Areva MiCOM P921 - Page 128

P92x/EN FT/E11 Technical Guide
User Guide
Page 50/110 MiCOM P921-P922-P923
10.7 Rate of change of frequency (MiCOM P923 only)
The calculation of the rate of change of frequency is an average measurement of the
instantaneous values over a programmable number of cycles (1 to 200) ; refer to the
"CONFIGURATION" menu. The instantaneous values of rate of change of frequency
are measured every cycle. The rate of change of frequency elements are very
important to detect any active power loss under severe disturbances : they can be
used for load shedding schemes. These elements offer the possibility to detect the
tendency of the variation of frequency, and thus re establish the correct
load/generation without waiting for big frequency reduction. These elements could be
combined to the frequency elements using the AND logic equations to provide a very
usefull mechanism allowing a more secure trip decision to be achieved during
transient system disturbances.
This function will be inhibited if the voltage level for each phase is below the settable
undervoltage blocking value (see menu "CONFIGURATION", sub-menu "FREQ and
df/dt CONFIG").
The information "freq out of range" will be generated :
· in the above mentioned application
· if the frequency is out of range : f
measured
> (fn+20Hz) or f
measured
< (fn–20Hz)
To gain access to this menu the default display,press 2 once, 6 4 times, 2 once and
4 once.
10.7.1 HMI description
[81R] FREQ CHANGE
OF RATE
Heading of the “Rate of change of Frequency” sub-
menu
[81R] df/dt1 =
NO
Description : configuration of the 1
er
stage
Range : YES/NO
[81R] df/dt1 =
1.0 Hzs
Description : setting of the 1
er
stage
Range : [ – 10Hz/s to + 10Hz/s], step = 0.1
[81R] df/dt2 =
NO
Description : configuration of the 2
nd
stage
Range : YES/NO
[81R] df/dt2 =
1.0 Hzs
Description : setting of the 2
nd
stage
Range : [ – 10Hz/s to + 10Hz/s], step = 0.1
[81R] df/dt3 =
NO
Description : configuration of the 3
rd
stage
Range : YES/NO
[81R] df/dt3 =
1.0 Hzs
Description : setting of the 3
rd
stage
Range : [ – 10Hz/s to + 10Hz/s], step = 0.1