On 17/05/2018 20:13, Rod Speed wrote:


"Bill Wright" wrote in message
news
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

Cant seeÂ* how that is relevant given that
they are locked to the engine speed.

It was just a general observation.

Bill

On 18/05/2018 12:51, The Other Mike wrote:
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.

Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip rings
and produces AC that has to be rectified.

"Dynamo" comes from a Greek word "dynamis" meaning force or power. Not
that the Ancient Greeks would have known the difference between AC and
DC. Or force and power. Heck, they knew hardly anything about
electricity: they generated electricity by rubbing a piece of amber on a
cat.

--
Max Demian

On Fri, 18 May 2018 14:03:24 +0100, Dave Plowman (News) wrote:

In article ,
Max Demian wrote:
I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

They are both generators - but the definition of a dynamo is a generator
which produces DC by use of a commutator.

That's the very definition of a dynamo (if you more precisely define the
commutator as being an integral part of the armature assembly) so there's
no possibility of any confusion.

The motor trade called the modern DC generators "Alternators", even
though they output DC voltage via their integral 3 phase fullwave bridge
rectifier, simply to distinguish them from the earlier dynamo technology.

It was the advent of silicon diode rectifiers with average current
ratings of 50A or more which released the industry from the tyranny of
the carbon brushed commutator assembly. The output carrying windings
could now be placed in a stator where they were no longer subject to
centripetal forces, delegating the task of supplying a rotating magnetic
field in a field coil rotor assembly that could withstand much higher
rotational speeds without danger of burst windings or fragile laminated
armature cores flying apart.

Also, the field could be energised via low friction/wear slip rings
which only had to deal with 4 or 5 amps of excitation current rather than
the 22 amps or more of the classic dynamo's high friction/wear of a
segmented slipring to mechanically 'rectify' the armature's internal AC
voltage.

In fact, it's quite possible to eliminate even the slip ring connection
to the rotating field winding by locating the field coils externally so
as to magnetise the rotating poles via conduction of magnetic flux across
the small clearance gap at each end of the shaft and into the rotor
assembly.

However, this creates a more bulky and intricate design for which the
automotive industry would gain no benefit by supplying alternators whose
life is limited only by that of its bearings which could well exceed that
of the engine's bearings by an order of magnitude.

The 75,000 miles or longer rating of the slipring/brush assembly on a
conventional alternator is more than ample for the task, aided by the
fact that only the long life brushes themselves need be replaced,
normally as a cheap sub-assembly that can be replaced in a matter of
minutes for very little cost.

Modern switching voltage regulator technology now allows the use of
permanent magnet rotors which not only simplifies construction (no field
coil, no slip rings) but also improves efficiency. However, when you've
got several dozen or more horsepower to tap into, efficiency improvements
are quite low on the car manufacturer's agenda so the traditional slipring
energised rotating field coil alternator design is unlikely to be usurped
for the sake of a mere quarter to one third of a horsepower's worth of
savings.

When it comes to building your own wind turbine, permanent magnet
alternators are king. Anyone seriously into such projects would never
consider re-purposing a car alternator (or even the more efficient truck
alternator with its 28v output) as the core of a wind turbine generator
since the vampire drain, feeding the rotor field winding with 4 or 5
amps, seriously cuts into the low wind speed range of such a setup.

When it comes to modern suitcase sized portable inverter generators
(typically in the 700 to 2KVA peak output range) they all use a 3 phase
permanent magnet (PM) alternator to generate either a nominal 200 or 400
volts DC[1] via a 6 diode fullwave bridge rectifier feeding what is in
essence, a bridged pair of class D amplifiers, typically using a sampling
rate of 5KHz, to amplify a pure 60 or 50Hz sinewave reference signal to
120 or 230 volts ac (the so called inverter).

The whole lot is microprocessor controlled so that the engine revs can
be ramped up with load via a stepper motor controlling the carburettors
butterfly valve (throttle). this takes care of increasing the torque
output requirement to match the amperage demand and also to compensate
the voltage drop from the PM alternator by increasing the revs.

Most of these inverter gensets have an eco-mode setting to not only
reduce fuel consumption under very light loading conditions, but also to
mitigate the noise pollution. However, even when eco-mode is disabled and
the engine is running at a higher rpm, the revs will still increase with
electrical loading.

In order to keep these small (1 to 2 KVA peak) inverter gensets down to
a manageable size and weight, they typically use a small single cylinder
4 stroke 50cc engine running from just under 4000rpm up to around 4600rpm
or so (classic 50Hz gensets in this power range run a 45 to 80cc single
cylinder 2 or 4 stroke engine at a steady 3000rpm).

You might think the higher rpms would create more of a noise nuisance
but it's worth bearing in mind that the higher the noise frequency, the
easier it is to soundproof as Honda with its eu series have demonstrated
for many years now with their enclosed suitcase designs (sadly, their
much cheaper imitators rather fall down on this aspect of enclosed
suitcase inverter genset design - the recent Generac design excepted).

