Siemens 7UT51 Instruction Manual page 97

7UT51 v3
Ground Differential Protection (87N) Occurrence
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
for the new status. The normal operational status is set in
Address 1901.
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.
Pickup and Dropout
The 87N function will pickup (event 5817C) if the measured ground
current I reaches or exceeds 75% of the pickup threshold
g
(Address 1903). If no fault log is already open, a new one will open.
The function will dropout (event 5817G) if I
the pickup threshold.
Time Delay Before Trip
If a pickup occurs, the time
(Address 1925) is zero, this event does not occur.
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
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.
If an 87N trip occurs, the magnitude of the ground current (5826)
-
and phase angle difference (5827) values are logged.
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.
Both ground CT current
same side of the protected object (addresses 7806 and 7807).
Neither ground CT current
a side of the protected object (addresses 7806 and 7807).
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.
-
Current matching factor for phase
-
Current matching factor for ground
The 87N function is set to exist (Address 7819), but other settings
(i.e.: the system frequency) make the 87N function unavailable.
Table 7.1 Events Related to Ground Differential Protection (87N)
PRIM-2330C
drops below 70% of
g
- -
to trip delay starts. If the delay
) is not zero (see Section 7.5
rest
-
inputs (I and I ) are assigned to the
Ga Gb
-
input (I or I ) has been assigned to
Ga Gb
-
current CTs.
-
current CT
Ground Differential Protection (87N)
LCD Abbreviation
RGFOFF
- RGF ACTIVE
event
RGF BLOCK
>RGF BLOCK
>RGF BlkTrip
RGF GenFlt
RGF T Start
RGF Gen. Trip
RGF D= value
RGF S= value
RGF Err S3
RGF Err2CTsta
RGF Err 0CTsta
RGF ErrVir ob
RGF k CT= factor
RGF ksCT= factor
RGF no exist
Event Oper Fault In/Out
5811 C G
5813
C G
5812
C G
5803
5805
5817 C G
5816 C
5821 C
5826 C
5827
C
5828 C
5829 C
5830 C
5831 C
5832 C
5833 C
5834 C
7
S
S
S
I S
I S
S T
S T
S T
S
S
S
S
S
97