ABB RELION 620 Series Technical Manual page 398

Section 4
Protection functions
392
2

  
I

=  + K ×
θ
 
A 2
 k I × k I
  
r

GUID-9C893D3E-7CAF-4EA6-B92D-C914288D7CFC V2 EN
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 overload
B
limit, that is, k x I . The equation θ
r
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
θ with a speed of 1.66 percent per second. For the motor at standstill, that is, when the
B
current is below the value of 0.12 x I
− t
= × e τ
θ θ
02
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θ initial thermal level when cooling begins
02
2


I
( )
− t /
2
 τ
× − 1 e × 100 %

× 

r

is used when the value of any one of the phase currents
A
, the cooling is expressed as:
r
1MAC504801-IB E
(Equation 28)
in
B
to
A
(Equation 29)
620 series ANSI
Technical Manual