a rotary phase converter circuit for equal phase voltages under maximum load may be quite important. Power quality A common measure of the quality of the power produced by an RPC or any phase converter is the voltage balance, which may be measured while the RPC is driving a balanced load such as a three-phase motor. Other quality measures include the harmonic content of the power produced and the power factor of the RPC motor combination as seen by the utility. Selection of the best phase converter for any application depends on the sensitivity of the load to these factors. Three-phase induction motors are very sensitive to voltage imbalances. The quality of three-phase power generated by such a phase converter depends upon a number of factors including: Power capacity of the phase converter (idler horsepower rating). Power level demands of the equipment being supplied. For instance, "hard starting" loads such as heavily loaded machinery or well pumps may have higher requirements than other loads rated at the same horsepower. Power quality demands of the equipment being supplied (CNC equipment may have more stringent power quality requirements than a welding machine) Use of techniques to balance the voltage between the three legs. Quality improvement RPC manufacturers use a variety of techniques to deal with these problems. Some of the techniques include, The insertion of capacitors between the terminals to balance the power at a particular load. The use of idlers with higher power ratings than the loads. The construction of special idler motors with more windings on the third terminal to boost the voltage and compensate for the sag caused by the load. The use of electronics to switch in capacitors, during start up or otherwise, based on the load. The use of filters. Uses General Demand exists for phase converters due to the use of three-phase motors. With increasing power output, three-phase motors have preferable characteristics to single-phase motors; the latter not being available in sizes over and, though available, rarely seen larger than . (Three-phase motors have higher efficiency, reduced complexity, with regards to starting, and three-phase power is significantly available where they are used.) Electric railways Rotary phase converters are used to produce a single-phase for the single overhead conductor in electric railways. Five European countries (Germany, Austria, Switzerland, Norway, and Sweden), where electricity is three-phase AC at 50 Hz, have standardised on single-phase AC at 15 kV