INS Arihant (ATV) News and Discussion -2

[geeth]

>>>Not to be splitting hairs but I stuck by the choice of words used by Shri Kakodkar very fast response and also speaking of it as one of the key challenges.

I pointed it out to say that we may not be able to say conclusively that a steam turbine is driving the shaft. I could be in all probbaility, but if it is motor driven, then also you need fast response from reactor, unless there is a large array of batteries, which is unlikely.

[harbans]

The reactor is producing steam that will drive a turbine that will generate electricity that drives a motor that will be geared through reduction gearing to drive the screws. So as long as the turbine is made to turn at the desired speeds the frequency and voltage generated will be steady to turn a motor/s that will be coupled to the screws. Minor fluctuations in reactor output can easily be managed within the turbine design specs. Modulating the reactor output to those specs/ limits is what Ak is talking about. And doing that while miniaturizing the design is certainly no easy feat.

[K Mehta]

Singhaji's description of this thread as a Pasthun Swayamvar has been the most apt one.
Instead of news and discussion, maybe this thread should be called news and speculation thread.

[Gerard]

When all there is to discuss is the coconut, what else is there but speculation?

[pankajs]

Saar allow me to present my case.

1. Our jurnos ask "Deemag Ki batti jala de" questions.
Was this completely made in India?
Designed, fabricated and executed in India?
And by Indian scientists?
So this is not a Russian design?
Indian design, made in India, by Indians?
I am told it is about ten times smaller than a normal power reactor, is that correct?
So would it be fair to call it a baby reactor?
The above key questions have enhanced our understanding of INS Arihant

2. Our scientists could have, in reply to a specific question said "Off Limits" or "No Comments" or perhaps "it will provide the submarine with agility comparable to others in its class both under water and on the surface”
The reply was a verbal googly “It is a small reactor compared to, say, for example a commercial power station, 1000 MW (electric) would generate more than 3000 MW of heat, which is about 30 times what we produce here.”

3. We jingos, for the lack of any creditable information, read and then re-read what ever tidbits are available and try to make sense of it. In the process we end up creating more noise (Speculation)

[vina]

I pointed it out to say that we may not be able to say conclusively that a steam turbine is driving the shaft. I could be in all probbaility, but if it is motor driven, then also you need fast response from reactor, unless there is a large array of batteries, which is unlikely.

Only Frog (french ) boats seem to have electric drive. All boats from all other countries (Unkil, Russians, UKstan, Chinis) have steam turbine drives. I doubt India would have gone the French way, especially when we have zero experience with having implemented on even on a surface ship. We have experience with steam drives (leander class) and I suspect it is a scaled up version of that machinery basically.

[Arun_S]

I know nothing about motors - but do motors tend to be connected with largish capacitors to provde power for a surge?

No saar that is not correct.

Caps do not have enough capacity to store energy to power the motor for even 0.1 second.

Small capacitors are used on DC motors, but they are for EMI (Electro Magnetic Interference) reduction (Typical valie 0.1 micro Farad).

Somewhat large size caps are used in AC powered motors used in home fans. The AC induction motors require a rotating magnetic field and for that it requires 2 windings that carry current that are phase offset with each other. Industrial motors may have 3 phase power but home power is only single phase. Thus for small motor power (fractional horse power motors) they use a AC capacitor (~ 1 - 3 micro farad / 350 Volts rated) in series with one of the winding that is enough to introduce significant phase difference in the winding current w.r.t. the winding that has no capacitor, thus generating a rotating magnetic field in the stator.

[shiv]

Aaah - thanks. I did see a capacitor on a fan - hence the (silly) doubt.

[Charu]

Submarine Electric Propulsion Motor from SIEMENS



Source:
http://www.industry.siemens.com/marine/ ... roc_06.htm
-----------------------------------------------------------------------------------------------
http://www.industry.siemens.com/broschu ... syn_en.pdf

[John Snow]

Arun saar already covered, in single phase motors some start with capacitors and are thrown out of circuit by a centrifugal switch once the speed is attained (some of the icream boxes use this in refrigerating compressors also fridges in home, ther is relay). Some are capacitors start capacitor run in which the capacitor is always in the circuit.

from the siemens picture I am sure therw will be fluid coupling / torque convertor between the propeller and the shat of the motor ( or it could be built in the cage of the motor itself) as can be seen in this case with piping on the photo

[shiv]

I am sure therw will be fluid coupling / torque convertor between the propeller and the shaft of the motor

What does this mean?

