Three-phase power can be drawn by either the Delta configuration or the Wye configuration. In the Delta configuration, two of the power wires are combined to create a circuit that looks like an equilateral triangle (or Delta). A neutral is combined with any of the power wires in the “Wye” configuration.
Three-phase electric power is a common method of alternating-current generation, transmission and distribution. Indeed, most AC power is produced and distributed as three-phase power with three sinusoidal voltages 120 degrees out of phase with each other.
120 V and 240 V residential power, on the other hand, is a single-phase connection—a two-wire AC power circuit that is used to power home TVs, other appliances, lights, etc. Typically, there is one power wire and one neutral wire. Power flows between the power wire through the load and the neutral wire.
A three-phase system uses less conductor material to transmit electric power than equivalent single phase due to the higher loss on long power lines at lower voltages.
Another choice might be to just take 480 VAC, three phase directly to the cabinet. There are some advantages to doing so, which might include eliminating the need for the transformer. Lines for 480 V / 277 V provide more power to operate machinery and a lot of fixtures using lower amps and therefore smaller wires, so they can be run without losing a significant percentage of voltage. Running a long lighting circuit, such as one for a parking lot, using 277 V might be more advantageous because of the voltage drop. Since 277 V also requires less current for a given lighting load, it is advantageous for large loads.
Noise: An Unwelcome Addition
EMI is uncontained electrical noise that is propagated over a wide range of frequencies. It can be generated by sparking on motor brushes, machines (like welding equipment), power circuit switches, activation of inductive and resistive loads and more. In particular, direct current motors and traction motors are very noisy. Every kind of switch-mode power converter also produces a broadband interference spectrum and harmonics as byproducts of its operation.
Introduced noise can find its way into sensitive electronics, causing spurious performance. While some EMI noise sources are difficult to eradicate, most of the time they can be contained and isolated. This is always a challenge for the design engineer.
EMI Filters: The Solution
To address this interference, an EMC filter should be employed. Schaffner, a well-known manufacturer of power filters and components, offers a variety of filter products. While Schaffner can offer three-phase filtering, a more effective solution both for cost and performance could be the implementation of an appropriately rated single-phase filter closer to the noise source. This could be a board-level or in-line filtering solution.
The Schaffner RN choke, for example, is rated to 300 VAC to cover 277 V applications. The choke can be used on a PCB, on a lighting ballast or in other applications. RN chokes attenuate common-mode or asymmetric interference signals by connecting in series with the phase and neutral lines of an AC powerline input. Symmetrical components of the noise are attenuated by the stray inductance of the windings. These chokes are typically used in conjunction with suppression capacitors.
Schaffner’s FN2410H and FN2412H families rated 480 V + 10 percent can cover either 277 V (single phase) and 480 V (two phase) requirements. FN2410Hs are designed for traditional chassis mounting installation while FN2412 filters can be snapped-in on popular TS 35 DIN-rails, which are common in most electrical cabinets. These filters are ideally suited for operation for phase to phase or phase to neutral in a three-phase power network. If higher power single-phase—100 A, 200 A or 500 A—is required, Schaffner can supply that as well.
In a single-phase system, noise can occur between phase (P) and neutral (N) lines. To counteract this EMI, filters should be placed as close to the noise source as possible to ensure that electrical and electronic products comply with National (FCC) and International EMC standards. Schaffner is the best source for EMI solutions, with the world's broadest selection of EMC/EMI filters and chokes. For further information, please visit www.schaffner.com.