Siemens 7UT51

7
Ground Differential Protection (87N)
7UT51 v3
96 PRIM-2330C
7.6 Harmonic Restraint
Harmonic restraint of the 87N function during
transformer energization can be turned off or on
(Address 1910). It is based on the evaluation of the
second harmonic content of the inrush current. Since
the inrush current is a through-flowing current, as
registered by the restricted ground-fault protection, it is
preset to
OFF
. For exceptional conditions it can be
switched on (Address 1910), and the second
harmonic content which is necessary to block the
protection can be configured (Address 1911).
If the differential current exceeds a certain multiple of
the rated current of the protected object
(Address 1912) no more restraint of the second
harmonic takes place.
7.7 Time Delays
If an 87N pickup occurs, the function will immediately
trip unless a time delay has been set in Address 1925.
If an 87N trip occurs, the function will reset when the
same conditions occur that would cause the function
to dropout. The time before reset (the “dwell time”) can
be extended to ensure that the trip state lasts long
enough for the circuit breaker to operate by specifying
a time delay in Address 1927.
7.8 Events and Actions
Table 7.1 on page 97 describes the events that control
and are generated by the 87N function. They are listed
in the order that they are likely to occur, which is
roughly in numerical order by their event identification
number (shown in the “Event” column). The text in the
“LCD Abbreviation” column is the corresponding text
that will appear when viewing logs on the front panel
LCD display. In the “Oper” column, a letter “C” or “G”
indicates that the “Coming” and/or “Going” events are
logged in the Operational Log, while if in the “Fault”
column they indicate that the events are logged in the
open fault log. A letter in the “In/Out” column indicates
that the event can be controlled by a binary-signal
input (“I”), control an LED and/or signal contact (“S”),
and/or control a trip contact (“T”).
1910 HARMN RSTR
Inrush restraint with second harmonic protection
Option Description
OFF turned off (default)
ON turned on
1911 %2nd HARMN
Amount of second
-
harmonic content in the
ground
-
differential current that will block the 87N
function (specified as a percentage of the fundamental
component of the ground
-
differential current).
Range: 10
–
80%
Default: 15%
1912 I RGF max 2
Upper limit of the second harmonic restraint current
above which restraint does not occur, specified as a
multiple of the rated current of the protected object.
Range: 1.0
–
20.0 I
n
Default: 10.0 I
n
1925 Tdly
-
RGF
Time delay between pickup and trip for 87N ground
differential function (in addition to the inherent
operating time of the relay).
Range: 0.00
–
60.00 s or ∞
Default: 0.00
1927 T
-
RESET
Reset delay after trip signal has disappeared (in
addition to the inherent reset time of the relay).
Range: 0.00
–
60.00 s
Default: 0.10 s