CA1199673A - Brushless exciter for use with a variable speed synchronous motor - Google Patents
Brushless exciter for use with a variable speed synchronous motorInfo
- Publication number
- CA1199673A CA1199673A CA000422858A CA422858A CA1199673A CA 1199673 A CA1199673 A CA 1199673A CA 000422858 A CA000422858 A CA 000422858A CA 422858 A CA422858 A CA 422858A CA 1199673 A CA1199673 A CA 1199673A
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- CA
- Canada
- Prior art keywords
- phase
- winding
- closed condition
- brushless exciter
- power
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/022—Synchronous motors
- H02P25/03—Synchronous motors with brushless excitation
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Synchronous Machinery (AREA)
Abstract
IMPROVED BRUSHLESS EXCITER
ABSTRACT OF THE DISCLOSURE
An improved brushless exciter for use with a variable speed synchronous motor which operates from a variable frequency source to run over a wide range of speeds, has a three phase brushless exciter stator winding connected wye. A first series of switches connects each phase of the stator winding to a respective phase of a fixed frequency source of AC
power. A second series of switches connects two of the phases of the stator winding in series to a source of DC power. The same stator winding is used for an AC
feed and a DC feed. A switch control switches the first and second series of switches between open and closed positions and has an interlock which permits only one series of switches to be closed at any one time.
ABSTRACT OF THE DISCLOSURE
An improved brushless exciter for use with a variable speed synchronous motor which operates from a variable frequency source to run over a wide range of speeds, has a three phase brushless exciter stator winding connected wye. A first series of switches connects each phase of the stator winding to a respective phase of a fixed frequency source of AC
power. A second series of switches connects two of the phases of the stator winding in series to a source of DC power. The same stator winding is used for an AC
feed and a DC feed. A switch control switches the first and second series of switches between open and closed positions and has an interlock which permits only one series of switches to be closed at any one time.
Description
~ 1 - Case 2847 IMPROVED BRU.':17T.l;~ S EXCITER
This invention relates to an improved brushless exciter for use with a variable speed synchronous motor drive.
With xelatively recent improvements in the 5 design of inverters and the like or providing controlled variable frequency alternating current, the use o~ variable speed synchronous motor drives has become more prevalent. For example, variable speed synchronous motor drives are uced for driving large industrial equipment where the speed must be varied over a range of operating speeds, and for dxiving grinding mills where the mill normally runs at a rated operating speed but wh0re occasionally very low speeds are required for "inching" the mill. A grincling mill is inched when it is necessary to inspect the liner~ in a mill that is not loaded, or when the mill is stopped with a load that may tend to freeze and slow operation enables the mill to be rotated until the load starts to tumble or if it does not tumble it enables the mill to ~0 be stopped before the load falls and damages the mill.
It is convenient to use a brushless exciter in a synchronous motor to avoid connection of the field winding on th~ rotor to an external direct current source. When a variable speed synchrono~s motor drive is operated at synchronous speeds in a ~ull range of Case 2847 operating speeds, for example, from standstill to a rated operating speed, the motor will require a variable level of field excitation depending on the load relationship. Because a conventional direct current (DC) fed brushless exciter does not provide the necessary output for excitation of the motor field at lower operating speeds and provides no output at zero speed, it is common practice to provide an alternating current (AC) fed brushles-~ exciter for excitation of the field winding of the synchronous motor.
An AC fed brushless exciter will provide adequate field excitation power at all operating speeds. However, the package cost of an AC fed exciter and the operating cost of an AC fed exciter are both higher than for an equivalent DC fed exciter. That is, the equipment cost of a controlled variable AC fed brushless exciter is greater than a comparable controlled DC fed exciter, and the input power factor of an AC exciter is poor compared to the near unity operating power actor of a DC fed exciter~
The present invention provides an arrangement where a stator winding of a brushless exciter is fed with AC from zero speed (i.e. from start up to a predetermined speed and then the same stator windings are fed with DC up to rated speed. It is unusual -to have a stator win~ing utilizing both AC and DC as required, however, the arrangement works well and redu~es costs with respect to a full AC excitation.
It is therefore a feature of the invention to provide an improved brushless exciter system for use with a variable speed synchronous ~notor drive.
