ABB RELION REX640 Technical Manual page 385

1MRS759142 F
Θ
final
I
I
ref
T
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 higher than the set
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
n
Θ
n
Θ
n-1
Θ
final
Δt
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
output signal ALARM is set. When the component temperature reaches the set trip
level
pulse length is fixed to 100 ms.
REX640
Technical Manual
2
 
I
= ⋅
 
T
 
ref
I
 
ref
the highest phase current
Current reference
set
Temperature rise
set
( )
= Θ + Θ − Θ ⋅
− −
n 1 final n 1
calculated present temperature
calculated temperature at previous time step
calculated final temperature with actual current
time step between calculation of actual temperature
thermal time constant for the protected device (line or cable), set
stant
Maximum temperature , the OPERATE output is activated. The OPERATE signal
Maximum temperature , the START output is
∆
 
t
−
 
−
1 e τ
 
 
Protection functions
(Equation 31)
(Equation 32)
Time con-
Alarm value , the
385