ABB Relion 611 Series, Technical Manual

Page: 139 / 536

Θ Θ Θ Θ
∆
n n final n
t
e
= + −
( )
⋅ −








− −
−
1 1
1 τ
A070781 V2 EN
(Equation 3)
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.
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:
t
operate
final operate
final n
= − ⋅
−
−








τ
ln
Θ Θ
Θ Θ
A070782 V2 EN
(Equation 4)
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
OPERATE
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 .
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 setting) via a control parameter that is located under the clear menu. This
is useful during testing when secondary injected current has given a calculated false
temperature level.
1MRS757454 D
Section 4
Protection functions
611 series 133
Technical Manual