It is another feature of ~he invention to provide a brushless exciter syste~ having selectable AC
and DC excitation available for the brushless excitsrO
~9~
Case 2847 Accordingly there is provided an improved brushless exciter arrangement for use with a three phase variable speed synchronous motor adapted to start and to operate over a range of speeds, comprising a three phase rotor winding for said brushless exciter, a three phase stator winding for said brushless e~citer, first ~witch means having an open and a closed condition, and in said closed condition adapted to connect each phas~ winding of said stator winding to a respective phase of a fixed frequency source of AC
power and in its open condition to disconnect each phase winding of said stator winding from said respective phase of said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect at least one phase winding of said stator winding to a source o~
DC power and in said open condition to disconnect said at least one phase winding of said stator windlng from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed conditions, said switch control means permitting only one of said first and second switch means to be in said closed condition at any one time.
The prior art and the invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 is a simplified schematic diagram showing a prior art arrangement of a synchronous motor with a brushless exciter fed by AC, Figure 2 is a simplified schematic diagram showing an arrangement according to one form of the invention, of a variabl~ speed synchronous motor having a br~shless exciter fed by AC or by DC, Case 2847 Figure 3 is a graph of percent rated exciter output plotted against percent speed, and useful in explaining the invention, and Figure 4 is a partial simplified schematic diagram showing another arrangement for the exciter stator windings.
Referring to Figure l, a synchronous ~otor is schematically represented at 10 having a stator winding ll and a rotor field winding 12. The stator winding 11 receives electrical power from a three phase source represented by conductors 14, 15 and 16 through switches or contactor~ 13. For the purpose of discussion of Figure l, the source conductors l4, 15 and 16 are assumed to be carrying power at a fixed frequency which is 60 Hertz in North America. The changes necessary for adapting to a variable frequency source will be discussed subsequently.
Th~ rotating portion of synchronous motor ll is indicated by line 17. The rotating portion includes field winding 12, rotating armature winding 18 for brushless exciter 20, diodes 21-26 for the converter for the exciter 20, two silicon controlled rectifiers (SCR~ 27 and 28, and a control 30. Stator winding 31 of brushless exciter 20 is connected through contactors 29 to the three phase AC souxce rep.resented hy conductors 14, 15 and 16.
As is known, during the starting of a conventional synchronous motor, large voltages can be developed initially across field winding 12. The SCRs 27 and 28 are gated on by control 30 during ~tarting to form a path across field winding 12 to prevent a build-up of high voltage. As the mo~or picks up speed, the SCRs 27 and 28 are no longer required to provide this path and control 30 operates to switch off the SCRs 27 and 28~
Case 2847 The output of -the ex~iter 20 may be considered as consisting of two components. The first component may be referred to as the electrical component and this arises as the rotating field from the stator winding links with the stationary (zero speed) rotor winding, The second component may be referred to as the mechanical component and it is the result of the movement of the rotor winding with respect to the stator winding, i.e. with respect to the rotating field from the stator winding. The mechanical component will, of course, change as the speed of rotation of the rotor changes~ It will be apparent that these two components do not appear as separate entities in practice, but they are a convenience in the description.
Thus, when an AC voltage is present on stator winding 31, and the rotor is not rotating, there will be an AC voltage on rotor winding 18 (the electrical component) which is rectified by diodes ~1-26 to provide a unidirectional current flow through field winding 12. When the rotor rotates, the mechanical component is present. This component normally increases, for any given rotation, as the speed is increased. The winding design will govern the degree in which it increases with speed. It is customary to add the mechanical component to the electxical component but, if necessary, it could be subtracted from it. Thus, the brushless exciter 20, with AC
applied to or fed to the stator winding 31, will provide an output to field winding 12 regardless of the speed~
Now, if we wish to run synchronous motor 10 as a variable speed drive motor, -the stator winding 11 would not be connected to a 60 Hertz supply~ i9e. ~
would not be connected directly to conductors 14, 15 and 16, but stator winding 11 would be connected to a v~riable frequency supply. The stator winding 31 of Case 2847 brushless exciter 20 would remain connected to conductors 14, 15 and 16, i.e., would rema~n c~nnected to the standard frequency 60 Hertz supply. Regardless of the speed at which synchronous motor 10 is operated, that is, regardless of the speed of rotation of the rotating portion 17, there will be an output fxom the exciter to supply field winding 12.
