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