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So why are rotary phase converters better?

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After all this you are probably wondering why a phase converter manufacturer can remain in business for any length of time and still sleep at night. Well a rotary converter improves things dramatically and so reputable manufacturers encourage clients to purchase rotaries rather than statics wherever reasonably possible. A basic rotary converter simply adds a correctly sized motor to a static converter. The motor has no mechanical function whatsoever and is simply there as an electrical component to create the third phase irrespective of what is happening to the driven loads. From a packaging perspective a motor is basically iron and copper, and a transformer is basically iron and copper, and there are designs on the market that wrap up the transformer inside specially wound motors, in which case they are called rotary transformers (this design is more widespread in the USA). The alternative approach is to use standard components, in which case the motor is known as a pilot, donkey, slave, idler, or auxiliary motor and it can either be housed within the phase converter cabinet or placed separately. For a basic converter from a technical perspective there is little to choose between using standard components versus manufacturing rotary transformers (each design has slightly different characteristics, but other technical factors are more important) and so commercial factors sway manufacturers to one design or the other. However for an advanced rotary phase converter there are technical reasons to use standard components (with some special tweaks) and so at Boost we don't use rotary transformers.

Irrespective of whether it uses a rotary transformer or a motor generator a rotary greatly reduces the need to adjust the capacitance and so phase converter manufacturers can then guarantee a certain amount of phase balancing across a given operating range - indeed there might be no level switches at all in a rotary phase converter.  Nevertheless Boost's more advanced D series converters do incorporate automatic electronic 'noiseless' switching to finely tune the capacitance and thereby increase the quality of the phase balancing.

A rotary completely eliminates the problem of having to start the largest load motor first (or the need to have a load motor at all), and similarly eliminates the possibility of load motors ever two-phasing. Provided a sufficiently good quality rotary phase converter is purchased it will give an output that is equal in quality to the utility company's three-phase supply.

There is an extra purchase cost associated with a rotary converter, as the motor needs to be provided and transported. Indeed in general transportation costs are significant for such a heavy and low volume item as a phase converter, which is why there is little competition from non-UK producers.