As was previously mentioned, the transfer of energy from the stator winding to the rotor winding via the rotating field is not particularly efficient. The equipment cost is high. In addition, the power factor is poor. The arrangement of Figure 2 minimizes these disadvantages.
Referring to Figure 2, similar parts to those in Figure 1 bear like designation numbers that are primed. Thus, in Figure 2 the synchronous motor 10' has a stator winding 11' and a rotor winding or field winding 12'. The exciter 20' has a rotor winding 18' and a stator winding 31' comprising wye connected phase windings 31a, 31b, and 31c. The exciter converter has diodes 21'-26' for rectifying the AC from winding 1~', and as before, control 30' gates on SCRs 27' and 28' when the in~uced field voltage is present during starting.
The stator winding 11' of synchronous motor 10' is connected to a supply 32 which has a controllable variable frequency for controlling the speed of synchronous motor 10'. The supply 32 may, for example, comprise a rectifier/inverter supplied from conductors 14', 15' and 16' and includes appropriate switching for connecting and disconnecting ~he supply.
A switch control 33 controls the operation of switches 34, 35 and 36. The switches 34, 35 and 36 connect and disconnect the three phase windings 31c, 31b and 31a respectively of stator windings 31 to respective Case 2~47 conductors lDr', 15' and 16' o:~ a standard frequency suppl~y. A rect.ifier 37 is also connected to conductors 14', 15' and 16' and has an output connected via switches 40 and 41 to phase windings 31b and 31a respectively of the wye connected stator windings 31'.
The switches 40 and 41, when closed, provide DC to windings 31b and 31al ~he switch control 33 cannot close switches 40, 41 until switches 34, 35, 36 are open, and s~annot close shlitches 34, 35, 36 until switches 40, 41 are open.
It should be noted that separate AC and DC
windings are not required for the stator windings 31 of exciter 20'. It was ound that separate windings are not necessary if the windings 31a, b and c are :L5 appropriately located according to good design practice Eor providin~ suitab:le DC energ.ization on windings 31a and 31b.
When the synchronous motor 10' is to be run at variable speeds ranging, for example, from standstill to a predetermined maximum operating speed, the variable frequency supply 32 provides power at a frequency which will give the required speed, and the switch control 33 is responsive to an input (conveniently RP~I) to change between AC and DC by operating switches 34, 35, 3G, ~n and 41 appropriately. Reference to Figure 3 will indicate one example of operation.
~eferring to Figure 3, the percent rated exciter output is plotted against percent speed. In an AC fed e~cciter the electrical component of the ou~put i8 represented by the shaded area 42 that is da:Eined by OAE~C. It is shown as providing about 50~ of rated exciter output, but this is a matter ~f dasign and it couid be more or less. The mechanical component is Case 2847 indicated by ABD. Again this is a matter o~ design.
In other words, in a conventional AC fed exciter, the exciter output for speeds from zero to 100~ would be represented by AD. Similarly, in a DC f~d exciter the exciter output would be represented by OD. It is likewise a matter of design that this is shown as linear.
~ ow, in the arrangement according to the invention, for ~peeds from zero to a percent speed represented by E, the exciter is AC fed and the exciter output is represented by line 43 between A and F~ At speed E the switch control 33 opens switches 34, 35 and 36 and closes switches 40 and 41 and the exciter is DC
fed over windings 31a and 31b. The exciter output, for speeds between E percent and 100% is represented by line 44 between G and D. It should be noted that the points of change are a matter of design and, if desired, points F and G could be made substantially the same. The points are selected to be in keeping with the description of single AC and DC fed exciters for ease of description.
Thus, if the synchronous motor 10' (Figure 2) is to be run at a percent speed less than E, then the exciter is AC fed. I it is to be run at a percent ~peed greater than E, the exciter is DC fed using the same windings.
If the synchronous motor 10' i5 to drive a grinding mill it will normally be required to run at a rated operating speed and the switches 34, 35 and 36 will remain open and switches 40 and 41 closed to provide the exciter with DC. When it is necessary to inch the ~ill, the switch control 33 will open switches 40, 41 and close switches 34, 35, 36 to provide AC feed to the exciter. The supply 32 (whic~ in this case could be a contactor arrangement operating with a DC
Case 28~7 g _ supply to provide a simulated alternating waveform of low frequency) provides the necessary low frequency power for inching.
