ABB REL670 2.2 IEC - Page 290

In dual polarization, zero sequence voltage polarization and zero sequence current
polarization elements function in a “one-out-of-two mode”. Typically when the
zero sequence current is high, then the zero sequence voltage is low and vice versa.
Thus combining a zero sequence voltage polarized and a zero sequence current
polarized (neutral current polarized) directional element into one element, the IED
can benefit from both elements as the two polarization measurements function in a
“one-out-of-two mode” complementing each other. In this mode, if IPOL is greater
than IPOL> setting, then only IPOL based direction is detected and UPOL based
direction will be blocked. Flexibility is also increased as zero sequence voltage
polarization can be used, if the zero sequence current polarizing source is switched
out of service. When the zero sequence polarizing current exceeds the set value for
IPOL>, zero sequence current polarizing is used. For values of zero sequence
polarizing current less than the set value for startPolCurrLevel, zero sequence
voltage polarizing is used.
Zero-sequence voltage polarization with zero-sequence current compensation (-
U0Comp) compares the phase angles of zero sequence current I
0
with zero-
sequence voltage added by a phase-shifted portion of zero-sequence current (see
equation
220) at the location of the protection. The factor k = setting K
mag
. This
type of polarization is intended for use in applications where the zero sequence
voltage can be too small to be used as the polarizing quantity, and there is no zero
sequence polarizing current (transformer neutral current) available. The zero
sequence voltage is “boosted” by a portion of the measured line zero sequence
current to form the polarizing quantity. This method requires that a significant
difference must exist in the magnitudes of the zero sequence currents for close-up
forward and reverse faults, that is, it is a requirement that |U0| >> |k · I0| for reverse
faults, otherwise there is a risk that reverse faults can be seen as forward.
AngleRCA
0 0
U k I e- + × ×
EQUATION1638 V2 EN-US (Equation 220)
The negative-sequence voltage polarization with negative-sequence current
compensation (-U2Comp) compares correspondingly I
2
with (see equation 221),
and similarly it must be ensured that |U
2
| >> |k · I
2
| for reverse faults.
AngleRCA
2 2
U k I e- + × ×
EQUATION1639 V2 EN-US (Equation 221)
Section 8 1MRK 506 369-UEN B
Impedance protection
284 Line distance protection REL670 2.2 IEC
Application manual