• measured and pre-processed frequency magnitudes.
The function outputs the START, TRIP and BLOCKED signals which can be used for direct I/O
controlling and user logic programming. The function generates general time-stamped ON/OFF events
to the common event buffer from each of the three (3) output signals. In the instant operating mode the
function outputs START and TRIP events simultaneously with an equivalent time stamp. The time stamp
resolution is 1 ms. The function also provides a resettable cumulative counter for the START, TRIP and
BLOCKED events.
The following figure presents a simplified function block diagram of the df/dt>/< function.
Figure. 5.3.16 - 149. Simplified function block diagram of the df/dt>/< function.
Measured input
The rate-of-change of frequency protection function compares the measured df/dt>/< ratio to the pick-
up setting (given in Hz/s). The source of the measured frequency depends on the factory-defined
tracking reference which can be checked from the
Frequency tab of the Measurement menu.
Table. 5.3.16 - 145. Measurement inputs of the df/dt>/< function.
Signals
Description
Time base
VT1 U1, U2, U3
L-N voltages of the first voltage transformer
5ms
VT2 U1, U2, U3
L-N voltages of the second voltage transformer
5ms
Pick-up and time delay
The df/dt>/< (1) pick-up, df/dt>/< (2) pick-up, etc. setting parameters control the pick-up of each stage
of the df/dt>/< function. They define the maximum or minimum allowed change of frequency before
action from the function. The function constantly calculates the ratio between the pick-up setting and
the measured df/dt>/<. The reset ratio of +/- 100 mHz/s is built into the function and is always
relative to the pick-up value. The f>/< limit value is used to block the funtion from operating near the
nominal frequency.
Table. 5.3.16 - 146. Pick-up settings.
Name
Description
Range
Step
Default
Max allowed df/
dt rate
If df/dt rate exceeds this setting, the function is blocked.
0.10...50.00Hz/s
0.10Hz/
s
20Hz/s
A
AQ
Q-F215
-F215
Instruction manual
Version: 2.04
214
