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2.4.8
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 (Zone1G, FDOG and PLTG) should be supervised
under this condition. This can be achieved (as shown in Figure 2-16) by inserting a 0/
20 ms timer (controlled by the 52b signal) to supervise the Zone1G trip AND-3. It
should be noted that the 20 ms time delay will have no effect on a normal fault clear-
ing.
2.4.9
Loss-of-Load Accelerated Trip Logic
NOTE:
The load-loss speedup Zone2 trip logic senses remote 3-pole clearing on all faults ex-
cept 3 phase to complement 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 2-17). Under normal system conditions, 3-phase load
currents are balanced, the low set overcurrent units (IAL, IBL, ICL satisfy both AND-
24 and OR-13). On remote internal faults, Zone2 Phase (Z2P) or Zone2 Ground(Z2G)
picks-up and satisfies the third input 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 re-
mote 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 provides speedup Zone2 trip. The (10/0 ms) time delay is for coordina-
tion on external faults with unequal pole clearing. The 0/32 ms timer is needed for
security on external faults without load current condition. Target LL Trip (LLT) will
turn on after an LL Trip. The LL Trip (LLT) function is selected by setting LL Trip "YES,
FDOG, NO", where YES = LL Trip with Z2 supervision; FDOG = LL Trip with both Z2
and (FDOG/I
2.4.10 Current or Voltage Change Fault Detector (∆I, ∆V)
The REL 301/302 relay normally operates in the Background mode, where it experi-
ences phase current or voltage disturbances. During background mode, the four input
currents (I A , I B , I C and I
of 8 p er c y cl e t o t e st a l in e fa ult . W h en a ph as e d is tur ban c e ( ∆ I o r ∆V )
i s d et e ct e d, t he r el ay en te rs a f ault mo de fo r sev eral cycle s to pe rf o rm
pha s e a n d g r ou n d unit distance computation for each zone. The criteria for deter-
mining a disturbance in the REL 301/302 design are as follows:
Ea c h ph a se ∆ I : i f [ I
1)
A nd [ I
Ea ch ph a s e ∆V : i f [ V
2)
a n d [ V
(10/94)
The LLT function doesn't need to be set for normal operation of the re-
lay. While it can provide faster tripping for end-Zone faults, it may not
be used in all situations. It should be applied with caution based on
thorough knowledge of the system characteristics where the relay is ap-
plied. It is definitely not applicable where maximum tapped load may
exceed minimum through-load in the protected line.
) supervision; the NO = LL Trip function is not used.
OM
) and the three voltages (V A , V B , V C ) are sampled at a rate
p
Kn
- I
] / I
Kn
(K -1 )n
(K -1 )n
Kn
- V
] / V
Kn
( K-1 )n
- I
] > 1 .0 a mp.
(K - 1 )n
x 1 00% > 12 .5 %
- V
] > 7. 0 vo lt s
(K - 1 )n
x 10 0% > 12. 5%
(K - 1 )n
I.L. 40-386.3
2-9
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