CA1048127A - Wheel slip correction system - Google Patents
Wheel slip correction systemInfo
- Publication number
- CA1048127A CA1048127A CA239,250A CA239250A CA1048127A CA 1048127 A CA1048127 A CA 1048127A CA 239250 A CA239250 A CA 239250A CA 1048127 A CA1048127 A CA 1048127A
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- Canada
- Prior art keywords
- current
- series
- wheel slip
- auxiliary
- rectifier
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A wheel slip control system for electric traction motor drives employing series-type direct current traction motors having field and armature windings connected in series electrical circuit relationship.
The improvement comprises a current transformer having primary and secondary windings wound on a common core.
The primary winding is serially connected in the supply connec-tion between an alternating current power source and a power rectifier. The secondary rectifier is provided with its out-put connected to supply auxiliary field current to the field winding of each series-type direct current traction motor in addition to the normal direct current excitation supplied through the power rectifier. The polarity of the auxiliary field current is such that upon addition to the normal excitation direct current, the field current is maintained substantially constant or slightly less from what it had been prior to a wheel slippage condition.
A wheel slip control system for electric traction motor drives employing series-type direct current traction motors having field and armature windings connected in series electrical circuit relationship.
The improvement comprises a current transformer having primary and secondary windings wound on a common core.
The primary winding is serially connected in the supply connec-tion between an alternating current power source and a power rectifier. The secondary rectifier is provided with its out-put connected to supply auxiliary field current to the field winding of each series-type direct current traction motor in addition to the normal direct current excitation supplied through the power rectifier. The polarity of the auxiliary field current is such that upon addition to the normal excitation direct current, the field current is maintained substantially constant or slightly less from what it had been prior to a wheel slippage condition.
Description
. 20~C~368 8~
This invention relates to a new and .improved wheel . slip control for electric drive systems.
More particularly, the invent.ion relates to an im-proved wheel slip control for electric drive systems of the type employed on electric driven vehicles such as diesel-electric locomotives, and which employ an alternating ~urrent supply and series-type direct current traction motorsO The improved wheel slip control provides for the selective redu~tion in tractive ef~ort of any one of a plurality of series-type direct current traction motors to arrest whael slippage without requiring that the tractive effort of non-slipping motors be reduced, unless the connection is applied simultaneously to ;~ two or more motors, and accomplishes this in a reliable and - relatively low cost manner.
An improvsd whePl slip control system for electric locomotives and the like employing series-typ~ direct current trac ion motors~ is disclosed in U~ S. Patent ~o. 3,737,745 -issued June 5~ 1973 to Russell Mo Smith and Rene J. Chevaugeon for WHEEL SLIP CO~TROL SYSTEM, Assigned to the Genexal Electric Co. The wheel slip control system described in Patent No.
3,737,745 is intended for use primarily with traction motor drive systems having relatively stable (stiff) supply voltaga ~, sources of either direct or alternating current. Because of their nature, diasel-electric locomotives and like e~uipment : employing series~type direct currant traction motor drives, do not have available a stable supply voltage source that can be raadily used with wheel slip control systems of the type dis-closed and claimed in Patent ~o~ 3,737,745. To overcome this problem, the present invention was developed.
It is, therefore, a primary object of tha present . .
~: invention to provide a new and improved wheel slip control system ~ for controlling slippage of individual ones of a plurality of "', ~e~ ~
. ., . .
, :. .
.. . ..
series-type direct current motors comprising a traction motor drive system, without requiring that the tractive e~fort of non-slipping motors be reduced.
A further object of the invention is to provide such a wheel slip control ~ystem which is capable of use with rela-tively unstable, variable voltage power supply sources of the kind available with diesel-electric locomotives and like equip-- ment~
A ~till further feature of the invention is to provide a wheel slip control system having all of the above-set-forth characteristics and which is reliable in operation, easily - maintained and relatively inexpensive to manufacture and install.
In practicing the invention, a wheel slip control systam for electric traction motors employing series-type direct current traction motors having field and armature windings connected in series electrical circuit relationship, power rectifier means and means for supplying alternating current to-`-the power rectifier means, is provided. The series-type traction motors are connectad across the output from the powar rectifier means for ths supply of normal excitation direct current to the motors~ The improvement comprises current trans-former m~ans having primary and secondary windings wound on a common core. The primary winding is serially connected in the supply connection between the maans for suppLying alternating :
current and ths power rectifier means. Secon~ary rectifier meanq are provided having the output thereo~ (upon excitation) coupled to supply auxiliary fi~ld current to the field winding of each series-type direct current traction motor in addition to the normal direct current excitation from the power recti~ier ... ~
means~ The polarity of the auxiliary field current is such ~;- that upon addition to the normal excitation direct current, the total current flowing in the field winding is maintained .
~ -2-. ~
.' --~ 20-LC-368 48~27 .`...... at a substantially constant value or slightly less from that which had bean Elowing prior to the occurrence of a wheel slippage conditionO Means are provided which are responsive ~ to the occurrence of a wheel sli.ppage condition for effectively supplying output current from the secondary winding of the current tran-~former means to the~ sscondary rectifier means to excite the same whereby the aluxiliary field current is `:~ supplied to the series field winding o the direct current trac-. tion motor that is slipping. The current transformer means is - 10 designed such that it has a current transformation ratio : corresponding in number to the number oi~ serie~ connected direct ... curren~ traction motor excitation circuit paths connected in parallel circuit relationship across the output of the main . power rectifier means.
.: These and other objects, features and many of the -. attendant advantages of this invention will be appreciated .. more readily as the same becoi~es better underætood by reference ~` to the following detailsd description, when considered in con-:, nection with the accompanying drawings, wherein like parts in ....
~ 20 each of the several flgures are identified by the sams refer- !
ence character, and wherein:
Figure 1 is a functional block diagram of a new .~ and improved wheel slip control system constructed according to the invention;
- Figure 2 is a functional block diagram of a modified .. ~ form of the wheel slip control system shown in Figure l;
Figure 3 is a functional block diagram of still a , different form of wheel slip control system constructed .:~
~;~. according to the invention, and which requires lower cost and fewer power rated components than the embodiments of the in-~ ..,i vention shown in Figures 1 and 2; and Figure 4 is a detailed schematic circuit diagram of .,'~
.~ -3-:
;~!
~' ' ' '' , ' "
. '. ,, ' ' ; . ', , ; 20-LC-368 a preferred form of the invention which obviates the need for a separate wheel slippage detector and associated control circuitry.
Figure 1 is a functional block diagram of a wheel slip correction system constructed according to the preæent inven-tion. In this system, a conventional, large, power rated ~hree-phase alternator is shown at (11) which may be of the type gensrally found in diesel-electric locomotive and like e~uip-: ment. The alternator (11) ~upplies variable voltage, three-.-~ 10 phase altarnating current electric power across the conductor~
(12, 13,14) to a three-phase, full wave rectiier bridge ~15) comprised by the diode rectifiers (Dl-D6). The diode rectifier .~ bridge (15) is connected across a palr of direct currant power ~upply terminal~ (16,17) ~or supplying ~ull wave rectified direot current voltage to traction motors (Ml-M4).
The traction motors (Ml-~4) are of tha ~eries type wherein the armature winding indicated at (Ml, M2, etc,) are connected in series circuit electrical ralationship with the corrasponding field windings (Fl, F2, etc)~ In the traction .
drive arrangement shown in Figure 1, the seri~s traction motor ~: (M1) and its associated serieæ connacted fie~d winding (Fl) is -~ connected in series circuit relationship with the series field .~.,.
: winding (F3) and armature winding of series traction motor (M3) .: and the series circuit thus comprised, is connected across the ;~ direct curr~nt power supply terminals (16, 17). For convenience ~:
and simplicity of illustration, the usual ~peed ragulating, series-parall~l connected resistor speed controlling network, : :.
and other ~ontrol f2atureæ normally associated with traction motor drive systems hav~ not baen illustrated since they do .:
not ~omprise a part of the present invention~
The improvement made available by the present in~ention comprises a wheel slip correction system formed by a pair vf .'`~
~ 4-' .' :', :~,, . . :
IL6~4~ 7 cur~ent transformers (CTl and CT2) whose primary wi.ndings are connected in series circuit relationship in the conductors ~12, 14), respectively, betwesn alternator (11) and the diode rectifier bridge (15). Each of the current transEormers is comprised by a common core member (18A, 18B), a primary winding (19A, l9B) and a secondary winding (21A, 21B~. The primary and secondary windings of each currant transformer are wound on separate legs of their respective core members (1~3A, 18B).
