Function Block; Functionality; Operation Principle - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.5.1.2
4.5.1.3
4.5.1.4
374

Function block

A07069-ANSI V2 EN
Figure 172: Function block

Functionality

The increased utilization of power systems closer to the thermal limits has generated a
need for a thermal overload function for power lines as well.
A thermal overload is in some cases not detected by other protection functions, and the
introduction of the thermal overload function 49F allows the protected circuit to operate
closer to the thermal limits.
An alarm gives an early warning to allow operators to take action before the line trips. The
early warning is based on the three-phase current measuring function using a thermal
model with first order thermal loss with the settable time constant. If the temperature rise
continues the function will operate based on the thermal model of the line.
Re-energizing of the line after a thermal overload operation can be inhibited for a time to
allow the line to cool. The time for the line to cool is estimated by the thermal model.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of the three-phase thermal protection for feeders, cables and distribution
transformers can be described using a module diagram. All the modules in the diagram are
explained in the next sections.
1MAC504801-IB E
620 series ANSI
Technical Manual