Ice NP900 Series, Инструкция по применению

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Application Guide - NP900 Series 178 (504
)
A996A
NOV function is capable to use measured neutral voltage as well. In case line to line
voltage of system is 100 V secondary the earth fault is 100% of Un when measured
neutral voltage is 100 V. See picture below.
Figure 3.2.17-91 Measured neutral voltage example.
For monitored voltage magnitudes can be selected fundamental component RMS and
TRMS values (including harmonics up to 31
st
). Blocking signal and setting group selection
controls the operating characteristics of the function during normal operation.
Outputs of the function are Start Trip and Blocked signals. Setting parameters are static
inputs for the function which are changed only by user input in the setup phase of the
function. Neutral overvoltage function utilizes total of eight separate setting groups which
can be selected from one common source.
The function can be operating on instant or time delayed mode. In time delayed mode the
operation can be selected for definite time or IDMT. For IDMT operation IEC and ANSI
standard time delays are supported as well as custom parameters.
The operational logic consists of input magnitude processing, input magnitude selection,
threshold comparator, block signal check, time delay characteristics and output
processing.
Inputs for the function are the operating mode selections, setting parameters and
measured and pre-processed voltage magnitudes and binary input signals. Function
outputs START, TRIP and BLOCKED signals which can be used for direct IO controlling
and also for user logic programming. The function registers its operation into 12 last time-
stamped registers and also generates general time stamped ON/OFF events to the
common event buffer from each of the three output signal. In instant operating mode the
function outputs START and TRIP events simultaneously with equivalent time stamp.