RESOURCES
Adapting Single-Phase Products Into Three-Phase Power Systems
Executive Summary
In many industrial facilities or environments, only three-phase power is available. Many lower-power products operate off a single-phase input. This paper will demonstrate how to easily adapt a single-phase input product into a three-phase power system.
Introduction
Depending on the facility and the installation, the three-phase power source may or may not include a neutral connection in addition to Phase A, Phase B, and Phase C.
Common voltages for three-phase systems in North America include 4-wire Delta Systems with a phase-to-phase voltage of 208VAC/60Hz (phase-to-neutral voltage of 120V), or 480VAC/60Hz (phase-to-neutral voltage of 277V). In other parts of the world, typical power line voltages include 50Hz 5-wire WYE systems with a phase-to-phase voltage of 398VAC and a phase-to-neutral voltage of 230VAC, or a phase-to-phase voltage of 380V with a phase-to-neutral voltage of 220V.
Power conversion systems will typically be designed to draw power evenly from each phase so as not to overload wiring, distribution transformers, or circuit breakers. Managing the loading of the three phases can be done by connecting apparatus separately to each phase in such a way that loading is balanced, or by using power converters that connect to all three phases simultaneously, automatically providing phase balance.
How to Adapt a Single-Phase Input Power Module into a Three-Phase Power System
Not just any single-phase input power module may be used in a three-phase power system. Wide operating input voltage range and droop output current sharing are among a few important features that are required. One of Astrodyne TDI’s flagship products is the Mercury Flex. It is a 3.8kW per module, high power density variable output, and wide operating input product that accepts an input voltage of up to 265VAC. Three of these modules can be connected to either a three phase 208VAC Delta connection or a 220V WYE connection as long as the voltage between the two input legs of each Mercury Flex does not exceed 265VAC. An example of these configurations is shown in Figure 3.
The Mercury Flex features advanced droop current-share technology that allows the outputs to be connected in parallel and equally share the load current. This allows the Mercury Flexes to act as a balanced load to the three-phase power source. A minimum of three MercuryFlex modules are required while more can be connected to increase redundancy in case one module should fault or shut down. Whichever input configuration is used, keep in mind the voltage the input pins see which will also determine the maximum power allowable by the module.
Single-phase input modules of any power level can be adapted to a Three-Phase Power System. The Astrodyne TDI ASM series or similar are high-power density medical and industrial grade power supplies with various output voltage ratings up to 550W. The input and output connections can be connected similarly as shown in Figure 4. The ASM550 features droop current sharing as well as a sense line to compensate for line voltage drop. It also features certification to Medical IEC 60601-1 which allows for a robust, redundant, and flexible power system.
A single-phase product can also be adapted into an industrial or medical application where backup AC power is required, and only three-phase power is available.
Astrodyne TDI’s Power Bridge AC UPS can be used in a single-phase or three-phase power system as shown in Figure 5. The voltage between the two input legs of each product should never exceed the maximum input voltage rating. Keep in mind the final voltage that the product sees as this will determine the maximum allowable output power.
Conclusion
Astrodyne TDI offers many single-phase input products that are flexible and robust enough to handle your input power and output power and reliability requirements. With the flexibility and redundancy available with multiple single-phase input power products along with Astrodyne TDI’s legacy of reliable power supplies and systems, why worry? Now you have power.