Ice NP900 Series, Инструкция по применению

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Application Guide - NP900 Series 100 (504
)
A996A
3.2.8 H
ARMONIC OVER CURRENT
I
H
> (50
H
/51
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/68
H
)
Harmonic overcurrent function (HOC) is used for non-directional instant- and time delayed
harmonic overcurrent detection and clearing for various applications including feeder, filter
and machine applications of utilities and industry. The number of available instances of
the function depends of the IED model. Function measures constantly selected
measurement channels selected harmonic component either on absolute value or relative
to the fundamental frequency component. 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. Non directional overcurrent 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. If the stage is used in the
instant mode (e.g. set operating time delay is 0 s) for blocking purposes of other
protection stages either Start or Trip signal can be used. In time delayed mode the
operation can be selected for definite time or IDMT and the function Start signal can be
used for blocking other stages while in cases when the situation prolongs can Trip signal
be used for other actions as time delayed. 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,
saturation check, threshold comparator, block signal check, time delay characteristics and
output processing. The basic design of the protection function is 3-pole operation.
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 HOC
function.