ABB REC650 Technical Manual page 106

Section 6
Current protection
100
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
the pre-processing block by using the following formula:
UPol =3U0 =(UL1+UL2+UL3)
IECEQUATION2407 V1 EN
where:
UL1, UL2 and UL3
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:
×
U =(UL1+alpha UL2 + alpha UL3)/3
2
GUID-87DA8E2C-B3E5-42D6-B909-59EA3F9309D8 V1 EN
where:
UL1, UL2 and UL3
alpha
The polarizing 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 (U
to determine the location of the earth fault. This insures the required inversion of the
polarizing voltage within the earth-fault function.
are fundamental frequency phasors of three individual phase voltages.
×
are fundamental frequency phasors of three individual phase voltages.
unit phasor with an angle of 120 degrees.
) or negative sequence voltage (U
n
1MRK 511 287-UEN A
from the first three inputs into
0
(Equation 9)
(Equation 10)
2
Technical manual
) is used