ABB RELION 620 Series Technical Manual page 405

1MAC504801-IB E
620 series ANSI
Technical Manual
When protecting the objects without hot spot tendencies, for example motors started with
soft starters, and cables, the value of Weighting factor p is set to 100 percent. With the
value of Weighting factor p set to 100 percent, the thermal level decreases slowly after a
heavy load condition. This makes the protection suitable for applications where no hot
spots are expected. Only in special cases where the thermal overload protection is required
to follow the characteristics of the object to be protected more closely and the thermal
capacity of the object is very well known, a value between 50 and 100 percent is required.
For motor applications where, for example, two hot starts are allowed instead of three cold
starts, the value of the setting Weighting factor p being 40 percent has proven to be useful.
Setting the value of Weighting factor p significantly below 50 percent should be handled
carefully as there is a possibility to overload the protected object as a thermal unit might
allow too many hot starts or the thermal history of the motor has not been taken into
account sufficiently.
Section 4
Protection functions
399