9.12.2 Application
GUID-66CBDF76-B548-478F-8D59-CBAC4F6C1F85 v1
GUID-ED2E176E-BE14-45C2-875F-369E1F27BC29 v1
Negative sequence overcurrent protection for machines NS2PTOC
(46I2) is intended
primarily for the protection of generators against possible overheating of the rotor
caused by negative sequence component 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 ground faults
• Broken conductors
• Malfunction of one or more poles of a circuit breaker or a disconnector
NS2PTOC (46I2) can also be used as a backup protection, that is, to protect the
generator in the event line protections or circuit breakers fail to perform for unbalanced
system faults.
To provide an effective protection for the generator for external unbalanced conditions,
NS2PTOC (46I2) is able to directly measure the negative sequence current. NS2PTOC
(46I2) also have a time delay characteristic which matches the heating characteristic of
the generator I
2
2
t = K as defined in standard.
where:
I
2
is negative sequence current expressed 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
A wide range of I
2
2
t settings is available, which provide the sensitivity and capability
necessary to detect and trip for negative sequence currents down to the continuous
capability of a generator
.
A separate output is available as an alarm feature to warn the operator of a potentially
dangerous situation.
9.12.2.1 Features
GUID-9B139200-C5FD-4870-93FD-2EB16B206B25 v4
Negative-sequence time overcurrent protection NS2PT
OC (46I2) is designed to
provide a reliable protection for generators of all types and sizes against the effect of
unbalanced system conditions.
The following features are available:
Section 9 1MRK 502 071-UUS A
Current protection
418 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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