Instruction manual –AQ F210 Feeder Protection IED
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)
4.2.3
N
ON
-
DIRECTIONAL EARTH FAULT
I0>
(50N/51N)
Non directional earth fault function (NEF) is used for instant- and time delayed earth fault
protection 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 neutral current magnitudes which on the operating
decisions are based. Monitored phase current magnitudes can be selected fundamental
component RMS, TRMS values (including harmonics up to 32
nd
) or peak-to-peak values of
residual current measurement inputs I01 and I02 or from phase current measurements
calculated zero sequence current I0Calc. 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. 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. Function includes
saturation checking which allows the function to start and operate accurately also in case
of CT saturation condition.
The operational logic consists of input magnitude processing, input magnitude selection,
saturation check, 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 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 NEF function.