[1] When I was researching ways and means of quieting my Parkside
inverter genset, I came across many forum postings which not only dealt
with the noise pollution issue (very badly imo) but also included seeking
advice on home built inverter generators using car alternators with a
heavy duty 12v sine wave inverter, either using a repurposed lawn mower
engine or else as a repair or an upgrade to an existing conventional
genset.

I rather pitied the (misguided) fools for even considering such an
inefficient way to produce sine wave quality mains voltage power. The
rectifier volt drops in the alternator alone represent at least a 12.5%
loss of efficiency before you then have to deal with at least another 10%
loss in even a very efficient 12 to 120/230v sine wave inverter. Ignoring
the vampire load from the field current, you'd be looking at an
electrical efficiency from the alternator ac output through to the final
230v 50Hz ac output of a mere 78% at best.

There's an excellent reason as to why a PM 3 phase alternator output
voltage of 200 or 400 volts was chosen by the inverter genset
manufacturers. Firstly, it generates the required 170 or 350v peak
voltage with a little something to spare for the 'inverter' to generate
the mains voltage peaks of a 120/240vac sine wave, leaving the 'inverter'
with merely the task of turning this source of DC voltage directly into a
50/60Hz sine wave of 240 or 120 rms volts using pulse width modulation
switching (effectively a class D amplifier with an unusually low sampling
rate, circa 5KHz for improved efficiency).

The rectifier volt drops for even the lower 200 volt alternator case
will now only represent a mere 1% loss (the 230/240 inverter genset's
400vdc alternator output reduces this to a 0.5% loss). The inverter
losses are unlikely to exceed 2 or 3 % making such a genset a whole lot
more efficient than even a simple basic single phase 230/120vac 50/60 Hz
alternator driven directly at 3000/3600 rpm let alone a franken-genset
comprised of car alternator and 12v to 120/230v inverter box.

This, BTW, was a heads up for any of the more ambitious DIY enthusiasts
monitoring this thread who might happen to be contemplating homebrewing
their own inverter genset 'on the cheap'. :-)


--
Johnny B Good

On 18/05/18 19:53, tony sayer wrote:
In article , The Other Mike
scribeth thus
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip rings
and produces AC that has to be rectified.

Never hear then referring to the Alternators in a power station as
Dynamo's!..

Mmm. The Lord of the Dynamo?

http://www.online-literature.com/wellshg/9/



--
Climate Change: Socialism wearing a lab coat.

On Friday, 18 May 2018 22:45:49 UTC+1, Johnny B Good wrote:
On Fri, 18 May 2018 14:03:24 +0100, Dave Plowman (News) wrote:

In article ,
Max Demian wrote:
I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

They are both generators - but the definition of a dynamo is a generator
which produces DC by use of a commutator.

That's the very definition of a dynamo (if you more precisely define the
commutator as being an integral part of the armature assembly) so there's
no possibility of any confusion.

The motor trade called the modern DC generators "Alternators", even
though they output DC voltage via their integral 3 phase fullwave bridge
rectifier, simply to distinguish them from the earlier dynamo technology.

It was the advent of silicon diode rectifiers with average current
ratings of 50A or more which released the industry from the tyranny of
the carbon brushed commutator assembly. The output carrying windings
could now be placed in a stator where they were no longer subject to
centripetal forces, delegating the task of supplying a rotating magnetic
field in a field coil rotor assembly that could withstand much higher
rotational speeds without danger of burst windings or fragile laminated
armature cores flying apart.

Also, the field could be energised via low friction/wear slip rings
which only had to deal with 4 or 5 amps of excitation current rather than
the 22 amps or more of the classic dynamo's high friction/wear of a
segmented slipring to mechanically 'rectify' the armature's internal AC
voltage.

In fact, it's quite possible to eliminate even the slip ring connection
to the rotating field winding by locating the field coils externally so
as to magnetise the rotating poles via conduction of magnetic flux across
the small clearance gap at each end of the shaft and into the rotor
assembly.

However, this creates a more bulky and intricate design for which the
automotive industry would gain no benefit by supplying alternators whose
life is limited only by that of its bearings which could well exceed that
of the engine's bearings by an order of magnitude.

The 75,000 miles or longer rating of the slipring/brush assembly on a
conventional alternator is more than ample for the task, aided by the
fact that only the long life brushes themselves need be replaced,
normally as a cheap sub-assembly that can be replaced in a matter of
minutes for very little cost.

Modern switching voltage regulator technology now allows the use of
permanent magnet rotors which not only simplifies construction (no field
coil, no slip rings) but also improves efficiency. However, when you've
got several dozen or more horsepower to tap into, efficiency improvements
are quite low on the car manufacturer's agenda so the traditional slipring
energised rotating field coil alternator design is unlikely to be usurped
for the sake of a mere quarter to one third of a horsepower's worth of
savings.

