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
A070783 V3 EN
(Equation 12)
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 49F.
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 49F 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 disabled and enabled back 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.
49F thermal model complies with the IEC 60255-149 standard.
4.1.4.5
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
Section 4
1MAC059074-MB A
Protection functions
272
615 series ANSI
Technical Manual
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