In the embodiment of the invention shown in Figure 1, the core members (18A, 18B) have been illustrated as oval or square - shaped with csntral openings therein7 however, the current transformers may have any desired physical configuration and may comprise conventional, commercially available current trans--~ formers having an appropriate current transfcrmation ratio as described hereinafter~
Each of the secondary windings (21A, 21B) of current transformers (CTl, CT2) are connected across one set of dia-gonally opposite terminals of an auxiliary diode xeckifier bridge ~22 or 23), respectively. The remaining set of diagon-ally opposed terminals of the respective auxiliary rectifiar bridges (22,23) are connected across the series connected field . windings (F2, F4) of series traction motors (M2, M4) and the ; series field windings (Fl, F3) of series traction motors ' (Ml, M3), respectivaly~ Ths polarity of the connection of ths auxiliary diode rectifier bridges (22, 23) is such that when the secondary rectifier bridges conduct, they supply an auxiliary direct current which is circulated through the respective sets of field windings (F2, F4) and (Fl, F3) in an aiding direction , That is to say~ normally, the same armature and field current circulates through the respective series traction motors such as (Ml) and (Fl) and thereafter through (F3) and (M3) in series between the direct current positive p~wer supply conductor (16) , , .
3 l.~ 7 -':
and nega~ive supply conductor (17). The auxiliary current supplied rom the auxiliary rec1:.ifier ~23) augments or adds to whatever field current is flowing in the field windings (Fl, F3) under the conditions to be described hereinafter. A
similar connection is provided i-^or the auxiliary field current ~ed to the ield winding~ (F4, F2) in series fxom tha auxiliary iode rectifier bridge (2~).
. :-The secondary windings (21A, 2lB) of current trans-,: ' formers (CTl, CT2) have their outputs connected across the dia-gonally opposite terminals Qf their respective secondary rect-.. ifier bridges throu~h conductors (24, 25) and conductors (26, 27), respectively~ Each set of auxiliary supply conductors f (24, 25) and (26, 27) are short circuited by a pair of reverse polarity, parallel connected silicon control rectifiers (SCRl, SCR2) connected across the respective supply conductors.
' The short circuiting silicon control rectifiers (SCRl, SCR2) .~ for supply conductors (24, 253 have their control qates con-nected to the output of a wheel slip detector (29) for the traction motors (M2, M4), and the silicon control rectifiers `. 20 (SC~l, SCR2) connected across upply conductors (26, 27) have their control gates connectad to the output from a wheel slip detector (28) for the traction motors (Ml, M3). The wheel slip . detector~ (28, 29) may comprise any conventional means for detecting a wheel slippage condition of any one of the traction ~, .
.; motors (M1- M4). For example, th~se devices may comprise i tachometer generators, voltage measuring bridges, etc.~ of the ,- type described in greater de~ail in the above-reference U, S.
:: Patent ~o~ 3,737,745. The connection of the wheel qlip detectors : to the respective short circuiting silicon control rectifiers (SCR1, SCR23 is such that the SCRs normally are conducting in ~- ~he absence of a wheel slippage condition~ Upon the occurrence of a wheel slip condition in either of the series connected , . .
dl ~ A 1~
motors of a set, such as (M~, M3), the associated short cir-cuiting SCRs will have the gate signal removed therefrom so that they aCsume a current blocking (nonconducting) condition. That is to say, the SCRs become open circuited and any voltage appearing across the auxiliary supply terminals (26, 27) will be applied across the diagonally opposite terminals of aux-iliary rectifier (23) and will result in the supply of an auxiliary field currsnt through the series connected field windings (Fl, F3).
; 10 In operation, the wheel slip correction system shown in Figure 1 (as well as in the other figures~ attempts to keep the field current of a series typa traction motor detected to be slipping approximately constant after wheel slip occurs.
Consequently~ the motor is made to exhibit shunt motor charac-taristics resulting in reduction of the tractive effort quite rapidly as the wheel slippage causes its speed to sxceed that of the locomotive or other unit being driven by the traction motor drive system~ In the wheel slip control systems describ :~.
ed in Patent ~o~ 3,737,745, it is necessary that the supply voltage to the traction motors be maintained approximately constant~ This condition is difficult to satisfy in a diesel electric locomotive or other similar traction motor drive sys-tem so that some other method of varying field excitation to t provide a decreasing torque characteristic as wheel slip occurs, becomes necessary~ In the wheel slip correction system herein described, after wheel slip is detected, the field current . .
~ of the slipping traction motor is either increased so that the , .
torque of the motor falls off even more rapidly than that of ~- a comparable shunt motor, or as wheel slip occurs, the field current of the slipping motor is allowed to decay but at a rate which is less than that of the armature current. In other words, the auxiliary field current introduced from the auxiliary .
power supply keeps the field current well above -the armature current but still allows it to dlecrease. This results in slowly decreasing the tractive effort of the slipping motor so that it `~ i5 self-correcting without raquiring the ramo~al of large amount~ of power from the entire traction motor drive sy~tem, or from other, non-slipping traction motors.
In the arrangament sho~wn in Figur~ 1, the current transformers (CTl, CT2) sense the current being supplied to the traction motor drive system through the alternating supply conductors (12, 13, 14)~ In normal operating conditions with-out wheel slippage, it is expected that the total aurrent supplied to the traction motor drive system will split about ~` evenly between ~he two parallel circuit paths comprised by ths series connected motors (Ml, M3) and the series connected motors (M~, M2), respectively, and the current tran~formers (CTl, CT2) must be designed to accomodate currents of this magnitude.
In this arrangement, a current transformation ratio of 2-1 which pro~ides a current flowing in the secondary winding that is one half of the current flowing in the primary winding, provides auxiliary field current tha~ is more than ad~quate to meet anticipated needs.
As stated earlier, the short circuiting silicon control rectifiers (SCRl, SCR2) are normally conductin~ so as to short circuit the secondary windings of the current transformers and provide lit$1e or no loading on the overall system during nor-mal operationO Only enough voltage is developed across sacondary windings (21A, 21B~ to make up or losse~ in the ~ystem, ~owever, upon the occurrence of a slipping condition in ona o~ the motors, for example, Imotor ~1)' the armature current through the motor will decrease rapidly due to the increased back EMF ge~erated by reason of the slipping condition.
The slipping condition will be detectad instantaneously by the '`
: . . . .
''- .
wheel slip detector (28~ which thereafter turns off short circuitiny SCRl and SCR2. Just prior ~o the establishment of the above-described conditions, the normal current flowing in the primary winding (19B) of current transformer (CT2) will have astablished a magnetic flux condition in the core which will require that the secondary current then flowing in : .
secondary winding (21B) be maintained in accordance with Lenæ's Law. Consequently, with the short circuiting (SCRl, SCR2) turned off, a rather large voltage is develop~d across the ~; 10 secondary field winding (21B) which supplies current through auxiliary rectifier (23) to the series connected field windings (Fl~ F3) to maintain the current through the field windings at a substantially constant value or perhaps somewhat less than , ......
the value previously maintained under normal, non-slipping operating conditions. As a result of the supply of this aux-iliary field current in aiding relationship to the suddenly reduced, normally supplied field excitation current, the series type traction motor will be caused to exhibit shunt motor characteristics, and the tractive effort of the slipping motor :;, will be gradually reduced until the slipping condition i9 corrected~ The particular phenomenon whereby this reduction in tractive effort is achieved, is described in greater detail in the abova-referenced~Patent No. 3,737,745 and particularly .,.
with respect to Figure 3 thereof. While Figure 1 illustrates . . .
- what is essentially a single phase arrang~ment o~ the current tran former and auxiliary rectifierst a complete three-phase arrangament readily could be provided by one skilled in the art in the light of the above teachings~
The circuit shown in Figure 1 has some faults in that the short circuit silicon control rectifiers (SCRl, SCR~) must rate the full KVA of the power to be supplied to the traction ~ motor field windings ~Fl, F3), and further they must have a high .,, .j ,... .
,. .~
'~. 9_ . .
,.~..
