Ice NP900 Series, Инструкция по применению

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Application Guide - NP900 Series 75 (504
)
A996A
3.2.5 D
IRECTIONAL EARTH FAULT
I0D
IR
> (67N)
Directional earth fault function (DEF) is used for instant- and time delayed earth fault
protection for various applications including feeder and machine applications of utilities
and industry. IED with both voltage and current protection module may have four available
instances of the function (I0Dir>, I0Dir>>, I0Dir>>>, I0Dir>>>>). Function measures
constantly selected neutral current –or voltage magnitudes which on the operating
decisions are based. Monitored residual current magnitudes can be selected fundamental
component RMS, TRMS values (including harmonics up to 31
st
) or peak-to-peak values of
residual current measurement inputs I01 and I02 or from phase current measurements
calculated residual current I0Calc. Current angle is based compared to the angle of
measured or calculated zero sequence voltage. Also certain amount of zero sequence
voltage has to be present to activate the trip. 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. Directional earth fault 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, angle check, 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 current 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.
Time stamp resolution is 1ms. Function provides also cumulative counters for START,
TRIP and BLOCKED events.
In the following figure is presented the simplified function block diagram of the DEF
function.