Temperature
estimator
Thermal
counter
ENA_MULT
ALARM
BLK_CLOSE
OPERATE
BLK_OPR
START
Max
current
selector
I_A
I_B
I_C
AMB_TEMP
Figure 169: 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
temperature estimator.
Temperature estimator
The final temperature rise is calculated from the highest of the three-phase
currents according to the expression:
Θ
final
ref
ref
I
I
T
=
⋅
2
(Equation 11)
I
the largest phase current
I
ref
set
Current reference
T
ref
set
Temperature rise
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
START
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:
Protection functions
1MRS757644 H
338
620 series
Technical Manual
