ABB RELION REX640 Technical Manual page 397

1MRS759142 C
REX640
Technical Manual
t
−
e
τ
θ θ
= ⋅
02
GUID-DB478ADF-BD47-4A6A-8E1B-3FE4E9DF8A10 V1 EN
θ initial thermal level when cooling begins
02
GUID-DB9F72C2-99D6-4BA7-BEBC-2D8AD0FF17AC V1 EN
Figure 214: Thermal behavior
The required overload factor and negative sequence current heating effect factor are
set by the values of the Overload factor and Negative Seq factor settings.
In order to accurately calculate the motor thermal condition, different time constants
are used in the above equations. These time constants are employed based on different
motor running conditions, for example starting, normal or stop, and are set through the
Time constant start, Time constant normal and Time constant stop settings. Only one
time constant is valid at a time.
Table 442: Time constant and the respective phase current values
Time constant (tau) in use
Time constant start
Time constant normal
Time constant stop
The Weighting factor p setting determines the ratio of the thermal increase of the two
curves θ and θ .
A B
The thermal level at the power-up of the protection relay is defined by the Initial
thermal Val setting.
The temperature calculation is initiated from the value defined in the Initial thermal
Val setting. This is done if the protection relay is powered up or the function is turned
off and back on or reset through the Clear menu.
Protection functions
Phase current
Any current whose value is over 2.5 x I
Any current whose value is over 0.12 x I
currents are below 2.5 x I
r
All the currents whose values are below 0.12 x I
Section 4
(Equation 39)
r
and all
r
r
391