07-09-2022, 05:49 AM
I did mention VARs and power factor. For most kit with poor PF, VARs will scale with watts as you change the voltage. Your electric meter meter measures watts and ignores VARs though this isn't true for larger non-domestic users who pay for VARs too.
VARs still mean current in the cables that heat them up and cause losses. VARs still have to be generated though to a first approximation they don't use any fuel to do this. VARs and harmonics are generally bad news for power distribution systems. For example 3rd harmonic causes high neutral current in a 3 phase system.
Although all modern SMPS are PF corrected (apart from the very smallest) they still make harmonics. I've put a scope* on a couple and it's not pretty. The input current is in phase with the voltage but it's peaky. Some may be better than the ones I've tried.
Old fashioned radios and TVs with half-wave rectifiers were really bad offenders. They only took power during part of half of a cycle of mains. The waveform distortion could get serious in residential areas when lots of people were watching TV.
*You need to know what you're doing to do this safely.
VARs still mean current in the cables that heat them up and cause losses. VARs still have to be generated though to a first approximation they don't use any fuel to do this. VARs and harmonics are generally bad news for power distribution systems. For example 3rd harmonic causes high neutral current in a 3 phase system.
Although all modern SMPS are PF corrected (apart from the very smallest) they still make harmonics. I've put a scope* on a couple and it's not pretty. The input current is in phase with the voltage but it's peaky. Some may be better than the ones I've tried.
Old fashioned radios and TVs with half-wave rectifiers were really bad offenders. They only took power during part of half of a cycle of mains. The waveform distortion could get serious in residential areas when lots of people were watching TV.
*You need to know what you're doing to do this safely.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
