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Lurer litt på dette med DC på nettet og harmoniske.Er DC komponenter på nettet det samme som overharmoniske spenninger/strømmer?Eller er overharmoniske et resultat av DC på nettet?
Legger ved litt lesestoff hentet fra støy i yrkesbygg fra statsbygg og linker til DC-filtre fra Sjøstrøm,LC Audio og den "nye" Syncro fra Isotek
Harmoniske strømmer og spenninger:
I økende grad benyttes apparater og utstyr som forvrenger spenningens kurveform fordi
strømmen som disse apparatene opptar fra nettet, ikke er sinusformet. Den forvrengte
spenningen vil bestå av en grunnharmonisk (50 Hz) og et antall harmoniske. Det er ofte 3-,
5- og 7-harmoniske som er fremtredende. Kraftelektronikk i apparater, f.eks. PC'er og
annet datateknisk utstyr, avbruddsfrie strømforsyninger (UPS'er) osv. er slike ulineære
laster som genererer støy på nettet. Et stort innslag av harmoniske i nettet kan gi
støyproblemer for annet elektronisk utstyr.
2.3 Beskrivelse av harmoniske
Strømmer i kraftsystemer var før kraftelektronikkens tid svært rene og sinusformede.
Kraft-elektronikk, dvs. likerettere, power supply, etc. benyttes nå i de fleste lastkilder
tilknyttet elektriske lavspenningsanlegg, og medfører at det genereres harmoniske
strømmer. For store harmoniske strømmer og spenninger i et elektrisk anlegg kan føre til
ekstra tap, over-opphetning og feilfunksjoner av tilkoblet utstyr og vern.
2.4 Årsaker til harmoniske strømmer
For fysiske laster vil frekvensene alltid bli oddetalls multiple av grunnfrekvensen f. Det er
belastningstypen som bestemmer hvilken harmonisk som vil bli fremhevet. De ulike
harmo-niske strømmene vil påvirke ulike deler av det elektriske anlegget. Kilder til
harmoniske er:
Lysbueprosesser. På grunn av lysbuens ulineære strøm-spenningskarakteristikk vil
denne type belastning forvrenge strømmens kurveform og generere harmoniske.
Typisk er lysbueovner og sveisestrømkilder
Elektriske maskiner. På grunn av at viklingene ikke er jevnt fordelt, men plassert i
spor, vil det i elektriske maskiner også bli produsert harmoniske i strøm og spenning
Krafttransformatorer. Her kan harmoniske oppstå på grunn av kjernematerialets
ulineære egenskaper, dvs, jernets metning:
- magnetiseringsstrøm i tomgang
- påslagsstrøm ved maksimal usymmetri
- likestrømsmagnetisering
Lysrøranlegg. Ved utladningslamper benyttes reaktansspoler for strømbegrensning,Kraftelektronisk utstyr (likerettere, PCer, frekvensomformere, lysarmaturer,
etc.). Dette utstyret er den største kilden til harmoniske strømmer og spenninger i
fordelings-nettet. Elektrisk ekvivalent for en kraftelektronisk krets vil være en
impedans som vari-erer i sprang flere ganger pr nettperiode. Det gir forstyrrelser på
samt diverse tennings- og reguleringsutstyr. På grunn av gassens ulineære elektriske
egenskaper vil denne typen lyskilder trekke en ikke-sinusformig strøm og generere
harmoniske på nettet.
http://www.isoteksystems.com/cgi-bin/products.pl?id=9http://www.lcaudio.com/index.php?page=316
http://sjostromaudio.com/pages/hifi-projects/36/109-dct02-the-dc-trap-high-end-style?showall=1
LC-Audio
This filter is inserted between the mains grid and the primary winding of the transformer. This way you can avoid mechanical humming from the mains transformer, caused by a varying DC component on the mains grid's AC voltage. The DC component comes from unbalanced loads on the mains grid, such as hair dryers, industrial machinery etc. with only half wave rectification. One half of the AC sine wave is loaded while the other is not. This cause imbalance, and a DC.