:
, ~ . 20-Lc-36a 8~27 current and low voltage rating. The circuit shown in Figure
This invention relates to a new and .improved wheel . slip control for electric drive systems.
More particularly, the invent.ion relates to an im-proved wheel slip control for electric drive systems of the type employed on electric driven vehicles such as diesel-electric locomotives, and which employ an alternating ~urrent supply and series-type direct current traction motorsO The improved wheel slip control provides for the selective redu~tion in tractive ef~ort of any one of a plurality of series-type direct current traction motors to arrest whael slippage without requiring that the tractive effort of non-slipping motors be reduced, unless the connection is applied simultaneously to ;~ two or more motors, and accomplishes this in a reliable and - relatively low cost manner.
An improvsd whePl slip control system for electric locomotives and the like employing series-typ~ direct current trac ion motors~ is disclosed in U~ S. Patent ~o. 3,737,745 -issued June 5~ 1973 to Russell Mo Smith and Rene J. Chevaugeon for WHEEL SLIP CO~TROL SYSTEM, Assigned to the Genexal Electric Co. The wheel slip control system described in Patent No.
3,737,745 is intended for use primarily with traction motor drive systems having relatively stable (stiff) supply voltaga ~, sources of either direct or alternating current. Because of their nature, diasel-electric locomotives and like e~uipment : employing series~type direct currant traction motor drives, do not have available a stable supply voltage source that can be raadily used with wheel slip control systems of the type dis-closed and claimed in Patent ~o~ 3,737,745. To overcome this problem, the present invention was developed.
It is, therefore, a primary object of tha present . .
~: invention to provide a new and improved wheel slip control system ~ for controlling slippage of individual ones of a plurality of "', ~e~ ~
. ., . .
, :. .
.. . ..
series-type direct current motors comprising a traction motor drive system, without requiring that the tractive e~fort of non-slipping motors be reduced.
A further object of the invention is to provide such a wheel slip control ~ystem which is capable of use with rela-tively unstable, variable voltage power supply sources of the kind available with diesel-electric locomotives and like equip-- ment~
A ~till further feature of the invention is to provide a wheel slip control system having all of the above-set-forth characteristics and which is reliable in operation, easily - maintained and relatively inexpensive to manufacture and install.
In practicing the invention, a wheel slip control systam for electric traction motors employing series-type direct current traction motors having field and armature windings connected in series electrical circuit relationship, power rectifier means and means for supplying alternating current to-`-the power rectifier means, is provided. The series-type traction motors are connectad across the output from the powar rectifier means for ths supply of normal excitation direct current to the motors~ The improvement comprises current trans-former m~ans having primary and secondary windings wound on a common core. The primary winding is serially connected in the supply connection between the maans for suppLying alternating :
current and ths power rectifier means. Secon~ary rectifier meanq are provided having the output thereo~ (upon excitation) coupled to supply auxiliary fi~ld current to the field winding of each series-type direct current traction motor in addition to the normal direct current excitation from the power recti~ier ... ~
means~ The polarity of the auxiliary field current is such ~;- that upon addition to the normal excitation direct current, the total current flowing in the field winding is maintained .
~ -2-. ~
.' --~ 20-LC-368 48~27 .`...... at a substantially constant value or slightly less from that which had bean Elowing prior to the occurrence of a wheel slippage conditionO Means are provided which are responsive ~ to the occurrence of a wheel sli.ppage condition for effectively supplying output current from the secondary winding of the current tran-~former means to the~ sscondary rectifier means to excite the same whereby the aluxiliary field current is `:~ supplied to the series field winding o the direct current trac-. tion motor that is slipping. The current transformer means is - 10 designed such that it has a current transformation ratio : corresponding in number to the number oi~ serie~ connected direct ... curren~ traction motor excitation circuit paths connected in parallel circuit relationship across the output of the main . power rectifier means.
.: These and other objects, features and many of the -. attendant advantages of this invention will be appreciated .. more readily as the same becoi~es better underætood by reference ~` to the following detailsd description, when considered in con-:, nection with the accompanying drawings, wherein like parts in ....
~ 20 each of the several flgures are identified by the sams refer- !
ence character, and wherein:
Figure 1 is a functional block diagram of a new .~ and improved wheel slip control system constructed according to the invention;
- Figure 2 is a functional block diagram of a modified .. ~ form of the wheel slip control system shown in Figure l;
Figure 3 is a functional block diagram of still a , different form of wheel slip control system constructed .:~
~;~. according to the invention, and which requires lower cost and fewer power rated components than the embodiments of the in-~ ..,i vention shown in Figures 1 and 2; and Figure 4 is a detailed schematic circuit diagram of .,'~
.~ -3-:
;~!
~' ' ' '' , ' "
. '. ,, ' ' ; . ', , ; 20-LC-368 a preferred form of the invention which obviates the need for a separate wheel slippage detector and associated control circuitry.
Figure 1 is a functional block diagram of a wheel slip correction system constructed according to the preæent inven-tion. In this system, a conventional, large, power rated ~hree-phase alternator is shown at (11) which may be of the type gensrally found in diesel-electric locomotive and like e~uip-: ment. The alternator (11) ~upplies variable voltage, three-.-~ 10 phase altarnating current electric power across the conductor~
(12, 13,14) to a three-phase, full wave rectiier bridge ~15) comprised by the diode rectifiers (Dl-D6). The diode rectifier .~ bridge (15) is connected across a palr of direct currant power ~upply terminal~ (16,17) ~or supplying ~ull wave rectified direot current voltage to traction motors (Ml-M4).
The traction motors (Ml-~4) are of tha ~eries type wherein the armature winding indicated at (Ml, M2, etc,) are connected in series circuit electrical ralationship with the corrasponding field windings (Fl, F2, etc)~ In the traction .
drive arrangement shown in Figure 1, the seri~s traction motor ~: (M1) and its associated serieæ connacted fie~d winding (Fl) is -~ connected in series circuit relationship with the series field .~.,.
: winding (F3) and armature winding of series traction motor (M3) .: and the series circuit thus comprised, is connected across the ;~ direct curr~nt power supply terminals (16, 17). For convenience ~:
and simplicity of illustration, the usual ~peed ragulating, series-parall~l connected resistor speed controlling network, : :.
and other ~ontrol f2atureæ normally associated with traction motor drive systems hav~ not baen illustrated since they do .:
not ~omprise a part of the present invention~
The improvement made available by the present in~ention comprises a wheel slip correction system formed by a pair vf .'`~
~ 4-' .' :', :~,, . . :
IL6~4~ 7 cur~ent transformers (CTl and CT2) whose primary wi.ndings are connected in series circuit relationship in the conductors ~12, 14), respectively, betwesn alternator (11) and the diode rectifier bridge (15). Each of the current transEormers is comprised by a common core member (18A, 18B), a primary winding (19A, l9B) and a secondary winding (21A, 21B~. The primary and secondary windings of each currant transformer are wound on separate legs of their respective core members (1~3A, 18B).
In the embodiment of the invention shown in Figure 1, the core members (18A, 18B) have been illustrated as oval or square - shaped with csntral openings therein7 however, the current transformers may have any desired physical configuration and may comprise conventional, commercially available current trans--~ formers having an appropriate current transfcrmation ratio as described hereinafter~
Each of the secondary windings (21A, 21B) of current transformers (CTl, CT2) are connected across one set of dia-gonally opposite terminals of an auxiliary diode xeckifier bridge ~22 or 23), respectively. The remaining set of diagon-ally opposed terminals of the respective auxiliary rectifiar bridges (22,23) are connected across the series connected field . windings (F2, F4) of series traction motors (M2, M4) and the ; series field windings (Fl, F3) of series traction motors ' (Ml, M3), respectivaly~ Ths polarity of the connection of ths auxiliary diode rectifier bridges (22, 23) is such that when the secondary rectifier bridges conduct, they supply an auxiliary direct current which is circulated through the respective sets of field windings (F2, F4) and (Fl, F3) in an aiding direction , That is to say~ normally, the same armature and field current circulates through the respective series traction motors such as (Ml) and (Fl) and thereafter through (F3) and (M3) in series between the direct current positive p~wer supply conductor (16) , , .
3 l.~ 7 -':
and nega~ive supply conductor (17). The auxiliary current supplied rom the auxiliary rec1:.ifier ~23) augments or adds to whatever field current is flowing in the field windings (Fl, F3) under the conditions to be described hereinafter. A
similar connection is provided i-^or the auxiliary field current ~ed to the ield winding~ (F4, F2) in series fxom tha auxiliary iode rectifier bridge (2~).
