ABB RER620 Technical Manual page 108

Section 4
Protection functions
102
polarizing voltages (healthy voltages). The polarizing method is defined with the Pol
quantity setting.
Table 125: Polarizing quantities
Polarizing quantity
Pos. seq. volt
Neg. seq. volt
Self pol
Cross pol
The directional operation can be selected with the Directional mode setting. The user can
select either "Non-directional", "Forward" or "Reverse" operation. By setting the value of
Allow Non Dir to "True", the non-directional operation is allowed when the directional
information is invalid.
The Characteristic angle setting is used to turn the directional characteristic. The value of
Characteristic angle should be chosen in such a way that all the faults in the operating
direction are seen in the operating zone and all the faults in the opposite direction are seen
in the non-operating zone. The value of Characteristic angle depends on the network
configuration.
Reliable operation requires both the operating and polarizing quantities to exceed certain
minimum amplitude levels. The minimum amplitude level for the operating quantity
(current) is set with the Min Trip Current setting. The minimum amplitude level for the
polarizing quantity (voltage) is set with the Min operate voltage setting. If the amplitude
level of the operating quantity or polarizing quantity is below the set level, the direction
information of the corresponding phase is set to "Unknown".
The polarizing quantity validity can remain valid even if the amplitude of the polarizing
quantity falls below the value of the Min operate voltage setting. In this case, the
directional information is provided by a special memory function for a time defined with
the Voltage Mem time setting.
DPHxPDOC is provided with a memory function to secure a reliable and correct
directional relay operation in case of a close short circuit or an earth fault characterized by
an extremely low voltage. At sudden loss of the polarization quantity, the angle difference
is calculated on the basis of a fictive voltage. The fictive voltage is calculated using the
positive phase sequence voltage measured before the fault occurred, assuming that the
voltage is not affected by the fault. The memory function enables the function to operate
up to a maximum of three seconds after a total loss of voltage. This time can be set with
the Voltage Mem time setting. The voltage memory cannot be used for the "Negative
sequence voltage" polarization because it is not possible to substitute the positive sequence
voltage for negative sequence voltage without knowing the network unsymmetry level.
This is the reason why the fictive voltage angle and corresponding direction information
are frozen immediately for this polarization mode when the need for voltage memory
arises and these are kept frozen until the time set with Voltage Mem time elapses.
When the voltage falls below Min operate voltage at a close fault, the fictive voltage is
used to determine the phase angle. The measured voltage is applied again as soon as the
voltage rises above Min operate voltage and hysteresis. The fictive voltage is also
discarded if the measured voltage stays below Min Trip Voltage and hysteresis for longer
Description
Positive sequence voltage
Negative sequence voltage
Self polarization
Cross polarization
1MAC309294-MB F
RER620
Technical Manual