It is not a simple problem, the Generac XG series has a total harmonic distortion from 4.7 t0 25% , the XP series, less than 5%. But what is THD?.
The AC voltage supplied by the grid has a sinusoidal form (as shown in the next post) , very near to the ideal smooth curve represented by the math function sine. The main characteristic of this ideal curve is that it has not sharp changes in its trajectory. When this curve is converted in voltage, and is fed to a resistive device, such as an incandescent lamp, it impulses a current with the same wave form, a smooth variable current waveform.
Any deviation from this ideal sine waveform is called distortion. In the AC supplied by the grid, there are many big generators carefully designed to produce the best waveform and quality electrical power. In a 60 cycles per second (60 Hz) system, this frequency is named the fundamental frequency.
Due to design difficulties and costs, many portable generators produce not only a non sinusoidal waveform but more than the funamental frequency; along with the 60Hz, there are multiples of this freq., double, triple etc and they are called harmonics.
If the fundamental frequency is 60 cycles per second, at to say 120 volts, the other unwanted frequencies, especially the third harmonic (180 Hz), are present in a variable amount, to say 5volts, 12 volts etc. the fifth may be 3 volts in example. The sum up of the total amount of unwanted voltages, generated at frequencies different to 60 Hz, expressed as a percentage of the the fundamental 60 Hz 120 volts, is called Total Harmonic Distortion.
This THD, is fed mixed with the 60 Hz, deforming the smooth curve, and depending of the load, may or may not be too harmful. An incandescet lamp or a portable drill are not affected, but a sofisticated electronic control may be alterated in its functions seriously, induction motors may overheat, as power transformers.
To filter this harmonics, there are special harmonic filters. Most common filters or economic line conditioners, merely filter out spikes or noise, regulators mantain line voltage inside safe margins, but to avoid harmonics out of your delicate electronics, you will need dedicated harmonic filters, that will control spikes too.
An UPS (uninterruptible power supply), may or not may solve the problem.
Be aware of simple UPS that will provide an horrible "square" wave full of power spikes and deformations ( see the photo) that will harm anything but an incandescent lamp. There are other that provide a "modified sine wave", similar to the produced by the common inverters, better than square . The pure sine wave inverters or UPS produce a clean, distortless voltage wave appropiate for all kind of equipment.
But, UPSs and inverters (domestic) run on low voltage DC current. UPSs have an internal battery, used only when normal AC supply is cut. Most of them (the small ones ) have a by pass relay to feed directly the protected equipment with the AC mains. The true online UPSs convert the AC supply to DC and then generates an AC sinusoidal, clean voltage wave, independent of the incomming supply. This is a solution, costly but solution.
The other solution would be exchange your generator for an XP10000.
In few words:
Harmonic filter, true online UPS, XP10000 genset, or take the risk to damage your equipment.
Last edited by Osviur; 05-25-2016 at 07:01 PM.