. :-The secondary windings (21A, 2lB) of current trans-,: ' formers (CTl, CT2) have their outputs connected across the dia-gonally opposite terminals Qf their respective secondary rect-.. ifier bridges throu~h conductors (24, 25) and conductors (26, 27), respectively~ Each set of auxiliary supply conductors f (24, 25) and (26, 27) are short circuited by a pair of reverse polarity, parallel connected silicon control rectifiers (SCRl, SCR2) connected across the respective supply conductors.
' The short circuiting silicon control rectifiers (SCRl, SCR2) .~ for supply conductors (24, 253 have their control qates con-nected to the output of a wheel slip detector (29) for the traction motors (M2, M4), and the silicon control rectifiers `. 20 (SC~l, SCR2) connected across upply conductors (26, 27) have their control gates connectad to the output from a wheel slip detector (28) for the traction motors (Ml, M3). The wheel slip . detector~ (28, 29) may comprise any conventional means for detecting a wheel slippage condition of any one of the traction ~, .
.; motors (M1- M4). For example, th~se devices may comprise i tachometer generators, voltage measuring bridges, etc.~ of the ,- type described in greater de~ail in the above-reference U, S.
:: Patent ~o~ 3,737,745. The connection of the wheel qlip detectors : to the respective short circuiting silicon control rectifiers (SCR1, SCR23 is such that the SCRs normally are conducting in ~- ~he absence of a wheel slippage condition~ Upon the occurrence of a wheel slip condition in either of the series connected , . .
dl ~ A 1~
motors of a set, such as (M~, M3), the associated short cir-cuiting SCRs will have the gate signal removed therefrom so that they aCsume a current blocking (nonconducting) condition. That is to say, the SCRs become open circuited and any voltage appearing across the auxiliary supply terminals (26, 27) will be applied across the diagonally opposite terminals of aux-iliary rectifier (23) and will result in the supply of an auxiliary field currsnt through the series connected field windings (Fl, F3).
; 10 In operation, the wheel slip correction system shown in Figure 1 (as well as in the other figures~ attempts to keep the field current of a series typa traction motor detected to be slipping approximately constant after wheel slip occurs.
Consequently~ the motor is made to exhibit shunt motor charac-taristics resulting in reduction of the tractive effort quite rapidly as the wheel slippage causes its speed to sxceed that of the locomotive or other unit being driven by the traction motor drive system~ In the wheel slip control systems describ :~.
ed in Patent ~o~ 3,737,745, it is necessary that the supply voltage to the traction motors be maintained approximately constant~ This condition is difficult to satisfy in a diesel electric locomotive or other similar traction motor drive sys-tem so that some other method of varying field excitation to t provide a decreasing torque characteristic as wheel slip occurs, becomes necessary~ In the wheel slip correction system herein described, after wheel slip is detected, the field current . .
~ of the slipping traction motor is either increased so that the , .
torque of the motor falls off even more rapidly than that of ~- a comparable shunt motor, or as wheel slip occurs, the field current of the slipping motor is allowed to decay but at a rate which is less than that of the armature current. In other words, the auxiliary field current introduced from the auxiliary .
power supply keeps the field current well above -the armature current but still allows it to dlecrease. This results in slowly decreasing the tractive effort of the slipping motor so that it `~ i5 self-correcting without raquiring the ramo~al of large amount~ of power from the entire traction motor drive sy~tem, or from other, non-slipping traction motors.
In the arrangament sho~wn in Figur~ 1, the current transformers (CTl, CT2) sense the current being supplied to the traction motor drive system through the alternating supply conductors (12, 13, 14)~ In normal operating conditions with-out wheel slippage, it is expected that the total aurrent supplied to the traction motor drive system will split about ~` evenly between ~he two parallel circuit paths comprised by ths series connected motors (Ml, M3) and the series connected motors (M~, M2), respectively, and the current tran~formers (CTl, CT2) must be designed to accomodate currents of this magnitude.
In this arrangement, a current transformation ratio of 2-1 which pro~ides a current flowing in the secondary winding that is one half of the current flowing in the primary winding, provides auxiliary field current tha~ is more than ad~quate to meet anticipated needs.
As stated earlier, the short circuiting silicon control rectifiers (SCRl, SCR2) are normally conductin~ so as to short circuit the secondary windings of the current transformers and provide lit$1e or no loading on the overall system during nor-mal operationO Only enough voltage is developed across sacondary windings (21A, 21B~ to make up or losse~ in the ~ystem, ~owever, upon the occurrence of a slipping condition in ona o~ the motors, for example, Imotor ~1)' the armature current through the motor will decrease rapidly due to the increased back EMF ge~erated by reason of the slipping condition.
The slipping condition will be detectad instantaneously by the '`
: . . . .
''- .
wheel slip detector (28~ which thereafter turns off short circuitiny SCRl and SCR2. Just prior ~o the establishment of the above-described conditions, the normal current flowing in the primary winding (19B) of current transformer (CT2) will have astablished a magnetic flux condition in the core which will require that the secondary current then flowing in : .
secondary winding (21B) be maintained in accordance with Lenæ's Law. Consequently, with the short circuiting (SCRl, SCR2) turned off, a rather large voltage is develop~d across the ~; 10 secondary field winding (21B) which supplies current through auxiliary rectifier (23) to the series connected field windings (Fl~ F3) to maintain the current through the field windings at a substantially constant value or perhaps somewhat less than , ......
the value previously maintained under normal, non-slipping operating conditions. As a result of the supply of this aux-iliary field current in aiding relationship to the suddenly reduced, normally supplied field excitation current, the series type traction motor will be caused to exhibit shunt motor characteristics, and the tractive effort of the slipping motor :;, will be gradually reduced until the slipping condition i9 corrected~ The particular phenomenon whereby this reduction in tractive effort is achieved, is described in greater detail in the abova-referenced~Patent No. 3,737,745 and particularly .,.
with respect to Figure 3 thereof. While Figure 1 illustrates . . .
- what is essentially a single phase arrang~ment o~ the current tran former and auxiliary rectifierst a complete three-phase arrangament readily could be provided by one skilled in the art in the light of the above teachings~
The circuit shown in Figure 1 has some faults in that the short circuit silicon control rectifiers (SCRl, SCR~) must rate the full KVA of the power to be supplied to the traction ~ motor field windings ~Fl, F3), and further they must have a high .,, .j ,... .
,. .~
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,.~..
:
, ~ . 20-Lc-36a 8~27 current and low voltage rating. The circuit shown in Figure
2 of the drawings provides a better impedeance match for the shoxt circuiting SCRs; however, they still must rate the - full KVA o~ the power to ba supplied to the traction motor field winding The arranyement shown in Figure 2 is sub~tan-tially indentical to that of Figure 1 with the exception that two ~econdary windings t21A, 21A') and (21B, 21B'), are provid-ed for each of the current trans~ormars (CTl~ CT2). The secondary windings (21A, 21B3 are connected directly across the diagonally opposite input terminals of the auxiliary rect ifier bridges (22, 23), respeatively, without any short cir-cuiting SCR devicesO The additional secondary windings J- (21A' J 21B') are connected directly across the respe~tive sets of short circuiting silicon control rectifiexs (SCRl, SCR2) with the gates of the short circuiting SCRs being connected to the output from the wheel slip detector (29, 28), respectively~
In operation, the circuit o Figure 2 functions in the following manner. Under normal eperating conditions without wheel slippage, short circuiting silicon control rectifiers (SCRl, SCR2) are turned on and conducting. Conqequently, ; current will be allowed to flow through the secondary windings `; (21A', 21B') causing the cores to be operated in a substantially saturated condition so that essantially no power is tra~sferred through the secondary windings (21A, 21B), xespectively, to the ; field windings o~ the traction motor~ Upon the occurrence o~
a wheel slippage on any of the traction motorsO for example motor (Ml), the short circuiting silicon control rectifiers connected across the additional secondary winding (21B') will be turned off thereby open circuiting these winding~ As a conRequence, current must ~low in winding (21B) due to the action of Lenzls Law and will be coupled through the auxiliary rectifier (23) to the series field winding (F1, F3) in the manner , . ' .
