Electrical System

[mike disch]

I work at the L.A. Titanica exhibit. Two questions have been asked more than once by visitors, so I'm on to the mavens for assistance before giving out bad info.
1. Voltage, what was it? Shipbuilder Magazine lists 100 Volts in the chapter on the Olympic elect system, so I'm guessing that's the answer, and I assume the present-day standards (110V / 220 V) were not yet standardized. Correct?
2. Titanic/Olympic - the only ships with electricity? Did any other ship at sea have electric lighting and refrigeration? Were T/O the only ones, or perhaps one of the very few, so that it would be accurate to say that even 1st class on another ship (or most other ships) wouldn't have some of the benefits of 3rd Cl on the Titanic?

 

[Bill Sauder]

Mike:

The Titanic's service voltage was 100 volts D.C. The volts of 1912 are the same volts of today, so unlike pounds sterling and British vs. American gallons, this needs no conversion.

Off the top of my head, I think that electricity goes back on the Atlantic as far as the Umbria, so maybe 20-30 years before Titanic came out. Same with refrigeration.

Bill Sauder

 

[John Senchak]

At 100 D.C. the generators must have produced some serious amperage for the total load that was needed. The efficiency alone on the four steam powered dynamos/engine must have been real low. I have seen real old steam powered (A.C.) dynamos with their open chassis design. You are looking at some major copper inside to generate the current needed for fluctuating loads.

I don't know if the Titanic had some type of regulating diodes to keep the one hundred volts stable as the load increased. More then likely the workers just pushed more low pressure steam in to compensate for the heat loss in the dynamos along with the increased loads. On the D.C. level it's the current output that matters over the voltage.

Each dynamos/engine produced 400 Kilowatts of power. This gives you a total of 1.6 megawatts that the dynamos/engine could produce One point six megawatts divided into 100 volts gives you 16,000 amps total output at maximum steam level.
This means each dynamos/engine could at maximum load produce 4000 amps. Not much by today's standards but the total power of the dynamos/engine could light about sixteen thousand 100 watt D.C. light bulbs.

The two auxiliary dynamos/engine produced 30 kilowatts each (60K.W. total) and produced a total of 600 amps. These where used on a separate bus-bar system that ran all the emergency lighting though out the ship. The ship had change-over switches (or breakers) that allowed the auxiliary circuit to be sent to the certain rooms or functions like the boat winches or elevators. The two auxiliary dynamos/engine had enough power to run about 600 one hundred watt light bulbs at maximum load.

 

[mike disch]

Thank you for your detailed responses, and the time you put into them. Perhaps my first question wasn't completely clear. I understand that a 1912 volt is the same as a 2003 volt; however, today in the U.S. most residential hookups are at 110V, with a few heavy duty appliances at 220V. My understanding is that 220V is standard for Europe. So my last question for the moment (not of earthshaking importance--just curious--not being an electrical engineer-although I can change a lightbulb--sometimes) is if you know when 110V/220V became standardized (vs. Titanic's 100V).

 

[mike disch]

Also, I just noticed that you refer to 100V D.C.. In layman's terms, is there any significant difference between 100V D.C. vs. 100V A.C.? Would a 60 Watt A.C. lightbulb (as in my living room. at 110V A.C.) burn equally brightly if, for some obscure reason, I was using a power source that produced 100V D.C.?
By the way, when I think of D.C. vs. A.C., I think of two things: One, the batteries in my flashlight/torch (which are either D size, C, AA or AAA, and god only knows what happened to "B" and single "A".
Two, Thomas Edison's (who everyone's heard of)dream to have millions of D.C. generating plants in every building in America, with a staff of maintenance engineers for each one, vs. N. Tesla (who hardly anybody knows about) telling him the future was A.C.. Just needed to mention it. I identify with the Teslas of the world.

 

[John Senchak]

Mike

Check out this site for a explanation on the difference between A.C. and D.C.

www.satcure-focus.com/tutor/page1.htm

Actual their is a difference between one hundred volts D.C. and one hundred volts A.C. One hundred volts D.C. is just that, one hundred volts constant. It's level is very dependant on the current load that is being put upon it.
The is why flashlights go dim after a long period. Batteries are rated on ampere hours which means they will give a certain current over a period of time, after which the voltage drops. At this voltage level , the battery changes it's internal resistance and the ampere hours decreases. Again the voltage drops due to the current demand and that increases the internal battery resistance. After a period the battery will go dead because it can't supply the constant current level for the voltage and internal battery resistance.

