This 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 the open delta winding of a three-phase main VT.
2. calculated from three-phase voltage input within the IED (when the fourth
analog input of 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 a case, the pre-processing block will calculate -3U
0
from
the first three inputs into the pre-processing block by using the following
formula:
UPol = -3U
0
= -(UL1 + UL2 + UL3)
EQUATION1875 V2 EN-US (Equation 25)
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.
This phasor is used together with the phasor of the operating directional current, in
order to determine the direction to the earth fault (Forward/Reverse). In order to
enable voltage polarizing the magnitude of polarizing voltage shall be bigger than a
minimum level defined by setting parameter UPolMin.
It shall be noted that residual voltage (-3U
0
) or negative sequence voltage (-3U
2
) is
used to determine the location of the earth fault. This ensures the required inversion
of the polarizing voltage within the earth-fault function.
Current polarizing
When current polarizing is selected, the function will use an external residual
current (3I
0
) as the polarizing quantity IPol. This current can be:
1. directly measured (when a dedicated CT input of the IED is connected in
PCM600 to the fourth analog input of the pre-processing block, connected to
EF4PTOC function input I3PPOL). This dedicated IED CT input is then
typically connected to one single current transformer located between power
system star point and earth (current transformer located in the star point of a
star connected transformer winding).
1MRK 505 394-UEN A Section 8
Current protection
Line differential protection RED650 2.2 IEC 193
Technical manual
To Next Page
Loading...
