ABB 615 Series ANSI, Technical Manual

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1MAC050144-MB C
Section 4
Protection functions
615 series ANSI 295
Technical Manual
(Equation 14)
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
Շ 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. 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. The value is available in the monitored data view as T_TRIP in
seconds:
(Equation 15)
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
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.
(Equation 16)
Here the final temperature is equal to the set or measured ambient temperature.
In some applications, the measured current can involve a number of parallel lines. This is
often used for cable lines where one bay connects several parallel cables. By setting the
Θ Θ Θ Θ
Δ
n n final n
t
e
= + −
( )
⋅ −
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
− −
−
1 1
1

t
trip
final trip
final n
= − ⋅
−
−
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟

ln
Θ Θ
Θ Θ
t
lockout release
final lockout release
final n
_
_
ln = − ⋅
−
−
⎛
⎝
⎜⎜

Θ Θ
Θ Θ
⎞⎞
⎠
⎟⎟