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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
Summary of Contents for Relion 615 series
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