Siemens 6MD86 - Page 813

Measured Value
With the Measured value parameter, you define whether the stage analyzes the phase-to-phase voltages
V
AB
, V
BC
, and V
CA
, or the phase-to-ground voltages V
A
, V
B
, and V
C
.
If the measured value is set to phase-to-phase, the function reports those measuring elements that have
picked up.
Pickup Mode
With the Pickup mode parameter, you define whether the stage picks up when there is a lower threshold-
value violation in one measuring element (1 out of 3) or when there is a lower threshold-value violation in
all 3 measuring elements (3 out of 3).
Pickup and Operate Curve
When the input voltage falls below the threshold value by a settable value Pickup factor, the stage picks
up and the inverse-time characteristic curve is processed. The operate delay starts. The operate delay is the
sum of inverse-time delay and additional time delay.
T
op
=T
Inv
+ T
add
Where:
T
op
Operate delay
T
Inv
Inverse-time delay
T
add
Additional time delay (Parameter Additional time delay)
After pickup the time value T
Inv
is calculated for every input voltage less than the dropout value. An integrator
accumulates the value 1/T
Inv
. Once the accumulated integral reaches the fixed value 1, the inverse-time delay
expires. The stage operates after the additional time delay.
The inverse-time delay is calculated with the following formula:
[fo_UVP3ph_inverse, 2, en_US]
Where
T
Inv
Inverse-time delay
T
p
Time multiplier (Parameter Time dial)
V Measured undervoltage
V
Thresh
Threshold value (Parameter Threshold)
k Curve constant k (Parameter Charact. constant k)
α Curve constant α (Parameter Charact. constant α)
c Curve constant c (Parameter Charact. constant c)
Protection and Automation Functions
7.16 Undervoltage Protection with 3-Phase Voltage
SIPROTEC 5, High-Voltage Bay Controller, Manual 813
C53000-G5040-C015-9, Edition 11.2017