,. . --10-- , -. ' ' ' . ' , , ' ' :,, , ~
`...... ;
described above with respect to Fiyure 1~ This results in the introduction of sufficient auxiliary ield current to re-duce the tractive effort of the slipping motor (~) un-~il the slippage condition is corrected and the traction motor drive system returns to a normal opercltion conditionO
In the arrangemenks shown in Figures 1 and 2, the full KVA of the auxiliary power supply to the series field i . . .
: windings of the æeries type DC traction motor~ is required in the three main components, namelyO the short circuiting silicon i~ 10 control rectifiers, the curr~nt transformer and the auxiliary :
bridges and, thus, these components must be rated to handle the power rec~ired. Providing a full three-phase system will ~` incrsase the number of individual components, but it would not c result in changing the total KVA rating of the elements. To . .
~; reduce the costs of the wheel slip correction system then, it ~i becomes necessary to reduce the K~A rating of any or all of the i~` abo~e-listed main components of the ~heel correction system~
Figure 3 of the drawings illustrates a whe~l slip control -~ system incorpo~ating many of the ~eatures of the ~ystems shown ; 20 in Figures 1 and 2, but which also allows a reduction in the KVA rating of certain of the components~
In Figure 3, it will be seen that for a single axle drive arrangement comprised of two series type DC traction motors ~onnectecl in series across the main direct current excitation supply terminals (16, 17), two curxent trans~ormers (CTl, CTl'), are provided. The setup for additional axles ~, , would be the sameî however, for convenience and simplicity o~ illustration, the arrangement for a second axle comprised by traction motors (M2, M4) is shown only in block diagram , 30 form.
In Figure 3, the current transformers (CTl~ CTl') for each given axle are idsntical in construction and rating~
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:
. ;, .
The secondary windings (21A) of both current transformers (CTl, C~ are connected so that they add in voltage9 Negl~cting for the moment the e~-fect of the additional secon-dary windings (21A') on each of the respective core members (18A, 18A'), the primary windin~s (19A, l9A') are wound in a direction such that the ~lux ~rom the secondary windings (21A) on each cora msmber opposes the flux ~rom the primary windings ~19A, l9A'), respectively~ Thucl, the ampere turns (NI) from each of the windings (21A) on the respective core members :~ 10 (18A, 18A') should be equal and opposite to the ampere turns (~I) of the respective primary windings (19A, l9A').
The two additional secondary windings (21A') on the respective cor~ members (18A, 18A') are connected in opposing relationship so that the alternating current voltage from the sum of the two windings (21A') is zero or substantially zero.
The voltage handlin~ requirem2nts ~or the control transistor (Tl) therefore is only the voltage of the battery source ~B~
The arrangement is such that the control transistor (Tl) is turned on by the wheel slip detector (28) only under 20 normal operating conditions where there is no wheel slippage, and i8 cauqed to turn off upon the occurrence o~ a wheel slip condition o either of the motors (Ml, M3). Under the normal operating conditions with no wheel slippage, direct cuxrent ~low~ in the t~o additional secondary windings, (21A') on each of the cores causing the resp~ctive core members (18A, 18Ai) to be drivsn into saturation. For this to happen, the ampere turns ~I) supplied by control transistor (Tl), battery lBl) and the windings ~21A') must be greater than the maximum ampere turns .; :
.. (~I) from the supply conductor (12) and primary windings . 30 (19A, l9A'). Upon the occurrence o a wheel slippage condition, for example ~eries type traction motor ~Ml), control transistor :. (T~ turned off by wheel slip detector (28)~ Remvval of the. :
~",'`
.
20-I,C-368 direct current flowing through the additional windings (21A') allows the core members (18A, 18A') to be driven out of satur-`~ ation by the primary windings tl9A, l9A') and to couple power through the secondary windings (21A) on each core member.
This results in the production of an auxiliary current flow that is supplied through the auxiliary rectifier (23) to the series field windings (Fl, F3) in an aicling direction to thereby correct ' the wheel slippage condition.
In the arrangement of Figure 3, only the current trans-former and auxiliary rectifier (23A) need carry the full KVA
: rating of the auxiliary current to be supplied to the field windings of the series type DC traction motorsO The control transistor (Tl), battery (Bl~ and associated windings (21A') r need to carry only adequate current to assure saturation o~ the , -core members ~(18A) during normal operating conditions of the traction motor drive system.
A preferred embodiment of the invention is shown in Figure 4 o~ the drawings wherein no wheel slip detection and control elements are required. The wheel slip correction - 20 control system shown in Figure 4 provides to the series traction motors a characteristic very close to that which would be ,' obtained by a shunt or separately excited traction motor. In Figure 4, a complete three-phase system is disclosed for ex-citing three seri2s type traction motors (~1~ M2, M3) which are connected in three separate parallel paths across the output of the main power rectifier (153 through the main direct current .~
power supply terminals (16, 17~. The series connected field windings of the respective series type DC traction motors are shown at ~Fl, F2, F3). A three-phase alternator (ll) which is driven by the prime mover such as a diesel engine of a diesel-electric locomotive, supplies three-phase, variable voltage alternating current power to the main power rectiier bank ~15) , : .
., .
20-LC~368 ~L~48~Z7 through the conductors (12, 13, 14).
Three current transformers (CTl, CT2, CT3), one for each traction motor, are provided. Each current transformer has a three-phase connection ancl, for this purpose, is provided with a three leg core member tl8A, 18B, 18C) with the respective legs of the core members having a primary winding, such ~s (19A, l9B, l9C) for core member (18A), connected in series cir-cuit relationship in the three-phase connectlon to the main power rectifier bank (15) provided by conductors (12, 13, 14).
Current transformers ~CT2, CTl) have corresponding primary . :
winding connections, with all of the primary windings (19A, l9A', ;~ l9A'') for all three core members being connected in series circuit relationship in the single phase connection comprised by conductor (12), for example. The primary windings (19B, l9B', l9B ") and the primary windings (lgC, l9C', l9C'') are similarly connected in series circu~t relationship in their respective phase supply conductors (13, 14~.
The secondary windings of the current transformers - (CTl, CT2, CT3) are wound around corresponding legs of the respective core members (18A, 18B, 18C) in tightly coupled relationship with their respective corresponding primary - windings. For example, the secondary winding (21A~ is wound on a common leg of core member (18A) with primary winding (19A), (21B) with (19B) and(~lC) with (19C), etcO Each set of secondary : ::. , .
~s l windings of a respsctive current transEormer is connected in a . , three-phase Y connection and, for this purpose, on terminal of each secondary winding on a respective core member is connected i in common with the corresponding terminal of the two remaining secondary windings on the particular core member. The remaining terminals of the secondary winding axe connected to an inter~
mediate tap point of one set of a pair of series connected diode rectifiers, such as (Dl, D4) comprising part of a three-... .
~ -14-;:: ' . .. :
i 20-LC- 368 ~L~4~ 7 phase auxiliary rectiEier bridge (31, 32, or 33) that is connected in series circuit relationship between the respec-tive series traction motors and their series connected field windings~ For example, in the series path comprised by traction motor armature ~Ml) and series field winding (Fl) the a~xiliary three-phase bridge rectifier (31) is connected in series cir-cuit relationship with it through a set of common, diagonally opposed terminals indicated at (~ and B)~ The intermediate tap points of sets of series connected diode rectifiers of bridge rectifier 131), namely, the intermediate tap points of (Dl', D4'3, (D2', D5') and (D3',D6') are connected through the conductors (34, 35, 36) to the remaining three terminals of the ~econdary windings (21C'', 21B'', 21A'') of the current transformer (CT~), respectively. While in this arrangement, these secondary windings of the current transformers are con-nected in a three-phase Y connection, a delta connection could be employed if desired. Further, it is, of course, possible to fabricate the wheel slip control system of Figure 4 in a single phase arrangement used to control slippage of a single traction . .
motor in place of the three-phase arrangement shown, should it be desired to do so.
