ABB RED615 Technical Manual page 256

Section 4
Protection functions
250
I TRMS value of the measured max of phase currents
Rated current , FLC or internal FLC
I set
r
I measured negative sequence current
2
Overload factor
k set value of
Negative Seq factor
K set value of
2
p set value of Weighting factor
time constant
t
The equation θ is used when the values of all the phase currents are below the
B
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 with a speed of 1.66 percent per second. For the motor at standstill, that is,
A B
when the current is below the value of 0.12 x I
−
t
= × e τ
θ θ
02
GUID-2C640EA9-DF69-42A9-A6A8-3CD20AEC76BD V2 EN
θ initial thermal level when cooling begins
02
GUID-A19F9DF2-2F04-401F-AE7A-6CE55F88EB1D V2 EN
Figure 126: 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,
. The equation θ is used when the value of any one of
r A
, the cooling is expressed as:
r
1YHT530004D05 D
in
B
(Equation 12)
615 series
Technical Manual