Operation Principle - ABB RED615 Technical Manual

1YHT530004D05 D
4.1.6.4
615 series
Technical Manual

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of the three-phase thermal overload, two time constant protection for
power transformers can be described using a module diagram. All the modules in
the diagram are explained in the next sections.
I_A
Max
I_B
current
I_C selector
BLOCK
AMB_TEMP
GUID-FF965F1C-6039-4A01-9A4F-B378F8356279 V2 EN
Figure 118: 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
counter.
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 
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
T the set value of the
ref
I
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 operate
temperature level, the START 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.
Temperature
estimator
Thermal
counter
Section 4
Protection functions
START
OPERATE
ALARM
BLK_CLOSE
(Equation 7)
233