ABB 615 series Technical Manual page 283

1MAC059074-MB A
615 series ANSI
Technical Manual
GUID-FF965F1C-6039-4A01-9A4F-B378F8356279-ANSI V2 EN
Figure 133: Functional module diagram
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 thermal estimator.
Temperature estimator
The final temperature rise is calculated from the highest of the three-phase currents
according to the expression:
2
 
I
T
Θ =   ⋅
final ref
 
I
ref
 
GUID-06DE6459-E94A-4FC7-8357-CA58988CEE97 V2 EN
I highest measured phase current
Current reference setting
I the set value of the
ref
Temperature rise setting (temperature rise (°C) with the steady-state current I
T the set value of the
ref
The ambient temperature value is added to the calculated final temperature rise
estimation. If the total value of temperature is higher than the set trip temperature level, the
PICKUP output is activated.
The Current reference setting is a steady-state current that gives the steady-state end
temperature value Temperature rise. It gives a setting value corresponding to the rated
power of the transformer.
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.
Section 4
Protection functions
(Equation 13)
ref
277