Multipurpose Protection; General Calculation; Secondary System Supervision - ABB Relion 670 Series Product Manual

Generator protection REG670
Version 2.2
counters. FTAQFVR for generator protection provides
the START output for a particular settable frequency
limit, when the system frequency falls in that settable
frequency band limit and positive sequence voltage
within settable voltage band limit. The START signal
triggers the individual event timer, which is the
continuous time spent within the given frequency band,
and the accumulation timer, which is the cumulative
time spent within the given frequency band. Once the
timers reach their limit, an alarm or trip signal is
activated to protect the turbine against the abnormal
frequency operation. This function is blocked during
generator start-up or shut down conditions by
monitoring the circuit breaker position and current
threshold value. The function is also blocked when the
system positive sequence voltage magnitude deviates
from the given voltage band limit which can be enabled
EnaVoltCheck setting.
by
It is possible to create functionality with more than one
frequency band limit by using multiple instances of the
function. This can be achieved by a proper configuration
based on the turbine manufacturer specification.

10. Multipurpose protection

General current and voltage protection CVGAPC
The protection module is recommended as a general
backup protection with many possible application areas
due to its flexible measuring and setting facilities.
The built-in overcurrent protection feature has two
settable current levels. Both of them can be used either
with definite time or inverse time characteristic. The
overcurrent protection steps can be made directional
with selectable voltage polarizing quantity. Additionally
they can be voltage and/or current controlled/
restrained. 2nd harmonic restraining facility is available
as well. At too low polarizing voltage the overcurrent
feature can be either blocked, made non directional or
ordered to use voltage memory in accordance with a
parameter setting.
Additionally two overvoltage and two undervoltage
steps, either with definite time or inverse time
characteristic, are available within each function.
The general function suits applications with
underimpedance and voltage controlled overcurrent
solutions. The general function can also be utilized for
generator transformer protection applications where
positive, negative or zero sequence components of
current and voltage quantities are typically required.
Additionally, generator applications such as loss of field,
inadvertent energizing, stator or rotor overload, circuit
breaker head flash-over and open phase detection are
Hitachi Power Grids
M13083-3 v6
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just a few of possible protection arrangements with
these functions.
Rotor earth fault protection using CVGAPC
The field winding, including the rotor winding and the
non-rotating excitation equipment, is always insulated
from the metallic parts of the rotor. The insulation
resistance is high if the rotor is cooled by air or by
hydrogen. The insulation resistance is much lower if the
rotor winding is cooled by water. This is true even if the
insulation is intact. A fault in the insulation of the field
circuit will result in a conducting path from the field
winding to earth. This means that the fault has caused a
field earth fault.
The field circuit of a synchronous generator is normally
unearthed. Therefore, a single earth fault on the field
winding will cause only a very small fault current. Thus
the earth fault does not produce any damage in the
generator. Furthermore, it will not affect the operation
of a generating unit in any way. However, the existence
of a single earth fault increases the electric stress at
other points in the field circuit. This means that the risk
for a second earth fault at another point on the field
winding has increased considerably. A second earth
fault will cause a field short-circuit with severe
consequences.
The rotor earth fault protection is based on injection of
an AC voltage to the isolated field circuit. In non-faulted
conditions there will be no current flow associated to
this injected voltage. If a rotor earth fault occurs, this
condition will be detected by the rotor earth fault
protection. Depending on the generator owner
philosophy this operational state will be alarmed and/or
the generator will be tripped. An injection unit RXTTE4
and an optional protective resistor on plate are required
for correct rotor earth fault protection operation.

11. General calculation

Multipurpose filter SMAIHPAC
The multi-purpose filter function block (SMAIHPAC) is
arranged as a three-phase filter. It has very much the
same user interface (e.g. inputs and outputs) as the
standard pre-processing function block SMAI. However
the main difference is that it can be used to extract any
frequency component from the input signal. Thus it can,
for example, be used to build sub-synchronous
resonance protection for synchronous generator.

12. Secondary system supervision

Current circuit supervision CCSSPVC
Open or short circuited current transformer cores can
cause unwanted operation of many protection functions
1MRK 502 074-BEN M
SEMOD151286-4 v8
GUID-EB0B11C3-FF79-4B8D-A335-649623E832F9 v3
M12444-3 v10
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