Smith Electric Motorworks ©  Legal

Automatic Voltage Regulation


Variable Capacitor Voltage Regulation

The rotary phase converter--for all its nuances--is still the most efficient and economical way to operate multiple 3-phase loads from single-phase. But a reliable method of varying the capacitor bank to balance loads appears desirable.


Unfortunately, a reliable method of capacitor switching that does not damage operated equipment requires complicated technology and is fairly expensive to build. In 1988, GWM Corp. collaborated with Tom Lehman of Adaptive Design Company to build a computerized phase converter that would switch capacitors to adjust for varying load conditions. After a number of revisions and several thousand hours of work, the result was the Substation SS-1, rev. 7.0, which achieved stellar performance, but it was very complicated and expensive to manufacture.


Since we wanted the SS-1 to have stand-alone capability as an alternative to a rotary converter on moderately-loaded multi-motor applications such as machine shops, we were forced to add some very elaborate and expensive surge protection devices, mainly to protect the Substation's electronics from sudden load changes.


As a complement to a rotary motor, the SS/Rotomax became a variable-capacitor rotary converter that would produce very clean power and well-regulated voltages under a wide load range.


Because of its high-cost and limited applicability, however, Substation production is currently suspended. An abbreviated version of the SS-1, as an enhanced voltage regulation device for rotary converters, may be available at a later date, to facilitate operation of increasingly voltage sensitive motors.

Substation™

It's like a big, computer-controlled static phase converter that automatically adjusts itself to the load. When hooked up to a rotary it automatically balances the voltages.

Problematic Voltage Regulation Attempts


I want to draw a contrast here between the computerized voltage regulation device we developed--the Substation--and a mechanism that is making the rounds of more than one converter manufacturer under the guise of "automatic voltage regulation." The device simply consists of a voltage sensing relay linked to a contactor that divides the rotary's capacitor bank. At load, about half of the rotary's capacitors are switched off. As the load increases, one of the voltages drops to a preset threshold and the contactor adds back the other half of the capacitor bank.


We noticed the above devices popping up a few years ago when we began advertising our Substation. What troubles me is that this device is a voltage regulator in the same fashion that a guy standing over a car engine with a garden sprayer full of gasoline has fuel injection--the aim and regulation is terrible, and has the potential to cause a great harm. Here's the problem: when capacitors are switched under load, bad things can happen, since capacitors will store a charge at full voltage, and the line--which, remember, we said changes from positive (+) to negative (-) 60 times a second--can have a different charge than the capacitors do when the device switches "on". The sensor used on this "voltage regulator" has no way of relating to the line or capacitor charge, it just switches arbitrarily.


And that's another thing: our Substation varied power in 447 steps, not just two (off-on). And the SS-1 used a computer and triac switching to ensure that no reverse charges would resonate the transformers in your equipment or double the voltage going to your sensitive CNC electronics through random switching.


I am presuming the existence of some type of bleeder resistor on the device. But, absent a microprocessor drive, there is no guarantee that the device won't chatter-- negating the bleeder effect--or continue working if the bleeder malfunctioned.


Don't make the mistake of using any kind of "voltage regulation" such as I've described here with a phase converter. It can be damaging to your equipment. I'm not criticizing the method without good reasons. My company--along with a few other major manufacturers of phase converters--has worked to minimize damage to our industry by hare-brained speculators and people who should know better. We all get tarred with a big brush when one of these ideas bears rotten fruit. Please don't fall for it.


And if you are thinking the "regulator" would work well on CNC--it doesn't at all. Any capacitor switching device--our SS-1 included--could not anticipate a load change--it only responds after the load is initiated or removed. Best results are obtained by using an oversized converter designed for CNC and dedicating one converter to one machine. A steady power supply to your CNC gives it the freedom to run smoothly and do what it does best--make parts with no alarms and no downtime. This will make you the most money.

GWM's DIGI-Series produces ±5% voltage balance for operation of computerized machine tools and other voltage-sensitive equipment.

There actually is a significant design controversy in rotary converter construction which may account for some of the problems dealt with thus far, and a digression on the two schools of thought follows.