TOSHIBA
PROTECTIVE DETECTION SCHEME
This chapter describes how the protective unit of the
detects failures.
7.1 Overload Unit
This is a function to thermally protect the motor insulations.
The component to
be protected is mainly the
Changes in
temperature when the motor
is in operation and at rest are represented by the following formula.
[During operation]
1
=
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*........*..
where
e
:
Temperature rise in time t
Final temperature rise that occurs when the
current It flows
continuously and which is determined by
of It.
TR:
Motor’s heating time constant
[At rest]
=
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
where
Temperature rise in time t
:
Temperature rise when the motor is at rest =
TD:
Motor’s cooling time constant
The equations
and
are represented in the following diagrams.
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