ABB RELION 620 Series Technical Manual page 382

Section 4
Protection functions
376
(
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 monitored if the final temperature is calculated to be above the
operation temperature. If the final temperature is below the operation temperature,
maximum estimated time to trip is monitored. The value is available in the monitored data
view as T_TRIP in seconds:
Θ − Θ
 
final trip
t τ ln
= − ⋅
 
trip
Θ − Θ
 
final n
A070782-ANSI V2 EN
After operating, caused by the thermal overload protection function, there can be a lockout
to reconnect the tripped circuit. 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. BLK_CLOSE works
also as hysteresis for the TRIP signal preventing a new TRIP signal activation until
BLK_CLOSE has reset. The Maximum temperature value must be set at least 2 degrees
above the set value of Reclose temperature.
The time to lockout release is calculated, that is, the calculation of the cooling time to a set
value. The calculated temperature can be reset to its initial value (the Initial temperature
∆ t
 
−
)
 
⋅ 1 − e τ
1
 
 
1MAC504801-IB E
(Equation 21)
Time constant
(Equation 22)
620 series ANSI
Technical Manual