ABB RELION 611 Series Technical Manual page 154

Section 4
Protection functions
148
I TRMS value of the measured max of phase currents
I set Current reference , FLC or internal FLC
r
I measured negative sequence current
2
Overload factor
k set value of
Negative Seq factor
K set value of
2
Weighting factor
p set value of
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
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, when
B
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 67: 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
. The equation θ is used when the value of any one of the
r A
, the cooling is expressed as:
r
1MRS757454 D
in
B
A
(Equation 8)
611 series
Technical Manual