Single and Three-Phase Pump Configurations: What Do You Really Need?

February 28, 2018

Single-phase and three-phase pumps, what's the difference? That's a hard question to answer unless the reader knows something about how electricity works. More power load capability, that's the advantage of a three line power supply. But why do three separate conductors yield extra pumping force? Well, this is alternating current, not direct current. It's a polyphase sensation, a technology that needs some explaining before it can be properly appreciated.

A Brief Look at the Principles Behind Phased Electricity

Traditional single-phase pumps utilize a single waveform, a 50 or 60-Hertz AC power supply that induces a magnetic field. The electromagnetic force then produces motion. The pump rotor, locked by a shaft coupler, also spins. Polyphase systems use three separate AC power supplies. Pages of electrical principles explain how this technology works, but we choose to summarize the key elements. In brief, the discrete power lines furnish three differently timed waveforms, and those peaks and troughs are 120° apart. Remember, AC power is produced by rotating metal coils and magnets, so everything comes down to circles and degrees.

There are Two A.C. Pumping Forces at Work

The polyphase system bolsters its cycling power so that an energetic magnetic field is on hand to propel a heavy load. Meanwhile, the single-phase solution drives light-to-medium burdens, perhaps with the aid of a mechanical gearing system. Clearly, a three-phase machine, thanks to those three harmonized power lines, can push harder, so why isn't it used in every pumping system? Well, single-phase pumps are more than enough for most applications. Three-phase devices are only required when a pump is impelling a heavy fluid load. After all, the addition of more wires and more magnetic fields are required to build a polyphase electrical motor, so an engineer isn't about to install this expensive machinery unless the application absolutely calls for extra drive muscle.

There's one other thing about that polyphase solution we should mention. Tasked with starting a stubborn fluid mass, a three-phase rotating magnetic field isn't particularly efficient. We use special wiring configurations to solve this issue, but that means yet more expense. Electrical switches (contactors) enter the equipment rack. They use what's called a STAR configuration to first get the pump rotor moving, then the DELTA contactor takes the place of the first three-phase switch as the pump runs up to full speed. So, although that polyphase solution is the obvious load champion here, it does require more parts, including those out of phase power lines. Employ those costlier systems when the pumping application needs extra muscle. Otherwise, install a capable single-phase solution.

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