ABB RED615 Technical Manual page 240

Section 4
Protection functions
234
The Temperature rise setting is used when the value of the reference temperature
rise corresponds to the Current reference value. The temperature values with the
corresponding transformer load currents are usually given by transformer
manufacturers.
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:
2
 
 
I
 
∆Θ = p T
*   *
ref
   
I
ref
 
 
 
GUID-27A879A9-AF94-4BC3-BAA1-501189F6DE0C V2 EN
ΔΘ calculated temperature rise (°C) in transformer
I measured phase current with the highest TRMS value
Current reference setting (rated current of the protected object)
Iref the set value of the
Tref the set value of the Temperature rise setting (temperature rise setting (°C) with the steady-state
current I )
ref
Weighting factor p setting (weighting factor for the short time constant)
p the set value of the
Δt time step between the calculation of the actual temperature
Short time constant setting (the short heating / cooling time constant)
the set value of the
t
1
Long time constant setting (the long heating / cooling time constant)
the set value of the
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 Short time constant and Long time
constant settings. The Short time constant setting describes the warming of the
transformer with respect to windings. The Long time constant setting describes the
warming of the transformer with respect to the oil. Using the two time-constant
model, the IED is able to follow both fast and slow changes in the temperature of
the protected object.
The Weighting factor p setting is the weighting factor between Short time constant
τ and Long time constant τ
1
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 Long time constant is used.

∆ t
 

−
I I

 
1 ( )
⋅ − e + − p ⋅
1 τ 1 
 
 
I
ref

  

. The higher the value of the Weighting factor p
2
1YHT530004D05 D
2

∆ t
 

−

 
2
⋅ T ⋅ − e
 1 τ
ref
 
 

  

Technical Manual
(Equation 8)
615 series