Frequency Protection - ABB Relion 650 series RET650 Product Manual

Transformer protection RET650
Product version: 1.1
outages or as long-time delayed back-up to
primary protection.
UV2PTUV has two voltage steps, where step
1 is settable as inverse or definite time
delayed. Step 2 is always definite time delayed.
Two step overvoltage protection
OV2PTOV
Overvoltages may occur in the power system
during abnormal conditions such as sudden
power loss, tap changer regulating failures,
open line ends on long lines etc.
OV2PTOV has two voltage steps, where step
1 can be set as inverse or definite time
delayed. Step 2 is always definite time delayed.
OV2PTOV has an extremely high reset ratio
to allow settings close to system service
voltage.
Two step residual overvoltage
protection ROV2PTOV
Residual voltages may occur in the power
system during earth faults.
Two step residual overvoltage protection
ROV2PTOV function calculates the residual
voltage from the three-phase voltage input
transformers or measures it from a single
voltage input transformer fed from an open
delta or neutral point voltage transformer.
ROV2PTOV has two voltage steps, where
step 1 can be set as inverse or definite time
delayed. Step 2 is always definite time delayed.
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. The function
has settable inverse operating curves and
independent alarm stages.
20
1MRK 504 127-BEN -
Issued: February 2011

7. 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 undervoltage
blocking.
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.
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.
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
and remedial action schemes. SAPFRC can
discriminate between positive or negative
change of frequency.
SAPFRC is provided with an undervoltage
blocking.
ABB