ABB RELION REX640 Technical Manual page 413

1MRS759142 F
=
θ
A
I
I
r
I
2
k
K
2
p
t
The equation θ
overload limit, that is, k x I
the phase currents exceeds the overload limit.
During overload condition, the thermal level calculator calculates the value of θ
background, and when the overload ends the thermal level is brought linearly from θ
to θ
A
when the current is below the value of 0.12 x I
θ
=
θ
02
Figure 239: Thermal behavior
The required overload factor and negative sequence current heating effect factor
are set by the values of the
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
constant stop settings. Only one time constant is valid at a time.
REX640
Technical Manual

2
  
I I

 + × 2
 
K
2
× ×

 k I   k I
 r
TRMS value of the measured max of phase currents
Current reference , FLC or internal FLC
set
measured negative sequence current
Overload factor
set value of
set value of Negative Seq factor
Weighting factor
set value of
time constant
is used when the values of all the phase currents are below the
B
with a speed of 1.66 percent per second. For the motor at standstill, that is,
B
− t
τ
θ
× e
02
initial thermal level when cooling begins
Time constant start , Time constant normal and Time

2
 ( )
−

t / τ
× − ×

1 e 100 %


r 
. The equation θ is used when the value of any one of
r A
, the cooling is expressed as:
r
Overload factor and Negative Seq factor settings.
Protection functions
(Equation 39)
in
B
(Equation 40)
413