CA1179010A - Control system for ac induction motors - Google Patents
Control system for ac induction motorsInfo
- Publication number
- CA1179010A CA1179010A CA000372163A CA372163A CA1179010A CA 1179010 A CA1179010 A CA 1179010A CA 000372163 A CA000372163 A CA 000372163A CA 372163 A CA372163 A CA 372163A CA 1179010 A CA1179010 A CA 1179010A
- Authority
- CA
- Canada
- Prior art keywords
- power
- wye
- connection
- primary windings
- motor
- 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
Links
- 230000006698 induction Effects 0.000 title claims abstract description 20
- 238000004804 winding Methods 0.000 claims abstract description 28
- 239000007858 starting material Substances 0.000 claims abstract description 8
- 230000000694 effects Effects 0.000 claims abstract description 7
- 230000008878 coupling Effects 0.000 claims description 9
- 238000010168 coupling process Methods 0.000 claims description 9
- 238000005859 coupling reaction Methods 0.000 claims description 9
- 230000004044 response Effects 0.000 claims description 6
- 239000004020 conductor Substances 0.000 description 4
- 230000008859 change Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000013016 damping Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/26—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor
- H02P1/32—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor by star/delta switching
-
- 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
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/26—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual polyphase induction motor
-
- 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
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/42—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor
-
- 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
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/42—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor
- H02P1/44—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor by phase-splitting with a capacitor
-
- 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
- H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
-
- 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
- H02P25/04—Single phase motors, e.g. capacitor motors
-
- 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
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
- H02P27/16—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using ac to ac converters without intermediate conversion to dc
-
- 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
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
Abstract
ABSTRACT
A control system is disclosed for connecting the primary windings of a three-phase AC induction motor in a delta-connection at heavy loads and for automatically reconnecting the windings in a wye-connection at light loads to effect energy savings. A power sensor produces a control signal which is directly proportional to the power applied to the induction motor. A differential comparator responds to the control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching a wye-delta starter between two conditions, one of which effects the wye-connection and the other the delta connection. When the power input is below the preselected level the wye-connection is established, whereas the delta-connection is made when the power input is above the preselected level.
A control system is disclosed for connecting the primary windings of a three-phase AC induction motor in a delta-connection at heavy loads and for automatically reconnecting the windings in a wye-connection at light loads to effect energy savings. A power sensor produces a control signal which is directly proportional to the power applied to the induction motor. A differential comparator responds to the control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching a wye-delta starter between two conditions, one of which effects the wye-connection and the other the delta connection. When the power input is below the preselected level the wye-connection is established, whereas the delta-connection is made when the power input is above the preselected level.
Description
L7~
CONTROL SYSTEM FOR AC INDUCTION MOTORS
Description This invention relates generally to a control system for AC induction motors and more particularly, it relates to a control system for reconnecting the primary windings of an AC induction motor in a wye-connection at light loads to effect energy savings.
In U. S. Patent No. 2,106,833 issued to W. F.
Eames on February 1, 1938, there is disclosed a motor and control system for operating a moving s~airway by connecting the primary windings of the motor in a star connection for low speed and changing the primary windings from the star connection to a delta connection for high speed when needed for carrying passengers. A light-sensitive device was utilized to detect the presence of persons for controlling the stairway to operate at the low and high speeds.
In U. S. Patent No. 2,709,775 issued to A. Del Carlo on May 31, 1955, there is disclosed an auto-matic regulation system for electric machines in whichthe motor windings are switched from delta to star connection only for such load variations which are maintained for a certain length of time. The switching operation is in response to the amount of current supplied to the motor which corresponds to a predetermined load condition.
In U. S. Patent No. 3,764,872 issued to W. ~.
Boice on October 9, 1973, there is disclosed an apparatus for damping motor speed oscillations in an a-c adjustable speed motor drive system which includes a current detector to provide an in-phase signal that varies in accordance with the variations in the speed of the motor.
In U. S. Patent No. 3,863,741 issued to Y.
Mitsuishi on February 4, 1975, there is shown a control system for reel assembly winding and unwinding a power supply cable of an electrically powered earth-moving machine which includes a three-phase induction torque motor mechanically driving the reel assembly.
The torque motor is selectively connected to an electric source by a wye-connection when the machine moves forward and by a delta-connection when the machine moves backward. A shift lever is utilized for changing the moving direction of the machine which is connected to the gear box.
