3.7
Date Code 20170601
Instruction Manual
SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Differential Element
Figure 3.6
Differential Element Harmonic Blocking Logic
If IHBL is set to Y (Yes), the logic shown in
in the bottom drawing,
IHBL = Y, is enabled. Here, the logic pairs 87R1 with negated 87BL1, 87R2
with negated 87BL2, and 87R3 with negated 87BL3 at separate AND gates. In
this logic, blocking in a given element will only disable tripping of that
element. In general, this mode of operation might only be used where three
single-phase transformers are used to make up a three-phase bank, and
independent-pole breaker operation is possible, in the harmonic blocking
mode. When harmonic restraint is selected, the relay operates only in the
individual blocking mode.
Relay Word bits 87R and 87U are high-speed elements that must trip all
breakers. Our example assigns 87R and 87U to trip variable setting TR4. If
either bit asserts, this variable asserts bit TRIP4, which drives contact
OUT104
.
OUT104
connects to an 86 lockout device, which trips all breakers via multiple
sets of contacts.
Harmonic Blocking
(SEL-387-0) and
(all but SEL-387-0) show how the
87BL1 blocking element will pick up if the second-, fourth-, or fifth-harmonic
operating current, as a percentage of fundamental operating current, is above
the PCT2, PCT4, or PCT5 setting threshold, respectively. The blocking
element will also pick up if the ratio of positive and negative dc exceeds a
threshold as shown in
. The blocking prevents improper tripping
during transformer inrush or allowable overexcitation conditions.
Elements 4HB1, 4HB2, and 4HB3 are combined to form element 4HBL as
shown at the bottom of
. 4HBL is available as a Relay Word bit but
elements 4HB1, 4HB2, and 4HB3 are not.
An additional alarm function for fifth harmonic, to warn of overexcitation,
employs a separate threshold (TH5P) and an adjustable timer (TH5D). This
threshold and timer may be useful for transformer applications in or near
generating stations.
87R1
87R2
87R3
87BL1
87BL2
87BL3
87R
87BL
87R1
87BL1
87R2
87BL2
87R3
87BL3
87R
87BL
(A) IHBL = N
Common Harmonic Blocking
(B) IHBL = Y
Independent Harmonic Blocking
Содержание SEL-387-0
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