With this filter module, which also doubles as a safe mains distributor for your DIY power amplifier, you can remove the DC component and keep your power transformer quiet. It can be used for up to 500 VA idle load, and 1000 VA max load.
Sjøstrøm
Why does the transformer hum
Why does especially the toroid transformer hum, sometimes hard? The iron core is very efficient and the magnetic flux is high, very near magnetic saturation of the core. This gives very little room for "extra" flux which DC can cause. DC on AC mains is simply unsymmetrical waveform of the sinus wave. What happens if you have a hair drier with half speed? This is accomplished with a diode and halfway rectification, causing the positive peak voltage become lower than the negative. This creates a small DC level which some apparatus don't like, especially toroids. An another reason for DC on the mains is switching transients in large networks.
The DC trap makes sure that no DC slips through. The primary winding is AC coupled with help from two big electrolytic capacitors. The inrush current will go through the diodes when the capacitors have been charged over 1 or 3 volts and the normal current will only go through the capacitors.
Og til slutt Isotek syncro som det vistnok kommer en anmeldese på i Fidelity.
How Does Syncro Improve Audio Performance?
As we fill our homes with an ever-increasing number of electrical devices, we further degrade the mains supply, interfering with its quality and consistency. Audio equipment uses electricity to generate signals, amplified by more electricity to drive a pair of loudspeakers; the quality of the electricity that feeds an audio system has a direct impact on the resulting quality of sound.
IsoTeks extensive range of mains conditioning components improves the quality of the mains supply significantly, filtering out contaminants like RFI and EMI, and ensuring each component in the audio chain receives pure and consistent power in line with its specific requirements. However, there is a further issue with the electricity supply in our homes that has existed for years, without a truly effective commercial solution. The problem in question is sometimes referred to as DC on the mains. In terms of audio equipment, it is often signified by a buzzing sound emitted by a transformer in a power amplifier. Of course, this buzz is extremely distracting to the listener, and hardly in keeping with the concept of high-resolution audio. In addition, the mechanical vibration within the power transformer, created by core saturation, results in microphony in the internal components, leading to further degradation of sound quality.
These issues have nothing to do with the quality of the audio equipment used. In fact, some of the best amps available are the most seriously affected. The problem is a symptom of the poor state of mains electricity available in most homes, affecting not only amplifiers but source components, too.
Most of the DC-related issues suffered by audio systems are brought into being by the electrical devices we own, directly rectifying the mains from AC to DC (where a diode is used in series to allow either the positive or negative cycle of the mains sine wave to pass). The use of switch-mode power supplies exacerbates the problem, introducing measurable mains distortion. These devices create a lack of symmetry in the mains sine wave where it is displaced from the zero voltage line, leading to the aforementioned hum thats often noticeable from power amplifiers, as the DC voltage saturates the core of the transformers with DC current. This, in turn, generates unwanted mechanical vibration, resulting in audible noise and microphony, and increased power consumption and heat.
To give an example, if a sine wave reaches a peak of 326 Volts in the positive direction, it should also reach 326 volts in the negative direction to have perfect symmetry. This actually describes the reality of a 230 Volt AC wave form; the 230 Volts describes the heating effect of a sign wave whose peak is 326 Volts. If one peak reaches 327 Volts and the other 325 Volts, there is lack of symmetry. Although common sense suggests that such small variations should have no effect, in reality they create serious problems for audio systems; even tiny changes registering no more than a few millivolts create significant operational difficulties for amplifiers.
Inadequate remedies of the past
Historically, IsoTek advocated the use of huge isolating transformers to improve the cleanliness of the electricity supply (the company has since developed more advanced components for use in its power conditioners). A by-product of this technology helped to compensate for DC elements on the mains. However, this merely shifted the problem away from the audio equipment to the isolating transformer itself; audible mechanical hum may have been removed from the transformer in the power amp, but the isolating transformer would hum instead.
Ironically, in order to try to reduce dynamic loss in the amplifier created by the insertion of the isolation transformer, larger and larger devices were needed. However, the bigger the transformer, the louder the mechanical noise; the problem was never truly solved, merely shifted and often made worse.
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