Re: [CAD_CAM_EDM_DRO] VFD superceeds Motor Starter?

scyvt wrote:

> Electromechanical motor starters, as have been in general use for at
> least 70 years, offer motor protection from overvoltage, undervoltage,
> and overcurrent. From an operator safety standpoint, perhaps the most
> important feature is no-voltage protection; that is, if there is an
> interruption of power, the machine will not automatically start up
> when power is restored.
>
> Modern electronic VFD's offer all the above functions, plus of course
> variable speed and a raft more. But are they considered as reliable as
> the time-tested electromechanical motor starters as far as guarding
> operator safety? In other words, can I use a VFD alone where a motor
> starter was used before?
>

If properly configured, and the control circuits are wired with this
concern in mind, then yes, and it is done in industry all over the place.
In general, a single power component failure might make the motor wires
"live", but would never be able to start the motor turning.
I don't know how they deal with the possibility of a failure in the
control inputs to the microprocessor, but I suspect that the various
safety rating agencies require a design such that at least two
components need to fail for the motor to start without a proper command
from outside.

Jon