High Voltage Direct Current electrification

 
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
What sort of ships????
Bulk carriers, container carriers, oil tankers, roll on/roll off carriers ..... Real ships of the merchant marine. And NO very few of
them have "Shore Supply" facilities.
They use common mains voltage and frequency so that they can purchase "off the shelf" electrical equipment and not need specially made items (This is called Common Sense)
Pressman
Are you saying that some of them, but not most, have shore supply? The reason that the mains frequency is much less than 400Hz has to do with the distance that the power has to be transmitted, given the impedance of the great length of power lines.
But conductor distance wouldn't be a major issue on ships, and actually, plenty of 400Hz equipment is available given its commonality in aircraft and airport equipment, and in some other places too.
Also, 400Hz equipment isn't that much different from standard frequency equipment. For example, if it uses D.C internally, and at a lower voltage than the mains, as is the case with things like desktop computers, amplifiers, etc, running it on 400Hz could be done just by changing the transformer. Appliances containing 50Hz motors could likely run on 400 Hz simply by replacing them by motors with 8 times as many poles.
In addition, I suspect that a 400Hz transformer would offer a greater performance to cost ratio than a 50Hz transformer, even though the former are produced in smaller quantities.

I am a fully qualified Special Class Electrician and Armature Winder Myrtone, so I Do know what I am talking about.
AC motor speed IS determined by the number of poles and the frequency, not voltage ratios
Pressman
Your comments are valid for synchronous motors, because the rotor must turn in synchronism with the field of the stator. But I do wonder if voltage alone can affect the speed of an induction motor, frequency being equal. And A.C motors do seem to produce back E.M.F. While the frequency supplied to a synchronous motor with a given number of poles does determine the speed of the rotor, it also determines the amount of back E.M.F, and the field of the rotor would add to that. Induction motors too would produce back E.M.F owing to the rotating magnetic field. So the voltage of the supply to the motor must be varied whenever the frequency is varied.

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  M636C Minister for Railways

Navy ships use 220V 3Ph 60Hz AC, although minor ships such as patrol boats use 50 Hz to allow the use of commercial equipment and to simplify shore power.

Ships with aviation facilities usually have 400Hz power, often provided by a static frequency converter from the 60Hz supply.

Some communication and sensor equipment on major ships is 400Hz, supplied from the SFC.

M636C
  rwatts Junior Train Controller

Location: Adelaide SA
Ships with aviation facilities usually have 400Hz power, often provided by a static frequency converter from the 60Hz supply.

M636C
M636C
Our old mainframe computer (think single IBM 370 era system, late 70s, early 80s, in a room the size of two tennis courts) used 400Hz power to feed the various power supplies in the central processor frames. This was derived from 60kVA rotary converters (Jones&Rickard and GE motor-generator sets) driven from 3-phase mains.  The additional efficiency of the many power supplies running at 400Hz apparently made it worth while.  
Richard.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
Well myrtone, I and the worldwide community of ship builders from Europe, Asia, and the America's bow down to your infinite wisdom as it appears we have all got it wrong! (according to you)


Along with TAFE, the Universities and the Australian society of engineers who have obviously been training everyone in error for
so many years!

We all bow down to your superior wisdom!


Dayum I need a drink!
  LancedDendrite Chief Commissioner

Location: North Haverbrook; where the monorail is king!
Well, I do see that this thread has been quite literally de-railed.

But I do wonder if voltage alone can affect the speed of an induction motor, frequency being equal.
Myrtone
No, it doesn't. The maximum speed of an induction motor is set by the supply frequency and the number of poles in the stator. The actual speed of the induction motor varies with the torque required of it (i.e loading), and is always equal to or less than the no-load (maximum) speed.