When it comes to building your own wind turbine, permanent magnet
alternators are king. Anyone seriously into such projects would never
consider re-purposing a car alternator (or even the more efficient truck
alternator with its 28v output) as the core of a wind turbine generator
since the vampire drain, feeding the rotor field winding with 4 or 5
amps, seriously cuts into the low wind speed range of such a setup.

When it comes to modern suitcase sized portable inverter generators
(typically in the 700 to 2KVA peak output range) they all use a 3 phase
permanent magnet (PM) alternator to generate either a nominal 200 or 400
volts DC[1] via a 6 diode fullwave bridge rectifier feeding what is in
essence, a bridged pair of class D amplifiers, typically using a sampling
rate of 5KHz, to amplify a pure 60 or 50Hz sinewave reference signal to
120 or 230 volts ac (the so called inverter).

The whole lot is microprocessor controlled so that the engine revs can
be ramped up with load via a stepper motor controlling the carburettors
butterfly valve (throttle). this takes care of increasing the torque
output requirement to match the amperage demand and also to compensate
the voltage drop from the PM alternator by increasing the revs.

Most of these inverter gensets have an eco-mode setting to not only
reduce fuel consumption under very light loading conditions, but also to
mitigate the noise pollution. However, even when eco-mode is disabled and
the engine is running at a higher rpm, the revs will still increase with
electrical loading.

In order to keep these small (1 to 2 KVA peak) inverter gensets down to
a manageable size and weight, they typically use a small single cylinder
4 stroke 50cc engine running from just under 4000rpm up to around 4600rpm
or so (classic 50Hz gensets in this power range run a 45 to 80cc single
cylinder 2 or 4 stroke engine at a steady 3000rpm).

You might think the higher rpms would create more of a noise nuisance
but it's worth bearing in mind that the higher the noise frequency, the
easier it is to soundproof as Honda with its eu series have demonstrated
for many years now with their enclosed suitcase designs (sadly, their
much cheaper imitators rather fall down on this aspect of enclosed
suitcase inverter genset design - the recent Generac design excepted).

[1] When I was researching ways and means of quieting my Parkside
inverter genset, I came across many forum postings which not only dealt
with the noise pollution issue (very badly imo) but also included seeking
advice on home built inverter generators using car alternators with a
heavy duty 12v sine wave inverter, either using a repurposed lawn mower
engine or else as a repair or an upgrade to an existing conventional
genset.

I rather pitied the (misguided) fools for even considering such an
inefficient way to produce sine wave quality mains voltage power. The
rectifier volt drops in the alternator alone represent at least a 12.5%
loss of efficiency before you then have to deal with at least another 10%
loss in even a very efficient 12 to 120/230v sine wave inverter. Ignoring
the vampire load from the field current, you'd be looking at an
electrical efficiency from the alternator ac output through to the final
230v 50Hz ac output of a mere 78% at best.

There's an excellent reason as to why a PM 3 phase alternator output
voltage of 200 or 400 volts was chosen by the inverter genset
manufacturers. Firstly, it generates the required 170 or 350v peak
voltage with a little something to spare for the 'inverter' to generate
the mains voltage peaks of a 120/240vac sine wave, leaving the 'inverter'
with merely the task of turning this source of DC voltage directly into a
50/60Hz sine wave of 240 or 120 rms volts using pulse width modulation
switching (effectively a class D amplifier with an unusually low sampling
rate, circa 5KHz for improved efficiency).

The rectifier volt drops for even the lower 200 volt alternator case
will now only represent a mere 1% loss (the 230/240 inverter genset's
400vdc alternator output reduces this to a 0.5% loss). The inverter
losses are unlikely to exceed 2 or 3 % making such a genset a whole lot
more efficient than even a simple basic single phase 230/120vac 50/60 Hz
alternator driven directly at 3000/3600 rpm let alone a franken-genset
comprised of car alternator and 12v to 120/230v inverter box.

This, BTW, was a heads up for any of the more ambitious DIY enthusiasts
monitoring this thread who might happen to be contemplating homebrewing
their own inverter genset 'on the cheap'. :-)

of course that isn't true if you let the alternator produce more than 12v


NT

On 18/05/2018 22:45, Johnny B Good wrote:


They are both generators - but the definition of a dynamo is a generator
which produces DC by use of a commutator.
snip

That was very long but very very interesting. Full of facts.

Bill

On Sat, 19 May 2018 19:23:15 +0100, Bill Wright wrote:

On 18/05/2018 22:45, Johnny B Good wrote:


They are both generators - but the definition of a dynamo is a
generator which produces DC by use of a commutator.
snip

That was very long but very very interesting. Full of facts.

Thanks for that, Bill.

