CastroPussSorry, but it is still not clear how locomotive AC dynamic braking process works, particularly with respect to the alternator, dynamic braking resistors, inverters, and DC Link capacitor. Only two aspects are (partially) clear at this time - 1) In order for the AC traction motors to generate power in dynamic braking mode, some 'excitation' power has to be applied to the traction motors stators. This excitation power either originates from the alternator, and/or from the DC Link capacitor. 2) Braking power generated by the traction motors is dissipated in the dynamic braking resistors. Again, more questions. 1) What supplies excitation power to the traction motors during dynamic braking? Is it from the alternator? Or is it from the DC Link capacitor? Or is it some combination of both the alternator and the DC Link capacitor? If a combination, how does that work? 2) As excitation power is, presumably, still being sent to the traction motors at the same time, how does the generated power from the traction motors while in dynamic braking mode get back to the dynamic braking resistors? The excitation power going to the traction motors would surely conflict with the generated power somewhere (the inverters?) before the generated power could reach the dynamic braking resistors? And wouldn't the generated power tend to charge the DC Link capacitors also? The status (either on, or off, or what?) of the alternator, dynamic braking resistors, DC Link capacitors, and inverters during (different phases of the) dynamic braking process would be helpful.
The easiest way of thinking about this is that the stator windings make a rotating magnetic field, driven by the invertor. If this field rotates faster than the rotor it will magnetically try to speed it up, taking power from the inverter, if the field rotates slower it tries to slow the rotor down, this generates power that feeds back in to the invertor. Unless it can feed that back to the supply (i.e. electric loco) the d.c. bus voltage rises, the resistors are switched in to dump that excess energy to keep the voltage under control. If the field is cut off the motor will just coast, with no electrical breaking.
There is another way to brake an a.c. motor that is to put d.c. into the windings this can cause a heavy braking action and prolonged use will overheat the motor. It is often used to stop machinery quickly in an emergency.
Of course the motor without load will not go faster than the speed of rotation of the field. And the speed of rotation of the field is controlled by the frequency of the inverters. My impression is that the slant-bar version can be started from standstill, by deternmining the direction of field rotaton with a very low frequency start.
daveklepper Unsure if this is required by the slant-bar hysteristes type. I think this type is self starting, and always runs slower than the rotating field, with greater load = greater lag in speed.
Unsure if this is required by the slant-bar hysteristes type. I think this type is self starting, and always runs slower than the rotating field, with greater load = greater lag in speed.
The speed of this type of motor does not vary significantly with load within the capacity of the motor and power supply, a few RPM at most. Yes, it does turn a little slower than synchronous speed and it does fall off a few RPM from no load to full load.
When BN was testing the first AC SD60M they broke a pinion, removing the motor load. The motor continued to spin at the same RPM instead of bird nesting like a DC motor would have and they didn't even realize the pinion had failed.
Again this kind of drive has nothing to do with the drive system on a GG1 or any other electric or diesel locomotive produced prior to the early 90's.
NO!!!
All induction motors require inductive excitation (lagging VARs), supplied either from capacitors, or from the line voltage; this is true regardless of opearion as a motor or as a generartor........
from the Far East of the Sunset Route
(In the shadow of the Huey P Long bridge)
I believe their program is now on hold, waiting for others to come up with the required batteries, which does seem likely from what I read in Physics Today.
carnej1erikem GE had been working on a hybrid lcomotive back in 2008-09 when the oil prices peaked. Haven't heard much about it since then. The general operating concept is a whole lot more practical with the IGBT inverters as those inverters are happy to run off a constant potential DC bus. - Erik GE determined that Lithium Ion batteries would not hold up well in mainline freight locomotive service and instead developed a new technology molten sodium Battery. https://renewables.gepower.com/content/dam/gepower-renewables/global/en_US/documents/GEBrochureWeb.pdf They built a brand new plant in Schenectady, NY to manufacture the batteries (after obtaining loans form the US government). The plant opened in 2012 and GE initially focused on selling the batteries to Industrial and utility operators for static installations (solar and wind power operators in particular). This market did not meet GE's sales expectations and they scaled battery production way back: http://www.greentechmedia.com/articles/read/ge-scales-back-production-of-grid-scale-durathon-batteries From this I conclude that the GE hybrid locomotive program is at least on the back burner (over a very low flame) if it hasn't been discontinued outright..