One hundred volts A.C. is actual 141.4 volts peak (100 times 1.414). Household A.C. at 120 volts is actual 169.68 volts peak.
(120 times 1.414). The main difference between D.C. and A.C. is that one is very dependant on current (D.C.) and the other
(A.C.) is more stable over current loads. This is because the use of A.C. transformers which can take power from one side (primary) when the demand of the other side (secondary) is increasing. You can supply a line pole transformer with fifteen thousand volts at a low current level and the secondary will output 120/240 at hundreds or thousands of amps.
It's taking a high voltage with a low current and doing the complete opposite at the secondary side. This is what makes A.C. more efficient over D.C. . Direct current is not dependant on voltage but rather on load.

 

[Cal Haines]

Mike,

Just to expand on what John said. DC, direct current, has a constant voltage which (in theory) does not change with time. AC, alternating current, is constantly changing, cycling back and forth from positive to negative voltage. The first diagram in the link that John provided shows how the voltage changes with time. Each complete excursion of the voltage from zero to the + peak value, back through zero and the - peak and back once again to zero is called a cycle. In the US, AC voltage has 60 cycles per second; in Europe they use 50 cycles per second. The reason that the US line voltage is called 120 volt, rather than referring to it's 170 volt peak value, is that the average power that will be transferred to a load, over time, is the same as that provided by a 120 volt DC source. Since the electrical power business is all about moving power around, it is much easier to think about the average or DC equivalent voltage of the AC rather than worry about the peak value.

Your 60 watt light bulb would consume the same power (60 watts) and have the same brightness on 120 volts AC as it would on 120 volts DC (you probably have 120 volt rather than 110 volt service). On 100 volts DC the bulb would be a bit dimmer and use less power (about 42 watts). Electric heaters and light bulbs don't care if you feed them AC or DC. Most motors are a different deal.

AC won out over DC because the voltage can be easily changed using transformers. High voltage is used to move power around and results in less loss due to heating of the wires. DC just can't compete when it comes to moving electrical power. It is the current in the wire that causes the loss due to resistance of the wires. When the voltage is increased, the current and thus the losses go down in direct proportion. If you live in the US, the power to your neighborhood is probably supplied at about 14,400 volts. There is a transformer near your house to drop the voltage down to 120/240 volts for your house.

Transformers work by using the changing magnetic field that appears around a current-carrying wire to induce voltage in the secondary (output) half of the transformer. By having a different numbers of turns in the coils on both halves, the output voltage can be stepped up or down at will. For example, if you want to double the output voltage, you wrap twice as many turns of wire on the secondary as you have on the primary. With DC, the voltage does not change with time and transformers do not work. Prior to solid-state devices, the best way to step up DC voltage was mechanically, with a motor-generator pair. (As was done in Titanic's Marconi system.)

Hope that helps.

Cal

 

[Erik Wood]

Good to see you back and posting Cal. Your posts are informative as always.

 

[John Senchak]

Cal

You actual did a better job explaining the difference between and AC and DC. I disagree with delta current change over time unless you have some real good regulation to provide a stable, DC source.
120 volts line current is also know as RMS (root means square) value or the average value that will do the most work over a given time ( 60 cycles per sec.)

 

[Cal Haines]

Cap'n Erik, I havn't really been gone, just lurking. Too busy to post as often as I once did...

John,
What I meant to say was that ideally the DC voltage would not change. As you point out, in the real world it does vary a bit; the goal of voltage regulation is to keep the variation as small as possible. As long as the load does not change, the output voltage of a DC generator will remain pretty steady. With as many load points as Titanic had, I suspect that the load averaged out fairly well. Maybe just after dinner you would have a lot of folks returning to their cabins and turning on the lights, increasing the load and causing the voltage to sage a bit. As I understand the setup on Olympic/Titanic, there was an engineer on the platform with the switch gear and he would monitor the voltage of the buses. As necessary, he would use a lighted sign (sort of a telegraph) to signal the "engine attendant" to raise or lower the speed of dynamos, as needed. I'm not sure why they didn't just put volt meters on the dynamo floor and have the attendants adjust speed as necessary to maintain desired voltage.

As you say, the 120 volts RMS is an "average" value, or DC equvalent voltage. It's actually the average of the absolute value of the voltage, that is, what you would get if you ignored the sign of the negative part of the cycle when averaging the voltage over time. The arithmetic average of the AC waveform is, of course, zero since it's constantly swinging from positive to negative voltage. (That's why you get a zero volts DC reading on an AC outlet.)

Cal

 

[Stephen Hinkle]

Well, I do have some history for you, on this:

One, the batteries in my flashlight/torch (which are either D size, C, AA or AAA, and god only knows what happened to "B" and single "A".

Well, the Battery history, goes back to the old days of radio, with vaccum tubes, and before there was rectifier tubes.

"A" Battery refered to the low voltage battery that powered the tube filaments. This was often a lead acid wet cell, often between 2V and 6V.

