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
(Equation 33)
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.
t
lockout release
final lockout release
final n
_
_
ln= − ⋅
−
−
τ
Θ Θ
Θ Θ
(Equation 34)
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
Current multiplier
parameter to the number of parallel lines (cables),
the actual current on one line is used in the protection algorithm. To activate this
option, the ENA_MULT input must be activated.
The ambient temperature can be measured with the RTD measurement. The
measured temperature value is then connected, for example, from the AI_VAL3
output of the X130 RTD function to the AMB_TEMP input of T1PTTR.
The
Env temperature Set
setting is used to define the ambient temperature if
the ambient temperature measurement value is not connected to the AMB_TEMP
input. The
Env temperature Set
setting is also used when the ambient temperature
measurement connected to T1PTTR is set to “Not in use” in the X130 RTD function.
The temperature calculation is initiated from the value defined with the
Initial
temperature
setting parameter. This is done in case the protection relay is powered
up, the function is turned "Off" and back "On" or reset through the Clear menu.
The temperature is also stored in the nonvolatile memory and restored in case the
protection relay is restarted.
The thermal time constant of the protected circuit is given in seconds with the
Time
constant
setting. Please see cable manufacturers manuals for further details.
T1PTTR thermal model complies with the IEC 60255-149 standard.
Protection functions 1MRS759142 F
386 REX640
Technical Manual
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