OK, so on a multi-unit consist, only one Genesis unit is in HEP mode and the remaining units run up and down in RPM with throttle notch?
And the fuel penalty of running at full RPM all the time to get HEP off the prime mover is less than the cost of a separate HEP genset (as was done on the Chicago and Northwestern when HEP was introduced)?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
pajrrI don't know if a Genesis has a "No HEP" setting.
Sometimes there is a place for a quick Wikipedia reference to save typing:
All Genesis engines can provide head-end power (HEP) to the train drawn from an alternator or inverter powered by the main engine at a maximum rating of 800 kilowatts (1,100 hp), making each unit capable of providing HEP for up to 16 Superliner railcars. The P40DC and P42DC power plants can supply 60-hertz head-end power either from the HEP alternator with the engine speed-locked to 900 rpm (normal mode) or from the traction alternator with the engine speed-locked to 720 rpm (standby mode). In the latter case, traction power is unavailable. The P32AC-DM powerplant does not have to be locked at a certain rpm because it utilizes an HEP inverter, which allows the prime mover to run at 1047 rpm when providing both traction power and HEP, and to idle at 620 rpm (or notch three) while still providing HEP for lighting and air-conditioning when not providing traction power.
I have seen a table that indicates that a P42DC idles at HEP-specific 900rpm 'out of HEP mode' in both notch 3 and 4. It also, interestingly, notes higher fuel consumption when the engine is 'governed' to HEP mode at higher throttle notches, which I presume is a consequence of essential overfueling to make power at the restricted RPM.
Obviously an independent inverter providing the HEP frequency reference and phase is a better solution for operation; the point has been made that using the traction alternator for HEP is a much better solution for even medium-distance passenger trains than a separate 1800rpm genset -- the latter making best sense in commuter service where high repeated acceleration is a cardinal value, and at least in theory some of the dynamic braking power could be 'inverted' to HEP and the genset regulated accordingly with a quicker response time with better emissions than you'd get from the main engine.
I live in NJ and the EL had the GE U34CH, which was a U36C equipped with constant speed engine to provide HEP. When "idling" at a station they were running in run 8. When the throttle opened, the prime mover loaded down and made a great sounding "chug", complete with smoke and sometimes flames. They sounded great as they worked to come up to speed with the prime mover trying to work to keep at the max rpm. If you stand next to a Genesis (GE P42) as it accelerates you hear almost the same chug as the engine works to maintain max RPM. I don't know if a Genesis has a "No HEP" setting. The U34CH had a switch that when set to the freight setting the locomotive acted like a standard U series freight locomotive. It also had a "Standby" setting which provided HEP to the trainset on weekends, but the locomotive couldn't operate otherwise.
The Genesis is constant prime-mover RPM? I knew they did that on the F40PH's -- you could hear them going-a-mile-a-minute standing still.
I am surprised this is what is going on with a Genesis. I remember watching the Empire Builder pull out of the station and hearing a much slower "chug-chug-chug" as the Diesels loaded up?
Perhaps to add a needful detail to this: in addition to increasing crankshaft speed to make more power out of the engine, many of the 'cheap' HEP setups require the advanced speed to give expected AC frequency out of the alternator, as is the case with many commercial gensets. An alternator basically uses a rotating magnetic field to induce an alternating flow of electricity in surrounding 'stator' coils; the voltage of this AC is determined by the strength of 'excitation' electricity e.g. fed to what is basically wire coils in the rotating armature, but the frequency is determined by the rotational speed.
On a diesel engine, there is no 'throttle' restricting air flow; the engine speed is determined entirely by the amount of fuel injected, just as the output power is. Unfortunately, since a substantial amount of the fuel used by a compression-ignition engine is required just to rotate it (against its own compression) at a particular speed, it doesn't help fuel economy that much to reduce field when the engine is turning at what corresponds to a particular governed speed.
I had thought the Charger (and the EMD Spirit 'competition') used a HEP strategy similar to that on the ACS64, where the AC frequency is synthesized independent of electrical load under any demand conditions, using the same kind of hardware provided in the traction inverters.
Put the reverser in neutral and put the throttle in Run 8. How much power will the engine put out?
Not much--right? Nowhere near 4000 hp. Why not?
Because no excitation current to the main generator/alternator. So it takes no effort to spin it at 900 RPM-- just have to overcome the bearing friction.
In other words, the power produced by the generator/alternator at 900 RPM increases from zero with zero excitation current to 3600 hp (or whatever) with X amps excitation current. When the throttle is in Run 5 (but the diesel is still at 900 RPM) the locomotive control system arranges for something less than X amps of excitation. Then the generator is easier to spin than it was with X amps, so the governor will cut down the fuel to the diesel to maintain 900 RPM.
In principle, I suspect it's not much different than using a dimmer on a light in your home. The available power for the locomotive is constant (ie, 900 RPM) and the control circuits for the traction motors send the appropriate amount of power to the traction motors, to coincide with the throttle setting.
As Mr Upton notes, the governor will send more fuel to the prime mover if it detects a decrease in RPM, which would be signalling an increased load.
Another comparison would be a portable generator, such as you might have at home. You can generally tell when more load has been added. The genset will slow briefly until it can get back to speed, and you can often tell that it's working that much harder by listening to the exhaust.
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Electric power for "Hotel" use must be of stable frequency & voltage. For an alternator to do this, the speed must be stable (constant, with very minor variations), and the rotating field (excitation) must be regulated to maintain fairly constant voltage.
The nature of regulators is that they respond to deviations from set point to correct the deviation. A speed regulator (governer) increases fuel supply in response to falling speed (& vice versa); a voltage regulator increases exciting current in response to falling voltage.
When operating at constant frequency & voltage, Stator Current is porportional to torque. Thus any increase in power demanded of the alternator will result in an increased torque demand on the engine, resulting in a reduction in speed, and subsequently the governor increasing fuel to maintain desired speed. At the same time, the increased current demand causes the voltage to drop (Ohm'sLaw), and the voltage regulator acts to adjust the field current & return the voltage to normal.
On the other hand, if an variating source is provided, a frequency converter will be required. Modern devices that perform this function are often electronic Rectifier / Inverter combinations, and can easily correct frequency problems.
Finally, remember the power formulas:
Electrical power is Voltage times Curent;
Mechanical power is Torque times Speed
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I work on GE genesis locomotives and have often wondered how the locomotive is able to provide more horse power or tractive effort while the HEP is on, but keeping engine RPM constant? I guess I don't understand how alternators work in general. I thought the faster it turns the more electrical juice is produced like while driving a car, but the engine RPM is limited to 879+/- (900) while HEP on P42 locomotive. and 3600hp. When we knock the HEP down the engine will change RPM (not constant) with each throttle notch accordingly and max out at 1050RPM with 4250 horsepower. When under load or accelerating ( building power) you can hear the turbo winding up( whistling sound) but I again don't understand its full function.
I am sorry if this has been asked before but if anyone has information on how these parts work or how the additional power (tractive effort) is provided with out changing engine speed I would really like to know.
Thanks,
Chris
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