TOSHIBA
6F9EOlll
7.
PROTECTIVE DETECTION SCHEME
This chapter describes how the protective unit of the
SZE21
detects failures.
7.1 Overload Unit
This is a function to thermally protect the motor insulations.
The component to
be protected is mainly the
stator.
Changes in
stator
temperature when the motor
is in operation and at rest are represented by the following formula.
[During operation]
0
1
(t)
=
6
l=(lt).
(I-e-‘/Y
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...*........*..
(1)
where
e
i
(t)
: Temperature rise in time t
Bm(1t.j:
Final temperature rise that occurs when the
stator
current It flows
continuously and which is determined by
the.magnitude
of It.
TR:
Motor’s heating time constant
[At rest]
0
Z(t)
=
0
d(D)
.e-“ro
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(2)
where
82(t):
Temperature rise in time t
0
(0)
: Temperature rise when the motor is at rest
(t
=
0).
TD:
Motor’s cooling time constant
The equations
(1)
and
(2)
are represented in the following diagrams.
--
--
www . ElectricalPartManuals . com
To Next Page
Loading...
