ABB RELION 670 Series Technical Manual page 554

Section 8
Current protection
activation of any of the two stages a common signal PICKUP 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
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
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 ·
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 pickup signal will drop out and that the timer of the
stage will reset.
8.11.7.1 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:
S TD S
=
EQUATION1959-ANSI V1 EN-US
Where
S
S
old
S
Calculated
TD
Default value for parameter
given out without any filtering (that is without any additional delay). When
bigger than 0, the filtering is enabled. A typical value for
functions.
8.11.7.2 Calibration of analog inputs
Measured currents and voltages used in the Power function can be calibrated to get class 0.5
measuring accuracy. This is achieved by amplitude and angle compensation at 5, 30 and 100% of
rated current and voltage. The compensation below 5% and above 100% is constant and linear in
between, see example in figure 291.
548
Hysteresis1(2) = abs (Power1(2) + drop-power1(2)). For generator low forward
the Power1(2), Hysteresis1(2) : drop-power1(2) = Power1(2) + Hysteresis1(2)
1 TD S
( )
⋅ + − ⋅
Old Calculated
is a new measured value to be used for the protection function
is the measured value given from the function in previous execution cycle
is the new calculated value in the present execution cycle
is settable parameter by the end user which influence the filter properties
TD is 0.00 . With this value the new calculated value is immediately
Power1(2) ) is corrected to the minimal
TD is set to value
TD=0.92 in case of slow operating
1MRK 502 066-UUS B
SEMOD172136-39 v3
(Equation 151)
SEMOD172136-57 v3
Technical manual