[John Snow]

Shiv saar> Simply said Put one fan in front of another fan run only one fan (by switching only one) the other fan will start rotating, the air being the fluid to couple them.

The torque convertor has a fixed turbine vanes on a racthet so that the torque generated by the rotating fan gets multiplied. Also the transmission will be jerk free (all automatic transmission equiped cars have this torque convertor)
Since there is fluid coupling the car/submarine cant be push started (just kidding).

The torque converter reduces shock loading of the prime mover, in this case the DC motor (or thyristor controlled AC motor)

Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission.
At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power.

The slip here is same as the slip between the rotating magnetic field and the rotors (rpm) s= N-n


from how stuff works

[negi]

The driving shaft from the Turbine and the propeller head are directly coupled via a set of reduction gears ; this is required because the screw is a fixed pitch propeller hence any sort of control over the submarine's speed can be only had by varying the RPM of the propeller (unlike in Turboprop AC where variable pitch propellers can operate at a fixed optimum RPM and yet achieve varying mass flow).

In case of turbo-electric propulsion (French and PRC employ this Chicom has this on board the TYPE093 while French have it on Rubis,Redoutable and even on Baracuda ) the steam turbine actually drives a turbo alternator (AC generator) which inturn drives an AC motor which is coupled with the propeller shaft ,I guess the speed can be controlled without any reduction gear by varying the slip angle for an AC motor (induction type) or by actually changing the frequency of the electrical power supplied to the motor (synchronous).

Iirc USN Narwhal had a gigantic Steam turbine in order to achive low RPM at the rotor head itself this enabled them to directly couple the propeller shaft with the turbine without any need for the reduction gear (one of the sources of noise emanating from a nuke sub).

[John Snow]

Reduction gears and torque converters are not mutually exclusive ( as can be seen in the auto transmissions, strictly speaking the automatic transmission is nothing but conventional transmission with clutch packs actuated by hydraulic servo controls in the transmission, if you pay close attention to automatic trans car you can feels the shifting of the gears but it will be very smooth compared to manual shift a good driver can replicate the auto smoothnes in manual transmission too).

The torque converter if and when used takes away the shock loading of the prime mover.
(ex a conventional lathe has reversable head stock coupled to a AC motor, if the lathe operator reverses the head stock before it comes to complete stop the a/c motor is shock loaded actually it is like short cicuiting the secondary of a transformer, if there was to be for example a fluid coupling the shock is absorbed by eddy currents, remember though the rversal of a transmission is achieved by inserting an idler gear so that the prime mover continues to rotate only one direction. Except in yezdi motor cycles some times they start in reverse rotation and if you put first gear you will travel backwards!)

In nut shell even though a electric motor can be reversed in many ways it has to come to complete stop before it can reverse other wise shocking ( ) loads will come into play on the rotor sator windings. A fluid coupling also detaches the prime mover (electric motor) from mechanical gearing of the propeller.

Steam turbine have a rpm which would be excess of 10,000 rpm, and has to be reduced to get the torque, which obviously means worm reduction box coupled with spur gears, helical etc. assuming it is directly connected to the prop shaft. HP = 2piNT/4500. so speed and torque are inverse just like series wound dc motor Speed vs Torque curves (actually most often compund wound motors are used to propell, but A/c motors can also with thyristor/thyratron controls.

I think I ma rambling no more inspite of Negi Naveen garu...

( note this

Typically the turbines are equipped with an Integrated Turbine Control (ITC) system which is designed to interface with the KMW CP Propeller Control System to provide a suitable combination of propeller pitch and propeller RPM.

[geeth]

Snow Garu,

What you say was the case with older ships with Diesel propulsion (Old Brahmaputhra Class) - there you have fluid couplings with less than 5% slippage.

