ABB RET670 Product Manual page 18

Transformer protection RET670
Pre-configured
Product version: 1.1
Overexcitation protection OEXPVPH
When the laminated core of a power
transformer or generator is subjected to a
magnetic flux density beyond its design
limits, stray flux will flow into non-laminated
components not designed to carry flux and
cause eddy currents to flow. The eddy
currents can cause excessive heating and
severe damage to insulation and adjacent
parts in a relatively short time. Overexcitation
protection OEXPVPH has settable inverse
operating curve and independent alarm stage.
Voltage differential protection VDCPTOV
A voltage differential monitoring function is
available. It compares the voltages from two
three phase sets of voltage transformers and
has one sensitive alarm step and one trip
step. It can be used to supervise the voltage
from two fuse groups or two different voltage
transformers fuses as a fuse/MCB supervision
function.
Frequency protection
Underfrequency protection SAPTUF
Underfrequency occurs as a result of lack of
generation in the network.
Underfrequency protection SAPTUF is used
for load shedding systems, remedial action
schemes, gas turbine startup and so on.
SAPTUF is provided with an under voltage
blocking.
The operation may be based on single-phase,
phase-to-phase or positive-sequence voltage
measurement.
Overfrequency protection SAPTOF
Overfrequency protection function SAPTOF is
applicable in all situations, where reliable
detection of high fundamental power system
frequency is needed.
Overfrequency occurs at sudden load drops
or shunt faults in the power network. Close
to the generating plant, generator governor
problems can also cause over frequency.
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1MRK 504 091-BEN B
SAPTOF is used mainly for generation
shedding and remedial action schemes. It is
also used as a frequency stage initiating load
restoring.
SAPTOF is provided with an undervoltage
blocking. The operation is based on single-
phase, phase-to-phase or positive-sequence
voltage measurement.
Rate-of-change frequency protection
SAPFRC
Rate-of-change frequency protection function
(SAPFRC) gives an early indication of a main
disturbance in the system. SAPFRC can be
used for generation shedding, load shedding,
remedial action schemes. SAPFRC can
discriminate between positive or negative
change of frequency.
SAPFRC is provided with an undervoltage
blocking. The operation may be based on
single-phase, phase-to-phase or positive-
sequence voltage measurement.
Multipurpose protection
General current and voltage protection
CVGAPC
The protection module is recommended as a
general backup protection with many
possible application areas due to its flexible
measuring and setting facilities.
The built-in overcurrent protection feature
has two settable current levels. Both of them
can be used either with definite time or
inverse time characteristic. The overcurrent
protection steps can be made directional with
selectable voltage polarizing quantity.
Additionally they can be voltage and/or
current controlled/restrained. 2nd harmonic
restraining facility is available as well. At too
low polarizing voltage the overcurrent feature
can be either blocked, made non directional
or ordered to use voltage memory in
accordance with a parameter setting.
Additionally two overvoltage and two
undervoltage steps, either with definite time
or inverse time characteristic, are available
within each function.
Issued: June 2010
ABB