1.0 Vac and 3I
≥ 0.5A.
2
If DUAL is selected, the FDOG and RDOG will be
determined by either zero-sequence voltage polariz-
ing element, as the setting of ZSEQ or current polar-
izing directional element (I
1FT-14/12 and 1FT-14/11 and is from power trans-
former neutral (ct). The maximum torque angle be-
tween 3I
and I
equals zero degrees, i.e., the
0
P
forward direction is identified when 3I
to 90° or lags by 0° to 90°. The sensitivity of this ele-
ment is 3I
>0.5 and I
>0.1 Amps.
0
P
, I
and I
) and the three
B
C
P
- I
] > 1.0 amp.
Kn
(K-1)n
x 100% > 12.5%
(K-1)n
- V
] > 7.0 volts
Kn
(K-1)n
x 100% >12.5%
(K-1)n
] > 0.5 amp.
(K - 1)n
leads 3V
between 30°
0
0,
> 0.5A
0
leads V
by 98°, with V
2
2
), which is connected to
P
leads I
by 0°
0
P
(5/92)
2
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