Pretty well all of that info is available[1] over the internet
(wikipedia is a good starting point for those interested in such
technicalities[1]). Indeed, until I checked out 'my facts', I hadn't
quite realised just how serious an issue there was in drawing power via
the commutator/brush gear - at least half of each of those old Edison
100v dynamos you see archive pictures of are just to accommodate the
several banks of commutators/brush sets required to draw their designed
amperage.

[1] Blimey! I managed to spell "technicalities" correctly first go, yet
still managed to misspell "available". :-( :-)

--
Johnny B Good

On Sat, 19 May 2018 09:58:43 -0700, tabbypurr wrote:

On Friday, 18 May 2018 22:45:49 UTC+1, Johnny B Good wrote:

====snip====


The rectifier volt drops for even the lower 200 volt alternator case
will now only represent a mere 1% loss (the 230/240 inverter genset's
400vdc alternator output reduces this to a 0.5% loss). The inverter
losses are unlikely to exceed 2 or 3 % making such a genset a whole lot
more efficient than even a simple basic single phase 230/120vac 50/60
Hz alternator driven directly at 3000/3600 rpm let alone a
franken-genset comprised of car alternator and 12v to 120/230v inverter
box.

This, BTW, was a heads up for any of the more ambitious DIY
enthusiasts
monitoring this thread who might happen to be contemplating homebrewing
their own inverter genset 'on the cheap'. :-)

of course that isn't true if you let the alternator produce more than
12v

If you're prepared to run the alternator fast enough and replace/modify
the regulator, you could probably get away with letting it output 28 or
maybe even 42 volts (assuming you limit the excitation voltage source to
14v to prevent burning out the field coil). The PIV rating of the
rectifier pack is probably 200v or more which should leave some margin
for voltage spikes.

However, you might do better to start with a 28v truck alternator and
double up to 56 volts to feed a 48v inverter module (perhaps one
recovered from a defunct SmartUPS2000 or another 48v battery backed UPS).
In this case, the excitation voltage source can be limited to the higher
28v max limit but there's no guarantee that the PIV rating will be any
higher than that of a diode pack used in a 12v alternator - you might
need to upgrade the rectifier pack to one with a three or four hundred
volt rating. It is possible to test the PIV ratings of silicon diodes
when you can't identify them in order to look it up on a datasheet.

All this assumes a very keen polymath DIY enthusiast prepared to
assemble such a franken-beast of a genset made up of cast off bits of
24/36/48 volt battery backed UPS inverters and cobble up a controller
using an Arduino or RPi with a stepper motor bolted onto the carburettor
body. Somehow or other, it just seems so much easier to simply[1] spend
99 quid on a Lidl Parkside PGI 1200 B2 inverter genset and have done with
it. :-)

[1] It's a relative term as I eventually discovered during my own genset
purchasing saga just last month. The trouble with "Lidl Specials" like
this is they may well have clocked a few thousand miles in the back of 38
tonners going up and down UK motorways before you even get your grubby
mitts on one at your local store.

Such treatment often leaves them with a couple easy to fix (once you
know how) stock faults for the more nervous purchaser to return as DoA
faulty goods in the small hope of getting working genset in exchange or
else a full refund (small consolation for those who truly appreciate just
what a bargain a *working* 1200W peak (30 seconds, not 5!) inverter genset
is at this price).

All this is a direct result of Lidl's policy of never allowing such
'promotions' to last more than a week or two at each of their stores
before the arrival of the "Next Promotion" forces the store manager to
make room for the 'new line' and ship them off once more to stores in
other UK regions. It seems the store itself is its own warehousing space.
What's hidden, back of store, is just a small temporary holding pen for
stock that's about to be sent on yet another motorway journey.

For all I know, Aldi might be using exactly the same strategy but I
don't seem get to visit Aldi stores when such "generator specials" are
being promoted. Indeed, it's been several years now since I last saw any
type of genset on sale in an Aldi store (mind you, until recently, I
could say the same of Lidl).

Indeed, the amount of 'interesting bargains' in electronic tech and
genset rarities seem to have become vanishingly rarified over the past
few years in both Aldi and Lidl stores. There was a time when I used to
look forward to browsing the non-food sections whilst SWIMBI did the
weekly shop but not for the past two or three years now. :-(

--
Johnny B Good

On Saturday, 19 May 2018 20:51:51 UTC+1, Johnny B Good wrote:
On Sat, 19 May 2018 09:58:43 -0700, tabbypurr wrote:
On Friday, 18 May 2018 22:45:49 UTC+1, Johnny B Good wrote:

The rectifier volt drops for even the lower 200 volt alternator case
will now only represent a mere 1% loss (the 230/240 inverter genset's
400vdc alternator output reduces this to a 0.5% loss). The inverter
losses are unlikely to exceed 2 or 3 % making such a genset a whole lot
more efficient than even a simple basic single phase 230/120vac 50/60
Hz alternator driven directly at 3000/3600 rpm let alone a
franken-genset comprised of car alternator and 12v to 120/230v inverter
box.

