ABB RELION RET670 Applications Manual page 641

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
RFLx: Is the setting of the voltage ratio compensation factor where possible differences
between the voltages is compensated for. The differences can be due to different
voltage transformer ratios, different voltage levels e.g. the voltage measurement inside
the capacitor bank can have a different voltage level but the difference can also e.g. be
used by voltage drop in the secondary circuits. The setting is normally done at site by
evaluating the differential voltage achieved as a service value for each phase. The
factor is defined as V2 · RFLx and shall be equal to the V1 voltage. Each phase has its
own ratio factor.
VDTrip: The voltage differential level required for tripping is set with this parameter.
For application on capacitor banks the setting will depend of the capacitor bank voltage
and the number of elements per phase in series and parallel. Capacitor banks must be
tripped before excessive voltage occurs on the healthy capacitor elements. The setting
values required are normally given by the capacitor bank supplier. For other
applications it has to be decided case by case. For fuse supervision normally only the
alarm level is used.
tTrip: The time delay for tripping is set by this parameter. Normally, the delay does not
need to be so short in capacitor bank applications as there is no fault requiring urgent
tripping.
tReset: The time delay for reset of tripping level element is set by this parameter.
Normally, it can be set to a short delay as faults are permanent when they occur.
For the advanced users following parameters are also available for setting. Default
values are here expected to be acceptable.
V1Low: The setting of the undervoltage level for the first voltage input is decided by
this parameter. The proposed default setting is 70%.
V2Low: The setting of the undervoltage level for the second voltage input is decided by
this parameter. The proposed default setting is 70%.
tBlock: The time delay for blocking of the function at detected undervoltages is set by
this parameter.
VDAlarm: The voltage differential level required for alarm is set with this parameter.
For application on capacitor banks the setting will depend of the capacitor bank voltage
and the number of elements per phase in series and parallel. Normally values required
are given by capacitor bank supplier.
For fuse supervision normally only this alarm level is used and a suitable voltage level
is 3-5% if the ratio correction factor has been properly evaluated during
commissioning.
For other applications it has to be decided case by case.
Section 10
Voltage protection
635