The Leander / Godavari Class had reduction gears (double helix Double reduction) which reduces the 5000 RPM of turbine to 200 odd propeller. It doesn't need a fluid coupling because, the steam turbines can be rotated at any RPM (during warming up, shutting down, you rotate it at less than 5 RPM) AND these ships have CPP. So during starting you can bring the pitch to zero and keep it at zero load.

That is what I remember, unless my memory is cheating me after so many years - I have served in these ships also.

[John Snow]

geeth garu>> Since you tasted the pudding, I yield to you. ( I mean you served)

I am assuming that INS Arihant will be electric propulsion and also my comment was about the Siemens picture posted, which appeared to have fluid hoses on top of it (unless they are specifically for cooling the motor). Notice the fins (cooling kind near the out put end) I was thinking it also has integrated braking system built on to the shaft.

All this is conjecture from the picture. I had several times passed in Groton USS Nautilus museum, I failed to take time to go and see it.

From the picture it looks like 17 to 20 feet in dia. (scaling the man to be 6 feet approx)

[negi]

KMW CP Propeller Control System is for surface ships and hence the reference to the variable pitch propellers ,most of the modern submarines across the globe (Akula,Ohio and even Jinn class) employ the fixed pitch 7 bladed propellers.

The Siemens electric motor in question is a highly evolved Permanent magnet synchronous motor where the rotor elements are made of permanent magnets (afaik neodymium) and I believe the stator windings are made of a high temperature superconducting material to allow for high current densities and a compact yet powerful design.

The three boxes at 10,12 and 2 O' clock positions imho are feeds to the stator windings and the fins are typical to any electric motor skeleton i.e. a roll cage construction , to save weight and for a designed level of ruggedness.

[shiv]

Very interesting stuff - thanks Spin and others. But aren't gearboxes inherently noisier than this fluid coupling thing?

Secondly I am reminded of the Airbus crash in Bangalore in the 1980s. The pilot revved up the engine but did not have altitude/time for the lag period when engine RPM increased by the necessary amount.

Supposing Arihant commander says "Full speed ahead" while travelling under water at initial speed of 5 knots. What happens?

First some neutron absorbing rods are pulled out of reactor core to increase fission. That heat gets transmitted to water which produces steam after a second lag period and the steam turbine goes faster and after a short lag that increased speed is transmitted via fluid viscosity/gearbox to a generator or screw itself.

If this is correct there is a direct link between screw speed and what the reactor core is doing. I guess this differs from a national electric grid where sudden demands can be met by load balancing from multiple sources while hydel stations are able to ramp up supply almost instantly.

I may be wrong on all counts - but knowing nothing I am allowed to speculate on everything

[vina]

INS Arihant will be electric propulsion

seriously doubt it , unless BHEL managed to fully indigenize/absorb the tech from the HDW program and build on it. I think the Siemens propulsion motor would be permanent magnet DC motor right ?. Point is on surface ships, for "all electric" "power station" kind of concept drives (like on cruise ships where there is a large hotel load anyways), ABB and others typically offer 3 phase AC thryistor controlled motors, similar to the controls and concept of the ones in the 3 phase AC locos that Indian Railways bought from ABB, back in the mid/late 90s when Jaffer Sharief was the Railway minister.

The thing is in locos, the single phase 25KV AC supply from the overhead catenary has to be changed to 3 phase (all the Power Electronics guys, help please .. that is what I understood from back then), and then then supplied to the traction motors.

Why AC --> No brushes, and hence no maintenance /wear unlike DC and why 3 Phase --> 1 phase to inefficient, 3 is probably okay ..

I guess in a ship, the diesel /gas turbine/nuke powered steam turbine can drive a 3 phase alternator(s), which can directly supply power to the electric propulsion motor. Point is, is is complex, heavy, less efficient and more points of failure, than mechanically coupling the turbine to the propeller via gearing .. The trade off is mechanical gearing vs, power electronic driven speed and power output control. Instead of weight of gearing , you have weight of propulsion motor and a big alternator. Advantage with power station , is if you have multiple shafts and multiple prime movers, splitting power and optimal use of prime mover becomes more efficient and you start saving weight and space, because of less complex gearing and shafting arragement and plus, the prime mover need not be in the same space as the shaft etc and you can distribute them around the ship.

