ABB RELION 620 Series Technical Manual page 381

1MAC504801-IB E
620 series ANSI
Technical Manual
A070747-ANSI V2 EN
Figure 173: Functional module diagram. I_A, I_B and I_C represent phase currents.
Max current selector
The max current selector of the function continuously checks the highest measured TRMS
phase current value. The selector reports the highest value to the temperature estimator.
Temperature estimator
The final temperature rise is calculated from the highest of the three-phase currents
according to the expression:
2
 
I
Θ = ⋅
  T
final ref
 
I
 ref 
A070780 V2 EN
I the largest phase current
Current reference
I set
ref
Temperature rise
T set
ref
The ambient temperature is added to the calculated final temperature rise estimation, and
the ambient temperature value used in the calculation is also available in the monitored
data as TEMP_AMB in degrees. If the final temperature estimation is larger than the set
Maximum temperature, the PICKUP output is activated.
Current reference and Temperature rise setting values are used in the final temperature
estimation together with the ambient temperature. It is suggested to set these values to the
maximum steady state current allowed for the line or cable under emergency operation for
a few hours per years. Current values with the corresponding conductor temperatures are
given in cable manuals. These values are given for conditions such as ground
temperatures, ambient air temperature, the way of cable laying and ground thermal
resistivity.
Thermal counter
The actual temperature at the actual execution cycle is calculated as:
Section 4
Protection functions
(Equation 20)
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