02/07/2013
Inexpensive Paralleling of Rotary Frequency Converters
http://www.georator.com/ProductRotaryMotorGenerator.html
Running rotary frequency converters, driven by induction motors, in a parallel mode, is made especially difficult because of drive motor slip, that is, the decrease of drive motor RPM with increasing loading. That, along with variations in the drive train, especially with belt-coupled motor-generator sets, make maintaining parallel operation a tricky process.
A solution to this dilemma is to use adjustable speed drives (ASD’s) to run the frequency converters, rather than traditional motor starters. Use of a single ASD to run multiple motor generator sets, together with feedback loops from the output of the individual generators back to the ASD, allows the MG sets to operate in parallel.
Unfortunately, the failure of one of the converters will cause the entire output to stop. Again, in critical situations, multiple ASD’s drive multiple motor generators, can address this issue, so that parallel redundant operation can occur. The failure of one converter will not stop the system, since the remaining motor generators will continue to operate. Expensive? Yes. Multiple ASD’s can run up the cost. But in those situations where failure of a converter stops the entire output, this expense may be critical to the success of the operation. A pharmaceutical processing plant that requires uninterruptible product flow, where stoppage causes a catastrophic loss of product, may well justify the expense.
