US power system

[Uncle Peter]

te:

The underground has it's own power station?

-- =

Why did the Blonde put ice in her boyfriend's condom? To keep the swelling down.

[Andrew Gabriel]

Residential roads normally only have a single phase HV feed, and then this is used to supply single-phase pole mount transformers (look like dustbins), which provide a 120-0-120 output to a few houses. The more main roads will have a 3-phase HV, which is used to feed a single phase HV up each residential street.

[Andrew Gabriel]

Whether it's called 2-phase or not is a never ending argument in US forums. In physics/maths terms, it's clearly valid to call it two phases, but in supply distribution jargon, they have a 2-phase supply which is something completely different (refers to a 4-wire circuit with 90 degrees between 2-phases).

[The Natural Philosopher]

Its single phase really or two 180 degree out of phases.

In physics/maths terms, it's clearly valid to call it

I doubt it.

no one uses 90 degree phase differences.

120 degrees as 3 phase is used for all transmission.

[Dave Plowman (News)]

Do you mean by that the mains would have to be 10Hz away from 50? I've seen 2 or 3 adrift on my meter here - but never that much.

But even then I'd be surprised if a tungsten filament lamp reacted at all. Things like some fluorescents and discharge lamps are a different matter if running at mains frequency. Which is why all the general purpose studio luminairs were all tungsten.

[Dave Plowman (News)]

But closely involved with actual shooting. My guess is you weren't?

When TV came off mains lock, it would have then been kept to an extremely accurate 50 Hz (or whatever). Mains can vary quite some way either side. Are you saying the mains feed to the lights at TC etc was in someway better in this respect?

[Dave Plowman (News)]

I'm not convinced that would be a problem with tungsten lighting anyway. Large filament tungsten takes ages to react to any change in voltage. If it reacted to an AC sine wave by switching on and off lots of humans would see it - as happens with fast reacting lights like some type of fluorescents.

[Dave Plowman (News)]

No it wasn't.

[The Natural Philosopher]

Nah. what I meant was that if it has contracted to take electricity it cannot use, it can sell that on.

I don't think the underground has its own power stations at all. Substations, yes. Got to turn into into DC somehow.

[Uncle Peter]

I would have thought they'd just sell it back to where they got it from. Perhaps the contract might say we will restock it for you at 20% fee.

[Tim Streater]

I think it's always had one, at least since it was electrified. I remember reading about it in the same book that had the article about the Norwich Heat Pump.

[Bill]

In message , "Dave Plowman (News)" writes

Not by a lot, take a look at this item.

[Johny B Good]

Less confusingly referred to as bi-phase.

True when it comes to distribution networks. It' only generated locally to the motors that use an approximation to 90 degree phases.

A fully balanced 3 phase supply only needs 50% more copper to triple the power delivery capacity of the cabling. Adding a neutral only doubles the copper costs for that 3 fold boost in line capacity. The neutral never has to carry more than any single phase current in the worst case imbalance (a loss of 1 or 2 of the 3 phases).

Polyphase using more than 3 phases aren't used because the copper savings return versus complexity rapidly diminish beyond the savings made with a 3 phase system.

[Tim Streater]

Not now, but see:

which is what I was referring to.

[Johny B Good]

Tungsten filament lamps generate a 100Hz component which can't be detected by normal human vision, not even peripherally where the eye is most sensitive to flicker. The only reason for fluorescent tube flicker to become detectable is when the tube starts to partially rectify the 50Hz ac waveform (only a 3% imbalance is required for this to become noticable).

The camera strobe effect with tungsten lighting is only a slight problem because of the very shallow modulation depth of the 100Hz flicker effect whereas, in the case of discharge tubes such as a fluorescent lamp, the depth of modulation is 100%, only mitigated by the decay emmission light curve of the phosphor coating.

The worse lamp types for this undesired strobing effect are the high pressure mercury vapour and xenon gas discharge lamps, not forgetting the sodium street lighting lamps, since these don't employ a phosphor coating which would otherwise 'smooth out' the flicker.

[charles]

If yiou are crating programmes using NTSC 525/60 in the UK, then the maisn is 10Hz away from field frequency.

yet a 10Hz beat was visible.

[charles]

No. TC had a 60Hz generator, but it only fed electronics, not lighting.

[Uncle Peter]

I take it at that time they couldn't just contact the national grid and say we need 50MW.

[Dave Plowman (News)]

Right. Well, despite working in TV all my life, the number of times I saw this done was near zero. More usual to standards convert it later.

You'll have to be more specific. What lamps were in use? Which studio?

[charles]

TC6 & 7 were equipped for NTSC 525/60 as well as PAL 625/50 when they were first equipped for colour, or perhaps I should say color. This facility was only used once and, as you not, standards converters were used there after. What lanterns? The same as in use in all the other colour studios at the time. The dual purpose (fresnel/flood) - a BBC spec, but I can't remebember who made them.