Siemens 7SJ82, Manual

Page: 546 / 1638

T
ext.
Defined time for extending the
Pickup
signal
Number of Pickups
The stage counts the number of
Pickup
signals during the intermittent ground fault. With the operate of the
stage this number is logged via the information
No. of pickups
.
Accumulation of the Intermittent Ground-Fault Current and Issuing the Operate Signal
An intermittent ground fault can result in thermal stress on the protected equipment. The magnitude and the
duration of the ground-fault current are decisive for the thermal stress. In order to calculate the thermal stress,
the stage sums up the duration of the stabilized pickups with an integrator. If the integration value reaches
the predefined
Sum of extended PU times
, the limit of the thermal load is reached. The stage issues the
signal
Sum limit reached
and operates when the signal
Pickup
is active.
Reset Timer for the Definition of the Interval between Independent Ground Faults
If there is a large interval between independent ground faults or if ground fault extinguishes and does not
restrike again within a larger time, the stressed equipment can cool down. In this case, an operation is not
necessary. The interval between ground faults is monitored with the reset timer. If a ground fault occurs, the
Timer T-reset with its setting
Reset time
is launched simultaneously with Integrator T-sum. Unlike the
integrator, each new ground fault restarts the reset timer with its initial value. If Timer T-reset expires, that is,
no new ground fault was detected during that period, all memories and the stage logics are reset. Timer T-
reset thus determines the time during which the next ground fault must occur to be processed yet as intermit-
tent ground fault in connection with the previous fault. A ground fault that occurs later is considered as a new
fault event.
Reset Conditions
Under one of the following 2 conditions, Timer T-reset is reset.
•
The Intermittent ground-fault protection stage operates.
•
The general operate indication is going.
Under one of the following conditions, Integrator T-sum and Counter are reset and the whole stage is reset
and returns to its idle state.
•
Timer T-reset expires without an operate signal of this stage or another function was issued.
•
The operate signal of the intermittent ground-fault protection stage is going.
•
The general operate indication is going without the operate signal of the intermittent ground-fault
protection stage issued.
Fault Log and Fault Recording
You can select between the ground-fault log without fault recording or the normal fault log with fault
recording. If you set the parameter
Operate & flt.rec. blocked
to
yes
, the operate of the stage and
fault recording are blocked and the information automatically appears in the ground-fault log. Otherwise, the
operate and fault recording are not blocked and the information appears in the normal fault log.
Start & Stop of Fault Recording, Fault Logging, and General Pickup
The
Stabilized pickup
signal initiates the fault recording, fault logging, and the general pickup of the
function group. The fault recording starts according to the pre-trigger time before the
Stabilized pickup
signal rises.
With the reset condition of this stage, the fault recording, fault logging, and the general pickup of the function
group are terminated.
Influence on Other Functions to Avoid a Burst of Signals
Intermittent ground faults may cause other functions, based on overcurrent measurement, to pick up, which
may result in a burst of signals. In order to avoid an overflow of the fault log, a special mechanism is applied to
Protection and Automation Functions
6.13 Non-Directional Intermittent Ground-Fault Protection
546 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017