Functionality
46 USER MANUAL FPC 200 - 3/2017
Rate of change of frequency protection - ANSI code 81R
Rate of change of frequency ROCOF protection is a function that indicated severity of the frequency transient. The result
can be used as preventive load shedding. It comprises of time-delayed characteristic.
2.4.3.1 Functionality
ROCOF protection is a function, used as time delayed
protection. It picks up when measured rate of change
frequency
exceeds the selected threshold. The
frequency threshold can be set on negative, positive or
both rates of change. The function operation can be
enabled or disabled through corresponding menu.
The selection of pickup value, pickup delay as well as
drop-out ratio and drop-out delay helps the user to fine
tune the protection according to the project
specifications.
81R ROCOF
Enabled:
1A 1B
No
Pickup val.:
0,20Hz/s
Trip delay:
0,02s
CONTROL SETTINGS
Pickup delay: 0ms
A
Figure 2.32: ROCOF protection setting as seen on HMI.
2.4.3.2 Measurement
Rate of change of frequency is determined based on
frequency change over specific amount of time. The
value is averaged to ensure proper function.
2.4.3.3 Delays
Function includes following delays explained in Chapter
2.1:
Pickup delay
Trip delay
Drop-out delay
2.4.3.4 Block settings
Pickup of any instance separately of protection can be
individually blocked by any user defined signal [2.6.5]. In
addition ROCOF function is blocked if all phase voltages
drops below 0,5 U
n
.
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