This, BTW, was a heads up for any of the more ambitious DIY
enthusiasts
monitoring this thread who might happen to be contemplating homebrewing
their own inverter genset 'on the cheap'. :-)

of course that isn't true if you let the alternator produce more than
12v

If you're prepared to run the alternator fast enough and replace/modify
the regulator, you could probably get away with letting it output 28 or
maybe even 42 volts (assuming you limit the excitation voltage source to
14v to prevent burning out the field coil). The PIV rating of the
rectifier pack is probably 200v or more which should leave some margin
for voltage spikes.

However, you might do better to start with a 28v truck alternator and
double up to 56 volts to feed a 48v inverter module (perhaps one

sure but making something on the cheap makes oh look, I have an alternator sat in the garage, let's use it.


body. Somehow or other, it just seems so much easier to simply[1] spend
99 quid on a Lidl Parkside PGI 1200 B2 inverter genset and have done with
it. :-)

today yes. Gennies used to cost far more. Your £99 job won't last long though.



Indeed, the amount of 'interesting bargains' in electronic tech and
genset rarities seem to have become vanishingly rarified over the past
few years in both Aldi and Lidl stores. There was a time when I used to
look forward to browsing the non-food sections whilst SWIMBI did the
weekly shop but not for the past two or three years now. :-(

ditto, I seldom bother now.


NT

On 18/05/2018 19:53, tony sayer wrote:
In article , The Other Mike
scribeth thus
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip rings
and produces AC that has to be rectified.

Never hear then referring to the Alternators in a power station as
Dynamo's!..

I don't know about power station generators, but when I was involved in
testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a DR-61
turbine and direct driving (according to the manufacturer's nameplate) a
"Brush AC Generator".

SteveW

On 18/05/2018 20:44, Max Demian wrote:
On 18/05/2018 12:51, The Other Mike wrote:
On Fri, 18 May 2018 12:16:41 +0100, Max Demian
wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.

Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a
commutator and
directly produces something resembling DC, an alternator usually has
slip rings
and produces AC that has to be rectified.

"Dynamo" comes from a Greek word "dynamis" meaning force or power. Not
that the Ancient Greeks would have known the difference between AC and
DC. Or force and power. Heck, they knew hardly anything about
electricity: they generated electricity by rubbing a piece of amber on a
cat.

Which is a lot easier than rubbing a cat on a piece of amber

SteveW

On 20/05/2018 19:14, Steve Walker wrote:
I don't know about power station generators, but when I was involved in
testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a DR-61
turbine and direct driving (according to the manufacturer's nameplate) a
"Brush AC Generator".

Oooh an expert

I always assumed that in those kind of tasks they just used the turbine
that normally drives the fan (which I assume isn't there!) Why not?
Doesn't it extract enough power?

Andy

On 20/05/2018 21:31, Vir Campestris wrote:
On 20/05/2018 19:14, Steve Walker wrote:
I don't know about power station generators, but when I was involved
in testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a DR-61
turbine and direct driving (according to the manufacturer's nameplate)
a "Brush AC Generator".

Oooh an expert

Not much of one.

I always assumed that in those kind of tasks they just used the turbine
that normally drives the fan (which I assume isn't there!) Why not?
Doesn't it extract enough power?

That's basically it.

From memory (this was nearly 25 years ago), an RB211 (for aircraft)
actually has three compressor stages (low, medium and high pressure), on
three co-axial shafts, driven by three turbines. The turbines are sized
to power the appropriate compressor stage and you get a lot of hot, fast
moving exhaust. The reaction to the exhaust escaping backwards is to
push the engine forwards.

An RB211 (for industrial use) only has two compressor stages (medium and
high pressure), on two co-axial shafts, driven by two turbines -
probably because the air at ground level is dense and the first stage is
redundant. Again, the turbines are sized to power the appropriate
compressor stage and you get a lot of hot, fast moving exhaust. In this
use, it is actually termed a gas generator (or was by the company I
worked for) and you don't want the GG to move. Instead it is bolted down
and the exhaust is directed into a power-turbine, which is driven by the
gas, before exhausting to a heat recovery plant. The power-turbine
drives whatever load you have attached.

There is no direct connection between the load and the GG. It is
impressive how well the control system (Woodward governor on those sets)
ramped up the fuel control to bring the power turbine up to running
speed with only a tiny overshoot and then settled to constant speed.
Although slamming a 10MW motor online REALLY made the revs/frequency
drop for a short while!

It amused me at the time that the Rolls-Royce manuals referred to
allowing the engine to cool before turning it off, by "taxiing for 3
minutes."

