Glad to see you maintained the correct phase colours.
Upgrade to 3 phase
- Thread starter SUNRAY
- Start date
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A lot of sound guys will categorically refuse to use different phases 'because it will create interference'.
I suppose that that might well be true, unless one has good balance over the three phases and all running in the same cable.
Kind Regards, John
Indeed... but, being a former "Noise Boy" before I moved over to power.....I believe that 'interference' is often earth hum because enough attention hasn't been paid to circular signal earth paths (ie. use a STAR earth regime) or using balanced lines or (audio) isolation transformers between various pieces of equipment (and NEVER EVER EVER disconnecting a (mains) earth to "stop hum")
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It is not a problem I have encountered, as long as the audio system is designed and installed correctly, ie see post #49
Yes, I can believe that - but it does depend upon the audio stuff being designed/constructed to be fairly immune to 50Hz fields - since there would presumably be plenty of that in the vicinity of a 3-phase cable carrying fairly high and unbalanced currents.
Kind Regards, John
What you need is the Russ Andrews¹ phase-balancing mains conditioner.
Interconnected sub-band resonant equalisers create inter-phase currents which are out of phase with the intra-phase current flows, resulting in perfect balance, removal of harmonics and lowering of the noise floor.
£17,320.51 for the 3kW model.
¹ Other snake-oil merchants are available.
Interconnected sub-band resonant equalisers create inter-phase currents which are out of phase with the intra-phase current flows, resulting in perfect balance, removal of harmonics and lowering of the noise floor.
£17,320.51 for the 3kW model.
¹ Other snake-oil merchants are available.
Why would the cable be unbalanced?
Even without a neutral the 3ph cable will be balanced, or else the RCD would trip.
Eh? I'm talking about between-phases balance (something which is by no means always the case). A 3-phase RCD will only trip if the vector sum of the three phase currents is different from that in the neutral.
Even if current is flowing in only one or two of the three phases (i.e. extreme cases of phase imbalance), provided nothing is leaking to earth, a 3-phase RCD will still not trip.
Kind Regards, John
The RCD doesn't know, or even care, what the selection of conductors are that it's monitoring. If there is no leakage, to earth or otherwise, then the resultant summed current in the cable will be zero regardless of how balanced the phases are, and the resultant magnetic field around the cable will be [relatively] minimal.
The time I'm wary of big fields is the main singles coming away from the generators, sometimes they are just a random heap or spread out over a wide area.
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Yes, but as I implied, the vector sum of currents in all the conductors will be zero only if either (a) all three phase and neutral conductors are in the cable or (b) if, when there is no neutral conductor in the cable, currents are identical in the three phase conductors (i.e. perfect phase balance).
As I said, the 'worst case' of (b) (the worst possible phase imbalance) is to have current flowing in only one of the three phase conductors, and no neutral. You've then got the equivalent of just a 'single', which will radiate 50Hz all over the place ... in other words, exactly the same as you go on to mention ....
Kind regards, John
This is the quote I have been referring to
Your later posts refer to a separate current carrying conductor external to the cable in which case the magnetic field could be huge [eg AFILS] and if the additional conductor does not pass through the RCD then it will trip. This would be an incorrectly designed/built system even though the supply could still be balanced.
As I understand it you are referring to a complete power line in one cable, ie it contains all of the current carrying conductors in a circuit. In this situation the CABLE will be carrying a balanced load regardless of how many phases are loaded, the RCD will be happy and there will be minimal magnetic field.
Your later posts refer to a separate current carrying conductor external to the cable in which case the magnetic field could be huge [eg AFILS] and if the additional conductor does not pass through the RCD then it will trip. This would be an incorrectly designed/built system even though the supply could still be balanced.
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Indeed, but when I wrote that the cable would only be balanced if it does contain "all of the current carrying conductors in a circuit" (i.e. including a neutral - I wrote "if it had a neutral"), you responded with ...
Which I'm afraid I did (and still do) struggle to understand.
Kind Regards, John
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