ABB RELION Series, Technical Manual

Page: 260 / 804

I the largest phase current
I
ref
set Current reference
T
ref
set
Temperature rise
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 final n
t
e
= + −
( )
⋅ −








− −
−
1 1
1 τ
A070781 V2 EN
(Equation 7)
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
OPERATE
output is activated. The
OPERATE
signal pulse
length is fixed to 100 ms.
Section 4
1MRS758755 A
Protection functions
254 REC615 and RER615
Technical Manual