GE had been working on a hybrid lcomotive back in 2008-09 when the oil prices peaked. Haven't heard much about it since then. The general operating concept is a whole lot more practical with the IGBT inverters as those inverters are happy to run off a constant potential DC bus.
- Erik
GE determined that Lithium Ion batteries would not hold up well in mainline freight locomotive service and instead developed a new technology molten sodium Battery.
https://renewables.gepower.com/content/dam/gepower-renewables/global/en_US/documents/GEBrochureWeb.pdf
They built a brand new plant in Schenectady, NY to manufacture the batteries (after obtaining loans form the US government). The plant opened in 2012 and GE initially focused on selling the batteries to Industrial and utility operators for static installations (solar and wind power operators in particular).
This market did not meet GE's sales expectations and they scaled battery production way back:
http://www.greentechmedia.com/articles/read/ge-scales-back-production-of-grid-scale-durathon-batteries
From this I conclude that the GE hybrid locomotive program is at least on the back burner (over a very low flame) if it hasn't been discontinued outright..
Redore Also a three phase induction motor will become a generator if externally driven. It only needs a very small starting current to start the magnetic fields in the coils. Once started, no external excitement is needed.
Also a three phase induction motor will become a generator if externally driven. It only needs a very small starting current to start the magnetic fields in the coils. Once started, no external excitement is needed.
An induction motor will, as you wrote, work as an induction generator if some source of reactive power is available, which could be the capacitance of a lightly loaded transmission line. A capacitor run single phase motor may have enough capacitance to be a self exciting induction generator.
Also a three phase induction motor will run just fine in single phase once rotation is started. It just won't start when single phased.
True, as the starting mechanism (split phase, capacitor start, etc) simply provides a rotating to get the motor turning.
The reason why a single phase induction motor produces zero torque at zero rpm in the abscense of a starting mechanism, is that the oscillating field from single phase operation can be devolved into two rotating fields rotating in opposite directions and the slip is equal for both directions. When the motor starts turning, the slip is no longer equal and the motor will get more torque from the low-slip direction than the opposing high slip direction.
daveklepper And most non-transportation uses, most industrial uses, are constant speed and constant load.
And most non-transportation uses, most industrial uses, are constant speed and constant load.
Constant speed, yes, because they are fed at 60 Hz. Some are also hooked up to inverters that vary the incoming frequency and are thus made variable speed.
They are not constant load. As load goes up and down, the amp draw of the motor goes up and down, but the speed remains relatively constant up to full load amps.
erikem GE had been working on a hybrid lcomotive back in 2008-09 when the oil prices peaked. Haven't heard much about it since then. The general operating concept is a whole lot more practical with the IGBT inverters as those inverters are happy to run off a constant potential DC bus. - Erik
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
Or it can be regenerative braking, either to storage batteries on the locomotive or feeding the catenary or third rail, if the voltaqe generated is slightly above than from the substation. And some modern substations have storage facilities, with batteries or flywheels; otherwise there must be enough load on the substation by othe trains requiring power for regenerative braking to work. Most modern electric (not diesel-electric) locomotives and electric rail cars of all types have both regenerative and dynamic braking. The resistive load is enabled when the catenary or third-rail voltage is too high for regenerative braking, indicating there is not sufficient load on the specific substation.
I also realize an efficient non-synchronous single-phase motor is possible, with the power seen in the field coils as square waves, not sinusoids. Inverters can provide such power, which is analogous to the "AC" actually seen by the armature coils of dc motors because of the action of the brushes and commutator. The single inverter would be quite complex however, and no power transformers could be used in the circuits to change voltage, because the square waveform would be corrupted. The design of the field coils and the rotating bars would be the same, but the numbers would always be even.
