Application - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.1.6.5
322
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.

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.
• Overheating can damage the insulation on cables which in turn increases the risk
of phase-to-phase or phase-to-earth faults.
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.
The thermal overload protection provides information that makes temporary
overloading of cables and lines possible. The thermal overload protection estimates
1MRS757644 F
620 series
Technical Manual