Low Pass Filtering - ABB Relion 670 Series Technical Reference Manual

Section 6
Current protection
6.6.2.1
188
Mode
Set value:
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 settable hysteresis in the power function. The
absolute hysteresis of the stage1(2) is Hysteresis1(2) = abs (Power1(2) + drop-
power1(2)). For generator low forward power protection the power setting is very
low, normally down to 0.02 p.u. of rated generator power. The hysteresis should
therefore be set to a smaller value. The drop-power value of stage1 can be
calculated with the Power1(2), Hysteresis1(2): drop-power1(2) = Power1(2) +
Hysteresis1(2)
For small power1 values the hysteresis1 may not be too big, because the drop-
power1(2) would be too small. In such cases, the hysteresis1 greater than (0.5 ·
Power1(2)) is corrected to the minimal value.
If the measured power drops under the drop-power1(2) value, the function will
reset after a set time DropDelay1(2). 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
1MRK 505 208-UEN B
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
Technical reference manual
(Equation 24)
(Equation 25)
(Equation 26)