High Voltage, high frequency?! - Page 3 - Electronic Circuits Projects Diagrams Free

**Nigel Goodwin** · 25th January 2008, 09:27 PM

Quote:

Originally Posted by RODALCO

Nigel, I didn't read the second page of this topic, hence this reply.

Electric master clocks as you probably aware from of my other posts, i collect them and know a bit about them too.

The power station masterclock had a differential mechanism in it which was driven via a mains operated clock and a pendulum precision clock,
( now these days the pendulum clock is a precision quartz clock which may even get corrected occasionaly via a satelite time signal when the drift is out more than 1 second or so. )

If the difference was say more than one or a couple of seconds slowly the governor is adjusted by a minute amount. This has to be done slow otherwise the risk exists that one or more power station alternators grab all the load and trips on overload. Reactors are fitted in the lines to the step up 11 kV / 220 kV transformers to dampen excess currents, also the transmission lines will absorb minor frequency differences in extra losses.
A thing you want to avoid in a grid is hunting of alternators which can cause instability and stations to trip out on over or underfrequency. Time delays are also applied to the controlgear to minimise it going back and forth.

Alternators, when synchronised will keep in synch with each other. If the prime mover loses power the alternator will run as a motor and will remain locked in untill taken off line by the protection settings.

Thanks for that information!.

Hero999 · 27th January 2008, 01:07 PM

Quote:

Originally Posted by Boncuk

In the beginning of supply of electric power to households just DC was used. Since DC tends to fry organisms like human bodies it was changed to AC later. Never touch a high tension DC power line. You'll not be able to separate from the cable and BBQ'ed right away!

Hans

It isn't that simple.

Low frequency AC power is actually more dangerous at low voltages because the peak voltage is higher and it takes less AC current to kill you than DC.

Quote:

AC is said to be four to five times more dangerous than DC. For one thing, AC causes more severe muscular contractions. For another, it stimulates sweating that lowers the skin resistance. Along that line, it is important to note that resistance goes down rapidly with continued contact. The sweating and the burning away of the skin oils and even the skin itself account for this. That is why it's extremely important to free the victim from contact with the current as quickly as possible before the climbing current reaches the fibrillation-inducing level.

http://pchem.scs.uiuc.edu/pchemlab/electric.htm

Quote:

Ventricular fibrillation

A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA. With DC, 300 to 500 mA is required.

http://en.wikipedia.org/wiki/Electric_shock

**Nigel Goodwin** · 27th January 2008, 01:23 PM

Quote:

Originally Posted by Hero999

It isn't that simple.

Low frequency AC power is actually more dangerous at low voltages because the peak voltage is higher and it takes less AC current to kill you than DC.

This is so old it's not worth arguing about, check the original fights between Edison and Westinghouse, which resulted in the creation of the electric chair.

Regardless of safety or not though, AC has too many advantages.

Hero999 · 27th January 2008, 02:49 PM

I totally agree, although they were more prominent back then then they are now. A DC distribution system is far more feasible than it used to be. I often think it'd be good to have a separate DC supply in the house for lighting and electronics items. You'd still need switch mode power supplies to convert them to different voltages but it'd be safer, more efficient and there wouldn't be all the problems associated with harmonics and power factor. I'd advocate a +/- 50V supply, which should be enough for most things.

I'm not talking about going to DC 100%, there will still be AC for appliances over 1kW. I suppose I know it isn't that practical as it'd mean changing the infrastructure but it's an interesting idea.

**Nigel Goodwin** · 27th January 2008, 03:33 PM

I would disagree with 'safer', most of the electronic and electrical trade consider AC far safer than DC (as do I). An AC shock will usually throw you clear, a DC shock tends to freeze you on the wire - and is much more likely to kill you.

I would also disagree with 'feasible distribution', it's far too inefficient, and the original DC premise was based on a small power station on every street corner.

It's also a very bad idea to have multiple mains supply sockets, that's been done, and is long over now (although you still do see it very occasionally) - different mains sockets upstairs and downstairs was never a good idea.

DC mains was also done years back, that was never a good idea either!.

Pommie · 27th January 2008, 03:41 PM

Here in Aus they are phasing out incandescent lights by 2010. It would make a lot of sense to have a 48V DC lighting system with compact fluorescents once this happens.

Mike.

**Nigel Goodwin** · 27th January 2008, 03:47 PM

Quote:

Originally Posted by Pommie

Here in Aus they are phasing out incandescent lights by 2010. It would make a lot of sense to have a 48V DC lighting system with compact fluorescents once this happens.

Why would it?.

Pommie · 27th January 2008, 03:58 PM

I believe this is the best voltage to run them at.

Mike.

**Nigel Goodwin** · 27th January 2008, 04:01 PM

Quote:

Originally Posted by Pommie

I believe this is the best voltage to run them at.

Buy why?, it sounds a really BAD voltage to run them off - presumably you must have some reason otherwise?.

Hero999 · 27th January 2008, 04:13 PM

Quote:

Originally Posted by Nigel Goodwin

I would disagree with 'safer', most of the electronic and electrical trade consider AC far safer than DC (as do I).

The IEE consider DC to be safer than DC (the maximum touch voltage in dry conditions is 60VDC or 25VAC) and I trust them more than I trust you or the service trade.

At least when you've had a shock from a DC source your heart can start beating again, AC tends to mess up the pace maker so it doesn't restart. Not to mention the fact that AC will kill you with one fith of the current of DC.

