Features - ABB REG670 Applications Manual

Section 9
Current protection
9.12.2.1
388
To provide an effective protection for the generator for external unbalanced
conditions, NS2PTOC is able to directly measure the negative sequence current.
NS2PTOC also have a time delay characteristic which matches the heating
characteristic of the generator I
where:
I is negative sequence current expressed in per unit of the rated generator current
2
t is operating time in seconds
K is a constant which depends of the generators size and design
2
A wide range of I t settings is available, which provide the sensitivity and capability
2
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 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 operate time delay for inverse time characteristic, freely settable. This
setting assures appropriate coordination with, for example, line protections.
• Maximum operate time delay for inverse time characteristic, freely settable.
• Inverse reset characteristic which approximates generator rotor cooling rates and
provides reduced operate time if an unbalance reoccurs before the protection
resets.
• Service value that is, measured negative sequence current value, in primary
Amperes, is available through the local HMI.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
2
t = K as defined in standard.
2
1MRK 502 071-UEN -
2
=
I t K
capability curve of
2
Application manual