ABB RELION REF615R, Technical Manual

Page: 303 / 664

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 final n
t
e
= + −
( )
⋅ −








− −
−
1 1
1 τ
A070781 V2 EN
(Equation 13)
Θ
n
calculated present temperature
Θ
n-1
calculated temperature at previous time step
Θ
final
calculated final temperature with actual current
Δt time step between calculation of actual temperature
t
thermal time constant for the protected device (line or cable), set Time constant
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:
t
trip
final trip
final n
= − ⋅
−
−






τ
ln
Θ Θ
Θ Θ
A070782-ANSI V2 EN
(Equation 14)
1MRS240050-IB C
Section 4
Protection functions
REF615R 297
Technical Manual