ABB RET670 Product Manual page 16

Transformer protection RET670
Pre-configured
Product version: 1.1
with the reach limited to less than typical
eighty percent of the transformer impedance
at minimum source impedance. EFPIOC can
be configured to measure the residual current
from the three-phase current inputs or the
current from a separate current input.
EFPIOC can be blocked by activating the
input BLOCK.
Four step residual overcurrent protection
EF4PTOC
The four step residual overcurrent protection
EF4PTOC 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,
current polarized or dual polarized.
EF4PTOC can be set directional or non-
directional independently for each of the steps.
A 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.
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.
Thermal overload protection, two time
constant TRPTTR
If the temperature of a power transformer/
generator reaches very high values the
16
1MRK 504 091-BEN B
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 oil.
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 trip of the protected transformer/
generator.
Breaker failure protection CCRBRF
Breaker failure protection (CCRBRF) ensures
fast back-up tripping of surrounding breakers
in case of own breaker failure to open.
CCRBRF can be current based, contact based,
or adaptive combination between these two
principles.
A current check with extremely short reset
time is used as check criteria to achieve a
high security against unnecessary operation.
A 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 one phase plus the
residual current start. This gives a higher
security to the back-up trip command.
CCRBRF function can be programmed to give
a single- or three-phase re-trip of the own
breaker to avoid unnecessary tripping of
surrounding breakers at an incorrect
initiation due to mistakes during testing.
Issued: June 2010
ABB