Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.1.4.6
REX640
Technical Manual
is useful during testing when secondary injected current has given a calculated false
temperature level.
Θ

final
t ln
τ
= − ⋅

lockout release _

GUID-8BA1EB12-51DB-4BF8-A912-44797DEFFD78 V1 EN
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
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 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.

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:
− Θ

lockout release _

Θ − Θ
final n
 
Section 4
Protection functions
(Equation 33)
363