ABB REG670 Applications Manual page 396

Section 9
Current protection
390
IEC08000358 V1 EN
Figure 201: Short-time unbalanced current capability of direct cooled generators
Continuous I - capability of generators is also covered by the standard. Table
2
below (from ANSI standard C50.13) contains the suggested capability:
Table 44: Continous I
Type of generator
Salient Pole:
Cylindrical Rotor
Indirectly cooled
Directly cooled
to 960 MVA
961 to 1200 MVA
1201 to 1500 MVA
As it is described in the table above that the continuous negative sequence current
capability of the generator is in range of 5% to 10% of the rated generator current.
During an open conductor or open generator breaker pole condition, the negative
sequence current can be in the range of 10% to 30% of the rated generator current.
Other generator or system protections will not usually detect this condition and the
only protection is the negative sequence overcurrent protection.
Negative sequence currents in a generator may be caused by:
• Unbalanced loads such as
• Single phase railroad load
• Unbalanced system faults such as
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
capability
2
with damper winding
without damper winding
1MRK 502 071-UEN -
en08000358.vsd
44
Permissible I (in percent of rated
2
generator current)
10
5
10
8
6
5
Application manual