CYG PRS-7367 - 81 URS Settings; Under Frequency Restore Protection 81 URE; 81 URE Overview

Protection Functions
108 PRS-7367
shedding, generator boosting, set point change in sub-transmission DC systems, gas turbine
startup and so on.
The 81URS function is very sensitive and accurate and can also be used to alert the operators that
the frequency deviates slightly from the set-point and that manual actions can be sufficient enough
to ensure the stability of the system. The under frequency signal is also used for over-excitation
detection. If the generator is still energized, the system experiences over-excitation due to the low
frequency.
3.19.4 81URS Settings
In the following table, i is the protection stage number, it can be set according to the requirements.
Table 3.19-3 81URS settings
No.
Name
Values(Range)
Unit
Step
Default
Description
1
81URSi_Fr_Str
30.00-50.00 at
Fn=50;
40.00-60.00 at
Fn=60
Hz
0.01
48.80
The Stage i Frequency setting/start
value
2
81URSi_Op_T
0.04 - 200.00
s
0.01
0.04
The Stage i Operate time delay
3
81URSi_Vol_Blk
18.00 – 100.00
V
0.01
30.00
The Stage i Block signal of the
function
4
81URSi_Ena
0-1
-
-
1
The Stage i Operation disable /
enable
5
81URSi_Alm_Ena
0-1
-
-
1
The Stage i Alarm Enable/Disable
6
81URSi_Dfdt_Blk_E
na
0-1
-
-
1
The Stage i slip-frequency criterion
disable/enable
7
81URSi_Dfdt_Blk
0-10.00
Hz/s
0.01
10.00
The Stage i slip-frequency setting
value
3.20 Under frequency restore protection 81URE
3.20.1 81URE Overview
The feeder relay provides a one-stage under frequency restore protection with independent
definite time delay characteristics.
A decrease in system frequency occurs when the system experiences an increase in the real
power demand, or when a malfunction occurs within a generator governor or automatic generation
control system. The under frequency protection will operate and disconnect load from the power
system. After the frequency recovers to normal level, the disconnected load will be restored by
using the under frequency restore protection.
The calculation of the frequency is based on the voltage sampled values.