Siemens 7UT51

7UT51 v3
Ground Differential Protection (87N)
7
PRIM-2330C 97
Table 7.1
Events Related to Ground Differential Protection (87N)
Ground Differential Protection (87N) Occurrence LCD Abbreviation Event Oper Fault In/Out
Change in Operational Status
When the operational status of the 87N function changes, a
going
-
event for the old status occurs followed by a coming
-
event
for the new status. The normal operational status is set in
Address 1901.
RGFOFF
RGF ACTIVE
RGF BLOCK
5811
5813
5812
C
C
C
G
G
G
S
S
S
A binary input can temporarily change the operational status of the
function (see Section 13.2 on page 126). Any outputs marshalled
to these events will remain actuated for as long as the binary input
remains actuated.
>RGF BLOCK
>RGF BlkTrip
5803
5805
I
I
S
S
Pickup and Dropout
The 87N function will pickup (event 5817C) if the measured ground
current I
g
reaches or exceeds 75% of the pickup threshold
(Address 1903). If no fault log is already open, a new one will open.
The function will dropout (event 5817G) if I
g
drops below 70% of
the pickup threshold.
RGF GenFlt 5817 CG S T
Time Delay Before Trip
If a pickup occurs, the time
-
to
-
trip delay starts. If the delay
(Address 1925) is zero, this event does not occur.
RGF T Start 5816 C S T
Trip and Reset
The 87N function will trip if and when all the following are true:
• an 87N pickup has occurred, and it has not yet dropped out or
already caused a trip,
• the 87N restraining current (I
rest
) is
not
zero (see Section 7.5
on page 95),
• the 87N time
-
to
-
trip delay (Address 1925) has expired,
• the 87N second
-
harmonic restraint is not presently restraining
a trip (see Section 7.6 on page 96).
With the default marshalling, an 87N trip will light LED 7 and
activate signal contact 8; and (as for a trip of any function) light and
latch LED 1, activate signal contact 1, and activate all the trip
contacts.
The function will reset (event 5817G, the same as for dropout)
when the same conditions that would cause a dropout occur, and
the reset time delay (Address 1927) expires.
RGF Gen. Trip 5821 C S T
If an 87N trip occurs, the magnitude of the ground current (5826)
and phase
-
angle difference (5827) values are logged.
RGF D=
value
RGF S= value
5826
5827
C
C
Configuration Errors and Data
The 87N function is set to monitor Side 3 (Address 7819), but the
protected object type (Address 7801) does not have three sides.
RGF Err S3 5828 C S
Both ground CT current
-
inputs (I
Ga
and I
Gb
) are assigned to the
same side of the protected object (addresses 7806 and 7807).
RGF Err2CTsta 5829 C S
Neither ground CT current
-
input (I
Ga
or I
Gb
) has been assigned to
a side of the protected object (addresses 7806 and 7807).
RGF Err 0CTsta 5830 C S
The 87N function is set to monitor Side 1 or 2 (Address 7819)
when the protected object is generator/motor or a bus
(Address 7801). In these applications, the 87N function can only
protect a virtual object.
RGF ErrVir ob 5831 C S
Current
-
matching factor for phase
-
current CTs. RGF k CT= factor 5832 C
Current
-
matching factor for ground
-
current CT RGF ksCT= factor 5833 C
The 87N function is set to exist (Address 7819), but other settings
(i.e.: the system frequency) make the 87N function unavailable.
RGF no exist 5834 C S