ABB RELION 670 SERIES REG670 - Generator Continuous Unbalance Current Capability

• 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
2
2
I t K=
capability curve of
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.
• Maximum trip 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.
9.12.2.2 Generator continuous unbalance current capability
GUID-7C2DBEA9-4423-47DD-90FD-88F4AAD2E9A9 v3
During unbalanced loading, negative sequence current flows in the stator winding.
Negative sequence current in the stator winding will induce double frequency current
in the rotor surface and cause heating in almost all parts of the generator rotor.
When the negative sequence current increases beyond the generator’s continuous
unbalance current capability, the rotor temperature will increase. If the generator is not
tripped, a rotor failure may occur. Therefore, industry standards has been established
that determine generator continuous and short-time unbalanced current capabilities in
terms of negative sequence current I
2
and rotor heating criteria
2
2
I t
.
Typical short-time capability (referred to as unbalanced fault capability) expressed in
terms of rotor heating criterion
2
2
I t K=
is shown below in Table 43.
1MRK 502 071-UUS A Section 9
Current protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 419
Application manual