t
lockout release
final lockout release
final n
_
_
ln= − ⋅
−
−
τ
Θ Θ
Θ Θ
A070783 V3 EN (Equation 6)
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 IED 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 IED
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.
4.1.5.5 Application
The lines and cables in the power system are constructed for a certain maximum
load current level. If the current exceeds this level, the losses will be higher than
expected. As a consequence, the temperature of the conductors will increase. If the
temperature of the lines and cables reaches too high values, it can cause a risk of
damages by, for example, the following ways:
• The sag of overhead lines can reach an unacceptable value.
• If the temperature of conductors, for example aluminium conductors, becomes
too high, the material will be destroyed.
• In cables the insulation can be damaged as a consequence of overtemperature,
and therefore phase-to-phase or phase-to-earth faults can occur.
In stressed situations in the power system, the lines and cables may be required to
be overloaded for a limited time. This should be done without any risk for the above-
mentioned risks.
1YHT530004D05 D Section 4
Protection functions
615 series 229
Technical Manual
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