ABB 615 Series - Page 307

I TRMS value of the measured max of phase currents
I
r
set Current reference , FLC or internal FLC
I
2
measured negative sequence current
k set value of Overload factor
K
2
set value of Negative Seq factor
p set value of Weighting factor
t
time constant
The equation θ
B
is used when the values of all the phase currents are below the overload
limit, that is, k x I
r
. The equation θ
A
is used when the value of any one of the phase currents
exceeds the overload limit.
During overload condition, the thermal level calculator calculates the value of θ
B
in
background, and when the overload ends the thermal level is brought linearly from θ
A
to
θ
B
with a speed of 1.66 percent per second. For the motor at standstill, that is, when the
current is below the value of 0.12 x I
r
, the cooling is expressed as:
θ θ
τ
= ×
−
02
e
t
GUID-2C640EA9-DF69-42A9-A6A8-3CD20AEC76BD V2 EN (Equation 18)
θ
02
initial thermal level when cooling begins
GUID-A19F9DF2-2F04-401F-AE7A-6CE55F88EB1D V2 EN
Figure 143: 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.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 301
Technical Manual