ABB 615 series Technical Manual page 277

1MAC059074-MB A
615 series ANSI
Technical Manual
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 TRIP output is activated. The TRIP signal pulse length is fixed to 100
ms.
There is also a calculation of the present time to operation with the present current. This
calculation is only performed if the final temperature is calculated to be above the
operation temperature:
Θ − Θ
 
final trip
t τ ln
= − ⋅
 
trip
Θ − Θ
 
final n
A070782-ANSI V2 EN
Caused by the thermal overload protection function, there can be a lockout to reconnect
the tripped circuit after operating. The lockout output BLK_CLOSE is activated at the
same time when the TRIP output is activated and is not reset until the device temperature
has cooled down below the set value of the Reclose temperature setting. The Maximum
temperature value must be set at least two degrees above the set value of Reclose
temperature.
t
∆
 
−
 
)
1 e τ
⋅ −
1
 
 
Section 4
Protection functions
(Equation 10)
Time constant
(Equation 11)
271