Bob (Iwire);
Let me see if I can add some confusion - err, insight, to your query.
When I see the diesel electric commuter trains coming into the station, they sound like the diesel is idling. When they leave they sound like they rev up.
They would normally approach with the Prime Mover in "Near Idle" position, with the Dynamic Brakes whining and the Air Brakes applied.
At departure, the Prime Mover (Main Diesel Engine) would be taken "Off Idle", as the "Power Throttle" will be placed in "Position 1" then increase towards 'position 8" in increments - which results in an increase of Prime Mover Speed (RPMs)
Depending on the type of Locomotive, the Prime Mover may be as "Small" as an 8 cylinder "645 E-3" (645 Cubic Inches per cylinder), or as "Large" as a 16V 645 E-3 (16 cylinder 45° "VEE" Block - 645 Cu. In. per Cyliner), and may be an "Old School" 2 Stroker, or a "Newbee" 4 Stroker.
Nevertheless, the Idle RPMs would top out around 200 RPMs, and the highest RPMs (at Throttle Position 8) would be 900 RPMs.
2 Strokers sound like they are really spinning fast because they fire each time the Piston comes up - as opposed to 4 Strokers, which fire every other time the Piston comes up.
When I think of a generator I imagine a constant speed to maintain a voltage.
The "Main Generator" - actually a Multipole 3Ø Alternator, is what gets "Coupled" between the Prime Mover and the Traction Motors on the drive Axles.
D.C. Traction Motors are preferred on High Speed Commuter Trains, due to their ability to get up and running fast, limited grade operations, and relatively short term operation.
Well, let me tell you, there's a lot of stuff going on - and things have really changed since I first began studying these interesting Animals!
I'll elaborate some stuff below.
If the generator is ramped up and down how is the voltage maintained for the aux systems like electronics, lighting, HVAC etc.
Very good question! It goes in hand with the next question (with an exception regarding separate units and the way the old F40PH Locomotive was designed)
Do they have more than one source of power?
Ok, I'll cover the subject with useful details now!
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To begin with, let me cover some "Basic Diesel-Electric Locomotive Information":
The Diesel-Electric Locomotive uses an onboard Internal Combustion Engine (Diesel Fueled), as the "Prime Mover", which is directly connected to a Multipolar Polyphase Alternator - known as the "Main Generator", in order to develope the Electrical Energy that is delivered to Electric Motors, permanently attached to the Axles of the Locomotive.
These Motors are known as the "Traction Motors" - and come in both DC and AC flavors.
The Traction Motors' Armatures (or Rotors), are in reality, connected to the Drive Axle via a set of gears - in order to achieve a gear reduction for torque purposes.
The typical Gear Ratios are:
- For "High Speed Service": 59:18;
- For "Low Speed" or "Grade Service": 62:15;
- For "Best Of Both Types Service": 60:17.
The Main Generator's output is rectified by a series of Diode Assemblies.
If Traction Motors are DC, the Rectifier output feeds the Motors through the "Speed Shunting Interlock System" - which places the Traction Motors in Series for Low Speeds, Series-Parallel for speeds between 20 and 35 MPH, and Parallel for high speeds.
If the Traction Motors are AC, the Rectifier output feeds into the primary VFD control system, then to the Traction Motors
(these control systems are really involved and interesting, but to keep this message relatively simple, I will not cover them. Feel free to ask for an additional post regarding the AC control systems available).
Speed of the Prime Mover is controlled in the Cab, via the "Power Throttle" located on the Control Console (on the Right-Hand side of the Locomotive - if viewed from the rear, or "Long Hood" end of the unit).
The Power Throttle has 9 "Positions:
"Idle" - which leaves the Prime Mover at idle speed;
"Position 1": which does not really increase Prime Mover speed, but does connect the Traction Motors to the Rectifier Output;
"Position 2": which increases the Prime Mover's RPMs by 10-15%,
"Position 3" is an additional increase;
"Position 4, 5, 6 and 7": increasing Prime Mover Speed;
"Position 8": Maximum Prime Mover RPMs.
The speed of the Prime Mover is "User Selectable" per the conditions required.
As the RPMs increase, so does the output power of the Main Generator.
