ABB RET670 Product Manual page 16

Transformer protection RET670 ANSI
Pre-configured
Product version: 1.2
5. Voltage protection
Two step undervoltage protection UV2PTUV (27)
Undervoltages can occur in the power system
during faults or abnormal conditions. Two step
undervoltage protection (UV2PTUV, 27) 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 (27) has two voltage steps, each with
inverse or definite time delay.
Two step overvoltage protection OV2PTOV (59)
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, 59)
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 (59) has two voltage steps, each of them
with inverse or definite time delayed.
OV2PTOV (59) has an extremely high reset ratio to
allow settings close to system service voltage.
Two step residual overvoltage protection
ROV2PTOV (59N)
Residual voltages may occur in the power system
during ground faults.
Two step residual overvoltage protection
ROV2PTOV (59N) function calculates the residual
voltage from the three-phase voltage input
transformers or measures it from a single voltage
input transformer fed from a broken delta or neutral
point voltage transformer.
ROV2PTOV (59N) has two voltage steps, each with
inverse or definite time delay.
Reset delay ensures operation for intermittent
ground faults.
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Overexcitation protection OEXPVPH (24)
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.
Loss of voltage check LOVPTUV (27)
Loss of voltage check (LOVPTUV, 27) is suitable for
use in networks with an automatic system
restoration function. LOVPTUV (27) 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.
6. Frequency protection
Underfrequency protection SAPTUF (81)
Underfrequency occurs as a result of lack of
generation in the network.
Underfrequency protection SAPTUF (81) is used for
load shedding systems, remedial action schemes,
gas turbine startup and so on.
SAPTUF (81) is provided with an 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 (81)
Overfrequency protection function SAPTOF (81) 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
1MRK 504 118-BUS A
ABB