ABB RELION REX640 Technical Manual page 375

1MRS759142 C
REX640
Technical Manual
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 
  
p T
1
∆Θ =  ⋅  ⋅  ⋅
 ref 
I
 
ref
  
 
GUID-EDAEFA49-4961-4684-BBE6-2BD8239237D9 V1 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
p the set value of the Weighting factor p setting (weighting factor for the short time constant)
Δt time step between the calculation of the actual temperature
the set value of the Short time constant setting (the short heating / cooling time constant)
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 protection
relay 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
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.
2
t
 I
∆
  
−
e 1 p
1
τ
( )
−  +  − ⋅  ⋅

I

ref
   

. The higher the value of the Weighting factor p setting, the
2
Section 4
Protection functions
t ∆

 
−
T e 2
1
τ
 ⋅ −
ref  

 

(Equation 35)
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