Referring now to Figure 4, there is shown one variation in exci~er windings. This is a three phase double wye connected exciter having stator windings 45, 46, 47 and 50, 51, 52. The windings 45 and 50 are connected to conductor 14' through contactors or switches 53 and 54 respectively. The windings 46 and 51 are connected to conductor 15' through contactors or switches 55 and 56 respectively. The windings 47 and 52 are connected to conductor 16' through contactors or switches 57 and 58 respectively. Switch control 33' operates switches 53-58 to connect the stator winding~
45-47 and 50-52 to an AC source and disconnect them from the source. Switch control 33' also operates switches or contactors 60-62. When switches 60-62 are closed the DC output from rectifier 37' is connected through windings 45, 47, 52 and 50 in series. The switch control 33' can close at one time only switches 53~58 or switches 60-62 to apply either AC or DC to the exciter ~indings.
Again, only one set of stator exciter windings is used for AC or DC.
2S Various other connections and arrangements of stator windings for the exciter could be made without departing from the invention.
This invention relates to an improved brushless exciter for use with a variable speed synchronous motor drive.
With xelatively recent improvements in the 5 design of inverters and the like or providing controlled variable frequency alternating current, the use o~ variable speed synchronous motor drives has become more prevalent. For example, variable speed synchronous motor drives are uced for driving large industrial equipment where the speed must be varied over a range of operating speeds, and for dxiving grinding mills where the mill normally runs at a rated operating speed but wh0re occasionally very low speeds are required for "inching" the mill. A grincling mill is inched when it is necessary to inspect the liner~ in a mill that is not loaded, or when the mill is stopped with a load that may tend to freeze and slow operation enables the mill to be rotated until the load starts to tumble or if it does not tumble it enables the mill to ~0 be stopped before the load falls and damages the mill.
It is convenient to use a brushless exciter in a synchronous motor to avoid connection of the field winding on th~ rotor to an external direct current source. When a variable speed synchrono~s motor drive is operated at synchronous speeds in a ~ull range of Case 2847 operating speeds, for example, from standstill to a rated operating speed, the motor will require a variable level of field excitation depending on the load relationship. Because a conventional direct current (DC) fed brushless exciter does not provide the necessary output for excitation of the motor field at lower operating speeds and provides no output at zero speed, it is common practice to provide an alternating current (AC) fed brushles-~ exciter for excitation of the field winding of the synchronous motor.
An AC fed brushless exciter will provide adequate field excitation power at all operating speeds. However, the package cost of an AC fed exciter and the operating cost of an AC fed exciter are both higher than for an equivalent DC fed exciter. That is, the equipment cost of a controlled variable AC fed brushless exciter is greater than a comparable controlled DC fed exciter, and the input power factor of an AC exciter is poor compared to the near unity operating power actor of a DC fed exciter~
The present invention provides an arrangement where a stator winding of a brushless exciter is fed with AC from zero speed (i.e. from start up to a predetermined speed and then the same stator windings are fed with DC up to rated speed. It is unusual -to have a stator win~ing utilizing both AC and DC as required, however, the arrangement works well and redu~es costs with respect to a full AC excitation.
It is therefore a feature of the invention to provide an improved brushless exciter system for use with a variable speed synchronous ~notor drive.
It is another feature of ~he invention to provide a brushless exciter syste~ having selectable AC
and DC excitation available for the brushless excitsrO
~9~
Case 2847 Accordingly there is provided an improved brushless exciter arrangement for use with a three phase variable speed synchronous motor adapted to start and to operate over a range of speeds, comprising a three phase rotor winding for said brushless exciter, a three phase stator winding for said brushless e~citer, first ~witch means having an open and a closed condition, and in said closed condition adapted to connect each phas~ winding of said stator winding to a respective phase of a fixed frequency source of AC
power and in its open condition to disconnect each phase winding of said stator winding from said respective phase of said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect at least one phase winding of said stator winding to a source o~
DC power and in said open condition to disconnect said at least one phase winding of said stator windlng from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed conditions, said switch control means permitting only one of said first and second switch means to be in said closed condition at any one time.
The prior art and the invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 is a simplified schematic diagram showing a prior art arrangement of a synchronous motor with a brushless exciter fed by AC, Figure 2 is a simplified schematic diagram showing an arrangement according to one form of the invention, of a variabl~ speed synchronous motor having a br~shless exciter fed by AC or by DC, Case 2847 Figure 3 is a graph of percent rated exciter output plotted against percent speed, and useful in explaining the invention, and Figure 4 is a partial simplified schematic diagram showing another arrangement for the exciter stator windings.
