This is the way GE is protecting the motor from being overheated. It is an electronic feature that simulates a bimetal relay based on internal measurements. The

characteristic is shown in the following figure:

Illustration 2.8: The X-axis is showing the ratio between I

Thermal Overload cuts off and trips the drive. The curves are showing the characteristic nominal speed at twice the nominal speed and at 0,2x the

nominal speed.

It is clear that at lower speed the Electronic Thermal Overload cuts of at lower heat due to less cooling of the motor. In that way the motor are protected from

being over heated even at low speed. The Electronic Thermal Overload feature is calculating the motor temperature based on actual current and speed. The

calculated temperature is visible as a read out parameter in par. DR-18 Motor Thermal in the frequency converter.

and I

nominal. The Y-axis is showing the time in seconds before the Electronic

motor

AF-600 FP Design Guide

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