PBSI Group - Protection Relays

Application Advice

The Thermal Model is the primary protective element of any motor protection relay, for some the thermal calculation is a well understood method, for others the thermal model is a mathematical conundrum.


In essence, the thermal model of todays P&B protection relays is a software modelled characteristic of the thermal motor protection relays which were developed by P&B in the 1940s' using the heating principle of a bimetallic element.

As they were in the 1940s, the electrical network principles of todays modern world are precisely the same, the difference simply is the use of new technology.

A modern microprocessor relay requires accurate and correctly calculated settings in order for the thermal model to operate properly and protect the motor. The advantage of the modern motor protection relay allows for much closer co-ordination and tighter operating limits for the machine as well as means to communicate those measured and metered values.

Please download the following application example which explains how the primary setting of the thermal model, t6x, is calculated and defined.

thermal application example

Other application issues may be answered in our FAQ pages, otherwise please do contact us if you do require application or setting assistance.