ABB RELION REX640 Technical Manual page 392

Protection functions
Thermal counter
T2PTTR applies the thermal model of two time constants for temperature
measurement. The temperature rise in degrees Celsius (°C) is calculated from the
highest of the three-phase currents according to the expression:
∆Θ
ΔΘ
I
I
ref
T
ref
p
Δt
t
1
t
2
The warming and cooling following the two time-constant thermal curve is a
characteristic of transformers. The thermal time constants of the protected
transformer are given in seconds with the
constant settings. The Short time constant setting describes the warming of the
transformer with respect to windings. The
warming of the transformer with respect to the oil. Using the two time-constant
model, the protection relay is able to follow both fast and slow changes in the
temperature of the protected object.
The
τ and
1
p setting, the larger is the share of the steep part of the heating curve. When
Weighting factor p =1, only Short-time constant is used. When Weighting factor p =
0, only
392
 

2
 
I
 

=   ⋅
p * * T 1
 
 ref 

I
 
 ref 

 
calculated temperature rise (°C) in transformer
measured phase current with the highest TRMS value
the set value of the
object)
the set value of the
with the steady-state current I
the set value of the
time constant)
time step between the calculation of the actual temperature
the set value of the
time constant)
the set value of the
time constant)
Weighting factor p setting is the weighting factor between Short time constant
Long time constant τ
Long time constant is used.

∆

t
 
−
I I


( )
− + − ⋅  
1
e τ 1 p
 


I
 
 ref


Current reference setting (rated current of the protected
Temperature rise setting (temperature rise setting (°C)
)
ref
Weighting factor p setting (weighting factor for the short
Short time constant setting (the short heating / cooling
Long time constant setting (the long heating / cooling
Short time constant and Long time
Long time constant setting describes the
. The higher the value of the
2

∆
 
2
t
−

 
⋅ ⋅ −
2
T 1 e τ
ref 
 

 

Weighting factor
Technical Manual
1MRS759142 F
(Equation 36)
REX640