Download 3 - Schneider Electric

Rate of change of frequency
ANSI code 81R
Protection functions
Operation
Protection function based on the calculation
of the frequency variation, used to rapidly
disconnect a source supplying a network or
to control load shedding.
The rate of change of frequency protection function is complementary to the under and
overfrequency protection functions in detecting network configurations that require
load shedding or disconnection.
The function is activated when the "rate of change of frequency" df/dt of the positive
sequence voltage is higher than a set point. It includes a definite (DT) time delay.
The protection function operates if:
b the positive sequence voltage is greater than 50 % of the rated phase-to-neutral
voltage
b the network frequency is between 42.2 Hz and 56.2 Hz for 50 Hz networks and
between 51.3 Hz and 65 Hz for 60 Hz networks.
Block diagram
de51554
3
Characteristics
Settings
dfs/dt set point
Setting range
Accuracy (1)
Resolution
Drop out/pick up ratio
Temporisation
Setting range
Accuracy (1)
Resolution
0.1 to 10 Hz/s
±5 % or ±0,1 Hz
0.01 Hz
93 %
0.15 to 300 s
±2 % or -10 at +25 ms
10 ms or 1 digit
Characteristic times (1)
Operation time
Overshoot time
Reset time
Pick-up < 150 ms (typically 130 ms)
< 100 ms
< 100 ms
Inputs
Designation
Protection reset
Protection inhibition
Syntax
Equations Logipam
P81R_x_101 b
b
P81R_x_113 b
b
Outputs
Designation
Syntax
Equations
Instantaneous output (pick-up)
P81R_x_1
b
Tripping output
P81R_x_3
b
Protection inhibited
P81R_x_16 b
Invalid voltage
P81R_x_42 b
Invalid frequency
P81R_x_43 b
Positive df/dt
P81R_x_44 b
Negative df/dt
P81R_x_45 b
x: unit number.
(1) Under reference conditions (IEC 60255-6) and df/dt < 3 Hz/s.
SEPED303001EN - 01/2013
Logipam
b
b
b
b
b
b
b
Matrix
b
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