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, where
step 1 is settable as inverse or definite time
delayed. Step 2 is always definite time delayed.
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.
OV2PTOV (59) has two voltage steps, where
step 1 can be set as inverse or definite time
delayed. Step 2 is always 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, where
step 1 can be set as inverse or definite time
delayed. Step 2 is always definite time delayed.
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.
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
generating plant, generator governor problems
can also cause over frequency.
SAPTOF (81) is used mainly for generation
shedding and remedial action schemes. It is
also used as a frequency stage initiating load
restoring.
SAPTOF (81) is provided with an undervoltage
blocking.
Breaker protection REQ650 ANSI
1MRK 505 269-BUS -
Product version: 1.1
Issued: April 2011
ABB
19