But this is the kind of inside-out "wheel motor" I first proposed in 1997 to convert buses to electric transmission, facilitating dual mode buses,
CastroPuss A lot of information being posted. Sorry, but it is still not clear how locomotive AC dynamic braking process works, particularly with respect to the alternator, dynamic braking resistors, inverters, and DC Link capacitor. Only two aspects are (partially) clear at this time - 1) In order for the AC traction motors to generate power in dynamic braking mode, some 'excitation' power has to be applied to the traction motors stators. This excitation power either originates from the alternator, and/or from the DC Link capacitor. 2) Braking power generated by the traction motors is dissipated in the dynamic braking resistors. Again, more questions. 1) What supplies excitation power to the traction motors during dynamic braking? Is it from the alternator? Or is it from the DC Link capacitor? Or is it some combination of both the alternator and the DC Link capacitor? If a combination, how does that work? 2) As excitation power is, presumably, still being sent to the traction motors at the same time, how does the generated power from the traction motors while in dynamic braking mode get back to the dynamic braking resistors? The excitation power going to the traction motors would surely conflict with the generated power somewhere (the inverters?) before the generated power could reach the dynamic braking resistors? And wouldn't the generated power tend to charge the DC Link capacitors also? The status (either on, or off, or what?) of the alternator, dynamic braking resistors, DC Link capacitors, and inverters during (different phases of the) dynamic braking process would be helpful.
A lot of information being posted.
Sorry, but it is still not clear how locomotive AC dynamic braking process works, particularly with respect to the alternator, dynamic braking resistors, inverters, and DC Link capacitor.
Only two aspects are (partially) clear at this time -
1) In order for the AC traction motors to generate power in dynamic braking mode, some 'excitation' power has to be applied to the traction motors stators. This excitation power either originates from the alternator, and/or from the DC Link capacitor.
2) Braking power generated by the traction motors is dissipated in the dynamic braking resistors.
Again, more questions.
1) What supplies excitation power to the traction motors during dynamic braking? Is it from the alternator? Or is it from the DC Link capacitor? Or is it some combination of both the alternator and the DC Link capacitor? If a combination, how does that work?
2) As excitation power is, presumably, still being sent to the traction motors at the same time, how does the generated power from the traction motors while in dynamic braking mode get back to the dynamic braking resistors? The excitation power going to the traction motors would surely conflict with the generated power somewhere (the inverters?) before the generated power could reach the dynamic braking resistors? And wouldn't the generated power tend to charge the DC Link capacitors also?
The status (either on, or off, or what?) of the alternator, dynamic braking resistors, DC Link capacitors, and inverters during (different phases of the) dynamic braking process would be helpful.
Since the motors are really 3 phase AC induction motors, and since the combination of the inverter, DC bus & link capacitors, and rectification front end together act as a variable speed AC generator, the energy exchange falls in only two of the four complex power quadrants: excitation power (lagging VARS) into the motor with (one quadrant) active power (real power, Watts) either into the motor for acceleration, or (an adjacent quadrant) active power out from the motor for regenerative braking.
Since AC circuits have currents for Real power operating at 90 degrees from excitation power (VARS), there is no conflict on the power exchanges)
Computer problem solved. Siemans and othe alternators connected directly to the diesel do not, of course, have commutators, but they do have slip rings, three being the minimum nummber. Rotating bars, as in induction motors, do not, of course, need slip rings. Alternators as generators built on the induction motor principle are possible, but are less efficient than armature and slip-ring alternators.
There are motors with one less bar than the number of field coils, and the bars are parallel to the shaft. There are motors with the same number of bars as field coils and the bars are slanted. The first type is more efficient but less tolerant of overload. If overloaded it will stall quickly if it cannot keep up very close to programmed speed. The second type always runs slightly under the speed of the signal rotating around the field coils and simply looses more and more speed, running slower and slower, until it stalls. I believe it is this second type in use in most modern locomotives. In either case, stalling does NOT mean exstreme heat and a flashover, as it usually would with a dc motor. Of course in real locomotives, a cicuit breaker woulod open and interrupt the current before flashover, most of the time.
YOU ARE CORRECT, AND ALL INDUJSTRIAL AND RAILROAD INDUCTION MOTORS ARE ESSENTIALLY THREE PHASE. IF THEY HAD AN EVEN NUMBER OF FIELD COILS AND ROTATING BARS, SAY SIX, OR TWELVE, OR EIGHTEEN, THEY COULD ALSO BE OPERATED IN SINGLE PHASE WAY, LIKE YOUR TYPICAL FAN MOTOR, BUT THIS WOULD BE AN INEFFICIENT USE OF THE WEIGHT AND SIZE OF THE MOTOR. FO RTHREE PHASE OPERATION, THE NUMBER MUST BE A MULTIPLE OF THREE, FOR SINGLE PHASE A MULTIPLE OF TWO.