Each current transformer ~CTl, CT2, CT3) is designed so that it provides approximately a three to one current trans-, formation ratio. That is to say, the secondary current flowing ;~ in each secondary winding i~ approximately one third of the current flowing in the primary winding. In the system of . ., Figure 4, three series type traction motors are shown connected - in three separate parallel connected paths with each parallel path taking approximately one third of the total current supplied ~":
through the main power.rectifier (15) from alternator (11)~
It will be appxeciated, therefore, that because of the three to one current transformation ratio the current capable of being , 20-LC-368 supplied from any one of the current transformers (CTl, CT2, CT3) through their respective auxiliary rectifier bridyes to the respective series connected field windings (Fl, F2, F3) will just about approximate the series field current normally flowing in the field winding. If four traction motors were used requiring four parallel, series connected paths, the current ratio required in the current transformers would be four to one, etc. In the case of the series parallel arrange-ments shown in Figures 1-3 of the drawings, the current ratio would correspond to the number of parallel paths or two in the particular instances of Figures 1-3 systems. Additionally, it should be noted that the number of current transformers required is equal to the number of parallel paths employed in the system~
In order to circulata auxiliary field current through the respective series field windings (Fl, F2, F3) from their associated auxiliary rectifier bridges (31, 32, 33), feedback diodes (D7, D8, Dg) are connected in reverse polarity, parallel circuit relationship across the series connectsd field windings and their respective auxiliary rectifier bridges in the manner shown in Figure 4. By reason of the inclusion of the feedback diodes, should the terminal (B) o~ auxiliary rectifier bridge (31), for example, being driven positive with re~pect to the terminal (A), auxiliary current will be circulated through the series connected field winding (Fl) back through the feed- -, back diode (D7) as will be described hereinafter.
In operation, the system of Figure 4 functions in the following manner. For so long as the current flowing in the armature of any given traction motor (for example, traction motor (Ml))remains constant or substantially so, then the current divides equally between the three legs of the asso-ciated auxiliary rectifier bridge (31). This ~ame situation ~ ' . .~
. ~ .
: .
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'`;`" ~ ~Lg~ lL27 will exist in the remaining two parallel paths compri~ed by the traction motors (M2, M3) ancl their associated auxiliary bridge rectifiers (32, 33) which, in the following example, will be assumed to continue to drive in a normal manner without slipping. A portion of the current flowing through .
the auxiliary rectifier bridge (31) will flow through the secondary windings (21A'', ~ls'', 21C'') of current transformer (CTl) so as to satisfy the current ratio demanded by the trans-former due to the current flowing in the respective associated : 10 primary windings. For so long as this normal drive condition ~ exists, there will be only a small voltage generated at the ..:
secondary terminals of current transformers (CTl) which is -~
equal only to supplying the losses in the system, and littla or no auxiliary current will be induced or supplied to the main `~ power circuit through auxiliary rectifier (31) and field .:..
winding (Fl~. This same condition will also pre~ail with respect to the remaining two traction motors (M2, M3) and their associated current transformers (CT2, CT3).
If it is assumed that a wheel slip occurs on the traction motor (Ml) only, then the armature current of traction motor (Ml) will drop suddenly due to the increased back EMF
generated by reason of the wheel slip. This sudden drop in the value of the armature current also tends to cause the current flowing through the auxiliary rectifier bridge (31) to drop.
The current transformer (CTl~, however, will develop whatever . . .
voltage is necessary to maintain its current ratio dependent upon of course the size of its core, number of turns in the primary and secondary windings, the current flowing under nor~
mal design operating conditions, etc. In order to maintain this current ratio, the voltage developed across the secondary . ~
-- windings of (CTl) will drive terminal (B) of auxiliary recti-.
fier bridge (31) positive with respect to terminal (A) and ':
. ~
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., .
; ~ 4 ~ 20-LC-368 .
current will circulate Erom terminal (s) through the field winding (Fl) and back through feedback diode (D7) to terminal (A) in order to complete the circuit. The circula-tion of this auxiliary feedback current through the feedback diode (D7) and through series ~ield winding (Fl) necessarily will be sufficient to satisfy the current ratio demanded by the current transformer (CTl) and results in maintaining the current flowing through field winding (Fl) at a substantially constant or only slightly lower value than that which pre~ailed prior to the onset of the slipping condition. The response is almost instantaneous, and does not require the use of a separate wheel detector and associated control system such as that employed in the previously described three embodiments of the invention. The circuit, however, still functions to causs the respective series type traction motors to exhibit shunt or separately excited DC traction motor characteristics upon occurrence of wheel slippage without the use of external control circuitry.
From the foregoing description, it will be appre-ciated that the invention provides a new and improved wheel slip correction system for controlling slippaye of individual ones of a plurality of series-type direct current traction motors comprising a traction motor drive system, without re-quiring that the tractive effort of non-slipping motors be reduced. The improved wheel slip control system is capable of use with relatively unstable, variable voltage power supply sources of the kind available with diesel-electric locomotives and like equipment. The wheel slip control system possesses all ., of the above-set forth characteristics, is reliable in opera-tion, easily maintained and relatively inexpensive to manufac-ture and install.
Having described several embodiments of a new and ; ' .
- 20-I,C-368 ~q~4~ 7 ; improved wheel slip correction syetem constructed in accor-dance with the invention, it i9 believad obvious that other modifications and variations of the invention will be suggested -to those skilled in the art in 1he li,ght of the above teachings.
It is, therefore, to be under~tood that changes may be made in ~',, the particular embodiments of the invention described which ~'-', are within the full intended scope of the invention as defined ., 1' by the appended claims.
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In operation, the circuit o Figure 2 functions in the following manner. Under normal eperating conditions without wheel slippage, short circuiting silicon control rectifiers (SCRl, SCR2) are turned on and conducting. Conqequently, ; current will be allowed to flow through the secondary windings `; (21A', 21B') causing the cores to be operated in a substantially saturated condition so that essantially no power is tra~sferred through the secondary windings (21A, 21B), xespectively, to the ; field windings o~ the traction motor~ Upon the occurrence o~
a wheel slippage on any of the traction motorsO for example motor (Ml), the short circuiting silicon control rectifiers connected across the additional secondary winding (21B') will be turned off thereby open circuiting these winding~ As a conRequence, current must ~low in winding (21B) due to the action of Lenzls Law and will be coupled through the auxiliary rectifier (23) to the series field winding (F1, F3) in the manner , . ' .
,. . --10-- , -. ' ' ' . ' , , ' ' :,, , ~
`...... ;
described above with respect to Fiyure 1~ This results in the introduction of sufficient auxiliary ield current to re-duce the tractive effort of the slipping motor (~) un-~il the slippage condition is corrected and the traction motor drive system returns to a normal opercltion conditionO
In the arrangemenks shown in Figures 1 and 2, the full KVA of the auxiliary power supply to the series field i . . .
: windings of the æeries type DC traction motor~ is required in the three main components, namelyO the short circuiting silicon i~ 10 control rectifiers, the curr~nt transformer and the auxiliary :
bridges and, thus, these components must be rated to handle the power rec~ired. Providing a full three-phase system will ~` incrsase the number of individual components, but it would not c result in changing the total KVA rating of the elements. To . .
~; reduce the costs of the wheel slip correction system then, it ~i becomes necessary to reduce the K~A rating of any or all of the i~` abo~e-listed main components of the ~heel correction system~
Figure 3 of the drawings illustrates a whe~l slip control -~ system incorpo~ating many of the ~eatures of the ~ystems shown ; 20 in Figures 1 and 2, but which also allows a reduction in the KVA rating of certain of the components~
In Figure 3, it will be seen that for a single axle drive arrangement comprised of two series type DC traction motors ~onnectecl in series across the main direct current excitation supply terminals (16, 17), two curxent trans~ormers (CTl, CTl'), are provided. The setup for additional axles ~, , would be the sameî however, for convenience and simplicity o~ illustration, the arrangement for a second axle comprised by traction motors (M2, M4) is shown only in block diagram , 30 form.
In Figure 3, the current transformers (CTl~ CTl') for each given axle are idsntical in construction and rating~
' , .,~,.
, ~ ., ,~.
:
. ;, .
The secondary windings (21A) of both current transformers (CTl, C~ are connected so that they add in voltage9 Negl~cting for the moment the e~-fect of the additional secon-dary windings (21A') on each of the respective core members (18A, 18A'), the primary windin~s (19A, l9A') are wound in a direction such that the ~lux ~rom the secondary windings (21A) on each cora msmber opposes the flux ~rom the primary windings ~19A, l9A'), respectively~ Thucl, the ampere turns (NI) from each of the windings (21A) on the respective core members :~ 10 (18A, 18A') should be equal and opposite to the ampere turns (~I) of the respective primary windings (19A, l9A').