Attention to low speed peak amperage must be done when dragging loads up extended grades, otherwise the unit will trip into emergency from extended overload.
Typical ratings would be like 900 amps for no more than 15 minutes on grades, etc.
This is carried over to other units in a Multi Unit lashup (when 2 or more Locomotives are used on a single Train).
RCE "Distributed Power" is now pretty much controlled by the lead unit, but back in the "old days" (1970's and 1980's), the way Engineers in "Helpers" would run them was to watch the Ammeter's needle.
If the load amperes was low - or dropping off without any change in grade or speed, then the Helpers were not doing any work ,and were being pulled by the Point Units - much like the rest of the Train is being pulled.
If the load amperes was high, then the Helpers were pushing way too much - and may result in a derailment or draft gear damage.
Direction is achieved at start via the "Reverser Key Handle" - this is the removable item on the control console, which if not in place, the direction of Forward or Reverse may not be achieved (only needed in the lead unit, of multiunit lashups - all other trailing units - except "Manned Helpers" have the Reverser Handle removed, and the selector is in the middle position).
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That's how to get a Train started (moving).
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Once the Train is started and going at desired Speed (per Timetable and District), the Power Throttle may be set back to Positions 2 or 3, and at times, Position 1 will work.
The stopping of the Train is acheived mostly by use of two sets of Air Brakes - The "Trainline" Brakes (controlls all trailing cars + locomotive) - AKA "Automatic Brakes" when the Locomotive's Brakes are set to be included; and the "Independent Brake" - which Air Brakes the Locomotives only.
There is a third Braking technique - known as "Dynamic Brakes", which is only effective at low speeds (no higher than 35 MPH, no lower than 10 MPH - with several exceptions and types).
For DC Traction Motors, Dynamic Braking is mostly Regenerative; using the Traction Motors as Generators and running the Generated DC Power from them into externally mounted Resistor Banks.
The sound of DC Dynamic Braking is very noticable - you will hear a strange "Howling-Whine" emmited from the Locomotive during Dynamic Brake operation.
Also, the Prime Mover will be set apx. +5 - 10% above idle speed, in order to energize the Pole Shoes / Field Windings on the Traction Motors.
Dynamic Braking for AC Traction Motors is achieved by injecting various levels of DC into the Traction Motor - much like the operation used on typical AC Induction Motors.
--- end of Basic Operation-------
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On Passenger Trains (more specific, modern Passenger Service - between late 1970's and today), the cars receive power from some type of "HEP Package" ("Head End Power").
One method was to use a "Certain Car / Cabless Unit" which contained a 300 to 500 H.P. Prime Mover (Diesel Fueled Internal Combustion Motor), coupled to an 8 Pole, 480Y/277V 3Ø 4 Wire - 20KW to 50KW Generator.
This "Stand-Alone" HEP Package has a Governer Controlled Speed of 900 RPMs, and is directly coupled to the "Aux. Generator"
Power is distributed to the trailing cars via "MU" cables.
Most "Modern" Locomotives use a variation of this technique.
The HEP Package is located inside the Locomotive, so the Locomotive has in fact two separate power systems:
A: The "Main Generator" assembly - for Tractive effort (Locomotive Power for Traction Motors and Locomotive equipment) - consisting of a very large Prime Mover and very large Alternator;
and
B: The "Auxiliary HEP System" - consisting of a smaller Prime Mover and smaller alternator.
Modern Locomotives' HEP Prime Movers usually run at 450 RPMs, and are coupled to 16 pole, 480Y/277VAC 3Ø 4 Wire alternators.
They are hard to hear over the sound of the Main Assembly's Prime Mover, along with the Air Compressor's whine, but if you go to the rear section of the Locomotive, you will be able to hear the HEP running at a steady speed.
Since these systems are independent, the Locomotive's Prime Mover will idle down at station stops, then rev up at departure.
The above information is the common design scenario, for the following Locomotives used in U.S. Passenger service - as of 1999:
- General Motors/EMD Models: F59 PH, F59 PHI;
- General Electric Models (commuter service): C40-8WM, B32-8WH, B39-8W;
- General Electric Models (Long Distance Road Service): P40-8WH, P42-8WH - AKA the "Genesis Series 1".
