ABB Relion 670 Series Product Manual page 35

Bay control REC670
Version 2.2
needed to correctly determine earth fault direction.
However, these neutral resistors can still be used if
already installed in the network.
The function is suitable to be used in distribution and in
meshed HV sub-transmission networks using high-
impedance grounding. In meshed systems a directional
permissive scheme is required in order to ensure
selective tripping of a faulty line. Alternatively, the
function can be used solely for signaling of the earth-
fault location to the SCADA system when the power
network is allowed to operate for a longer time with an
earth-fault being present.
9. Voltage protection
Two-step undervoltage protection UV2PTUV
Undervoltages can occur in the power system during
faults or abnormal conditions. The two-step
undervoltage protection function (UV2PTUV) can be
used to open circuit breakers to prepare for system
restoration at power outages or as a long-time delayed
back-up to the primary protection.
UV2PTUV has two voltage steps, each with inverse or
definite time delay.
It has a high reset ratio to allow settings close to the
system service voltage.
Two step overvoltage protection OV2PTOV
Overvoltages may occur in the power system during
abnormal conditions such as sudden power loss, tap
changer regulating failures, and open line ends on long
lines.
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 a high reset ratio to allow settings close
to system service voltage.
Residual overvoltage protection, two steps
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.
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ROV2PTOV has two voltage steps, each with inverse or
definite time delay.
A reset delay ensures operation for intermittent earth
faults.
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. Alternatively, it can be used as voltage
differential protection (VDCPTOV) for shunt capacitor
banks.
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.
The operation of LOVPTUV is supervised by the fuse
failure supervision FUFSPVC.
10. Unbalance protection
Cascading failure protection for shunt capacitor
bank SCCFPVOC
Cascading failures are series faults in shunt capacitor
banks involving more than one capacitor unit (or even
more than one rack). Cascading failures in shunt
capacitor bank (SCCFPVOC) function provides
protection against cascading faults and has the
following protection modes to detect the unbalances.
• Two step, negative sequence based voltage restrained
over-current protection
• Two step, zero sequence based voltage restrained
over-current protection
Current unbalance protection for shunt capacitor
bank SCUCPTOC
The current unbalance protection for shunt capacitor
bank (SCUCPTOC) function is used to protect the shunt
capacitor bank(SCB) from the unbalance due to internal
faults in elements or units. It is applicable for protecting
the following shunt capacitor bank configurations, only
when CT's available to measure the unbalance current
from the unbalance.
• Grounded and ungrounded double WYE
• Grounded and ungrounded single WYE with strings in
each phase
• Grounded and ungrounded H bridge configurations
The main features of the function are,
1MRK 511 404-BEN N
SEMOD153862-5 v7
SEMOD171457-5 v8
GUID-718C2B4C-6AFA-48E8-B322-0B1D845218D5 v1
GUID-29D8914A-371B-4E3B-A522-E5013EED5486 v1
35