The two additional secondary windings (21A') on the respective cor~ members (18A, 18A') are connected in opposing relationship so that the alternating current voltage from the sum of the two windings (21A') is zero or substantially zero.
The voltage handlin~ requirem2nts ~or the control transistor (Tl) therefore is only the voltage of the battery source ~B~
The arrangement is such that the control transistor (Tl) is turned on by the wheel slip detector (28) only under 20 normal operating conditions where there is no wheel slippage, and i8 cauqed to turn off upon the occurrence o~ a wheel slip condition o either of the motors (Ml, M3). Under the normal operating conditions with no wheel slippage, direct cuxrent ~low~ in the t~o additional secondary windings, (21A') on each of the cores causing the resp~ctive core members (18A, 18Ai) to be drivsn into saturation. For this to happen, the ampere turns ~I) supplied by control transistor (Tl), battery lBl) and the windings ~21A') must be greater than the maximum ampere turns .; :
.. (~I) from the supply conductor (12) and primary windings . 30 (19A, l9A'). Upon the occurrence o a wheel slippage condition, for example ~eries type traction motor ~Ml), control transistor :. (T~ turned off by wheel slip detector (28)~ Remvval of the. :
~",'`
.
20-I,C-368 direct current flowing through the additional windings (21A') allows the core members (18A, 18A') to be driven out of satur-`~ ation by the primary windings tl9A, l9A') and to couple power through the secondary windings (21A) on each core member.
This results in the production of an auxiliary current flow that is supplied through the auxiliary rectifier (23) to the series field windings (Fl, F3) in an aicling direction to thereby correct ' the wheel slippage condition.
In the arrangement of Figure 3, only the current trans-former and auxiliary rectifier (23A) need carry the full KVA
: rating of the auxiliary current to be supplied to the field windings of the series type DC traction motorsO The control transistor (Tl), battery (Bl~ and associated windings (21A') r need to carry only adequate current to assure saturation o~ the , -core members ~(18A) during normal operating conditions of the traction motor drive system.
A preferred embodiment of the invention is shown in Figure 4 o~ the drawings wherein no wheel slip detection and control elements are required. The wheel slip correction - 20 control system shown in Figure 4 provides to the series traction motors a characteristic very close to that which would be ,' obtained by a shunt or separately excited traction motor. In Figure 4, a complete three-phase system is disclosed for ex-citing three seri2s type traction motors (~1~ M2, M3) which are connected in three separate parallel paths across the output of the main power rectifier (153 through the main direct current .~
power supply terminals (16, 17~. The series connected field windings of the respective series type DC traction motors are shown at ~Fl, F2, F3). A three-phase alternator (ll) which is driven by the prime mover such as a diesel engine of a diesel-electric locomotive, supplies three-phase, variable voltage alternating current power to the main power rectiier bank ~15) , : .
., .
20-LC~368 ~L~48~Z7 through the conductors (12, 13, 14).
Three current transformers (CTl, CT2, CT3), one for each traction motor, are provided. Each current transformer has a three-phase connection ancl, for this purpose, is provided with a three leg core member tl8A, 18B, 18C) with the respective legs of the core members having a primary winding, such ~s (19A, l9B, l9C) for core member (18A), connected in series cir-cuit relationship in the three-phase connectlon to the main power rectifier bank (15) provided by conductors (12, 13, 14).
Current transformers ~CT2, CTl) have corresponding primary . :
winding connections, with all of the primary windings (19A, l9A', ;~ l9A'') for all three core members being connected in series circuit relationship in the single phase connection comprised by conductor (12), for example. The primary windings (19B, l9B', l9B ") and the primary windings (lgC, l9C', l9C'') are similarly connected in series circu~t relationship in their respective phase supply conductors (13, 14~.
The secondary windings of the current transformers - (CTl, CT2, CT3) are wound around corresponding legs of the respective core members (18A, 18B, 18C) in tightly coupled relationship with their respective corresponding primary - windings. For example, the secondary winding (21A~ is wound on a common leg of core member (18A) with primary winding (19A), (21B) with (19B) and(~lC) with (19C), etcO Each set of secondary : ::. , .
~s l windings of a respsctive current transEormer is connected in a . , three-phase Y connection and, for this purpose, on terminal of each secondary winding on a respective core member is connected i in common with the corresponding terminal of the two remaining secondary windings on the particular core member. The remaining terminals of the secondary winding axe connected to an inter~
mediate tap point of one set of a pair of series connected diode rectifiers, such as (Dl, D4) comprising part of a three-... .
~ -14-;:: ' . .. :
i 20-LC- 368 ~L~4~ 7 phase auxiliary rectiEier bridge (31, 32, or 33) that is connected in series circuit relationship between the respec-tive series traction motors and their series connected field windings~ For example, in the series path comprised by traction motor armature ~Ml) and series field winding (Fl) the a~xiliary three-phase bridge rectifier (31) is connected in series cir-cuit relationship with it through a set of common, diagonally opposed terminals indicated at (~ and B)~ The intermediate tap points of sets of series connected diode rectifiers of bridge rectifier 131), namely, the intermediate tap points of (Dl', D4'3, (D2', D5') and (D3',D6') are connected through the conductors (34, 35, 36) to the remaining three terminals of the ~econdary windings (21C'', 21B'', 21A'') of the current transformer (CT~), respectively. While in this arrangement, these secondary windings of the current transformers are con-nected in a three-phase Y connection, a delta connection could be employed if desired. Further, it is, of course, possible to fabricate the wheel slip control system of Figure 4 in a single phase arrangement used to control slippage of a single traction . .
motor in place of the three-phase arrangement shown, should it be desired to do so.
Each current transformer ~CTl, CT2, CT3) is designed so that it provides approximately a three to one current trans-, formation ratio. That is to say, the secondary current flowing ;~ in each secondary winding i~ approximately one third of the current flowing in the primary winding. In the system of . ., Figure 4, three series type traction motors are shown connected - in three separate parallel connected paths with each parallel path taking approximately one third of the total current supplied ~":
through the main power.rectifier (15) from alternator (11)~
It will be appxeciated, therefore, that because of the three to one current transformation ratio the current capable of being , 20-LC-368 supplied from any one of the current transformers (CTl, CT2, CT3) through their respective auxiliary rectifier bridyes to the respective series connected field windings (Fl, F2, F3) will just about approximate the series field current normally flowing in the field winding. If four traction motors were used requiring four parallel, series connected paths, the current ratio required in the current transformers would be four to one, etc. In the case of the series parallel arrange-ments shown in Figures 1-3 of the drawings, the current ratio would correspond to the number of parallel paths or two in the particular instances of Figures 1-3 systems. Additionally, it should be noted that the number of current transformers required is equal to the number of parallel paths employed in the system~
In order to circulata auxiliary field current through the respective series field windings (Fl, F2, F3) from their associated auxiliary rectifier bridges (31, 32, 33), feedback diodes (D7, D8, Dg) are connected in reverse polarity, parallel circuit relationship across the series connectsd field windings and their respective auxiliary rectifier bridges in the manner shown in Figure 4. By reason of the inclusion of the feedback diodes, should the terminal (B) o~ auxiliary rectifier bridge (31), for example, being driven positive with re~pect to the terminal (A), auxiliary current will be circulated through the series connected field winding (Fl) back through the feed- -, back diode (D7) as will be described hereinafter.
In operation, the system of Figure 4 functions in the following manner. For so long as the current flowing in the armature of any given traction motor (for example, traction motor (Ml))remains constant or substantially so, then the current divides equally between the three legs of the asso-ciated auxiliary rectifier bridge (31). This ~ame situation ~ ' . .~
. ~ .
: .
'','i'' . . .
'`;`" ~ ~Lg~ lL27 will exist in the remaining two parallel paths compri~ed by the traction motors (M2, M3) ancl their associated auxiliary bridge rectifiers (32, 33) which, in the following example, will be assumed to continue to drive in a normal manner without slipping. A portion of the current flowing through .
the auxiliary rectifier bridge (31) will flow through the secondary windings (21A'', ~ls'', 21C'') of current transformer (CTl) so as to satisfy the current ratio demanded by the trans-former due to the current flowing in the respective associated : 10 primary windings. For so long as this normal drive condition ~ exists, there will be only a small voltage generated at the ..:
secondary terminals of current transformers (CTl) which is -~
equal only to supplying the losses in the system, and littla or no auxiliary current will be induced or supplied to the main `~ power circuit through auxiliary rectifier (31) and field .:..
winding (Fl~. This same condition will also pre~ail with respect to the remaining two traction motors (M2, M3) and their associated current transformers (CT2, CT3).