Referring to Figure l, a synchronous ~otor is schematically represented at 10 having a stator winding ll and a rotor field winding 12. The stator winding 11 receives electrical power from a three phase source represented by conductors 14, 15 and 16 through switches or contactor~ 13. For the purpose of discussion of Figure l, the source conductors l4, 15 and 16 are assumed to be carrying power at a fixed frequency which is 60 Hertz in North America. The changes necessary for adapting to a variable frequency source will be discussed subsequently.
Th~ rotating portion of synchronous motor ll is indicated by line 17. The rotating portion includes field winding 12, rotating armature winding 18 for brushless exciter 20, diodes 21-26 for the converter for the exciter 20, two silicon controlled rectifiers (SCR~ 27 and 28, and a control 30. Stator winding 31 of brushless exciter 20 is connected through contactors 29 to the three phase AC souxce rep.resented hy conductors 14, 15 and 16.
As is known, during the starting of a conventional synchronous motor, large voltages can be developed initially across field winding 12. The SCRs 27 and 28 are gated on by control 30 during ~tarting to form a path across field winding 12 to prevent a build-up of high voltage. As the mo~or picks up speed, the SCRs 27 and 28 are no longer required to provide this path and control 30 operates to switch off the SCRs 27 and 28~
Case 2847 The output of -the ex~iter 20 may be considered as consisting of two components. The first component may be referred to as the electrical component and this arises as the rotating field from the stator winding links with the stationary (zero speed) rotor winding, The second component may be referred to as the mechanical component and it is the result of the movement of the rotor winding with respect to the stator winding, i.e. with respect to the rotating field from the stator winding. The mechanical component will, of course, change as the speed of rotation of the rotor changes~ It will be apparent that these two components do not appear as separate entities in practice, but they are a convenience in the description.
Thus, when an AC voltage is present on stator winding 31, and the rotor is not rotating, there will be an AC voltage on rotor winding 18 (the electrical component) which is rectified by diodes ~1-26 to provide a unidirectional current flow through field winding 12. When the rotor rotates, the mechanical component is present. This component normally increases, for any given rotation, as the speed is increased. The winding design will govern the degree in which it increases with speed. It is customary to add the mechanical component to the electxical component but, if necessary, it could be subtracted from it. Thus, the brushless exciter 20, with AC
applied to or fed to the stator winding 31, will provide an output to field winding 12 regardless of the speed~
Now, if we wish to run synchronous motor 10 as a variable speed drive motor, -the stator winding 11 would not be connected to a 60 Hertz supply~ i9e. ~
would not be connected directly to conductors 14, 15 and 16, but stator winding 11 would be connected to a v~riable frequency supply. The stator winding 31 of Case 2847 brushless exciter 20 would remain connected to conductors 14, 15 and 16, i.e., would rema~n c~nnected to the standard frequency 60 Hertz supply. Regardless of the speed at which synchronous motor 10 is operated, that is, regardless of the speed of rotation of the rotating portion 17, there will be an output fxom the exciter to supply field winding 12.
As was previously mentioned, the transfer of energy from the stator winding to the rotor winding via the rotating field is not particularly efficient. The equipment cost is high. In addition, the power factor is poor. The arrangement of Figure 2 minimizes these disadvantages.
Referring to Figure 2, similar parts to those in Figure 1 bear like designation numbers that are primed. Thus, in Figure 2 the synchronous motor 10' has a stator winding 11' and a rotor winding or field winding 12'. The exciter 20' has a rotor winding 18' and a stator winding 31' comprising wye connected phase windings 31a, 31b, and 31c. The exciter converter has diodes 21'-26' for rectifying the AC from winding 1~', and as before, control 30' gates on SCRs 27' and 28' when the in~uced field voltage is present during starting.
The stator winding 11' of synchronous motor 10' is connected to a supply 32 which has a controllable variable frequency for controlling the speed of synchronous motor 10'. The supply 32 may, for example, comprise a rectifier/inverter supplied from conductors 14', 15' and 16' and includes appropriate switching for connecting and disconnecting ~he supply.
