What is a Rotary Frequency Converter:

Series RFC

Rotary Frequency Converter
Rotary Frequency Converters are machines that convert power from one frequency to another.  This is achieved by coupling a motor to a generator, which is mechanically coupled and electrically isolated.  The coupling method can be direct or via belts & sheaves.  However, there are a few with a gear box connection and in this case, they are not electrically isolated.  In other words, this is completed by either changing the rotational speed of the generator (in the versions with belts & sheaves) or the gear box.  The motors and generators may or may not have the same number of poles, depending upon the output frequency.  The result is operating to achieve the same result of producing the desired output frequency.  A rotary frequency converter is also capable of producing a different voltage at the same time.  If you are operating at another voltage other than 208V, you will need to change the voltage.

Power Systems & Controls’ Series RFC's are Rotary Frequency Converters designed to convert utility power into many other frequencies.  For instance, the standard frequencies are 25Hz, 50Hz, 60Hz, 100Hz, and 400Hz power.  The rotary frequency converter will provide the rated kVA requirements at the output needed.  In addition, a motor and synchronous generator will provide the required frequency and voltage.  PS&C’s Rotary Frequency Converters are built with 2 bearing and 4 bearing solutions, as well as, vertical or horizontal configurations.  A precision voltage regulator integrated within the system maintains the output voltage at (+/- .5%) far better than the industry standard.

Rotary Converter Functionality:

Under normal operation, the Series RFC protects the critical load protected from utility transients and brownouts.  However, the Rotary Frequency Converter is available with either a synchronous motor or induction motor.  In other words, this will depend upon which product will be best for the application.  A synchronous motor creates an exact frequency output with no deviation.  This is ideal for lab testing, aircraft support, and weapon system applications.  A low slip induction motor causes the output frequency to deviate (.6Hz).  This might be acceptable for projects that require a more economical solution.

Similarly, when operated at the rated motor speed, the frequency of the generator is controlled by the RPM of the motor.  This will make the output frequency variable or uncontrolled.  It is also 100% effective for outages lasting less than 100ms.  Also the absence of brushes and slip rings in both the motor and generator allows for virtually maintenance free operation.  Furthermore, due to its rugged design the average end of life (EOL) of a Rotary Frequency Converter is well over 20 years.  Above all, there are also numerous options available ranging from remote controls and color touch screen displays to specialized NEMA and ISO enclosures.

Common Terms Associated with a Converter:

  • Motor Generator = (MG set)
  • Common Shaft = Direct coupled shaft to shaft MG set is 
  • Single Shaft = The MG set is a single forging with motor & generator winding(s) on one shaft
  • Belt Drive = Side-by-side MG set connected via belts and sheaves
  • Gear Drive = Side by side or direct coupled with offset MG set connected via gear drive

Why Purchase Rotary Frequency Conversion:

There are many applications (see below) for frequency converters.  However, some applications require the need for industrial grade machines with brute force, while others require the 100% isolation.  Therefore, isolation is inherently produced by a rotary machine.  Above all, electric isolation is achieved by a mechanically coupled motor generator that will not allow power to pass through the shaft.  Therefore, isolation accomplished from the motor into the generator and visa versa.  These machines are built rugged for very harsh environments.  They can survive in extreme conditions, where the Solid State equivalent will not be able to operate in the same.
Rotary Frequency
Converter Applications:
Rotary Frequency
Converter Benefits:
  • 100% True Electrical Isolation
  • Precision Voltage Regulation
  • 2 & 4 Bearing M-G Sets
  • Control & Fault Monitoring
  • Transient & Brownout Protection
  • Vertical & Horizontal Configurations
  • Common & Single Shaft Designs

Do I have to use a motor generator set:

There is another version of conversion other than rotary or motor generator. Similar to a rotary machine, PS&C builds static converters in both Single Phase and 3 Phase.