ABB RELION REX640 Technical Manual page 417

Protection and control

Hide thumbs Also See for RELION REX640:

Table of Contents

1MRS759142 F

Figure 242: Trip curves at prior load 1 x FLC and p=50 %. Overload factor = 1.05.

MPTTR is intended to limit the motor thermal level to predetermined values

during the abnormal motor operating conditions. This prevents a premature motor

insulation failure.

The abnormal conditions result in overheating and include overload, stalling, failure

to start, high ambient temperature, restricted motor ventilation, reduced speed

operation, frequent starting or jogging, high or low line voltage or frequency,

mechanical failure of the driven load, improper installation and unbalanced

line voltage or single phasing. The protection of insulation failure by the

implementation of current sensing cannot detect some of these conditions, such

as restricted ventilation. Similarly, the protection by sensing temperature alone

can be inadequate in cases like frequent starting or jogging. The thermal overload

Technical Manual

Protection functions