Rate-of-change frequency protection SAPFRC
M14965-3 v12
The rate-of-change frequency protection function SAPFRC
gives an early indication of a main disturbance in the system.
SAPFRC measures frequency with high accuracy, and can be
used for generation shedding, load shedding and remedial
action schemes. SAPFRC can discriminate between a
positive or negative change of frequency. A definite time delay
is provided for operate.
SAPFRC 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.
Frequency time accumulation protection FTAQFVR
GUID-020CE8CF-9BEA-455D-ACBD-13023B93B4D1 v4
Frequency time accumulation protection FTAQFVR is based
on measured system frequency and time 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 by
EnaVoltCheck
setting.
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.
8. Multipurpose protection
General current and voltage protection CVGAPC
M13083-3 v6
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 just a
few of possible protection arrangements with these functions.
Voltage-restrained time overcurrent protection VRPVOC
GUID-935E1CE8-601F-40E2-8D22-2FF68420FADF v6
Voltage-restrained time overcurrent protection (VRPVOC)
function can be used as generator backup protection against
short-circuits.
The overcurrent protection feature has a settable current level
that can be used either with definite time or inverse time
characteristic. Additionally, it can be voltage controlled/
restrained.
One undervoltage step with definite time characteristic is also
available within the function in order to provide functionality
for overcurrent protection with undervoltage seal-in.
Rotor earth fault protection using CVGAPC
SEMOD151286-4 v8
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
1MRK 502 068-BEN D
Generator protection REG670 2.1 IEC
Product version: 2.1
26
ABB
