ABB REG650 Technical Manual page 165

1MRK 502 034-UEN -
Technical Manual
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 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 –3U
insures the required inversion of the polarizing voltage within the earth-fault function.
Current polarizing
When current polarizing is selected the function will use the residual current (3I
as 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).
• For some special line protection applications this dedicated IED CT
input can be connected to parallel connection of current transformers in
all three phases (Holm-Green connection)
2. calculated from three phase current input within the IED (when the fourth
analog input into the pre-processing block connected to EF4PTOC function
analog input I3PPOL is NOT connected to a dedicated CT input of the IED in
PCM600). In such case the pre-processing block will calculate 3I
first three inputs into the pre-processing block by using the following formula:
= = + +
IPol 3I IL1 IL2 IL3
0
EQUATION2018 V2 EN
where:
IL1, IL2 and IL3 are fundamental frequency phasors of three individual phase currents.
The residual polarizing current is pre-processed by a discrete fourier filter. Thus
the phasor of the fundamental frequency component of the residual current is
derived. This phasor is then multiplied with pre-set equivalent zero-sequence
source Impedance in order to calculate equivalent polarizing voltage UIPol in
accordance with the following formula:
= × = + ×
UIPol Z IPol (RNPol
0s
EQUATION1877 V2 EN
is used to determine the location of the earth fault. This
0
×
j XNPol) IPol
Section 7
Current protection
)
0
from the
0
(Equation 41)
(Equation 42)
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