5.3.4. Directional earth fault (I0dir>; 67N)
The directional earth fault function is used for earth fault alarms. The operating decisions are based on
the selected neutral current or the selected voltage magnitudes, both of which the function measures
constantly. The monitored residual current magnitudes are equal to the RMS values from inputs I01
and I02 (residual current measerement) or from I0Calc (residual currents calculcated from phase
current measurement channels). The current angle is based on the angle of the measured or
calculated zero sequence voltage. In addition, a certain amount of zero sequence voltage has to be
present to activate the trip. The setting group selection controls the operating characteristics of the
function during normal operation, i.e. the user or user-de ned logic can change function parameters
while the function is running.
The output of the function is the ALARM signal. The directional earth fault function uses a total of eight
(8) separate setting groups which can be selected from one common source.
The operational logic consists of the following:
input magnitude selection
input magnitude processing
threshold comparator
angle check
output processing.
The inputs for the function are the following:
operating mode selections
setting parameters
digital inputs and logic signals
measured and pre-processed current magnitudes.
The function's output ALARM signal can be used for direct I/O controlling and user logic programming.
The function generates general time stamped ON/OFF events to the common event buffer from the
output signal. The time stamp resolution is 1 ms. The function also provides a resettable cumulative
counter for events.
Measured input
The function block uses analog current measurement values and always uses peak-to-peak
measurement from samples. The user can select the monitored magnitude to be equal to fundamental
frequency RMS values, to TRMS values from the whole harmonic specter of 32 components, or to
peak-to-peak values. A -20 ms averaged value of the selected magnitude is used for pre-fault data
registering.
The fault current angle is based on the neutral voltage
U
0
. Both
I
0
and
U
0
must be above the squelch
limit to be able to detect the angle. The squelch limit for the
I
0
current is 0.01 x
I
n
and for the
U
0
voltage
0.01 x
U
n
.
Table. 5.3.4. - 56. Measurement inputs of the I0dir> function.
Signal
Description
Time base
I01RMS
Fundamental RMS measurement of coarse residual current measurement input I01
5 ms
I02RMS
Fundamental RMS measurement of sensitive residual current measurement input I02
5 ms
I0Calc
Fundamental RMS value of the calculated residual current from the three phase currents
5 ms
U0RMS
Fundamental RMS measurement of zero sequence voltage measurement input U0
5 ms
U0Calc
Fundamental RMS value of the calculated zero sequence voltage from the three phase voltages
5 ms
AQ-E215
Instruction manual
Version: 2.01
73
© Arcteq Relays Ltd