[BC] Cyberpower brand UPS

[RichardBJohnson at comcast.net]

In an article about generators, some claimed that the AC output from a generator is always “clean” and that the load produces any distortion. This is not correct. The alternator portion of a standby generator is not a pure sine-wave source because it uses nonlinear magnetic materials. In a portable alternator, one of the design factors will be weight. One will optimize the performance vs. weight so that the machine can perform as intended without having weight that provides no useful purpose. It is well known that construction-site equipment such as power saws and welders will operate fine with a power source containing a high harmonic content. Therefore, the amount of heavy magnetic material used in the design of such alternators is minimized which produces an output waveform that is no longer sinusoidal.

For alternators designed as “bolt in place” units, there are other trade-offs including noise, efficiency, and harmonic content. As previously mentioned, alternators at permanent generating stations feeding the power grid will always produce less than one percent harmonic content because this was regulated by tariff. However, one cannot guarantee that the supplier of standby generating equipment considers this important. For the most part some harmonic content, produced both by the alternator and by any nonlinear loads, will not affect proper operation at a radio or television station. Unfortunately, this is not often true for solid-state UPS sets, which try to anticipate power outages by sampling peak voltage. The peak of the AC voltage waveform from many standby generators may be somewhat flattened because the magnetic materials in the field are nearing saturation. This is a well-known affect and one can “Google” for BH curves to refresh ones understanding.

Sizing a generating set for a larger capacity than required will not minimize harmonic distortion because it is the volts-per-turn and the mean magnetic field length that determines the magnetic field strength in the magnetic circuit, not the volt-amperes flowing in the windings.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/