ABB RELION Series Technical Manual page 260

Section 4
Protection functions
254
I the largest phase current
I set Current reference
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 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:
(
Θ = Θ + Θ − Θ
n n 1 final n
−
A070781 V2 EN
Θ calculated present temperature
n
Θ calculated temperature at previous time step
n-1
Θ calculated final temperature with actual current
final
Δt time step between calculation of actual temperature
thermal time constant for the protected device (line or cable), set
t
The actual temperature of the protected component (line or cable) is calculated by
adding the ambient temperature to the calculated temperature, as shown above. The
ambient temperature can be given a constant value or it can be measured. The
calculated component temperature can be monitored as it is exported from the
function as a real figure.
When the component temperature reaches the set alarm level Alarm value, the output
signal ALARM is set. When the component temperature reaches the set trip level
Maximum temperature, the OPERATE output is activated. The OPERATE signal pulse
length is fixed to 100 ms.
t
∆
 
−
 
)
1 e τ
⋅ −
1
−
 
 
1MRS758755 A
(Equation 7)
Time constant
REC615 and RER615
Technical Manual