115V/400Hz
Join Date: Apr 2007
Location: Amsterdam
Posts: 50
Likes: 0
Received 0 Likes
on
0 Posts
Volts/Amps
Being electrocuted is something one can get used to! I have a good friend who can take hold of domestic mains (240v/50Hz) and offer an opinion on whether the National Grid is delivering good quality power on any particular day! He was an electrician for many years but - crucially his skin/bodytissue resistance (a genetically endowed trait) was high. A potential difference of 250 volts could be applied across his fingers and because of his natural high resitance this was not enough to pass a lethal current through his body or vital organs (read heart)..
115 volts applied to damp skin on a person with normal conductivity may kill them..
As we used to say when we went through electrician school - 'It's Volts that jolts and mills (Milliamps) that kills' Meaning a big voltage can give you a shock but unless the voltage is sustained and the power source can deliver a sizeable current it won't kill you.
115 volts applied to damp skin on a person with normal conductivity may kill them..
As we used to say when we went through electrician school - 'It's Volts that jolts and mills (Milliamps) that kills' Meaning a big voltage can give you a shock but unless the voltage is sustained and the power source can deliver a sizeable current it won't kill you.
Join Date: Aug 2005
Location: fairly close to the colonial capitol
Age: 55
Posts: 1,693
Likes: 0
Received 0 Likes
on
0 Posts
3 phase motors (and generators) are more compact and lighter above a given HP (or KW) rating. 3 phase equipment makes more efficient use of power than single phase motors/generators.
3 phase motors also run smoother, start up with more torque than their single phase counterparts and are more reliable.
A single phase current crosses zero twice per cycle and has two peaks.
One negative and one positive.
With 3 phase power, these peaks and zero crossing points are staggered:
The graphics above should illustrate how 3 phase current can provide a broader area of max power transfer than single phase current.
411A mentions the original inverters - converting power by driving a generator with a motor. This is why we refer to current day electronic inverters as static.
Blah blah blah...
During a summer job at a plastics factory belonging to a friend of the family, I learned wiring of 3 phase motors was fairly simple - if you got it wrong the motor would just spin backwards - swap any two power wires and you're in business.
3 phase motors also run smoother, start up with more torque than their single phase counterparts and are more reliable.
A single phase current crosses zero twice per cycle and has two peaks.
One negative and one positive.
With 3 phase power, these peaks and zero crossing points are staggered:
The graphics above should illustrate how 3 phase current can provide a broader area of max power transfer than single phase current.
411A mentions the original inverters - converting power by driving a generator with a motor. This is why we refer to current day electronic inverters as static.
Blah blah blah...
During a summer job at a plastics factory belonging to a friend of the family, I learned wiring of 3 phase motors was fairly simple - if you got it wrong the motor would just spin backwards - swap any two power wires and you're in business.
Since you ask (post19) from memory, and it's a very long time ago, Comet was 115v frequency wild generation - this used for de-ice only, rectified and regulated to 28vDC. Instrument supplies from three? DC-AC 115v 400Hz motor driven inverters. Engine start was 120v DC. I Think the Brit was similar but might have been 28v starters. I seem to remember that the Caravelle had the same ground power requirements as the Comet which would imply the same starter. The GPU cables used to go rigid with the current on engine start !
Psychophysiological entity
Here's a typical 240 NM Weather Radar. Power Consumption: 4.2 amps @ 28 VAC 3.0 amps @ 115 VAC, 400 HZ Not much at all.
'It's Volts that jolts and mills (Milliamps) that kills' Meaning a big voltage can give you a shock but unless the voltage is sustained and the power source can deliver a sizeable current it won't kill you.
I can recall one of my lecturers at Cambridge (I was being polished, not the full degree) telling me about the time he copped hold of a 9kv winding from a hard-wired EHT transformer. When he left hospital he went back to his lab and looked at the scuff marks from his shoes trailing across the ceiling. They gave us plenty of amps to play with in those days.
Brits........Geeeeeeees, I have an old pilot's hand book at home, and the schematic is mind-blowing, let alone the full circuit.