All things point to direct mechanical drive, unless BHEL was on the ball and was working on it all the while. Doesn't seem plausible.

[shiv]

Do huge electric motors put out a huge electromagnetic signature? How to shield that?

[John Snow]

(the fins in the roll cage constructio are allways for heat transfer, actually if you see the back side of old siemens , NGEF, GEC, Crompton 3 phase motors there will be a fan in the back which directs the air flow into the groves along the motor (made by the protruding fins).

The 10 12 2 rock around the clock to mee look like hoses feeding some kind of fluid.
The important thing is what heat is trying to dissapate? brakes? fluid coupling/torque convertor (if any)

looks like the motor front end cap is a huge casting ( which is always for small motors)

[Cybaru]

For the un-informed, assuming its electric propulsion, do the figures for top speed and all change ? Is 80 MW enough ? If its not BHEL that made the motor, who else could have supplied the needed motor or tech ?

[pankajs]

Wouldn't adding another layer between the power plant and the propeller reduce the effective power delivered?

[John Snow]

no the only way to shield electromagnetic is grounding since the whole sub is made of metal that too a double hull it is the best shield by itself (IMO). The motor will be 3 pahse A/C because of the advances in control systems and power handling electronic/electric ( Thyristors, Thyratrons etc ). In actual generation it always A/c that is produced and then comutated to give DC via brushes or rectifier electronics. If it is dc motor then the commutator and maintenance are required, but the speed torque charecteristics of DC motors are very well suited for High strating torques.. ( full speed ahead situation here we come to speed response of the system from steam generation in the reactor to turbine reveing up to dc motor responding and the turning of propeller, then to cavitation limitations etc etc lot of noise as you can see )

In A/c traction usually 110KV single phase is rectified by ignitron or silicon rectifiers usually 750v AC ( drop from 110 KV)
driving.

But As Naveen Negi garu says, now a days AC asynch motors are equally adept.


notice the fan and groves for air circulation and cooling the right side picture is end cap( black of the left side) removed to reveal the white fan

[vina]

Very interesting stuff - thanks Spin and others. But aren't gearboxes inherently noisier than this fluid coupling thing?

Secondly I am reminded of the Airbus crash in Bangalore in the 1980s. The pilot revved up the engine but did not have altitude/time for the lag period when engine RPM increased by the necessary amount.

Shivji, gas turbines , unlike piston powered engines , have a big response lag time. Now a low bypass engine like the Kaveri and the one on IAF IL-76s have a better response than high bypass turbon fans like the IAE 2500 on the Airbus that crashed or even military ones like the ones on F16 , Su 30 etc.

Reason, the big fans need to spin up to the new (higher speed) when you demand more power and blip the throttle and being big heavy things, they need a couple of seconds to spool up , basic inertia like our babus I suppose. Low bypass engines have small fans and hence spool up much faster.

This lag response was the reason why the Airbus crash in Bangalore happened. The previous plans had low bypass engines and when the pilot found that he was going to land short, he slammed the throttles, but it takes around 6 to 7 seconds before the power is avialble and tap , but by then he ran out of altitude and crashed.

Supposing Arihant commander says "Full speed ahead" while travelling under water at initial speed of 5 knots. What happens?

There is enough inertia and energy reserves in the reactor, steam generator, boiler systems and there will be adequate steam available to give the power increase you want in a few seconds

First some neutron absorbing rods are pulled out of reactor core to increase fission. That heat gets transmitted to water which produces steam after a second lag period and the steam turbine goes faster and after a short lag that increased speed is transmitted via fluid viscosity/gearbox to a generator or screw itself.

This part comes after the 5 knot increase is achieved and you need to sustain it. Obviously the reactor has to put out more energy to sustain higher speed or you fall back to earlier energy levels and speed drops.