In U. S. Patent No. 4,084,406 issued to D. A.
Brenneman on April 18, 1978, there is shown a solid state starter for a chiller compressor motor which includes a motor current sensing circuit which controllably switches a bank of silicon-controlled rectifiers to conduct current to the motor for starting and running.
In various applications of machines such as centrifugal turbocompressors driven by AC induction motors, the operation of the motors is subjected to a wide range of load conditions. It is known that such motors can be constructed to operate with high efficiency and power factor values during full load conditions, but when the motors are operated at reduced or light load conditions the efficiency and power factor are substantially decreased thus causing ~79~
the waste of energy. It has been found that significant improvements in efficiency and power factor can be achieved by reconnecting the primary windings of such motors in a wye-connection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
Accordingly, it is a general object of the present invention to provide a new and improved control system for reconnecting the primary windings of an electric motor in a wye-connection at light loads to effect energy savings.
It is another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
It is another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection which includes a differential comparator circuit for generating an actuating signal to operate a switching device so as to establish alternately and selectively a first connection and a second connection between an electric motor and an electric source.
It is still another object of the present in-vention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection which includes a wye-delta starter for connecting the electric motor to a source of electric power.
79~
It is still another object of the present invention to provide a control system which includes a switching device, the power transducer, and a differential comparator circuit all operatively connected so as to reconnect the primary windings of an electric motor into a wye-connection Eor coupling to an electric source in response to the power delivered to the motor load dropping below a preselec-ted level.
It is yet still another object of the present invention to provide a control system which is relatively simple in construction and easy to manufacture.
In accordance with these aims and objectives, there is provided in accordance with the instant invention a control system for coupling the primary windings of an AC induction motor to a source of three-phase electric power. The system comprises a wye-delta starter for coupling the primary windings to the power source in order to apply power to the induction motor and which, in response to starting, connects the primary windings into a wye-connection to limit the inrush current normally occurring at start-up. Power sensing means are provided for generating a control signal which is directly proportional to the power applied to the induction motor. The system also comprises differential comparator means responsive to the control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching the wye-delta starter between a first condition, wherein the primary windings are connected in a wye-connection, and a second condition wherein the primary windings are connected in a delta-connection. The first ~, - 4 -` .'L~.79~
condition is established to effect energy savings, duriny light loads when the power applied to the induction motor is below the preselected power input level, whereas the second condition is established during heavier loads when the power applied to the motor is above the preselected power input level.
- 4a ~7~C) Normally, in the operation during full load conditions the switching device is in the second position for connecting the electric motor to the electric source by a delta connection. Upon the occurrence of the power applied to the motor load decreasing below a pre-selected level, the switching device is actuated by the actuating signal for re-connecting the switching device back to the first position so as to connect the electric motor to the electric source by a wye connection.
These and other objects and advantages of the present invention will become more fully apparent from the detailed description when read in conjunction with the acco~panying drawing in which there is shown a schematic block diagram of a control system for re-connecting the primary windings of an electric motor in a wye-connection for coupling to an electric source constructed in accordance with the present invention.
Referring now with particularity to the drawing, there is shown a schematic block diagram of a control system 10 constructed in accordance with the principles of the instant invention. The control system includes a switching device 12 such as a wye-delta controller or starter connected between a three-phase AC electric power source and a load circuit consisting of a three-phase AC induction motor 14. The power source is connectable to input terminals 16, 18, and 20 of the switching device 12 via the polyphase input lines Ll, L2 and L3. The output terminals 22, 24 and 26 of the switching device are joined to the respective polyphase lines 28, 30, and 32. The terminals 14a, 14b, and 14c are each tied to one end of the respective primary windings of the motor 14 and also to the respective polyphase lines 28, 30 and 32. Conductors 34, 36 and 38 are connected between the respective output terminals 40, 42, and 44 of the switching device and the respective terminals 14d, 14e, and 14f of the motor 14. These terminals 14d, 14e and 14f are also joined to the other ends of the primary windings of the motor 14.