"B" Battery refered to the high voltage battery that powered the tube plates. Usually these ranged from 45 Volts to as high as 108 Volts, with 45V, 67.5V and 90V being most common. If you don't beleive me that batteries of this high of voltage exist, see www.tubesandmore.com, although they are rare these days.

"C" Batteries refered to smaller batteries used for grid bias. The current draw of these is near-zero, and are used to produce negative voltage used for the grid control of the tubes. These typically range from 4.5V to 18V.

 

[Dennis Smith]

Hi Guys,
Just wondering where the DC generators came from, because today it is impossible to generate DC without first producing AC (As it was then). Why rectify the AC, maybe they thought there was a good reason for doing so, but no-one has given me a reason why. So why was the DC ship kept going until the 1950`s. I`ve asked people who have never given a reasonable answer - can you ???

Bst Rgds

Dennis

 

[Bill Sauder]

Dennis,

100 Volts DC was selected for the Titanic because:

1) Much if not most of the Titanic's electrical draw was taken up the metallic filament incandescent lamps, which operate at peak efficiency at about 100 volts.

2) The speed control of motors requires less complicated control devices with Direct Current rather than Alternating.

3) Operation of the generating plant is easier since multiple generators supplying the ship's needs only require matching voltages. In an AC system, the voltages and the phases must match.

4) DC offered a very simple single-wire solution for delivery of the current. Like a modern car, there were no return wires on Titanic, only supply lines. The ship's metal hull acted as a return path. (Unlike modern cars, Titanic was probably positive-grounded because of electro-corrosion considerations.)

With alternating current, you'd probably be looking at a three phase system. That means you need three wires for much of the heavy-current components (motors, etc.), and each phase is going to require protection, so you've tripled out capital outlay for wiring and circuit breakers, and have very little to show for it.

Bill Sauder

 

[steven weiss]

This is my first post guyz, I'm constantly impressed with Titanic'c electrics, they were the most advanced available at the time.

In the UK at the time, as had happened in the US, AC and DC were battling each other for superiority: Most industrial consumers of power had at least DC for the many motors in use and the Titanic seemed no different: lifts, cranes, hoists etc. DC motors develop full torque at zero speed and are more suited to this work, moreover they were (at that time) the only type capable of being directly speed-controlled. I suppose it made more sense to generate DC.

Steam engine driven dynamos would have been pretty much self-regulating by then: the dynamo shaft is run at a more or less constant speed thanks to centrifugal governors (the twirling balls!) and the DC volts would have been stabilized against load fluctuation via automatic electro-magnetic exciters. Load sharing between parallel dynamos was facilitated by manual switching of individual sets of windings on each genset whilst observing the load meters, meaning that all the dynamos could have been brought on line as demand dictated without one trying unduly to drive current back into another.

The lifts in Titanic used Shunt motors which give a pretty constant speed with varying load and are indeed easily speed regulated with a field controller rheostat. The cranes and hoists used continuously rotating Series-wound motors which meant heavy loads increased the torque at the expense of speed..light loads vice-versa, start-stop being provided by a clutch-brake coupling.

Only in the last few years have I seen similar Victorian standby generators taken out of service in certain parts of the UK! Many factories here still use 100V DC for overhead cranes (now via 3-phase AC rectifiers of course!) and large machine tools, and many british olde-tyme fairgrounds still have 100VDC rides with their traditional hand-operated speed resistance regulators.
According to The Shipbuilder article, the main switchgear in the generating compartment was by Dorman-Smith. They still make Distribution Boards in the UK today and are based in Preston Lancashire. They used wire fuses of course then, no miniature circuit breakers (MCB'S). The lifts (elevators) were made by Waygoods who were eventually taken over by the Otis Elevator Company of America.

As a previous poster mentioned, as far as power delivery goes, 100V DC is the same as 100V AC, since, by 100V AC, we mean 100V AC RMS..which is defined as that AC voltage that delivers the same amount of work as the equivalent DC voltage.

The Titanic did have wired return paths, but they were bonded to the hull at various points, the hull alone was not used as this could lead to the potentially dangerous situation of voltage differences between decks, (and stray currents between for example an appliance on a lighting circuit and one on a heating circuit)and any extraneous metal conductors, electrolytic action at any imperfect or dissimilar metal bonds etc. (also ref: shipbuilder).

 

[David Bubb]

Ok, I have what may be a strange question, but here goes. When the ship was being fitted out, I have noticed a couple of photographs that appear to have steam coming out of one of the funnels indicating that there is at least some activity in the boiler room. My question is this, how was the interior of the ship illuminated before she was actually "up and running". How did the crews in the boiler rooms initially find their way there to
stoke the coal in the boilers, to create the steam necessary to generate electricity and run the ship?
I'm no electrician, so anybody who replies, please keep it simple. I have scoured by copy of TITANIC The Ship Magnificent, but have not come across that information. Thanks in advance for any reply!