I often find myself in the position of trying to solve a problem or complete a project with a budget of small to none.
I was trying to come up with an economical reactor for VFD motor leads.
I thought of using transformer windings and this train of thought led to other thoughts.
- A transformer makes a good VFD filter but it is expensive.
- How about using a low voltage secondary winding of of a transformer as a reactor.
This will probably cost more than a reactor and is wasteful of material.
- How about combining the two ideas.
If we use a three phase auto transformer and boost the voltage, we have the advantage of the low voltage winding acting as a filter, and with extra voltage available at the motor, we can go somewhat above the supply frequency before we hit the Volts per Hertz limit.
10 HP, 208 Volt motor.
With a 120:24 Volt autotransformer between the drive and the motor, we can boost the 208 Volts to 250 Volts.
Now we can maintain our 3.47 Volts per Hertz ratio up to 72 Hz.
And at 72 Volts we now have 12.4 HP out of a 10 HP motor.
I am interested in comments as to the effectiveness of the filtering.
The extra HP will often be only an added safety factor.
And the HP boost helps to justify the cost of a transformer.