SteveW

On 20/05/18 22:25, Steve Walker wrote:
On 20/05/2018 21:31, Vir Campestris wrote:
On 20/05/2018 19:14, Steve Walker wrote:
I don't know about power station generators, but when I was involved
in testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a
DR-61 turbine and direct driving (according to the manufacturer's
nameplate) a "Brush AC Generator".

Oooh an expert

Not much of one.

I always assumed that in those kind of tasks they just used the
turbine that normally drives the fan (which I assume isn't there!) Why
not? Doesn't it extract enough power?

That's basically it.

From memory (this was nearly 25 years ago), an RB211 (for aircraft)
actually has three compressor stages (low, medium and high pressure), on
three co-axial shafts, driven by three turbines. The turbines are sized
to power the appropriate compressor stage and you get a lot of hot, fast
moving exhaust. The reaction to the exhaust escaping backwards is to
push the engine forwards.

An RB211 (for industrial use) only has two compressor stages (medium and
high pressure), on two co-axial shafts, driven by two turbines -
probably because the air at ground level is dense and the first stage is
redundant. Again, the turbines are sized to power the appropriate
compressor stage and you get a lot of hot, fast moving exhaust. In this
use, it is actually termed a gas generator (or was by the company I
worked for) and you don't want the GG to move. Instead it is bolted down
and the exhaust is directed into a power-turbine, which is driven by the
gas, before exhausting to a heat recovery plant. The power-turbine
drives whatever load you have attached.

There is no direct connection between the load and the GG. It is
impressive how well the control system (Woodward governor on those sets)
ramped up the fuel control to bring the power turbine up to running
speed with only a tiny overshoot and then settled to constant speed.
Although slamming a 10MW motor online REALLY made the revs/frequency
drop for a short while!

It amused me at the time that the Rolls-Royce manuals referred to
allowing the engine to cool before turning it off, by "taxiing for 3
minutes."

SteveW

A bog standard open cycle gas turbine then..




--
Microsoft : the best reason to go to Linux that ever existed.

On 21/05/2018 04:11, The Natural Philosopher wrote:
On 20/05/18 22:25, Steve Walker wrote:
On 20/05/2018 21:31, Vir Campestris wrote:
On 20/05/2018 19:14, Steve Walker wrote:
I don't know about power station generators, but when I was involved
in testing a couple of 3-phase, 60Hz, 11kV, 24MW generator sets for
North-sea oil rigs, they consisted of an RB211, exhausing into a
DR-61 turbine and direct driving (according to the manufacturer's
nameplate) a "Brush AC Generator".

Oooh an expert

Not much of one.

I always assumed that in those kind of tasks they just used the
turbine that normally drives the fan (which I assume isn't there!)
Why not? Doesn't it extract enough power?

That's basically it.

Â*From memory (this was nearly 25 years ago), an RB211 (for aircraft)
actually has three compressor stages (low, medium and high pressure),
on three co-axial shafts, driven by three turbines. The turbines are
sized to power the appropriate compressor stage and you get a lot of
hot, fast moving exhaust. The reaction to the exhaust escaping
backwards is to push the engine forwards.

An RB211 (for industrial use) only has two compressor stages (medium
and high pressure), on two co-axial shafts, driven by two turbines -
probably because the air at ground level is dense and the first stage
is redundant. Again, the turbines are sized to power the appropriate
compressor stage and you get a lot of hot, fast moving exhaust. In
this use, it is actually termed a gas generator (or was by the company
I worked for) and you don't want the GG to move. Instead it is bolted
down and the exhaust is directed into a power-turbine, which is driven
by the gas, before exhausting to a heat recovery plant. The
power-turbine drives whatever load you have attached.

There is no direct connection between the load and the GG. It is
impressive how well the control system (Woodward governor on those
sets) ramped up the fuel control to bring the power turbine up to
running speed with only a tiny overshoot and then settled to constant
speed. Although slamming a 10MW motor online REALLY made the
revs/frequency drop for a short while!

It amused me at the time that the Rolls-Royce manuals referred to
allowing the engine to cool before turning it off, by "taxiing for 3
minutes."

SteveW

A bog standard open cycle gas turbine then..

Indeed. Nothing special.

SteveW

There is no direct connection between the load and the GG. It is
impressive how well the control system (Woodward governor on those sets)
ramped up the fuel control to bring the power turbine up to running
speed with only a tiny overshoot and then settled to constant speed.
Although slamming a 10MW motor online REALLY made the revs/frequency
drop for a short while!



It amused me at the time that the Rolls-Royce manuals referred to
allowing the engine to cool before turning it off, by "taxiing for 3
minutes."


Just good Airmanship 'y know...


SteveW

--
Tony Sayer

On 11/05/2018 11:14, Dave Plowman (News) wrote:
he original post war Minor was of course meant to have a all new boxer
engine. But Morris accountants decided a pre-war side valve would be just
as good.;-) The traveller came rather later on in the model range.