DC motors are the only motors whose speed is affected by voltage.
  apw5910 Deputy Commissioner

Location: Location: Location.
DC motors are the only motors whose speed is affected by voltage.
LancedDendrite
You're counting "universal" AC/DC motors in that, aren't you Smile
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Whether those ship builders are right or wrong, the fact is that there are factors favouring frequencies less than 400Hz on land based power grids that don't apply to electrical systems on board ships. If all the ships and trains, in addition to planes, with A.C electrical systems all had 400Hz, then the market for 400Hz equipment would be higher. 400Hz is already quite common, and 400Hz equipment isn't that much different. If it uses extra low voltage D.C internally, only the transformer would need to be changed. Appliances with 50Hz motors could likewise be modified just by replacing them with motors with 8 times the pole count.
Induction motors always turn slower than the synchronous speed, this speed difference being slip. The question is whether the voltage, frequency being equal, can affect the amount of slip. Only synchronous motors turn at a speed proportional to frequency, and inversely proportional to pole count, but the voltage must be varied whenever the frequency is varied.
  NG Sulzers Deputy Commissioner

Location: Quorn
Having spent some 25 plus years in the Navy, I have been a maintainer of 400Hz supply equipment. Out of 24VDC, 115VAC 60Hz, 440VAC 60Hz, 115VAC/205VAC 400Hz, 220VDC and 440VDC, the 400Hz Static Inverters would have to have been the most unreliable pieces of kit that smoke was ever stored in. Never had much problem with any of the other supplies.
I have been on vessels where 400Hz has been produced by rotating machinery, and I have also been on vessels where 400Hz has been produced by Static Inverters. Surprisingly, notwithstanding the DC prime mover for the rotating machine, it was more reliable.
400Hz consumers belong to the 'Miliamp Tramps', combat, communications and weapons systems. 400Hz was never used to turn a motor,  or any serious amperage consumers.
AC motors all belonged in the 60Hz family, a 400Hz motor wouldn't wind up a mouse trap.
400Hz is certainly not a mountain mover, which is a desirable requirement in rail.
Also, 400Hz could not be supplied from shore connection, only 220VDC, 440VDC and 440VAC 60Hz were supplied from shore.
  LancedDendrite Chief Commissioner

Location: North Haverbrook; where the monorail is king!
DC motors are the only motors whose speed is affected by voltage.
You're counting "universal" AC/DC motors in that, aren't you Smile
apw5910
Using brushes is cheating! Laughing
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
AC motors all belonged in the 60Hz family, a 400Hz motor wouldn't wind up a mouse trap.
400Hz is certainly not a mountain mover, which is a desirable requirement in rail.
Also, 400Hz could not be supplied from shore connection, only 220VDC, 440VDC and 440VAC 60Hz were supplied from shore.
NG Sulzers
400Hz motors are technically possible. I don't see what frequency has to do with power rating other than higher frequency meaning transformers with more power rating for size and weight, similar with induction and synchronous motors.

But anyway, let's consider railway electrification. If you look at systems where the line voltage is the same as what is used internally, there is actually more than one good reason for using DC. One is the power characteristics of D.C motor (and inverter fed polyphase motors), another is that D.C is better suited than A.C to a system of current collection (usually third rail or single wire overhead) with only one ungrounded wire.
  NG Sulzers Deputy Commissioner

Location: Quorn
Myrtone - any chance of you sharing with us what you are smoking? It must be some good stuff.
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I don't understand the question.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
I don't understand the question.
Myrtone
You don't understand the answers either
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Does anyone know of examples of medium voltage D.C circuit breakers? How much space would they take up compared to a single phase circuit breaker of the same voltage and current rating?
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
Does anyone know of examples of medium voltage D.C circuit breakers? How much space would they take up compared to a single phase circuit breaker of the same voltage and current rating?
Myrtone
Ever tried Google?
  RustyRick Chief Commissioner

Location: South West Vic
Does anyone know of examples of medium voltage D.C circuit breakers? How much space would they take up compared to a single phase circuit breaker of the same voltage and current rating?
Ever tried Google?
Pressman
Myrtone is an avid user of Google. It's just he doesn't know the right question to ask. Rolling Eyes

Rick

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