larger than the set operation current and the step is used in non-directional mode a
signal from the comparator for this step is set to true. This signal will, without delay,
activate the output signal STx (x=step 1-4) for this step and a common START signal.
8.2.7.2 Internal polarizing
A polarizing quantity is used within the protection in order to determine the direction
to the earth fault (Forward/Reverse).
The function can be set to use voltage polarizing, current polarizing or dual polarizing.
Voltage polarizing
When voltage polarizing is selected the protection will use either the residual voltage
3U
0
or the negative sequence voltage U
2
as polarizing quantity U3P.
The residual voltage can be:
1. directly measured (when a dedicated VT input of the IED is connected in
PCM600 to the fourth analog input of the pre-processing block connected to
EF4PTOC function input U3P). This dedicated IED VT input shall be then
connected to open delta winding of a three phase main VT.
2. calculated from three phase voltage input within the IED (when the fourth analog
input into the pre-processing block connected to EF4PTOC analog function input
U3P is NOT connected to a dedicated VT input of the IED in PCM600). In such
case the pre-processing block will calculate 3U
0
from the first three inputs into
the pre-processing block by using the following formula:
IECEQUATION2407 V1 EN (Equation 49)
where:
UL1, UL2 and UL3 are fundamental frequency phasors of three individual phase voltages.
In order to use this, all three phase-to-earth voltages must be connected to three IED VT
inputs.
The residual voltage is pre-processed by a discrete fourier filter. Thus, the phasor of
the fundamental frequency component of the residual voltage is derived.
The negative sequence voltage is calculated from the three-phase voltage input within
the IED by using the pre-processing block. The preprocessing block will calculate the
negative sequence voltage from the three inputs into the pre-processing block by using
the following formula:
2
U =(UL1+alpha UL2 + alpha UL3)/3× ×
GUID-87DA8E2C-B3E5-42D6-B909-59EA3F9309D8 V1 EN (Equation 50)
1MRK 502 048-UEN A Section 8
Current protection
193
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