Phase Converters & Power Factor
Phase Converter Efficiency
Installing a Phase Converter
Rotary Phase Converters
Static Phase Converters
VFDs as Phase Converters
     • Harmonic Distortion
Three-Phase Motors
Phase Converters & Voltage Balance
Phase Converter Applications
     • Submersible Pumps
     • Woodworking Equipment
     • Dual Lift Stations
     • Phase Converters & Welders
     • Phase Converters & CNC Machines
     • Phase Converters & Air Compressors
     • Phase Converters & Elevators
     • Phase Converters & Wire EDM
     Phase Converters & HVAC
Phase Converters & Transformers
     • Step-up Transformers
     • Buck-Boost Transformers
     • Isolation Transformers
Phase Converter Experts
Digital Phase Converters
Regenerative Power
Three-Phase Power
     • Delta vs. Wye Configured Power
Motor Starting Currents

Phase Converter Efficiency


Efficiency can be an important factor to consider when choosing a phase converter.

Most three-phase loads are relatively large consumers of electrical power since they are used in commercial and industrial applications such as metal fabrication and pumping, so the operating efficiency of the system can have a significant economic impact over the life of the equipment.

There are two ways to measure efficiency of a phase converter the efficiency of the phase converter itself and the efficiency of the operated load. The quality of the three-phase power, primarily voltage balance, supplied by the phase converter can impact the efficiency of three-phase motors and rectifiers.

Static phase converters do not consume or waste much power in themselves. They are very simple devices with no moving parts. However, the operated motor will lose efficiency because it is being supplied with very poorly balanced power. For all intents and purposes, only two of the three windings of the motor are being supplied with power.

Because of this the motor must be severely de-rated.  If asked to perform more work than about half its rated capacity, the motor will begin to overheat and may suffer permanent damage

Rotary phase converters do a better job of supplying balanced voltages to a load but because their voltage balance is difficult to predict and impossible to control, the load may or may not be supplied with balanced three-phase power. If the load is not receiving balanced power, motor efficiency is lost and it must be de-rated to avoid damage. The rotary converter is also a consumer of power itself. It is usually built with a motor frame larger than the motor frame of the load it operates. And in order to improve the voltage balance and the ability of the converter to deliver starting currents, an even larger motor frame is used. It is common for the converter to be 2-3 times the size of the operated load for demanding applications. This contributes to losses in efficiency, especially when the converter is running with no load on it. The poor power factor of rotary converters also decreases their efficiency.  Oversized rotary converters may waste as much as 30% of the power they draw.

VFDs and digital phase converters are solid state devices with no moving parts that are very efficient. And because they supply the load with perfectly balanced power, the load operates at high efficiency. A digital phase converter is 95-98% efficient, slightly less efficient than a VFD. This is because the digital phase converter has filtering systems for both the input current and output voltage to remove harmonic distortion that can affect the load and the utility transformer. Removing these harmonics results in heat loss within the converter. A VFD generates less heat internally, so in itself, it is more efficient than a digital phase converter. However, the harmonics generated on the input and output of a VFD cause efficiency lost through generation of heat in the load and in the utility transformer. The efficiency loss is caused by the VFD, but occurs at other points in the system. In fact, the overall efficiency of a system powered by a digital phase converter is probably more efficient than one powered by a VFD because a digital phase converter only creates one voltage, while a VFD creates all three, leading to more heat losses in the motor windings.