My cousin had one when she was in the WRAF in 1968.

One day, trying to get up a hill near Brize Norton?,
or might have been Bicester.

It couldn't make it to the top unless the rear seat
passengers got out and walked to the top.

On Sun, 20 May 2018 22:25:03 +0100, Steve Walker
wrote:

An RB211 (for industrial use) only has two compressor stages (medium and
high pressure), on two co-axial shafts, driven by two turbines -
probably because the air at ground level is dense and the first stage is
redundant. Again, the turbines are sized to power the appropriate
compressor stage and you get a lot of hot, fast moving exhaust. In this
use, it is actually termed a gas generator (or was by the company I
worked for) and you don't want the GG to move. Instead it is bolted down
and the exhaust is directed into a power-turbine, which is driven by the
gas, before exhausting to a heat recovery plant. The power-turbine
drives whatever load you have attached.

This sounds similar to the GT used in the Royal Navy destroyers that
broke down when they went in tropical waters, a problem with an inter
cooler.

The conversion efficiency was claimed to be better than a diesel at
over 50%

AJH

On Mon, 21 May 2018 04:11:02 +0100, The Natural Philosopher
wrote:

On 20/05/18 22:25, Steve Walker wrote:

snip

before exhausting to a heat recovery plant.

A bog standard open cycle gas turbine then..

The mention of 'heat recovery plant' would suggest the exact opposite

--

On Fri, 18 May 2018 20:44:55 +0100, Max Demian wrote:

"Dynamo" comes from a Greek word "dynamis" meaning force or power. Not
that the Ancient Greeks would have known the difference between AC and
DC. Or force and power. Heck, they knew hardly anything about
electricity: they generated electricity by rubbing a piece of amber on a
cat.

Rubbing amber on a cat can also equal puncture wounds followed by a course of
intravenous antibiotics.
--

OKOn Fri, 18 May 2018 19:53:46 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
*** The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip rings
and produces AC that has to be rectified.

Never hear then referring to the Alternators in a power station as
Dynamo's!..

OK rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

The brushes on those are changed on load (as in hundreds of MW of main
alternator load and twirling round at 3000rpm)

Just stand on a carefully tested rubber mat, wear nice clean properly rated
rubber gloves and just don't get it wrong. But it's only about 600v or so and
there are quite a few brushes in parallel

But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

The hydrogen being sealed on the interface between the rotating shaft and the
outside world by pressurised oil. Get a rubbing seal and it might ignite the
hydrogen make a big bang and the oil fire will burn a very big hole in the roof.

--

"The Other Mike" wrote in message
...
On Fri, 18 May 2018 20:44:55 +0100, Max Demian
wrote:

"Dynamo" comes from a Greek word "dynamis" meaning force or power. Not
that the Ancient Greeks would have known the difference between AC and
DC. Or force and power. Heck, they knew hardly anything about
electricity: they generated electricity by rubbing a piece of amber on a
cat.

Rubbing amber on a cat can also equal puncture wounds
followed by a course of intravenous antibiotics.

Not if you whack if on the head with a mash hammer first.

An ice axe works well too.

On Tue, 29 May 2018 09:03:57 +0100, The Other Mike wrote:

On Fri, 18 May 2018 20:44:55 +0100, Max Demian
wrote:

"Dynamo" comes from a Greek word "dynamis" meaning force or power. Not
that the Ancient Greeks would have known the difference between AC and
DC. Or force and power. Heck, they knew hardly anything about
electricity: they generated electricity by rubbing a piece of amber on a
cat.

Rubbing amber on a cat can also equal puncture wounds followed by a
course of intravenous antibiotics.

Well, intravenous is the best way to administer anti-biotic courses of
treatment - it reduces unwanted side effects on the gut flora which often
makes the cure almost as bad as the disease (or, at best, the lesser of
two evils).

--
Johnny B Good

On 29/05/2018 09:03, The Other Mike wrote:
On Mon, 21 May 2018 04:11:02 +0100, The Natural Philosopher
wrote:

On 20/05/18 22:25, Steve Walker wrote:

snip

before exhausting to a heat recovery plant.

A bog standard open cycle gas turbine then..

The mention of 'heat recovery plant' would suggest the exact opposite

No, they were open cycle.

The heat recovery plant merely recovered waste heat from the exhaust for
other processes on the rig.

SteveW

On 29/05/2018 09:05, The Other Mike wrote:

OKOn Fri, 18 May 2018 19:53:46 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
Â*Â*Â* The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip rings
and produces AC that has to be rectified.

Never hear then referring to the Alternators in a power station as
Dynamo's!..

OK rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

The brushes on those are changed on load (as in hundreds of MW of main
alternator load and twirling round at 3000rpm)

Just stand on a carefully tested rubber mat, wear nice clean properly rated
rubber gloves and just don't get it wrong. But it's only about 600v or so and
there are quite a few brushes in parallel

But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

The hydrogen being sealed on the interface between the rotating shaft and the
outside world by pressurised oil.