Talking of rotary generator days, hands up who can tell me what a torque switch does.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
Post WWII the US military had some aircraft & systems that ran 800 Hz (they called it 800 cps back then). Same rationale, just taken a step further. I don't know why it was abandoned.
I used to use a pocket calculator in the jump seat to do engine performance checks. It had a wall wart to recharge the battery, said transformer labelled 120v 50/60 hz. It worked fine and ran cool on aircraft 400 hz. But don't try it the other way around!!!
I used to use a pocket calculator in the jump seat to do engine performance checks. It had a wall wart to recharge the battery, said transformer labelled 120v 50/60 hz. It worked fine and ran cool on aircraft 400 hz. But don't try it the other way around!!!
I rememebr the cables need to feed juice to the Ecko 190 radar. Thick as my arm! And the rotary inverters on the Jet Provost accounted for about 30% of it's AUW!
Looking back to aviation electronics history, the Handly Page Victor Mk1 of the early 1950s had 'Alternators' producing 208V frequency wild AC. Rotary inverters then provided frequency stable AC at 400 and 1600hz. As the aircraft had electric powered flying controls, a backup was needed. So it had ten (yes, ten!) 28V batteries! Hardly a weight efficient solution, but the best the age could produce.
Then in the late 50s, the Victor Mk2 came along with CSDU driven generators which produced 200v 3 phase 400hz power with backups of an APU and two ram air turbines. This system was very similar to the VC10's, (which I flew later) and the VC10's was almost identical to the 747's which didn't change much on the introduction of the -400.
I seem to remeber the Jetstream 200 had both AC generators and DC generators. Not many people copied that system!
The torque switch: If I remember correctly, it was on a rotary inverter and was held open by the current induced by the rotaion of the generator part of the inverter. If the rpm dropped, the switch closed and put on a warning light on the flight deck to tell you the AC supplies to you instruments were suspect. As always, I'm open to the inevitable correction on that piece of information.
Looking back to aviation electronics history, the Handly Page Victor Mk1 of the early 1950s had 'Alternators' producing 208V frequency wild AC. Rotary inverters then provided frequency stable AC at 400 and 1600hz. As the aircraft had electric powered flying controls, a backup was needed. So it had ten (yes, ten!) 28V batteries! Hardly a weight efficient solution, but the best the age could produce.
Then in the late 50s, the Victor Mk2 came along with CSDU driven generators which produced 200v 3 phase 400hz power with backups of an APU and two ram air turbines. This system was very similar to the VC10's, (which I flew later) and the VC10's was almost identical to the 747's which didn't change much on the introduction of the -400.
I seem to remeber the Jetstream 200 had both AC generators and DC generators. Not many people copied that system!
The torque switch: If I remember correctly, it was on a rotary inverter and was held open by the current induced by the rotaion of the generator part of the inverter. If the rpm dropped, the switch closed and put on a warning light on the flight deck to tell you the AC supplies to you instruments were suspect. As always, I'm open to the inevitable correction on that piece of information.
Join Date: Jan 2004
Location: LPPT
Age: 58
Posts: 431
Likes: 0
Received 0 Likes
on
0 Posts
There's another good reason for the 400Hz freq. and that is to provide greater DC quality (smooth and clean) as opposed to 50Hz. Weight and Volume are the other main reasons.
GD&L
GD&L
OK, the 400Hz and 115V Ac is for weight issues, but what I'd like to know is whether the 3-phase electric motors used in aircraft systems are delta or star-wound?
If I recall, delta-wound motors don't require a neutral wire, thus saving weight again. I think US 3-phase domestic electric motors are always delta-wound whereas in the Antipodes where we have 415V 3-phase power we use star-winding which requires a fourth wire, the neutral - and woe betide your equipment if you have the dreaded "floating neutral"!
I'm guessing the aircraft 3-phase motors would therefore be delta-wound to save wire and thus save weight.