The control system comprises power sensing means which includes a power or watt transducer 46, a wye-box 48, and a current transformer 50. For sensing the voltage from phase to neutral applied to the motor 14, the wye-box 48 is used to provide a pseudo-neutral point by having its input via lS lines 52 and 54 connected to the polyphase lines 30 and 28, respectively. For measuring the current drawn by the motor 14, the current transformer is disposed around the polyphase line 32. The power transducer 46 has its current input terminals connected to the current transformer 50 via con-ductors 56 and 58. The voltage input terminals of the power transducer 46 is connected to the output of the wye-bog 48 via line 60 and to the polyphase line 32 via conductor 62. A control signal is generated on the output of the power transducer 46 on the conductor 64 which is directly proportional to the power applied to the induction motor 14.
The differential comparator circuit consist of an operational amplifier 66 and a three pole double-throw relay 68 connected to the output of the amplifier 66 via line 70. The operational amplifier 66 has its inverting input terminal ~7~
connected to a positive dc voltage via a potentiometer 72 so as to provide an adjustable threshold or reference signal. The non-inverting input of the amplifier 66 is coupled to a fixed resistor 74 and a potentiometer 76. The other end of the resistor 74 is connected to the output of the power transducer 46 ~ia the line 64.
The other end of the potentiometer 76 is connected to the output of the operational amplifier 66. The relay 6~ is provided with three normally opened contacts (not sho~n) which are operatively in a conventional manner for operating the switching device 12.
The watt transducer 46 is preferably of the type manufactured and sold by Ohio Semitronics, Inc. under their designation of model number PC5-36D. The wye-box 48 is formed by interconnecting appropriate re-sistance values with the voltage terminals of trans-ducer 46 so as to produce a wye network with a pseudo-neutral point. The wye-delta con~roller 12 can be of any conventional commercially available type, the specific current rating on the controller contacts being selected to be of suitable value for the desired motor load.
Initially, it is assumed that the electric power is applied to the polyphase lines Ll, L2 and L3 and the operation of the induction motor 14 is to be at a reduced or light load. Thus, the control voltage on line 64 which is directly propor`tional to the power applied to the motor will be below the adjustable reference signal applied to the inverting input of the operational amplifier 66. Typically, this threshold or reference signal is set to a pre-selected value equal to approximately 40% of the full load condition.
In this condition, the output of the amplifier 66 on the line 70 will be a low voltage thereby maintaining ~7~
079191-Y - ~ -the relay 68 in its deenergized state. This causes the switching device to connect the electric power source to the primary windings of the motor 14 in the wye-connection.
Upon an increase in the control signal on line 64 due to an increase in the power applied to the load, the output of the amplifier 66 will change to a high voltage once the control signal exceeds the reference signal set by the potentio-motor 72. The high voltage on line 70 will cause the relay 68 to become energized so as to close the three not-shown normally open contacts. This causes the switching device to be switched selective-ly and alternately from the wye-connection to a delta-connection so that the motor can be operated for full load conditions. Once the power applied to the motor load decreases below a pre-determined value, the relay will become deenergized again and the switching device will automatically change back for reconnecting a primary windingsof the motor into a wye-connection for coupling to the electric source. The potentiometer 76 provided in the feed-back of the ampli~ier 66 defining a hysteresis adjustment is utilized to set this pre-determined level. Generally, the reconnection is effected when the power drops to 30% of the full load power value, which avoids the rapid switching of back and forth between the wye and delta connections due to spurious load fluctuations or oscillations.
From the foregoing detailed discussion it can thus be seen that the present invention pro-vides a new and improved control system which includes a power transducer for sensing the power applied to a motor load so as to cause reconnecting the primary windings of the electric motor into a wye conne~tion at light loads to effect energy savings. Further, the control system includes a differential comparator circuit for generating an actuating signal which causes operation of a switching device so as to establish alternately a~d selectively a wye-connection and a delta-connection between the induction motor and the electric power source.
While there has been illustrated and des~
cribed what is at present to be a preferred em-bodiment of the present invention, it will be under-stood by those skilled in the art that various changes and modifications may be made and equiva-lence may be substituted for elements thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the central scope thereof. There-fore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.
CONTROL SYSTEM FOR AC INDUCTION MOTORS
Description This invention relates generally to a control system for AC induction motors and more particularly, it relates to a control system for reconnecting the primary windings of an AC induction motor in a wye-connection at light loads to effect energy savings.
In U. S. Patent No. 2,106,833 issued to W. F.
Eames on February 1, 1938, there is disclosed a motor and control system for operating a moving s~airway by connecting the primary windings of the motor in a star connection for low speed and changing the primary windings from the star connection to a delta connection for high speed when needed for carrying passengers. A light-sensitive device was utilized to detect the presence of persons for controlling the stairway to operate at the low and high speeds.