Is that a multiple labyrinth seal with an oil seal between sections?
That's what we used to use on large axial and centrifugal compressors
for flammable gases.

SteveW

On Tuesday, 29 May 2018 09:06:24 UTC+1, The Other Mike wrote:
OKOn Fri, 18 May 2018 19:53:46 +0100, tony sayer wrote:

Never hear then referring to the Alternators in a power station as
Dynamo's!..

OK rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

The brushes on those are changed on load (as in hundreds of MW of main
alternator load and twirling round at 3000rpm)

Just stand on a carefully tested rubber mat, wear nice clean properly rated
rubber gloves and just don't get it wrong. But it's only about 600v or so and
there are quite a few brushes in parallel

But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

The hydrogen being sealed on the interface between the rotating shaft and the
outside world by pressurised oil. Get a rubbing seal and it might ignite the
hydrogen make a big bang and the oil fire will burn a very big hole in the roof.

what's the uspide of H2 over N2 or burnt air?


NT

On Tue, 29 May 2018 16:52:36 -0700 (PDT), wrote:


what's the uspide of H2 over N2 or burnt air?

About 14 x the specific heat capacity and half the drag
--

On Tue, 29 May 2018 19:10:28 +0100, Steve Walker
wrote:

On 29/05/2018 09:05, The Other Mike wrote:

The hydrogen being sealed on the interface between the rotating shaft and the
outside world by pressurised oil.

Is that a multiple labyrinth seal with an oil seal between sections?
That's what we used to use on large axial and centrifugal compressors
for flammable gases.

Yes
--

In article , The Other Mike
scribeth thus

OKOn Fri, 18 May 2018 19:53:46 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
On Fri, 18 May 2018 12:16:41 +0100, Max Demian wrote:

On 17/05/2018 12:26, Bill Wright wrote:
On 17/05/2018 11:07, Dave Plowman (News) wrote:
In article ,
*** The Natural Philosopher wrote:
I don't actually understand why alternators were capable of supplying
more current though.

Because they were designed to do so.

Larger dynamos were also fitted to larger cars, etc.


Alternators spun more freely than dynamos.

I'm surprised that some pedant hasn't pointed out that all alternators
/are/ dynamos - which can be AC or DC - it's just a motor trade
convention that the word "dynamo" was kept for the original DC
generators when alternators came in.

Possibly because the pedants know that a dynamo usually has a commutator and
directly produces something resembling DC, an alternator usually has slip
rings
and produces AC that has to be rectified.

Never hear then referring to the Alternators in a power station as
Dynamo's!..

OK rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

I suppose thats so it can start up by itself under shudder! Black Start
conditions;?..


The brushes on those are changed on load (as in hundreds of MW of main
alternator load and twirling round at 3000rpm)



Just stand on a carefully tested rubber mat, wear nice clean properly rated
rubber gloves and just don't get it wrong. But it's only about 600v or so and
there are quite a few brushes in parallel

But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

Why Hydrogen?...

The hydrogen being sealed on the interface between the rotating shaft and the
outside world by pressurised oil. Get a rubbing seal and it might ignite the
hydrogen make a big bang and the oil fire will burn a very big hole in the roof.


--
Tony Sayer

On Wed, 30 May 2018 14:24:40 +0100, tony sayer wrote:

In article , The Other Mike
scribeth thus
K rectified when fitted to a vehicle.

In a power station on the end of the alternator opposite from the turbine you'll
find a DC field excitation generator / pilot exciter that does have a
commutator.

I suppose thats so it can start up by itself under shudder! Black Start
conditions;?..

Not particularly, by the point you need excitation current at least for a coal
/oil / nuclear station you will have been heating the boiler for several hours
and the turbine and generator will be at or around full speed and getting ready
for synchronisation and load.

For a black start the DC supplies (from batteries) are used to start either
diesel generators or distillate fuelled gas turbines. That powers the AC
station bus supplies usually at 11kV or 3.3kV, with transformers for 415v and
lower supplies. From that point you can operate everything on site such as fans
pumps and valves etc.

In normal operation with a live grid the site would take a station transformer
backfeed to power everything until the main generator comes on load at which
point each individual generator transformer HV side (at 400 or 275kV) then feeds
a unit transformer that supplies 11kV to a AC bus for that specific unit. The
connection between the common station supply and unit supply is then severed.

There are some variations on this standard configuration at nuclear sites


But if you think that's dodgy they fill the stator with water and circulate
hydrogen in the gap between the stator and rotor to keep it cool.

Why Hydrogen?...

To cool the rotor and reduce windage losses compared to air cooling

Most large (as in 60MW+) power station generators from the late 50's onwards are
hydrogen and water cooled.

--