ALSTOM HAS AN INSIDE OUT MOTOR, WHERE THE ROTATING BARS ARE OUTSIDE, AND THE FIELD COILS INSIDE, AN AC WHEEL MOTOR, THAT CAN BE THE HUB OF THE WHEEL, WITH THE FIELD COILS ON A RIGID AXLE AND THE ROTATING BARS ON THE INSIDE OF THE WHEEL RIM. MAGNET MOTOR AND STORED ENERGY SYSTEMS HAVE ROTATING PERMANENT MAGNETS, A SORT OF INSIDE-OUT DC MOTOR IN PRINCIPLE, BUT AGAIN THREE PHASE EXCITATION OF THE INSIDE FIELD COILS, MULTIPLES OF THE THREE IN NUMBER. THESE MOTORS ARE WIDELY USED IN EUROPE ON LOW FLOOR BUSES, ESPECIALLY THOSE IN USE IN AIRPORTS FOR TERMINAL TO PLANE TRANSPORTATION
SORRY ABOUT A COMPUTER ISSUE FORCING USE OF CAPS
You people are making this way too complicated. Most three phase motors used in industry, and as traction motors in locomotives and mining trucks, are simple induction motors. Their rotating speed is proportional to the incoming frequency. Three phase is used because it is easy to reverse direction by either reversing the phase sequence or simply switching two of the leads around.
This type of motor has no commutator, slip rings, or anything like that.
There are no electrical connections to the rotor, only static coils in the stator. The rotating magnetic field in the stator coils drags the rotor around making the motor turn. I don't know about locomotives, but most of these rotors are just laminated "star" shaped steel sheets attached to the motor shaft. There is usually one fewer star point than field coils so that the magnetic forces are unbalanced and the motor will start.
Now for the magic. If there is an external load on the motor it will try to turn at an RPM proportional to the incoming frequency. This is why these motors will not "birds nest" or speed up uncontrollably if the load is lost. It's also why the adhesion factor is so high for these locomotives.
The higher the load, the more power it will draw until it consumes all the power available. If the motor is driven externally and tries to go faster than the incoming frequency would allow, like in dynamic braking, it will start generating power. This flows back through the inverter and is dissipated as DC in the dynamic brakes.
The motor needs to be at least "excited" to start generating. The larger the difference between the actual RPM and the excitation frequency RPM, the more power it will generate.
Forget everything you knew about AC locomotives produced before the 1990's. Inverter technology for locomotive size loads either wasn't available or was prohibitively expensive before then.
daveklepper Please describe in what way are they three phase? As far as I know they are the state-of-the art non-synchronous induction motors with slanted rotating aluminum or copper bars and a series of field coils with their appropriate magnet structure, and computer-timed rotating exitatation, with current reverswal alternating. Current in a coil has only two directions. Induced current in the rotating bars has only two directions. Back to the main argument. Possibly if specifications say "3-phase induction motor" they mean how the computer generates the impulses and the circuitry to the field coils, which could be handled in a variety of ways, some of which could be labeled three-phase. But this is outside the motor itself. What I am saying is the single-phase motor and three-phase aren't different, but are connected to the control and power circuits very differently. If I am wrong, then I am happy to learn something new.
Please describe in what way are they three phase? As far as I know they are the state-of-the art non-synchronous induction motors with slanted rotating aluminum or copper bars and a series of field coils with their appropriate magnet structure, and computer-timed rotating exitatation, with current reverswal alternating. Current in a coil has only two directions. Induced current in the rotating bars has only two directions.
Back to the main argument. Possibly if specifications say "3-phase induction motor" they mean how the computer generates the impulses and the circuitry to the field coils, which could be handled in a variety of ways, some of which could be labeled three-phase. But this is outside the motor itself. What I am saying is the single-phase motor and three-phase aren't different, but are connected to the control and power circuits very differently. If I am wrong, then I am happy to learn something new.
