ABB RET670 Product Manual page 17

ABB
Transformer protection RET670
Customized
Product version: 1.2
for negative sequence currents down to the
continuous capability of a generator.
A separate output is available as an alarm feature
to warn the operator of a potentially dangerous
situation.
6. Voltage protection
Two step undervoltage protection UV2PTUV
Undervoltages can occur in the power system
during faults or abnormal conditions. Two step
undervoltage protection (UV2PTUV) function can
be used to open circuit breakers to prepare for
system restoration at power outages or as long-
time delayed back-up to primary protection.
UV2PTUV has two voltage steps, each with
inverse or definite time delay.
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.
Two step overvoltage protection (OV2PTOV)
function can be used to detect open line ends,
normally then combined with a directional reactive
over-power function to supervise the system
voltage. When triggered, the function will cause
an alarm, switch in reactors, or switch out
capacitor banks.
OV2PTOV has two voltage steps, each of them
with inverse or 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, each with
inverse or definite time delay.
1MRK 504 117-BEN D
Reset delay ensures operation for intermittent
earth faults.
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.
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.
Loss of voltage check LOVPTUV
Loss of voltage check (LOVPTUV) is suitable for
use in networks with an automatic system
restoration function. LOVPTUV issues a three-
pole trip command to the circuit breaker, if all
three phase voltages fall below the set value for a
time longer than the set time and the circuit
breaker remains closed.
7. Frequency protection
Underfrequency protection SAPTUF
Underfrequency occurs as a result of a 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 also provided with undervoltage
blocking.
The operation is based on positive sequence
voltage measurement and requires two phase-
phase or three phase-neutral voltages to be
connected. For information about how to connect
analog inputs, refer to Application manual/IED
application/Analog inputs/Setting guidelines
Overfrequency protection SAPTOF
Overfrequency protection function SAPTOF is
applicable in all situations, where reliable
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