If this is correct there is a direct link between screw speed and what the reactor core is doing. I guess this differs from a national electric grid where sudden demands can be met by load balancing from multiple sources while hydel stations are able to ramp up supply almost instantly.

Basic statistics saar. If variance is addiviive, var total = var a + var a + ......... var a ntimes = n vara , while total std deviation sqrt(n)* stddev(a) . So even in a grid, if you swith on the A/C in your house, there is enough energy reserve/inertia to give you the power you demand without it showing an immediate increase in the rate at which fuel is burnt at an average in the grid supply . It will happen if you leave the A/C on long enough.

Now if all of Bangalore turns on their electric gysers at 6:00 am, that is a big increase in aggreate demand and the peaking plants kick in (either diesel, gas turbine or hydel etc), to supply the additional energy in a short time (even then, I guess the demand at the generating units are not felt instantenously, becuase of the reserves in the base load generating plants and there is enough time for the peak units to kick in and supply power)

[John Snow]

Vina garu>> you forgot the SEB might switch off the honest middle class paying electric bills sub staion and direct the
Kilo w(h)atts to Slums and VVIP colonies, that way you dont have to kick in diesel gen sets ( who disel was pifered for amma's shoping SE saabs wife)

[negi]

Shiv saar imho answer to your first question is 'REDUCTION GEAR' i.e the reactor and the steam generator will work at 'X'% or close to an optimum designed value all the time ; infact even the Turbine itself will be chugging at a fixed optimum RPM 'R1' it is the reduction gears which will do all the work and control the propeller speed. For emergency stops or reversals one will have dampeners which will engage the propeller shaft when required while the drive shaft will be disengaged.

coming to electromagnetic shielding well as far as electric field is concerned the stuff inside a submarine is shielded (thanks to Gauss) also modern sub hulls are treated so as to have a low EM signature; as far as magnetic shielding is concerned there exists active and passive means of containing/canceling magnetic flux a very rudimentary example would be helmholtz coil or a similar arrangement. Seawolf class employs such electromagnetic signature suppression measures to avoid underwater mines and even detection by MAD.

Btw Snow ji yes coolant is not ruled out infact you might be right specially if those windings on stator are indeed made of HTS then presence of a liquid coolant is but natural.

And I am no garu...just stirring the pot as always.

[vina]

Shiv saar imho answer to your first question imho is 'REDUCTION GEAR' i.e the reactor and the steam generator will work at 'X'% or close to an optimum designed value all the time ; infact even the Turbine itself will be chugging at a fixed optimum RPM 'R1' it is the reduction gears which will do all the work and control the propeller speed

No no.. Reduction Gear Speed is just a derived factor. You need to look at the fundamentals, the energy balance.

It will help to keep the characteristics of the different kind of prime movers. The transmission and gearing is used to ensure that the engine remains in the power band.. that is all. So keeping the following (ideal engines) in mind.

1) Diesel Engine --> Constant Torque engine
2) Electric Engine -- > Const RPM engine (AC motor esp)
3) Turbine --> Const POWER engine

Keeping that in mind, you need to design the gearing to make sure that the engine is in the power band ..

[John Snow]

for a given HP ( or power)
Speed Torque are inversly related.

But each prime mover canonly operate only in certain band or region of torque speed.

The best is always electric priome mover because of speed control is stepless or continously variable.
For instance the starting torque is always high in any application and once the desired speed is achieved the torque is more or less constant.

[Charu]

In case of the Siemens electric propulsion motor the RPM can be varied.

[Charu]

Sir(s)

From the Siemens website:


http://www.industry.siemens.com/marine/ ... t=&SIdent=


Continuous rpm adjustability throughout the entire operating range
Elimination of torque-free speed range switching, thus no high current peaks or switching noises

[Charu]

http://www.fuelcellseminar.com/assets/p ... -4.ppt.pdf

Slide 9 shows a cutaway section of a fuel cell based electric propulsion system in a German sub.

[Dileep]

It should be a DC motor then.

Commutators are no longer needed. Electronically controlled switching have replaced them in advanced electromechanical systems. You sense the shaft angle, and the actual flux drain, and switch the polarity right at the zero crossing point.

