Applying The Function Parameter Settings - Siemens siprotec 7SA6 User Manual

6.7.2

Applying the Function Parameter Settings

7SA6 Manual
C53000-G1176-C133-1
To avoid a faulty pick up of the weak infeed function following tripping of the line and
reset of the fault detection, the function cannot pick up any more once a fault detection
in the affected phase was present (RS flip-flop in Figure 6-81).
In the case of the earth fault protection, the release signal is routed via the phase
segregated logic modules. Single-phase tripping is therefore also possible if, besides
the distance protection, the earth fault protection also issues a release condition.
It is a prerequisite for the operation of the weak infeed function that it was enabled
during the configuration of the device (Section 5.1) under address  :HDN
,QIHHG = (QDEOHG.
With the parameter )&7 :HDN ,QIHHG (address ) it is determined whether the
device shall trip during a weak infeed condition or not. With the setting (&+2 DQG
75,3 both the echo function and the weak infeed tripping function are activated. With
the setting (&+2 RQO\ the echo function for provision of the release signal at the
infeeding line end is activated. There is however no tripping at the line end with
missing or weak infeed condition. As the weak-infeed measures are dependent on the
signal reception from the opposite line end, they only make sense if the protection is
coordinated with teleprotection (refer to Section 6.4 and/or 6.6).
The receive signal is a functional component of the trip condition. Accordingly, the
weak infeed tripping function must not be used with the blocking schemes. It is only
permissible with the permissive schemes and the comparison schemes with release
signals. In all other cases it must be switched off in address  2)). In such cases
it is better to disable this function from the onset by selecting the setting in address
 to 'LVDEOHG, during the device configuration. The associated parameters are
then not accessible.
The undervoltage setting value 81'(592/7$*( (address ) must in any event be
set below the minimum expected operational phase–earth voltage. The lower limit for
this setting is given by the maximum expected voltage drop at the relay location on the
weak-infeed side during a short-circuit on the protected feeder for which the distance
protection may no longer pick up.
The remaining settings apply to the echo function and are described in the
corresponding sections (6.4.2 and/or 6.6.2).
Functions
6-137