Low Pass Filtering - ABB REG650 Technical Manual

Section 8
Current protection
8.7.4.1
238
Set value: Mode
L1
L2
L3
The active and reactive power is available from the function and can be used for
monitoring and fault recording.
The component of the complex power S = P + jQ in the direction Angle1(2) is
calculated. If this angle is 0° the active power component P is calculated. If this angle
is 90° the reactive power component Q is calculated.
The calculated power component is compared to the power pick up setting
Power1(2). For directional underpower protection, a start signal START1(2) is
activated if the calculated power component is smaller than the pick up value. For
directional overpower protection, a start signal START1(2) is activated if the
calculated power component is larger than the pick up value. After a set time delay
TripDelay1(2) a trip TRIP1(2) signal is activated if the start signal is still active. At
activation of any of the two stages a common signal START will be activated. At trip
from any of the two stages also a common signal TRIP will be activated.
To avoid instability there is a hysteresis in the power function. The absolute hysteresis
for stage 1(2) is 0.5 p.u. for Power1(2) ≥ 1.0 p.u., else the hysteresis is 0.5 Power1(2).
If the measured power drops under the (Power1(2) - hysteresis) value, the over-power
function will reset after 0.06 seconds. If the measured power comes over the
(Power1(2) + hysteresis) value, the under-power function will reset after 0.06
seconds. The reset means that the start signal will drop out and that the timer of the
stage will reset.

Low pass filtering

In order to minimize the influence of the noise signal on the measurement it is possible
to introduce the recursive, low pass filtering of the measured values for S (P, Q). This
will make slower measurement response to the step changes in the measured quantity.
Filtering is performed in accordance with the following recursive formula:
1MRK 502 048-UEN A
Formula used for complex power calculation
*
= × ×
S 3 U I
L 1 L 1
EQUATION1703 V1 EN
*
= × ×
S 3 U I
L 2 L 2
EQUATION1704 V1 EN
*
= × ×
S 3 U I
L 3 L 3
EQUATION1705 V1 EN
(Equation 70)
(Equation 71)
(Equation 72)
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