Features - ABB RELION RET670 Applications Manual

1MRK 504 163-UUS A
9.16.2.1
Transformer protection RET670 2.2 ANSI
Application manual
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
2
the generator I t = K as defined in standard.
2
where:
I is negative sequence current expressed in per unit of the rated generator current
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t is operating time in seconds
K is a constant which depends of the generators size and design
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A wide range of I t settings is available, which provide the sensitivity and capability
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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.

Features

Negative-sequence time overcurrent protection NS2PTOC (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:
• Two steps, independently adjustable, with separate tripping outputs.
• Sensitive protection, capable of detecting and tripping for negative sequence
currents down to 3% of rated generator current with high accuracy.
• Two time delay characteristics:
• Definite time delay
• Inverse time delay
•
The inverse time overcurrent characteristic matches
the generators.
• Wide range of settings for generator capability constant K is provided, from 1 to
99 seconds, as this constant may vary greatly with the type of generator.
• Minimum trip time delay for inverse time characteristic, freely settable. This
setting assures appropriate coordination with, for example, line protections.
Section 9
Current protection
GUID-9B139200-C5FD-4870-93FD-2EB16B206B25 v4
2
=
I t K
capability curve of
2
601