ABB RELION REX640 Technical Manual page 391

1MRS759142 F
The function uses ambient temperature which can be measured locally or remotely.
Local measurement is done by the protection relay. Remote measurement uses
analog GOOSE to connect AMB_TEMP input.
AMB_TEMP
Figure 229: 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:
Θ
final
I
I
ref
T
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
end temperature value
the rated power of the transformer.
The
rise corresponds to the
the corresponding transformer load currents are usually given by transformer
manufacturers.
REX640
Technical Manual
If the quality of remotely measured temperature is invalid or
communication channel fails the function uses ambient temperature set
Env temperature Set .
in
I_A
I_B
I3P
I_C
BLOCK
2
 
I
=   ⋅
T
  ref
I
 
ref
highest measured phase current
the set value of the
the set value of the
steady-state current I
Current reference setting is a steady-state current that gives the steady-state
Temperature rise . It gives a setting value corresponding to
Temperature rise setting is used when the value of the reference temperature
Current reference value. The temperature values with
Max current Temperature
estimator
selector
Current reference setting
Temperature rise setting (temperature rise (°C) with the
ref
Protection functions
START
OPERATE
Thermal
ALARM
counter
BLK_CLOSE
(Equation 35)
391