ABB RELION 670 SERIES REG670 - Page 426

Table 43: ANSI requirements for unbalanced faults on synchronous machines
Types of Synchronous Machine
Permissible
[ ]
2
2
I t K s=
Salient pole generator 40
Synchronous condenser 30
Cylindrical rotor generators: Indirectly cooled 30
Directly cooled (0 – 800 MVA) 10
Directly cooled (801 – 1600
MVA)
See Figure
201
Fig 201 shows a graphical representation of the relationship between generator
2
2
I t
capability and generator MVA rating for directly cooled (conductor cooled) generators.
For example, a 500 MVA generator would have K = 10 seconds and a 1600 MV
A
generator would have K = 5 seconds. Unbalanced short-time negative sequence current
I
2
is expressed in per unit of rated generator current and time t in seconds.
en08000358.vsd
IEC08000358 V1 EN-US
Figure 201: Short-time unbalanced current capability of direct cooled generators
Continuous I
2
- capability of generators is also covered by the standard. Table
44 below
(from ANSI standard C50.13) contains the suggested capability:
Section 9 1MRK 502 071-UUS A
Current protection
420 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual