Application Guide - NP900 Series
200 (504
)
A996A
Table 3.2.22.5-140. Register content.
Date & Time
Event
code
f Pretrig (Hz)
f Fault (Hz)
Setting group in
use
dd.mm.yyyy
hh:mm:ss.mss
6336-
6383
Descr.
Start –20ms
averages
Fault frequency
Starts used at the
triggering moment
3.2.22
R
ATE OF CHANGE OF FREQUENCY
(ROCOF)
(81R)
Rate of change of frequency (df/dt or ROCOF) is used to detect fast drops or increases of
frequency. If the load changes fast df/dt protection will detect and clear the frequency
based faults faster than conventional under- and over frequency protections. One of the
most common causes for the frequency to deviate from nominal value is unbalance
between generated power and the load demand. If the unbalance is big frequency will
change rapidly.
Rate of change of frequency protection can also be applied to detect loss of mains
situation. Loss of mains is a situation where part of the network (incorporating generation)
loses connection with the rest of the system (i.e. islanded network). If the generator is not
disconnected from the network as well it can cause safety hazards. Generator can also be
automatically reconnected to the network which can cause damage to the generator and
the network.
Figure 3.2.23-2 Operation of df/dt function when the frequency starts but doesn’t trip.
Содержание NP900 Series
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Страница 49: ...Application Guide NP900 Series 49 504 A996A Figure 3 2 1 3 25 Definite time operating characteristics...
Страница 50: ...Application Guide NP900 Series 50 504 A996A Figure 3 2 1 3 26 IEC predefined characteristics NI VI LTI and EI...
Страница 52: ...Application Guide NP900 Series 52 504 A996A Figure 3 2 1 3 28 IEEE predefined characteristics EI MI and VI...
Страница 243: ...Application Guide NP900 Series 243 504 A996A Figure 3 3 2 1 122 NPS biased thermal trip curves with kNPS values 7 and 10...
Страница 491: ...Application Guide NP900 Series 491 504 A996A 3 7 5 6 SETTING EXAMPLE...
Страница 504: ...Application Guide NP900 Series 504 504 A996A A996A...