In U. S. Patent No. 2,709,775 issued to A. Del Carlo on May 31, 1955, there is disclosed an auto-matic regulation system for electric machines in whichthe motor windings are switched from delta to star connection only for such load variations which are maintained for a certain length of time. The switching operation is in response to the amount of current supplied to the motor which corresponds to a predetermined load condition.
In U. S. Patent No. 3,764,872 issued to W. ~.
Boice on October 9, 1973, there is disclosed an apparatus for damping motor speed oscillations in an a-c adjustable speed motor drive system which includes a current detector to provide an in-phase signal that varies in accordance with the variations in the speed of the motor.
In U. S. Patent No. 3,863,741 issued to Y.
Mitsuishi on February 4, 1975, there is shown a control system for reel assembly winding and unwinding a power supply cable of an electrically powered earth-moving machine which includes a three-phase induction torque motor mechanically driving the reel assembly.
The torque motor is selectively connected to an electric source by a wye-connection when the machine moves forward and by a delta-connection when the machine moves backward. A shift lever is utilized for changing the moving direction of the machine which is connected to the gear box.
In U. S. Patent No. 4,084,406 issued to D. A.
Brenneman on April 18, 1978, there is shown a solid state starter for a chiller compressor motor which includes a motor current sensing circuit which controllably switches a bank of silicon-controlled rectifiers to conduct current to the motor for starting and running.
In various applications of machines such as centrifugal turbocompressors driven by AC induction motors, the operation of the motors is subjected to a wide range of load conditions. It is known that such motors can be constructed to operate with high efficiency and power factor values during full load conditions, but when the motors are operated at reduced or light load conditions the efficiency and power factor are substantially decreased thus causing ~79~
the waste of energy. It has been found that significant improvements in efficiency and power factor can be achieved by reconnecting the primary windings of such motors in a wye-connection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
Accordingly, it is a general object of the present invention to provide a new and improved control system for reconnecting the primary windings of an electric motor in a wye-connection at light loads to effect energy savings.
It is another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection for coupling to the electric source in response to the power delivered to the motor load dropping below a pre-selected level.
It is another object of the present invention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection which includes a differential comparator circuit for generating an actuating signal to operate a switching device so as to establish alternately and selectively a first connection and a second connection between an electric motor and an electric source.
It is still another object of the present in-vention to provide a control system for reconnecting the primary windings of an electric motor in a wye-connection which includes a wye-delta starter for connecting the electric motor to a source of electric power.
79~
It is still another object of the present invention to provide a control system which includes a switching device, the power transducer, and a differential comparator circuit all operatively connected so as to reconnect the primary windings of an electric motor into a wye-connection Eor coupling to an electric source in response to the power delivered to the motor load dropping below a preselec-ted level.
It is yet still another object of the present invention to provide a control system which is relatively simple in construction and easy to manufacture.
In accordance with these aims and objectives, there is provided in accordance with the instant invention a control system for coupling the primary windings of an AC induction motor to a source of three-phase electric power. The system comprises a wye-delta starter for coupling the primary windings to the power source in order to apply power to the induction motor and which, in response to starting, connects the primary windings into a wye-connection to limit the inrush current normally occurring at start-up. Power sensing means are provided for generating a control signal which is directly proportional to the power applied to the induction motor. The system also comprises differential comparator means responsive to the control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching the wye-delta starter between a first condition, wherein the primary windings are connected in a wye-connection, and a second condition wherein the primary windings are connected in a delta-connection. The first ~, - 4 -` .'L~.79~
condition is established to effect energy savings, duriny light loads when the power applied to the induction motor is below the preselected power input level, whereas the second condition is established during heavier loads when the power applied to the motor is above the preselected power input level.
- 4a ~7~C) Normally, in the operation during full load conditions the switching device is in the second position for connecting the electric motor to the electric source by a delta connection. Upon the occurrence of the power applied to the motor load decreasing below a pre-selected level, the switching device is actuated by the actuating signal for re-connecting the switching device back to the first position so as to connect the electric motor to the electric source by a wye connection.
These and other objects and advantages of the present invention will become more fully apparent from the detailed description when read in conjunction with the acco~panying drawing in which there is shown a schematic block diagram of a control system for re-connecting the primary windings of an electric motor in a wye-connection for coupling to an electric source constructed in accordance with the present invention.