This text is from a Siemens brochure describing the AR15 locomotive used in Vietnam:
The DC link is supplied with power by means of the brushless three-phase synchronous generator flanged directly to the diesel engine and a B6 rectifier bridge. Each of the 3 three-phase asynchronous motors of a bogie is fed from one of the two partial DC link circuits (which are interconnected in normal operation) by means of a pulse-width modulated inverter; these 3 motors being controlled as a group. Water-cooled IGBT-type power electronics are used. This state-of-the-art propulsion technology enables maximum utilization of tractive effort.
If the field coils, which certainly are part of the motor, are supplied with three phase power, how is this not a three phase motor. As it is an induction motor, no current is supplied to the rotor directly, only to the field coils, and if these are three phase, the motor is three phase.
Alstom built a fifteen phase induction motor for use by the Royal Navy as a direct drive motor for destroyer class ships. The fifteen phases were supposed to increase the power density.
(Edit: This was posted simultaneously with the post above...)
M636C
APOLOGIES!!! PROBABLY ALL RAIL AND TRANSIT INDUCTION BASED MOTORS ARE THREE-PHASE, ANYTHING ELSE WOULD BE WASTEFUL!
By 3-phase, the number of rotating bars and field coils, the same number, is always a multiple of three, not two. 9, 12, 15, 18, 21, 24, 27, all are practical numbers, although the even ones could be operated as single-phase motors if the controls were so programmed. At a moment when coils 2, 5, 8, 11, are at "full power" at "positive polarity", 1, 4, 7, 10, etc are at approximately one-third-power at negative polarity and heading toward full power at negative polarity, while 3, 6, 9, 23, are at one-third power at negatifve polarity heading towards zero and positive polarity.
These motors thus develop almnost constant torque, whereas a single-phase motor would peak and drop 120 times a second on a 60-cycle feed, Like your typical constant-speed fan motor.
Again, apologies.
The classic three-pharse motors had three or six slip rings feeding a rotating arrmature that had, as a minimum, three coils, instead of a minimum of two, but could have a much larger number, again multiples of three instead of multiples of two. Is this the type of motor used?
If not, how does your three-phase non-synchronous induction motor differ from a standard non-synchronous induction motor, the kind that have been standard on ac-motor diesel-electrics, electrics, mu cars, light-rail cars, rapid-transit cars for some time?
The advantages of this motor over any ac motor (or dc motor) with slip rings (or commutator) are far better tolerance of heat overload and lack of maintenance requirements for the slip rings (or commutator).
Possibly, given improved technology and new products for insulation, the old armuture three-phase motor with slip rings is making a comeback. If so, it is news to me, and I would be happy to learn about it. Theoretically, it should have a slight advantage in efficiency.
Again, I wish to remind that neither motor powered the classic single-phase 25Hz electrics like the GG1. Those were commutator motors, basically a dc motor with specific supplementary coils to counter some of the effects of the current reversal and interruption, and they do also operate fine on dx, but would just shake and not rotate, even with no load, at 50 or 60 Hz.
Back to the main argument. Possibly if specifications say "3-phase induction motor" they mean how the computer generates the impulses and the circuitry to the field coils, which could be handled in a variety of ways, some of which coujld be labeled three-phase. But this is outside the motor itself. What I am saying is the single-phase motor and three-phase aren't different, but are connected to the control and power circuits very differently. If I am wrong, then I am happy to learn something new.
JC
Your last sentence-exactly what occurs on the EMD DE/DM passenger locos, with the other load(s) being HEP.
CPM500
CP,
The crux of the matter is how the inverters provide reactive power to the induction motors when in dynamic braking mode.
First point, the inverters can also act as rectifiers (i.e. power flows from AC (motor) side to DC side). The inverters on GE locomotives act like voltage sources, so the switching between inverter and rectifier happens automatically if for no other reason to handle the second point below.
Second point, due to the induction motor being a reactive load, the power on each phase feeding the motor will alternate direction of flow twice for each cycle of the output waveform. On a single phase inverter, this power reversal will be handled by the de-coupling capacitors in the inverter. On a three phase inverter, the net reactive power flow is zero across all three phases - i.e. the reactive power flowing out on one phase will be equal to the power flowing in on the other two phases.
