ABB Relion 670 Series Product Manual page 31

Generator protection REG670
Version 2.2
By using optional metering class CT inputs accuracy of
0,5% can be achieved for steam turbine applications.
Voltage-restrained time overcurrent protection
VRPVOC
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.
Negative sequence time overcurrent protection for
machines NS2PTOC
Negative-sequence time overcurrent protection for
machines (NS2PTOC) is intended primarily for the
protection of generators against possible overheating
of the rotor caused by negative sequence current in the
stator current.
The negative sequence currents in a generator may,
among others, be caused by:
• Unbalanced loads
• Line to line faults
• Line to earth faults
• Broken conductors
• Malfunction of one or more poles of a circuit breaker
or a disconnector
NS2PTOC can also be used as a backup protection, that
is, to protect the generator in case line protections or
circuit breakers fail to clear unbalanced system faults.
To provide an effective protection for the generator for
external unbalanced conditions, NS2PTOC is able to
directly measure the negative sequence current.
NS2PTOC also has a time delay characteristic which
matches the heating characteristic of the generator
2
=
I t K
as defined in standard IEEE C50.13.
2
where:
I is negative sequence current expressed
2
in per unit of the rated generator
current
t is operating time in seconds
K is a constant which depends of the
generators size and design
NS2PTOC has a wide range of
sensitivity and capability of detecting and tripping for
Hitachi Power Grids
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K settings and the
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negative sequence currents down to the continuous
capability of a generator.
In order to match the heating characteristics of the
generator a reset time parameter can be set.
A separate definite time delayed output is available as
an alarm feature to warn the operator of a potentially
dangerous situation.
Accidental energizing protection for synchronous
generator AEGPVOC
Inadvertent or accidental energizing of off-line
generators has occurred often enough due to operating
errors, breaker head flashovers, control circuit
malfunctions, or a combination of these causes.
Inadvertently energized generator operates as induction
motor drawing a large current from the system. The
voltage supervised overcurrent protection is used to
detect the inadvertently energized generator.
Accidental energizing protection for synchronous
generator (AEGPVOC) takes the maximum phase current
input and maximum phase to phase voltage inputs from
the terminal side. AEGPVOC is enabled when the
terminal voltage drops below the specified voltage level
for the preset time.
Stator overload protection GSPTTR
The generator overload function, (GSPTTR) is used to
protect the stator winding against excessive
temperature as a result of overcurrents. The functions
operating characteristic is designed in accordance with
the American standard IEEE-C50.13.
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. 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 stator winding or waited sum of the
positive and negative sequence components in the
stator winding.
The function is designed to work on 50/60 Hz systems.
Rotor overload protection GRPTTR
The generator overload function, (GRPTTR) is used to
protect the rotor winding against excessive temperature
as a result of overcurrents. The functions operating
characteristic is designed in accordance with the
American standard IEEE-C50.13.
1MRK 502 074-BEN M
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