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EXERCISE
: The
slightest error in connection of a motor can result in its instant
destruction when voltage is applied. In order to avoid this type
of disaster, try and complete the table below by indicating for
every case the connection that should be made (Y or D)
depending on the type of motor and the supply voltage involved.
|
Type
of motor
|
Connection
depending on supply voltage
|
|
Three-phase
ê
|
3
x 127 V
|
3
x 220 V
|
3
x 380 V
|
3
x 660 V
|
|
127
/ 220 V
|
|
|
|
MM
|
|
220 / 380 V
|
|
|
|
|
|
380 / 660 V
|
|
M
|
|
|
The sign
M
means that there is a supply under-voltage.
The consequences of too low a supply voltage are discussed on page 377
(and will be elaborated on in the next chapter). To remind us,
if the motor is being used to drive a machine with a large resistant
torque (a compressor, for example), it may not start to run. The
motor will "stall" whilst still having the starting
current passing through it. Hopefully, the thermal safety devices
and internal protection will cut off the supply to the motor before
it "burns out" once and for all.
The sign
MM
means that there is a supply
over-voltage. The serious consequences of over-voltage are described on page 377, but
there is usually no happy ending with this type of mistake: the
motor "burns out" almost immediately when voltage is
applied!
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