All these units have 4 stroke Prime Movers.
There is an exception to this design, which came from the General Motors' Electro-Motive Division ("EMD"), circa 1976 - and continued to be used upto the mid 1990's.
This is the infamous "F40PH" Passenger Service Locomotive.
Amtrak purchased close to 150 of these units, and used them exclusively for short haul high speed commuter service between 1976 and 1993.
All the Engineers loved them, but they were somewhat of a maintenance issue - especially for the "First Order" series (the first production line output from GM).
The 2nd series was much better, and the final production models were even better.
Still, the crews running Passenger Trains, preferred the F40's over the newly developed P40-8 Genesis series units from General Electric.
The F40 had great power flow, and braking abilities - whereas the G.E. units were very sluggish and non-responsive for power, and very difficult to "spot" at a certain point when the train was stopped (they would have to stop long before the "Spot", otherwise they would overshoot the "Spot").
G.E. called the prototype braking control system "Virtual Braking", whereas the Locomotive crews referred to it as "Other Than Virtual Braking".
Back to the F40PH:
What makes the F40PH different than any other Locomotive with an HEP Package, is that the HEP Alternator was connected to the Main Prime Mover - the large 16 Cylinder Diesel Motor!
The HEP Alternator - a 500 KW 480Y/277VAC 3Ø 4 Wire 8 Pole unit, was coupled to the Main Generator, and both were driven from the same 16V-645 E-3 Diesel Prime Mover.
The Prime Mover was a 2 Stroke, 16 Cylinder, 45° "VEE" Block, with 4 exhaust valves per cylinder. Air was forced into the cylinders via a Turbocharger which "Pulled Double Duty".
At low engine speeds, the Turbocharger was mechanically driven (acting more like a "Supercharger" or "Blower" at this point).
When the engine speed was high, the Turbocharger worked solely from the Exhaust gases intrduced to it (now works like a typical Turbocharger).
The Prime Mover developed 3000 (nominal) to 3200 (maximum) Horsepower - of which upto 710 H.P. would be drawn off by the Head End Power Package.
The remainder was available for Tractive Effort (Traction Motors).
These Locomotives were 4 Axle units, with DC Traction Motors - having a Gear Ratio of 59:18 for fast speeds (I rode in several F40PH's at speeds in excess of 90 MPH during normal operation).
These units had a noticably small fuel tank -which held only 1200 Gallons.
The units ordered for "Superliner" service had 800KW HEP Alternators, and 1800 Gallon fuel tanks.
These F40PH units were "Audiably Noticable" (sp??) from any other locomotive made!
Since the HEP Alternator was coupled to the one and only prime mover, the units never idled down at station stops!
A Train with upto 5 "Half Cans" (the original 85 foot "Amfleet Cars"), would - in my area, be dragged by a single F40PH.
The Prime Mover was always at top speed - this being 900 RPMs - regardless if it was climbing a 2% grade, sitting at a station, or cruising at 79 MPH.
Trains with 6 to 10 cars would be dragged by a lashup of two F40PHs.
The "Trailing Unit" was the one which the HEP was running AC Power for the Cars, and the Lead Unit's HEP was not used.
At station stops, the trailing unit's Prime Mover would remain at high speed, while the Lead unit's Prime Mover would idle down to the "around 200 RPMs speed".
Since these Units were 2 Strokers, at high speed, they sounded like the Prime Mover was just hauling butt! They sounded like they were spinning at 10,000 RPMs!
The fast sound was due to each of the 16 cylinders firing each time the piston came up.
Similar sounds of "must be spinning at 10KRPMs" were found in Freight Locomotives with the 2 stroker 16V-645 E-3 Prime Mover, and the 2 stroker 20V-645 E-3 Prime Mover, when throttle was in Positions 6 through 8.
These were the GM / EMD 4 Axle GP35, GP38, GP38-2, GP39-2, GP40, GP40X Models;
along with the 6 Axle SD40-2, SD45, SD45-2, SD40T-2, SD45T-2, F45 and FP45 Models.
OK, I need to stop! Fingeres are numb!
Hopefully this stuff will be of some insight to you, and maybe a bit of interest too!
I will add additional information later.
Scott35
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It was both interesting and insightful.
