Have you ever worked on a project that needed a three-phase connection, but changing the service from single-phase to three-phase was impractical or impossible?
Imagine a small kitchen with a sizeable 3-phase mixer. The building has an existing single-phase service and enough capacity to handle equipment connections. In this scenario, changing the service to three-phase to accommodate a single piece of equipment's needs is impractical. What do you think can be done?
Rotary Converter
A rotary converter takes a single-phase AC input to operate a generator motor. The output of this motor is similar to a traditional engine-based generator. The difference is primarily in the fuel: single-phase AC electricity turns the motor (as opposed to an internal combustion engine). As the generator motor turns, the winding configurations on the output induce currents in three circuits at 120 degrees out of phase from the other. The outputs can be configured for WYE or Delta. When paired with a transformer, the voltage can also be changed.
Rotary converters are practical when powering multiple large motors at a time. They are like mini-power stations.
Rotary converters can be either digital or analog:
Analog Rotary Converters
All controls are analog. These are the most affordable, user-friendly option. The downside is they are limited in features.
Digital Rotary Converters
All controls are digital and have more features and control over the operation. The digital circuit creates a clean output to run voltage-sensitive loads (e.g., welders, computer-controlled loads).
Rotary converters are practical when powering multiple large motors at a time. They are like mini-power stations.
Pros
Power more than one motor at a time.
Plug-and-play/user-friendly; these devices are generally easy to wire and get working without highly specialized knowledge.
Cons
Noisy. The generator motor can be loud and create nuisance vibrations.
Wastes energy with low/no load conditions. The generator motor will be powered undo low/no load conditions, which can be wasteful.
Consult directly with manufacturers when selecting a device for your specific application! Here are a few options:
VFD Converter
A VFD (variable frequency drive) converter does not operate using a generator motor. Instead, the analog AC input is converted to DC and inverted back to a three-phase system using solid-state and digital logic technologies. This gives the end-user superior control over the operation of a device, typically a single motor. A VFD is also capable of modulating the output frequency.
A VFD converter can be helpful in a single-purpose application with voltage and frequency-sensitive loads. An example may be a restaurant with highly specialized three-phase equipment manufactured for European countries. If the location has only single-phase power available, that power will also be at 60 Hz in the United States. A VFD Converter may be selected to generate three-phase power and simultaneously change frequency to 50 Hz.
A VFD converter can be helpful in a single-purpose application with voltage and frequency-sensitive loads.
Pros
Silent
High efficiency
Speed control
Soft start and stop
DC brake (easy way to add an emergency stop)
Cons
Limited to one VFD per motor
Must be motor matched (i.e., configured for the specific motor connected to the load)
No downstream switching
Less user-friendly (requires specialized knowledge for installation and commissioning)
Consult directly with manufacturers when selecting a device for your specification application! Here are a few options:
Other Resources
Please share additional thoughts and resources below!
Thanks,
- Kenny
In traditional three-phase power systems, the voltage and frequency of the power supply are constant. However, in situations where only single-phase power is available, a phase converter can be used to generate three-phase power for use with three-phase equipment. A VFD can be used as a phase converter by converting the single-phase power supply into variable frequency three-phase power. Using a VFD as a phase converter can offer several benefits. First, it can be more cost-effective than purchasing a dedicated phase converter. Additionally, VFDs are often more compact and efficient than traditional phase converters. Finally, because VFDs can adjust the frequency of the output power, they can be used to precisely control the speed of three-phase motors. However, it's important to note that using a VFD as a phase converter does have some limitations. The power output of a VFD may not be as stable as that of a dedicated phase converter, which can cause issues with sensitive equipment. Additionally, VFDs can generate harmonics, which can lead to electrical noise and interference in other equipment. Overall, using a VFD as a phase converter can be a cost-effective and efficient solution for generating three-phase power in situations where only single-phase power is available. However, it's important to carefully consider the limitations and potential drawbacks before making a decision Useful Links to Refer https://www.wolfautomation.com/blog/phase-converters-vs-vfds/
https://www.phasetechnologies.com/explore/solutions/phase-conversion
https://www.wolfautomation.com/blog/variable-frequency-drives-vs-phase-converters/
http://www.vfds.org/single-phase-vfd-with-220v-input-output-924125.html https://www.youtube.com/watch?v=bROusBnTrho
The motor nameplate details will be for three phase rating. Then is there any criteria for designing the single phase side of the VFD? Or we can directly go with NEC tables?
Post updated with a pretty cool video of someone building their own phase converter!