A switch control 33 controls the operation of switches 34, 35 and 36. The switches 34, 35 and 36 connect and disconnect the three phase windings 31c, 31b and 31a respectively of stator windings 31 to respective Case 2~47 conductors lDr', 15' and 16' o:~ a standard frequency suppl~y. A rect.ifier 37 is also connected to conductors 14', 15' and 16' and has an output connected via switches 40 and 41 to phase windings 31b and 31a respectively of the wye connected stator windings 31'.
The switches 40 and 41, when closed, provide DC to windings 31b and 31al ~he switch control 33 cannot close switches 40, 41 until switches 34, 35, 36 are open, and s~annot close shlitches 34, 35, 36 until switches 40, 41 are open.
It should be noted that separate AC and DC
windings are not required for the stator windings 31 of exciter 20'. It was ound that separate windings are not necessary if the windings 31a, b and c are :L5 appropriately located according to good design practice Eor providin~ suitab:le DC energ.ization on windings 31a and 31b.
When the synchronous motor 10' is to be run at variable speeds ranging, for example, from standstill to a predetermined maximum operating speed, the variable frequency supply 32 provides power at a frequency which will give the required speed, and the switch control 33 is responsive to an input (conveniently RP~I) to change between AC and DC by operating switches 34, 35, 3G, ~n and 41 appropriately. Reference to Figure 3 will indicate one example of operation.
~eferring to Figure 3, the percent rated exciter output is plotted against percent speed. In an AC fed e~cciter the electrical component of the ou~put i8 represented by the shaded area 42 that is da:Eined by OAE~C. It is shown as providing about 50~ of rated exciter output, but this is a matter ~f dasign and it couid be more or less. The mechanical component is Case 2847 indicated by ABD. Again this is a matter o~ design.
In other words, in a conventional AC fed exciter, the exciter output for speeds from zero to 100~ would be represented by AD. Similarly, in a DC f~d exciter the exciter output would be represented by OD. It is likewise a matter of design that this is shown as linear.
~ ow, in the arrangement according to the invention, for ~peeds from zero to a percent speed represented by E, the exciter is AC fed and the exciter output is represented by line 43 between A and F~ At speed E the switch control 33 opens switches 34, 35 and 36 and closes switches 40 and 41 and the exciter is DC
fed over windings 31a and 31b. The exciter output, for speeds between E percent and 100% is represented by line 44 between G and D. It should be noted that the points of change are a matter of design and, if desired, points F and G could be made substantially the same. The points are selected to be in keeping with the description of single AC and DC fed exciters for ease of description.
Thus, if the synchronous motor 10' (Figure 2) is to be run at a percent speed less than E, then the exciter is AC fed. I it is to be run at a percent ~peed greater than E, the exciter is DC fed using the same windings.
If the synchronous motor 10' i5 to drive a grinding mill it will normally be required to run at a rated operating speed and the switches 34, 35 and 36 will remain open and switches 40 and 41 closed to provide the exciter with DC. When it is necessary to inch the ~ill, the switch control 33 will open switches 40, 41 and close switches 34, 35, 36 to provide AC feed to the exciter. The supply 32 (whic~ in this case could be a contactor arrangement operating with a DC
Case 28~7 g _ supply to provide a simulated alternating waveform of low frequency) provides the necessary low frequency power for inching.
Referring now to Figure 4, there is shown one variation in exci~er windings. This is a three phase double wye connected exciter having stator windings 45, 46, 47 and 50, 51, 52. The windings 45 and 50 are connected to conductor 14' through contactors or switches 53 and 54 respectively. The windings 46 and 51 are connected to conductor 15' through contactors or switches 55 and 56 respectively. The windings 47 and 52 are connected to conductor 16' through contactors or switches 57 and 58 respectively. Switch control 33' operates switches 53-58 to connect the stator winding~
45-47 and 50-52 to an AC source and disconnect them from the source. Switch control 33' also operates switches or contactors 60-62. When switches 60-62 are closed the DC output from rectifier 37' is connected through windings 45, 47, 52 and 50 in series. The switch control 33' can close at one time only switches 53~58 or switches 60-62 to apply either AC or DC to the exciter ~indings.
Again, only one set of stator exciter windings is used for AC or DC.
2S Various other connections and arrangements of stator windings for the exciter could be made without departing from the invention.