When the power generated by dynamic braking is greater than the losses in the motor and inverter, the inverter will happily run off the power generated by the motors, with the resistors sinking the current needed to keep the DC voltage under control. At very low speeds, the isn't enough power generated to keep the inverter running, so the main traction alternator will then supply the power. In this case, the dymanic braking power is being dissipated in the motor.
daveklepper What gave you the impression that the traction motors are three-phase? They could be called infinite-phase, because of the varying frequency and the multiplicitiy of armature coils, but they are definitely not three-phase motors in the classic sense of what a three-phase motor might be. That does not prevent them from acting as generators under the conditions specified in a previous pose on this thread. Note also, that on electrified lines, mus and electric locos can feed the catenary, with the power from the dc buss converted to ac at exactly the right frequency, voltage, and phase by computer-controlled choppers with smoothing reactors. If there are any three-phase induction or hysterises non-synchronous motors, I'd like to know who builds them and where they are used. Their use would certainly complicate the computer control even further for varying speed operation.
What gave you the impression that the traction motors are three-phase? They could be called infinite-phase, because of the varying frequency and the multiplicitiy of armature coils, but they are definitely not three-phase motors in the classic sense of what a three-phase motor might be.
That does not prevent them from acting as generators under the conditions specified in a previous pose on this thread. Note also, that on electrified lines, mus and electric locos can feed the catenary, with the power from the dc buss converted to ac at exactly the right frequency, voltage, and phase by computer-controlled choppers with smoothing reactors.
If there are any three-phase induction or hysterises non-synchronous motors, I'd like to know who builds them and where they are used. Their use would certainly complicate the computer control even further for varying speed operation.
The traction motors on the new ACS-64s ARE 3 phase AC induction motors!
NO!!
The Power allways flows into the motor when operating as a motor and out from the motor when operating as an induction generator (as in dynamic breaking).
When operating as a motor, the inverter is supplies both motive power and excitation (reactive) current as well as reference frequency, with the mechanical speed a little slower than the "electrical" speed.
When operating as in the dynamic breaking mote the motor becomes an induction generator, the inverter is supplies excitation (reactive) current as well as reference frequency, with the mechanical speed a little faster than the "electrical" speed, and absorbs motive power. This energy is either dissipated in the DC dynamic breaking resistors, or could be "fed back" through an active fornt end, if equipped, to other AC loads.
As an aside, the TA doesn't supply tm excitation during braking except during changeover and low levels of braking.
The crux of the matter is as follows:
The power that flows into the AC motors is in alternating directions at all times. In power mode, power flows into the motor most of the time, but out of the motor some of the time. In braking mode, power flows out of the motor most of the time and into the motor for very brief intervals.
Power is defined by voltage and current, which can be shown as sine waves on a common axis. The direction of power flow depends on the relationship between voltage and current with respect to time, otherwise known as 'phase relationship.' The 'phase relationship' depends on the speed of the rotating field with to the rotating speed of the rotor. If rotor speed lags field speed, voltage and current are nearly in phase and current flows into the motor most of the time. If rotor speed exceeds field speed, voltage and current are out of phase by nearly 180 degrees,power flows out of the motor most of the time, as in dynamic braking.
I note that that the DC Link caps. excite dynamic braking except as described in the first sentence.
Yes, it is understood that the dynamic braking resistors are connected across the DC part of circuit ONLY when in dynamic braking mode. This wasn't made clear in my earlier posts.
While in dynamic braking mode, power still has to come from the alternator to provide the electromagnetic fields to the AC traction motors as part of the braking process. I don't think there is another source of power going to the traction motors(?)
As the dynamic braking resistors are now connected to the DC bus while in dynamic braking mode, surely, much (most?) of the power from the alternator would be dissipated in the dynamic braking resistors instead of going to the AC traction motors? This doesn't seem logical, as the traction motors need as much power as possible to provide braking.
Presumably, the AC traction motors while in dynamic braking mode, resist the braking effort by producing a back emf? This back emf, presumably, tends to generate a reverse current which goes back into the DC bus? But how can it do that when power from the alternator is still being provided to the traction motors? There, surely, there would be a conflict of current flow (power from alternator to tarction motors versus the current due to back emf)? And how would the back emf current reach the dynamic braking resistors for dissipation?
Again, if someone would explain the mechanics of how the dynamic braking system actually works in detail would be appreciated.
The dynamic braking resistor(s) is(are) not directly connected across the DC bus, but connected only when needed for braking. On a passenger locomotive using an inverter for HEP, some of the dynamic braking power can be used for HEP during braking.
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