ABB RELION REX640 Technical Manual page 431

1MRS759142 F
Figure 247: Trip time curves
In order to account for the difference between the warm and cold curves the
Weighting factor p is used. This defines the difference, which is based on the warm
and cold locked rotor times defined by the motor manufacturer.
can be calculated by the following equation:
k
LRT
LRT
The
temperature limit for the rotor is often higher. Therefore, the used thermal capacity,
when running at full load, can be quite low. For example, with warm and cold locked
rotor times being 5 and 6 seconds and
factor p could be set to 18.4%.
In addition, the
calculation. It is used to properly distinguish between short-time thermal stress
REX640
Technical Manual
2
ℎ =
Overload factor ,
is the
is the locked rotor time for warm start and
warm
is the locked rotor time for warm start.
cold
Weighting factor p for the rotor is usually lower than for the stator, since the
ℎ = 1.05
Weighting factor p is used in the cumulative thermal level
)
(
∙ 1 − ∙ 100%
Overload factor being 1.05, the Weighting
5
(
)
2
1 − 100% = 18.4%
∙ ∙
6
Protection functions
Weighting factor p
(Equation 53)
(Equation 54)
431