The inverse-time characteristic is shown in the following figure:
[dwUVP3ph_inverse, 1, en_US]
Figure 7-153
Inverse-Time Characteristics for Undervoltage Protection
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 stage picks up briefly. Use the Pickup delay
parameter to prevent the stage from briefly picking up in this way when the circuit breaker opens. This is
achieved by delaying pickup by approximately 40 ms.
Dropout Behavior
When the voltage exceeds the dropout value (1.05 x pickup factor x threshold value), the pickup signal is
going and the dropout is started. You can define the dropout behavior via parameter Reset time. Instanta-
neous reset takes place by setting Reset time to 0 s. A delayed reset takes place by setting the desired delay
time.
During the Reset time (> 0 s), the elapsed operate delay is frozen. If the stage picks up again within this
period, the stage operates when the rest of operate delay expires.
Current-Flow Criterion
The undervoltage protection stages work optionally with a current-flow criterion. The Current-flow
criterion works across all tripping stages.
When the Current-flow criterion parameter is activated, the undervoltage-protection stages only pick
up if a settable minimum current (Threshold I>) is exceeded. A current below the minimum current blocks
the stages.
The current-flow criterion can also be set to fulfilled with the binary input signal >Current flow-crite-
rion. The function reports when the current-flow criterion is fulfilled.
Figure 7-150 illustrates the influence of the current-flow criterion.
Protection and Automation Functions
7.16 Undervoltage Protection with 3-Phase Voltage
814 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
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