Voltage Protection - ABB Relion 670 Series Product Manual

Generator protection REG670
Version 2.2
If internal generator components exceed its design
temperature limit, damage can be the result. Damage to
generator insulation can range from minor loss of life to
complete failure, depending on the severity and
duration of the temperature excursion. Excess
temperature can also cause mechanical damage due to
thermal expansion. Rotor components such as bars and
end rings are vulnerable to this damage. Since
temperature increases with current, it is logical to apply
overcurrent elements with inverse time characteristics.
For its operation the function either measures the true
RMS current of the excitation transformer or calculates
the DC current in the rotor winding. The rotor winding
DC current can be calculated from the AC currents
measured on either high voltage side (HV) or low voltage
side (LV) side of the excitation transformer. For the HV
side measurement ratings of the excitation transformer
shall be given. The use of the DC current is default (i.e.
recommended) measurement for generators with static
excitation system. When the DC current is used, the
function can provide a DC current ripple alarm, due to
possible problem with the static excitation equipment.
The rotor DC current can be also sent to the plant
supervisory system via communication channel or
displayed on the IED built-in HMI.
The function can also detect undercurrent condition in
the rotor winding which indicates either under-
excitation or loss of excitation condition of the
generator.
The function is designed to work on 50/60 Hz systems.
Average Power Transient Earth Fault Protection
APPTEF
The APPTEF (Average Power Transient Earth Fault
Protection) function is a transient measuring directional
earth-fault protection. Determination of the earth fault
direction is based on the short-term built-up transient
at the beginning of the earth fault. This transient is to a
large extent independent of the neutral point treatment.
This means that the function can be used without any
modification in all types of high-impedance grounded,
resonant grounded or isolated power systems.
For a resonant grounded system, the correct directional
measurement is ensured regardless of how many
Petersen coils are used throughout the interconnected
power network. The function is not sensitive to the
actual compensation degree of the coils. It will operate
equally well in an under- or over-compensated system.
Parallel neutral resistor to the Petersen coil are not
needed to correctly determine earth fault direction.
However, these neutral resistors can still be used if
already installed in the network.
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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.

8. 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.
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.
ROV2PTOV has two voltage steps, each with inverse or
definite time delay.
A 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-
1MRK 502 074-BEN M
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