ABB RET670 Product Manual page 15

ABB
Transformer protection RET670
Customized
Product version: 1.2
IDir, UPol and IPol can be independently selected
to be either zero sequence or negative sequence.
Second harmonic blocking can be set individually
for each step.
EF4PTOC can be configured to measure the
residual current from the three-phase current
inputs or the current from a separate current input.
Four step negative sequence overcurrent
protection NS4PTOC
Four step negative sequence overcurrent
protection (NS4PTOC) has an inverse or definite
time delay independent for each step separately.
All IEC and ANSI time delayed characteristics are
available together with an optional user defined
characteristic.
The directional function is voltage polarized or
dual polarized.
NS4PTOC can be set directional or non-
directional independently for each of the steps.
Sensitive directional residual overcurrent and
power protection SDEPSDE
In isolated networks or in networks with high
impedance earthing, the earth fault current is
significantly smaller than the short circuit currents.
In addition to this, the magnitude of the fault
current is almost independent on the fault location
in the network. The protection can be selected to
use either the residual current or residual power
component 3U0·3I0·cos j, for operating quantity
with maintained short circuit capacity. There is
also available one nondirectional 3I0 step and one
3U0 overvoltage tripping step.
No specific sensitive current input is
needed.SDEPSDE can be set as low 0.25% of
IBase.
Thermal overload protection, one time constant
LPTTR
The increasing utilizing of the power system
closer to the thermal limits has generated a need
of a thermal overload protection also for power
lines.
A thermal overload will often not be detected by
other protection functions and the introduction of
the thermal overload protection can allow the
1MRK 504 117-BEN D
protected circuit to operate closer to the thermal
limits.
The three-phase current measuring protection
2
has an I t characteristic with settable time
constant and a thermal memory..
An alarm level gives early warning to allow
operators to take action well before the line is
tripped.
Thermal overload protection, two time constant
TRPTTR
If a power transformer or generator reaches very
high temperatures the equipment might be
damaged. The insulation within the transformer/
generator will have forced ageing. As a
consequence of this the risk of internal phase-to-
phase or phase-to-earth faults will increase. High
temperature will degrade the quality of the
transformer/generator insulation.
The thermal overload protection estimates the
internal heat content of the transformer/generator
(temperature) continuously. This estimation is
made by using a thermal model of the transformer/
generator with two time constants, which is
based on current measurement.
Two warning levels are available. This enables
actions in the power system to be done before
dangerous temperatures are reached. If the
temperature continues to increase to the trip
value, the protection initiates a trip of the
protected transformer/generator.
Breaker failure protection CCRBRF
Breaker failure protection (CCRBRF) ensures fast
back-up tripping of surrounding breakers in case
the own breaker fails to open. CCRBRF can be
current based, contact based, or an adaptive
combination of these two conditions.
Current check with extremely short reset time is
used as check criterion to achieve high security
against unnecessary operation.
Contact check criteria can be used where the
fault current through the breaker is small.
CCRBRF can be single- or three-phase initiated
to allow use with single phase tripping
applications. For the three-phase version of
CCRBRF the current criteria can be set to operate
only if two out of four for example, two phases or
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