Simple and efficient onlee.

[pankajs]

http://www.fuelcellseminar.com/assets/p ... -4.ppt.pdf

Slide 9 shows a cutaway section of a fuel cell based electric propulsion system in a German sub.

The link?

[Singha]

this is bringing back terrible memories of the snarling professor scowling at us in the BEM (basic electrical machines) lab wherein we had to wire up some motor ckts, run it for a minute and hence learn all these DC / AC motor business.

dont remember a line of of it now.

[vina]

Boss.. You are telling me. I nearly cupped in ETech 1 and E Tech 2 (dont remember the exact names of courses) but real night mare. Managed to scrape through with a C and D, after a massive rear guard action after a disastrous mid semester where I got 2 out of 40 or something.

I wonder what is it with the universal snarling profs in Electrical Engg. They used to be called "Man Eaters" at the Madrassa. Also, just remembering the E-Tech lab gives me a cold sweat. You had to work out the circuit diagram and do the exercises in advance before the prof would let us in. None of the usual slackers landing up there and trying to wing it. And god save you if you switch on anything before he comes and check out your wiring and gives you an okay.

I remember a neighbor of mine.He switched it on before the prof okayed it. The prof came over and quietly told him to switch everything off and go back to the hostel.. Poor guy stood around and said, "Sorry sir, it wont happen again" .. Prof laughs (first time I think I ever saw him do that), Of course, it wont happen again!. I have just thrown you out of the course!

[rakall]

Boss.. You are telling me. I nearly cupped in ETech 1 and E Tech 2 (dont remember the exact names of courses) but real night mare. Managed to scrape through with a C and D, after a massive rear guard action after a disastrous mid semester where I got 2 out of 40 or something.

I wonder what is it with the universal snarling profs in Electrical Engg. They used to be called "Man Eaters" at the Madrassa. Also, just remembering the E-Tech lab gives me a cold sweat. You had to work out the circuit diagram and do the exercises in advance before the prof would let us in. None of the usual slackers landing up there and trying to wing it. And god save you if you switch on anything before he comes and check out your wiring and gives you an okay.

Exactly... Can now.. but back then it was

I remember a neighbor of mine.He switched it on before the prof okayed it. The prof came over and quietly told him to switch everything off and go back to the hostel.. Poor guy stood around and said, "Sorry sir, it wont happen again" .. Prof laughs (first time I think I ever saw him do that), Of course, it wont happen again!. I have just thrown you out of the course!

You referring to a certain Prof. Ant Reddy by any chance from Madrassa..

[Singha]

>> You had to work out the circuit diagram and do the exercises in advance
>> before the prof would let us in

yeah after being thrown out and asked to walk in only with completed circuits, most of our
CSE class would be huddled around the corner in the stairwell for 20 mins, trying to figure
things out and copy from each other anything that looked remotely like it would unlock
the door.

meantime the prof sat alone in the lab. the lab assistants slunk around trying to escape his wrath.

he also sent many people back to hostel for wearing chappals. shirts also had to be tucked in. this was ok for safety purposes I think. in one senior yr one girl got her hair pulled by a lathe machine and her entire scalp got peeled off like a orange skin before someone stopped the lathe motor.

[vina]

dont remember a line of of it now

I remember just ONE number after all these years and it is 1440 .. You get a rev counter in the lab with a rubber headed tip , and you press it against a coupling hole in the output shaft of the motor to read the rotation speed. If the wiring is right and the induction motor runs as it should , that is the number you should get , round abouts. That was the only "fun" part of the lab , other than the smell of something burning (one guy actually managed to start melting something) and the sound of fuses and wires going pfftt...

Of course forgot why 1440 and how , now.

But one thing got burned into my head..
A/C Motors run at constant RPM and have piss poor speed control .. So all that ejjukashun at the ETech lab atleast managed to din that in to my head very hard I guess. .

[shiv]

http://www.fuelcellseminar.com/assets/p ... -4.ppt.pdf

Slide 9 shows a cutaway section of a fuel cell based electric propulsion system in a German sub.

Link not working