5.4.4. Directional overcurrent IDir> (67)
Directional overcurrent function (DOC) is used for directional instant- and time delayed
overcurrent/short circuit 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 (IDir>, IDir>>, IDir>>>, IDir>>>>). Function constantly measures phase
current magnitudes on which the operating decisions are based. Selectable monitored phase current
magnitudes are fundamental component RMS, TRMS values (including harmonics up to 31
st
) or peak-
to-peak values. 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
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
mode can be switched to de nite time or IDMT mode. For IDMT operation IEC and ANSI standard time
delays are supported as well as custom parameters. Function includes CT 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 and angle 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 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 signals. 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.
Simpli ed function block diagram of DOC function is presented in the gure below.
Figure. 5.4.4. - 36. Simpli ed function block diagram of the DOC function.
AQ-F255
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
68