If I recall, delta-wound motors don't require a neutral wire, thus saving weight again. I think US 3-phase domestic electric motors are always delta-wound whereas in the Antipodes where we have 415V 3-phase power we use star-winding which requires a fourth wire, the neutral - and woe betide your equipment if you have the dreaded "floating neutral"!
I'm guessing the aircraft 3-phase motors would therefore be delta-wound to save wire and thus save weight.
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
There's another good reason for the 400Hz freq. and that is to provide greater DC quality (smooth and clean) as opposed to 50Hz. Weight and Volume are the other main reasons.
GD&L
GD&L
Join Date: Jan 2006
Location: Cyprus
Posts: 19
Likes: 0
Received 0 Likes
on
0 Posts
Star/Delta Motors
Both configurations are used. Heavy duty motors (hydraulic pump drives etc.) are often started in Star to limit starting current. As the motor approaches full speed the connection is switched to Delta allowing full current and maximum torque.
Join Date: Apr 2000
Location: 30 West
Age: 65
Posts: 926
Likes: 0
Received 0 Likes
on
0 Posts
WRT to battery voltage.
Batteries are nominally 12 or 24 volt.
The busses that they run are normally powered from a generator or alternator source which provides 14 or 28 volt in order to be able to charge the battery in the circuit.
So a car or aeroplane may be 12 volt but it runs on 14 volt.
Batteries are nominally 12 or 24 volt.
The busses that they run are normally powered from a generator or alternator source which provides 14 or 28 volt in order to be able to charge the battery in the circuit.
So a car or aeroplane may be 12 volt but it runs on 14 volt.
Join Date: Jan 2001
Location: Around the world.
Age: 42
Posts: 606
Likes: 0
Received 0 Likes
on
0 Posts
Yay, I've had both US and UK mains shocks messing around with stuff in a stupid way. The only thing that scared me (and I never did) was catching hold of the high voltage DC line within a valve amp. People suggested this would cause a 'hold on until you are dead' situation....
Got bitten by the stored voltage in the cable of a colour TV tripler that had been switched off for 12 hours - just the voltage due to the stored charge in the capacitance of the cable. Dunno what it was (15Kv?) but it threw me backwards across the workshop, my hand was numb and the arm didn't work from the elbow down for about 12 hours.
Not intending to do that again in a hurry.
Not intending to do that again in a hurry.
Join Date: Aug 2005
Location: Not Ardua enough
Posts: 266
Likes: 0
Received 0 Likes
on
0 Posts
If we're talking belts....As a young sprog was absolutely fascinated by the rotating lights on a phase rotation meter placed across 3 phase 115v 4OOhz. Why I decided to remove it without isolating the power supply I will never know....ouch
None but a blockhead
Join Date: Nov 1999
Location: London, UK
Posts: 535
Likes: 0
Received 0 Likes
on
0 Posts
If we're talking HV anecdotes (glances warily at TPTB)...
I used to work in a TV repair shop in the early 80s in Plymouth. One of the owners came from the Rank Bush Murphy factory there, and _really_ should have known better, but...
There was a TV on the bench, back off, facing the wall, with a line output fault, and he wasn't sure whether it was it was in the EHT tripler/smoother circuit or earlier. I can't remember which chassis it was, but it was one of those more recent jobs where the LOPT also provided most of the rest of the voltages for the set, so all manner of problems could manifest as low/no line output.
Anyway, he had the EHT anode lead off, and the set on. He went to get the EHT meter, which was on a shelf above the bench, and in so doing bumped the chassis with his crotch. This had two immediate consequences, and one rather more long-term effect.
in short order, the EHT connector moved and made contact with the metal fly on his trousers, and the fault - subsequently traced to an intermittent solder joint in the line oscillator - temporarily cleared. The longer term consequences mostly wore off after a night in Freedom Fields hospital 'under observation' from a curiously attentive medical staff. Mostly.
Relevance to aviation? Yer man certainly got airborne.
R
I used to work in a TV repair shop in the early 80s in Plymouth. One of the owners came from the Rank Bush Murphy factory there, and _really_ should have known better, but...
