Ice NP900 Series, Инструкция по применению

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Application Guide - NP900 Series 202 (504
)
A996A
Figure 3.2.23-98 Simplified function block diagram of the ROCOF function.
3.2.22.1 M
EASURED INPUT VALUES
Rate of change of frequency protection function compares measured df/dt to pick-up
setting given in Hz/s. Source of measured frequency depends on the factory defined
tracking reference which can be checked from frequency tab behind measurements-
menu.
Table 3.2.23.1-141 Measurement magnitudes used by the ROCOF function (depends on
factory definition)
Signals Description Time base
VT1 U1,U2,U3
L-N voltages of first voltage transformer
5 ms
VT2 U1,U2,U3
L-N voltages of second voltage transformer
5 ms
3.2.22.2 P
ICK
-
UP CHARACTERISTICS AND TIME DELAY
Pick-up of each stage of ROCOF functions stage is controlled by
df/dt>/< (1) pick-up,
df/dt>/< (2) pick-up
etc. setting parameter, which defines the maximum allowed change of
frequency before action from the function. The function constantly calculates the ratio in
between of the pick-up setting and measured df/dt. Reset ratio of 20mHz is inbuilt in the
function and is always related to the pick-up value. The f>/< limit value is used to block the
operation of the function near the nominal frequency.