Quote:

An AC shock will usually throw you clear, a DC shock tends to freeze you on the wire - and is much more likely to kill you.

Don't count on being thrown free, AC can make your mussels freeze up too.

Quote:

I would also disagree with 'feasible distribution', it's far too inefficient, and the original DC premise was based on a small power station on every street corner.

Maybe in the 1980s, but today quasi resonant switch mode power supplies can be as efficient as any distribution transformer and there are no skin effect losses in the distribution system.

Quote:

It's also a very bad idea to have multiple mains supply sockets, that's been done, and is long over now (although you still do see it very occasionally) - different mains sockets upstairs and downstairs was never a good idea.

The US have 240V and 120V sockets and they don't have a problem.

We have 110V, 230V and 400V sockets at work and we've never had a problem. They are colour coded and keyed to prevent mistakes from being made.

Don't get me wrong, I'm not suggesting we should switch over to DC, I can just see the benifits of a DC system, especially for smaller appliances.

Pommie · 27th January 2008, 04:17 PM

I can't give you a technical reason but back in the UK I had a friend that built lights and he tried to introduce a 48V system for compact lighting. This was for two reasons, below 50V was unregulated and the electronic ballasts were much cheaper and I assume simpler at that voltage.

Mike.

**Nigel Goodwin** · 27th January 2008, 04:23 PM

Quote:

Originally Posted by Hero999

Don't count on being thrown free, AC can make your mussels freeze up too.

Under very rare conditions perhaps, but with DC it's almost certain to freeze you one the wire and kill you! - I'd sooner take the 99% chance of been thrown free, than the 99% chance of death!.

Quote:

Maybe in the 1980s, but today quasi resonant switch mode power supplies can be as efficient as any distribution transformer and there are no skin effect losses in the distribution system.

I'm sure a multi-KW switchmode power supply, fed from 300 or 4 thousand volts, is going to give similar reliability to a simple transformer!

Where's my databook?, I seem to have missed thouse 500KV 1000A MOSFET's

Quote:

The US have 240V and 120V sockets and they don't have a problem.

Primative as usual

Quote:

We have 110V, 230V and 400V sockets at work and we've never had a problem. They are colour coded and keyed to prevent mistakes from being made.

It's not a question of mistakes, more of convenience!.

Quote:

Don't get me wrong, I'm not suggesting we should switch over to DC, I can just see the benifits of a DC system, especially for smaller appliances.

Can you?, such as what? - and what's the source of the DC going to be?.

Pommie · 27th January 2008, 04:35 PM

While we're on the subject, which is better, earthing the neutral or not? (don't know what the US call it - the one that isn't hot)

Mike.

**Nigel Goodwin** · 27th January 2008, 04:39 PM

Quote:

Originally Posted by Pommie

While we're on the subject, which is better, earthing the neutral or not? (don't know what the US call it - the one that isn't hot)

Don't even go there!

Like most things, 'better' is a relative term.

**Nigel Goodwin** · 27th January 2008, 04:43 PM

Quote:

Originally Posted by Pommie

I can't give you a technical reason but back in the UK I had a friend that built lights and he tried to introduce a 48V system for compact lighting. This was for two reasons, below 50V was unregulated and the electronic ballasts were much cheaper and I assume simpler at that voltage.

No simpler, and I would doubt any cheaper now, even if it was back then?.

I also don't see any good reason for using a lower voltage just because it's unregulated - I'd rather see proper safety standards applied whatever the voltage.

I can only imagine he was wanting to use bare metal feed wires?, as is quite common with low voltage lighting.

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27th January 2008, 02:49 PM	#34
Hero999	I totally agree, although they were more prominent back then then they are now. A DC distribution system is far more feasible than it used to be. I often think it'd be good to have a separate DC supply in the house for lighting and electronics items. You'd still need switch mode power supplies to convert them to different voltages but it'd be safer, more efficient and there wouldn't be all the problems associated with harmonics and power factor. I'd advocate a +/- 50V supply, which should be enough for most things. I'm not talking about going to DC 100%, there will still be AC for appliances over 1kW. I suppose I know it isn't that practical as it'd mean changing the infrastructure but it's an interesting idea. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

27th January 2008, 03:33 PM	#35
Nigel Goodwin	I would disagree with 'safer', most of the electronic and electrical trade consider AC far safer than DC (as do I). An AC shock will usually throw you clear, a DC shock tends to freeze you on the wire - and is much more likely to kill you. I would also disagree with 'feasible distribution', it's far too inefficient, and the original DC premise was based on a small power station on every street corner. It's also a very bad idea to have multiple mains supply sockets, that's been done, and is long over now (although you still do see it very occasionally) - different mains sockets upstairs and downstairs was never a good idea. DC mains was also done years back, that was never a good idea either!. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

27th January 2008, 03:41 PM	#36
Pommie	Here in Aus they are phasing out incandescent lights by 2010. It would make a lot of sense to have a 48V DC lighting system with compact fluorescents once this happens. Mike.

27th January 2008, 03:58 PM	#38
Pommie	I believe this is the best voltage to run them at. Mike.

27th January 2008, 04:17 PM	#41
Pommie	I can't give you a technical reason but back in the UK I had a friend that built lights and he tried to introduce a 48V system for compact lighting. This was for two reasons, below 50V was unregulated and the electronic ballasts were much cheaper and I assume simpler at that voltage. Mike.

27th January 2008, 04:35 PM	#43
Pommie	While we're on the subject, which is better, earthing the neutral or not? (don't know what the US call it - the one that isn't hot) Mike.