Author Topic: Resistance heating  (Read 5636 times)

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SmoggyTurnip

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Re: Resistance heating
« Reply #33 on: March 04, 2006, 12:56:04 PM »
What do you mean by alternator efficiency?

If there is a dead short across the alternator does that not make

the alternator efficiency 0%?
« Last Edit: March 04, 2006, 12:56:04 PM by SmoggyTurnip »

scoraigwind

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Re: Resistance heating
« Reply #34 on: March 04, 2006, 02:20:05 PM »
"The simplest over voltage limit is to rectify the output( whether you need it or not for the heating ) and connect a thyristor (SCR) across it. You connect a zener"


We tried that out in Africa and it worked a bit but was too prone to nuisance tripping.  I reckon a battery is not a big deal to maintain on a system like that.  Using a battery and a couple of relays you can make what we here in the UK would call a "brick $#|+house" overvolt trip.


I would say that you should have both that and a furling tail.  The tail does a different job by protecting against high winds.  But you also need to protect against over voltage/overspeed - with all sorts of dangers.

« Last Edit: March 04, 2006, 02:20:05 PM by scoraigwind »
Hugh Piggott scoraigwind.co.uk

hvirtane

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Re: Resistance heating
« Reply #35 on: March 05, 2006, 10:20:27 AM »
Hugh: I would say that you should have

both that and a furling tail.

The tail does a different job by protecting against high winds.

But you also need to protect against over voltage/overspeed -

with all sorts of dangers.


---


I think that some kind of protection method

for high winds is at least needed.


Erkki Nousianen's machine in my pictures (below)

had originally a wind rotor with two blades

and a pitch control mechanism.


We made some time ago a new rotor with two blades

without the pitch control mechanism. The induction

generator didn't work and the rotor was broken

during a storm. Now he has made this new rotor

with eight blades (of quite similar design

as our design of two blades). His idea is that

this rotor will rarely overspeed.

The idea is that

the wind rotor with so many blades

would not vary its speed much

and moreover it

(because of the shape of the blades)

will become after some speed quite ineffective.

We will see, what will happen.

(More about the machine in my diary.)


The other machine in my pictures,

Kauko Kirmanen's machine,

has got only relays to switch

the load on and off.

The generator is an induction generator

with capacitors and with a gearbox

as with Erkki Nousianen's machine.

That machine has been quite successful

in that respect that it seems

to withstand high winds quite well

without almost any overspeed protection.

Probably because of the inefficient

and very robust blades.


I've been thinking about a system,

where the three phase induction

generator would be so big that

it could overpower the wind rotor

in most cases.

It seems to be that an induction generator

is quite happy with unbalanced loads

for the different phases.

At certain speeds first one phase load

would be switched on,

then next with a bigger load,

and finally the last with

an even bigger load.

There would be also a furling tail

to take care of even higher wind speeds.


Maybe also switching system for different

size capacitor banks would be needed.


What do you think?

Is it possible/practical to make?


- Hannu

« Last Edit: March 05, 2006, 10:20:27 AM by hvirtane »

willib

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Re: Resistance heating
« Reply #36 on: March 05, 2006, 01:36:52 PM »
you are right of course , but i didnt bring it up Peter did..

maximum power transfer would indeed bring the efficiency down to 50%, which is another reason  for a very low resistance stator
« Last Edit: March 05, 2006, 01:36:52 PM by willib »
Carpe Ventum (Seize the Wind)

dinges

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Re: Resistance heating
« Reply #37 on: March 05, 2006, 01:59:29 PM »
Passing the buck eh Willy? ;)


After thinking about it a bit more, I think I've found the error in my reasoning; maximum power transfer is good (in RF, e.g.). But in the case of generators, you not only want maximum power TRANSFER, but also maximum GENERATION (minimum losses in the stator). This changes the picture back to a stator design with minimum internal resistance (i.e. minimum losses).


Intuitively this sounded logical to me. But when I started comparing it with RF power transfer (impedance matching), it stopped making sense. Seems the assumptions have gotten me again...


Peter.

« Last Edit: March 05, 2006, 01:59:29 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)

willib

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Re: Resistance heating
« Reply #38 on: March 05, 2006, 06:11:16 PM »
yeah, well ... ;)

« Last Edit: March 05, 2006, 06:11:16 PM by willib »
Carpe Ventum (Seize the Wind)

chux0r

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Re: Resistance heating
« Reply #39 on: March 08, 2006, 11:35:34 AM »


nothing stopping you from using the heatsink from your rectifier


Except that I presume for resistive heating, he wouldn't have a rectifier.

« Last Edit: March 08, 2006, 11:35:34 AM by chux0r »