RGF 300
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1.4 ELECTRIC MOTORS
Three phase asynchronous motors can be connected to the
rgf300
regulator in applications where the torque-
motor speed characteristic is quadratic.
This mainly allows phase cutting application with axial and centrifugal fans used for control purposes.
The correct electrical connection and the supply voltage are given on the motor's specifications plate.
The sense of rotation of the motor can be altered by swapping the connections of two of the three supply
cables.
It is important to keep the motor power supply cable as short as possible to reduce the level of interference
and leakage currents to a minimum
(10 / 15 mt)
; if the cable has to be long, an auxiliary three-phase filter of
exactly the same power as the regulator must be installed on the regulator output.
The figure below shows the star and delta connection configurations.
fig. 8
The
rgf300
regulator can control several motors connected in parallel but the absorption of the motors' total
current must never exceed the rated current as given on the
rgf300
's specification plate.
The speeds of the motors vary at the same time though any differences in behaviour during start up and at
low speeds are due to slight differences between the motors even if they are of the same type. However, if
the required speeds of the motors are different, motors must be used with different rated speeds. Bear in
mind though that motors with very different characteristics create different electrical situations and these
may cause problems on start up and at low speeds caused by different resistances of the stators which require
different voltages on start up and at low speeds.
1.4.1 Magnetothermal protection
rgf300
devices must be protected by a magnetothermal switch fitted upstream of the cutting regulators.
Installation of magnetothermal protections is the responsibility of the installer
.
It is advisable to fit an automatic magnetothermal protection with a 'C' intervention curve having the
following capacity:
RGF 300 models
magnetothermal
carrying capacity
rgf 312 20 A
rgf 320 30 A
rgf 325 36 A
rgf 340 60 A
rgf 360 80 A
Table 2
U V W
Z X Y
U V W
Z X Y
STAR CONNECTION DELTA CONNECTION
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