Application And Setting Notes - Siemens 7SJ82 Manual

Protection and Automation Functions
6.30 Undervoltage Protection with Positive-Sequence Voltage
Pickup Delay
The Pickup delay parameter is only available and of relevance if you are using the current-flow criterion of
the function (parameter Current-flow criterion = on).
If the circuit breaker opens when the current-flow criterion is being used, the undervoltage detection and
current-flow dropout functions conflict with one another. Depending on the threshold value settings for
undervoltage detection and current-flow criterion, it is possible that the undervoltage is detected before the
current-flow criterion has dropped out. In this case, the tripping stage picks up briefly. Use the Pickup
delay parameter to prevent the tripping stage from briefly picking up in this way when the circuit breaker
opens. This is achieved by delaying pickup by approximately 40 ms.
Current-Flow Criterion
The undervoltage-protection stages work optionally with a current-flow criterion. The current-flow criterion
works across all stages.
When the Current-flow criterion parameter is switched on, the undervoltage protection stages only
pick up if a settable minimum current (Threshold I>) is exceeded in at least one phase. A current below the
minimum current blocks the tripping stages.
The current-flow criterion can also be set to fulfilled via the binary input signal >Current flow-crite-
rion. The function reports when the current-flow criterion is fulfilled.
Figure 6-206 illustrates the influence of the current-flow criterion.
NOTE
i
i
If the Current-flow criterion parameter is switched off, the device picks up immediately if a missing
measuring voltage is detected while the undervoltage protection is active. The parameter setting can be
changed even when the device has picked up.
Blocking the Stage
In the event of blocking, the picked up stage will be reset. The following blocking options are available for the
stage:
•
Via the binary input signal
•
From inside on pickup of the Measuring-voltage failure detection function (see chapter
view of Functions). The Blk. by meas.-volt. failure parameter can be set to either block or not
block the tripping stage when the measuring-voltage failure detection picks up.
•
From an external source via the binary input signal
b., which links in the tripping of the voltage-transformer circuit breaker. The Blk. by meas.-volt.
failure parameter can be set so that measuring-voltage failure detection blocks the stage or does not
block it.
6.30.4

Application and Setting Notes

Parameter: Threshold
•
Default setting (_:481:3) Threshold = 46 V
Specify the Threshold (pickup threshold) for the specific application. For the default setting, the lower limit
of the voltage range to be monitored is assumed to be 80 % of the rated voltage of the protected object.
Parameter: Pickup delay
•
Default setting (_:481:101) Pickup delay = no
The Pickup delay parameter is only available if you are using the current-flow criterion of the function
(parameter Current-flow criterion = on). If the current-flow criterion is deactivated, no pickup delay is
required.
752
>Block stage from an external or internal source
>Open of the function block Volt.-transf. c.
9.3.2.1 Over-
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017