Claims (6)
1. An improved brushless exciter arrangement for use with a three phase variable speed synchronous motor adapted to start and to operate over a range of speeds comprising a three phase rotor winding for said brushless exciter, a three phase stator winding for said brushless exciter, first switch means having an open and a closed condition, and in said closed condition adapted to connect each phase winding of said stator winding to a respective phase of a fixed frequency source of AC
power and in its open condition to disconnect each phase winding of said stator winding from said respective phase of said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect at least one phase winding of said stator winding to a source of DC power and in said open condition to disconnect said at least one phase winding of said stator winding from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed conditions, said switch control means permitting only one of said first and second switch means to be in said closed condition at any one time.
power and in its open condition to disconnect each phase winding of said stator winding from said respective phase of said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect at least one phase winding of said stator winding to a source of DC power and in said open condition to disconnect said at least one phase winding of said stator winding from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed conditions, said switch control means permitting only one of said first and second switch means to be in said closed condition at any one time.
2. An improved brushless exciter as defined in claim 1 in which said stator windings are wye connected.
3. An improved brushless exciter as defined in claim 2 in which said second switch means in its closed condition connects two of said stator windings in series to said DC source of power.
4. An improved brushless exciter as defined in claim 1 in which said stator windings are double wye connected windings.
5. An improved brushless exciter as defined in claim 4 in which said second switch means in its closed condition connects at least one winding in each of the double wye connected windings in series to said source of DC power.
6. A variable speed synchronous motor drive comprising a synchronous motor having a three phase stator winding and a field winding, means for connecting said synchronous motor stator winding to a source of variable frequency power to provide a variable speed, a brushless exciter having three phase rotor windings mounted for rotation with said field winding, rectifier means mounted for rotation with said field winding interconnecting said three phase rotor windings with said field winding to provide DC
excitation for said field winding, said brushless exciter having a three phase wye connected stator winding, first switch means having an open and a closed condition, and in said closed condition adapted to connect each phase of said three phase brushless exciter stator winding to a respective phase of a fixed frequency source of AC power and in said open condition disconnecting each phase of said three phase brushless exciter stator winding from said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect two phases of said three phase brushless exciter winding in series to a source of DC power and
6. A variable speed synchronous motor drive comprising a synchronous motor having a three phase stator winding and a field winding, means for connecting said synchronous motor stator winding to a source of variable frequency power to provide a variable speed, a brushless exciter having three phase rotor windings mounted for rotation with said field winding, rectifier means mounted for rotation with said field winding interconnecting said three phase rotor windings with said field winding to provide DC
excitation for said field winding, said brushless exciter having a three phase wye connected stator winding, first switch means having an open and a closed condition, and in said closed condition adapted to connect each phase of said three phase brushless exciter stator winding to a respective phase of a fixed frequency source of AC power and in said open condition disconnecting each phase of said three phase brushless exciter stator winding from said source of AC power, second switch means having an open and a closed condition, and in said closed condition adapted to connect two phases of said three phase brushless exciter winding in series to a source of DC power and
Claim 6 continued:
in said open condition disconnecting said two phases of said three phase brushless exciter winding from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed condition, said first switch being in said closed condition for running said synchronous motor at lower speeds and said second switch means being in said closed condition for running said synchronous motor at higher speeds, said switch control means permitting only one of said first and second switch means to be in a closed condition at any one time.
in said open condition disconnecting said two phases of said three phase brushless exciter winding from said source of DC power, and switch control means for switching said first and second switch means between said open and said closed condition, said first switch being in said closed condition for running said synchronous motor at lower speeds and said second switch means being in said closed condition for running said synchronous motor at higher speeds, said switch control means permitting only one of said first and second switch means to be in a closed condition at any one time.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000422858A CA1199673A (en) | 1983-03-04 | 1983-03-04 | Brushless exciter for use with a variable speed synchronous motor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000422858A CA1199673A (en) | 1983-03-04 | 1983-03-04 | Brushless exciter for use with a variable speed synchronous motor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1199673A true CA1199673A (en) | 1986-01-21 |
Family
ID=4124708
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000422858A Expired CA1199673A (en) | 1983-03-04 | 1983-03-04 | Brushless exciter for use with a variable speed synchronous motor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1199673A (en) |
-
1983
- 1983-03-04 CA CA000422858A patent/CA1199673A/en not_active Expired
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