There was a TV on the bench, back off, facing the wall, with a line output fault, and he wasn't sure whether it was it was in the EHT tripler/smoother circuit or earlier. I can't remember which chassis it was, but it was one of those more recent jobs where the LOPT also provided most of the rest of the voltages for the set, so all manner of problems could manifest as low/no line output.
Anyway, he had the EHT anode lead off, and the set on. He went to get the EHT meter, which was on a shelf above the bench, and in so doing bumped the chassis with his crotch. This had two immediate consequences, and one rather more long-term effect.
in short order, the EHT connector moved and made contact with the metal fly on his trousers, and the fault - subsequently traced to an intermittent solder joint in the line oscillator - temporarily cleared. The longer term consequences mostly wore off after a night in Freedom Fields hospital 'under observation' from a curiously attentive medical staff. Mostly.
Relevance to aviation? Yer man certainly got airborne.
R
A long time ago in a high-energy lab far, far away...
We were testing a transmitter for a phased-array military radar. These devices were pretty heavy duty as the peak power output ran into the MW range and the power supplies were just as beefy.
Because of the lethal potential (ha ha) of a lot of the equipment inside the room (about 30m x 20m x 10m, fully shielded), one of the rules was you didn't ever work on something on your own. I remember a pair of us coming in one afternoon and hearing this muffled rhythmical thumping from the other side of the room; on closer inspection we saw a twitching pair of legs sticking out from under the transmitter.
We immediately hit all the emergency cutoffs, then went in with the earthing sticks...
It turned out that one of our more senior engineers (who should have known better) had decided to do a bit of work on this device. After he came back from hospital, badly bruised but without long-term injury, he explained that he'd brushed a high voltage terminal whilst working under the radar and that had flung him away. Unfortunately, he bounced off the floor and straight back into the wiring, which threw him back at the floor etc. Very luckily for him we had chosen to walk into the lab, pretty much at the same time as this started - I've no doubt he would have been killed within minutes without intervention.
KIDS! DON'T DO THIS AT HOME!
We were testing a transmitter for a phased-array military radar. These devices were pretty heavy duty as the peak power output ran into the MW range and the power supplies were just as beefy.
Because of the lethal potential (ha ha) of a lot of the equipment inside the room (about 30m x 20m x 10m, fully shielded), one of the rules was you didn't ever work on something on your own. I remember a pair of us coming in one afternoon and hearing this muffled rhythmical thumping from the other side of the room; on closer inspection we saw a twitching pair of legs sticking out from under the transmitter.
We immediately hit all the emergency cutoffs, then went in with the earthing sticks...It turned out that one of our more senior engineers (who should have known better) had decided to do a bit of work on this device. After he came back from hospital, badly bruised but without long-term injury, he explained that he'd brushed a high voltage terminal whilst working under the radar and that had flung him away. Unfortunately, he bounced off the floor and straight back into the wiring, which threw him back at the floor etc. Very luckily for him we had chosen to walk into the lab, pretty much at the same time as this started - I've no doubt he would have been killed within minutes without intervention.
KIDS! DON'T DO THIS AT HOME!
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
Two spots of trivia....
German aircraft in WWII used 500Hz AC systems.
So why do we now use 400Hz? Guess who won the war....
To transport electric power over long distances, the lower the frequency the better. That's why Swiss railways use 16 2/3 Hz (one-third of 50Hz).
(DC would be even better, but unfortunately the wooden-core DC transformer is still a myth).
German aircraft in WWII used 500Hz AC systems.
So why do we now use 400Hz? Guess who won the war....
To transport electric power over long distances, the lower the frequency the better. That's why Swiss railways use 16 2/3 Hz (one-third of 50Hz).
(DC would be even better, but unfortunately the wooden-core DC transformer is still a myth).
Join Date: Feb 2005
Location: flyover country USA
Age: 82
Posts: 4,579
Likes: 0
Received 0 Likes
on
0 Posts
To transport electric power over long distances, the lower the frequency the better. That's why Swiss railways use 16 2/3 Hz (one-third of 50Hz).