If it is assumed that a wheel slip occurs on the traction motor (Ml) only, then the armature current of traction motor (Ml) will drop suddenly due to the increased back EMF
generated by reason of the wheel slip. This sudden drop in the value of the armature current also tends to cause the current flowing through the auxiliary rectifier bridge (31) to drop.
The current transformer (CTl~, however, will develop whatever . . .
voltage is necessary to maintain its current ratio dependent upon of course the size of its core, number of turns in the primary and secondary windings, the current flowing under nor~
mal design operating conditions, etc. In order to maintain this current ratio, the voltage developed across the secondary . ~
-- windings of (CTl) will drive terminal (B) of auxiliary recti-.
fier bridge (31) positive with respect to terminal (A) and ':
. ~
.~, ., .
., .
; ~ 4 ~ 20-LC-368 .
current will circulate Erom terminal (s) through the field winding (Fl) and back through feedback diode (D7) to terminal (A) in order to complete the circuit. The circula-tion of this auxiliary feedback current through the feedback diode (D7) and through series ~ield winding (Fl) necessarily will be sufficient to satisfy the current ratio demanded by the current transformer (CTl) and results in maintaining the current flowing through field winding (Fl) at a substantially constant or only slightly lower value than that which pre~ailed prior to the onset of the slipping condition. The response is almost instantaneous, and does not require the use of a separate wheel detector and associated control system such as that employed in the previously described three embodiments of the invention. The circuit, however, still functions to causs the respective series type traction motors to exhibit shunt or separately excited DC traction motor characteristics upon occurrence of wheel slippage without the use of external control circuitry.
From the foregoing description, it will be appre-ciated that the invention provides a new and improved wheel slip correction system for controlling slippaye of individual ones of a plurality of series-type direct current traction motors comprising a traction motor drive system, without re-quiring that the tractive effort of non-slipping motors be reduced. The improved wheel slip control system is capable of use with relatively unstable, variable voltage power supply sources of the kind available with diesel-electric locomotives and like equipment. The wheel slip control system possesses all ., of the above-set forth characteristics, is reliable in opera-tion, easily maintained and relatively inexpensive to manufac-ture and install.
Having described several embodiments of a new and ; ' .
- 20-I,C-368 ~q~4~ 7 ; improved wheel slip correction syetem constructed in accor-dance with the invention, it i9 believad obvious that other modifications and variations of the invention will be suggested -to those skilled in the art in 1he li,ght of the above teachings.
It is, therefore, to be under~tood that changes may be made in ~',, the particular embodiments of the invention described which ~'-', are within the full intended scope of the invention as defined ., 1' by the appended claims.
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Claims (11)
1. A wheel slip control system for electric trac-tion motors employing series-type direct current traction motors having field and armature windings connected in series electrical circuit relationship, power rectifier means and means for supplying alternation current to the power rectifier means, the series-type traction motors being connected across the output from the power rectifier means for the supply of normal excitation direct current thereto, the improvement com-prising current transformer means having primary and secondary windings wound on a common core, the primary winding being serially connected in the supply connection between the means for supplying alternating current and the power rectifier means, secondary rectifier means having the output thereof upon excitation coupled to supply auxiliary field current to the field winding of each series-type direct current traction motor in addition to the normal direct current excitation from the power rectifier means, the polarity of the auxiliary field current being such that upon addition to the normal excitation direct current a reduction in the tractive effort of the motor results, and means responsive to the occurrence of a slippage condition for effectively supplying output current from the secondary winding of the current transformer means to the secondary rectifier means to excite the same.
2. A wheel slip control system according to claim 1 wherein the current transformer means has a current trans-formation ratio corresponding in number to the number of series connected direct current traction motor excitation circuit paths connected in parallel circuit relationship across the output of the main power rectifier means.
3. A wheel slip control system according to claim 2 wherein the auxiliary rectifier means is connected in series circuit relationship with the field winding of a respective series-type direct current traction motor, and the system further includes feedback diode means connected across the series connected field winding and series connected auxiliary rectifier means in reverse polarity relationship with respect to the auxiliary rectifier means for circulating auxiliary field current through the series connected field winding.
4. A wheel slip control system according to claim 3 wherein the auxiliary rectifier means comprises a rectifier bridge having one set of diagonally opposed terminals connected in series circuit relationship with the series connected field winding and the remaining set of diagonally opposed terminals connected across the output from the secondary winding of the current transformer means.
5. A wheel slip control system according to claim 4 wherein the system is designed for use with a multi-phase source of alternating current, the current transformer means is a multi-phase transformer means having a number of separate core paths corresponding in number to the number of phases of the alternating current source with each core path supporting a corresponding set of primary and secondary windings, the auxiliary rectifier bridge has a number of branches correspond-ing in number to the number of phases with each branch of the auxiliary bridge being separately connected to a corresponding secondary winding of the multi-phase current transformer means whereby each phase connection to the multi-phase alternating current source excites a different set of primary and secondary windings on the current transformer means, and there are a number of series connected excitation circuit paths containing series-type direct current traction motors connected in parallel across the output from the main power rectifier with the number of parallel circuit paths corresponding in number to the current transformation ratio of the current transformer means.
6. A wheel slip control system according to claim 5 wherein each branch of each auxiliary rectifier bridge in-cludes a pair of series connected diode rectifiers with the output of each secondary winding of the multi-phase current transformer means having one terminal connected in common with a terminal of an adjacent secondary winding and the remaining terminal connected to the mid-tap point of the series connected diode rectifiers of an associated branch of the auxiliary rectifier bridge.
7. A wheel slip control system according to claim 6 wherein the multi-phase alternating current supply comprises a three-phase alternating current supply.
8. A wheel slip control system according to claim 1 wherein the secondary rectifier means comprises a secondary rectifier bridge and the output of the secondary winding is con-nected across the secondary rectifier bridge, and the system further includes short-circuiting silicon control rectifier means connected across the secondary rectifier bridge in parallel with the output from the secondary winding of the current transformer means, wheel slip detector means for sensing a wheel slip condition of the traction motor being controlled and deriving an output error control system, and means supplying the output from said wheel slip detector means to control conduction through said short-circuiting silicon control rectifier means is maintained in a conducting and short circuiting condition until the occurrence of a wheel slip condition.
9. A wheel slip control system according to claim 1 wherein the secondary rectifier means comprises a secondary rectifier bridge directly connected across the output of the secondary winding, and the system further includes auxiliary secondary winding means on each of the current transformer means, short-circuiting means connected across said auxiliary secondary winding means, and wheel slip detector means having the output thereof connected to and controlling said short-circuiting means in response to the occurrence of a wheel slippage condition.
10. A wheel slip control system according to claim 9 wherein said short-circuiting means comprises short-circuiting silicon control rectifier means connected across the auxiliary secondary winding means and responsive to the output of the wheel slip detector means such that the short-circuiting silicon control rectifier means is maintained con-ducting in the absence of a wheel slip condition and upon occurrence of wheel slippage, is turned off by the wheel slip detector means.
11. A wheel slip control system according to claim 9 wherein the short-circuiting means comprises control transistor means connected in series circuit relationship with a separate source of direct current and with the series circuit thus com-prised being connected across at least two auxiliary secondary windings of two separate current transformer means, the two auxiliary secondary windings being connected in current opposi-tion whereby the control transistor means controls only the auxiliary direct current energy source excitation of the two auxiliary secondary windings and the output of the sheel slip detector means controls operation of the control transistor means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA239,250A CA1048127A (en) | 1975-11-05 | 1975-11-05 | Wheel slip correction system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA239,250A CA1048127A (en) | 1975-11-05 | 1975-11-05 | Wheel slip correction system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048127A true CA1048127A (en) | 1979-02-06 |
Family
ID=4104470
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA239,250A Expired CA1048127A (en) | 1975-11-05 | 1975-11-05 | Wheel slip correction system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1048127A (en) |
-
1975
- 1975-11-05 CA CA239,250A patent/CA1048127A/en not_active Expired
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