I had a query this morning, somebody unsure whether or not he should use a square wave system. Well, what are the advantages and disadvantages of this type of system?
There is only one advantage – price. A square wave system is the cheapest to produce. It requires the fewest, and cheapest components available.
When I first became involved with UPS I was astonished that square wave UPS even existed. I thought a UPS provides power when the lights go out – right? My assumption was that the power it would deliver would be equivalent, if not better than the power that was originally present. After all, as an educated electrical engineer, I knew that the mains power was a 50Hz sinewave waveform, so you would assume that a device that simulated the mains power would generate exactly the same? How wrong this assumption is. A square wave is a nasty waveform, in effect bombarding your equipment with a high frequency transient (the leading edge of the squarewave) of a voltage up to 300V 50 or 100 times per second. These transients have a damaging effect on all electrical circuitry.
So why use them?
Well, as power cuts are usually infrequent, the damaging effect of the UPS is limited. In addition, a typical PC will have a Switched Mode Power Supply (SMPS) that will appear to work fine with a square wave input. So for a home PC, for protection against infrequent power cuts, and only to prevent annoyance, rather than any critical data, a square wave system provides a cost-effective power protection solution.
A square wave system has its place, but only for non critical applications, and only for protection against infrequent short term power cuts, and then again, only for systems that have a SMPS. For anything other than this, you need to look at sinewave systems.