Referring now with particularity to the drawing, there is shown a schematic block diagram of a control system 10 constructed in accordance with the principles of the instant invention. The control system includes a switching device 12 such as a wye-delta controller or starter connected between a three-phase AC electric power source and a load circuit consisting of a three-phase AC induction motor 14. The power source is connectable to input terminals 16, 18, and 20 of the switching device 12 via the polyphase input lines Ll, L2 and L3. The output terminals 22, 24 and 26 of the switching device are joined to the respective polyphase lines 28, 30, and 32. The terminals 14a, 14b, and 14c are each tied to one end of the respective primary windings of the motor 14 and also to the respective polyphase lines 28, 30 and 32. Conductors 34, 36 and 38 are connected between the respective output terminals 40, 42, and 44 of the switching device and the respective terminals 14d, 14e, and 14f of the motor 14. These terminals 14d, 14e and 14f are also joined to the other ends of the primary windings of the motor 14.
The control system comprises power sensing means which includes a power or watt transducer 46, a wye-box 48, and a current transformer 50. For sensing the voltage from phase to neutral applied to the motor 14, the wye-box 48 is used to provide a pseudo-neutral point by having its input via lS lines 52 and 54 connected to the polyphase lines 30 and 28, respectively. For measuring the current drawn by the motor 14, the current transformer is disposed around the polyphase line 32. The power transducer 46 has its current input terminals connected to the current transformer 50 via con-ductors 56 and 58. The voltage input terminals of the power transducer 46 is connected to the output of the wye-bog 48 via line 60 and to the polyphase line 32 via conductor 62. A control signal is generated on the output of the power transducer 46 on the conductor 64 which is directly proportional to the power applied to the induction motor 14.
The differential comparator circuit consist of an operational amplifier 66 and a three pole double-throw relay 68 connected to the output of the amplifier 66 via line 70. The operational amplifier 66 has its inverting input terminal ~7~
connected to a positive dc voltage via a potentiometer 72 so as to provide an adjustable threshold or reference signal. The non-inverting input of the amplifier 66 is coupled to a fixed resistor 74 and a potentiometer 76. The other end of the resistor 74 is connected to the output of the power transducer 46 ~ia the line 64.
The other end of the potentiometer 76 is connected to the output of the operational amplifier 66. The relay 6~ is provided with three normally opened contacts (not sho~n) which are operatively in a conventional manner for operating the switching device 12.
The watt transducer 46 is preferably of the type manufactured and sold by Ohio Semitronics, Inc. under their designation of model number PC5-36D. The wye-box 48 is formed by interconnecting appropriate re-sistance values with the voltage terminals of trans-ducer 46 so as to produce a wye network with a pseudo-neutral point. The wye-delta con~roller 12 can be of any conventional commercially available type, the specific current rating on the controller contacts being selected to be of suitable value for the desired motor load.
Initially, it is assumed that the electric power is applied to the polyphase lines Ll, L2 and L3 and the operation of the induction motor 14 is to be at a reduced or light load. Thus, the control voltage on line 64 which is directly propor`tional to the power applied to the motor will be below the adjustable reference signal applied to the inverting input of the operational amplifier 66. Typically, this threshold or reference signal is set to a pre-selected value equal to approximately 40% of the full load condition.
In this condition, the output of the amplifier 66 on the line 70 will be a low voltage thereby maintaining ~7~
079191-Y - ~ -the relay 68 in its deenergized state. This causes the switching device to connect the electric power source to the primary windings of the motor 14 in the wye-connection.
Upon an increase in the control signal on line 64 due to an increase in the power applied to the load, the output of the amplifier 66 will change to a high voltage once the control signal exceeds the reference signal set by the potentio-motor 72. The high voltage on line 70 will cause the relay 68 to become energized so as to close the three not-shown normally open contacts. This causes the switching device to be switched selective-ly and alternately from the wye-connection to a delta-connection so that the motor can be operated for full load conditions. Once the power applied to the motor load decreases below a pre-determined value, the relay will become deenergized again and the switching device will automatically change back for reconnecting a primary windingsof the motor into a wye-connection for coupling to the electric source. The potentiometer 76 provided in the feed-back of the ampli~ier 66 defining a hysteresis adjustment is utilized to set this pre-determined level. Generally, the reconnection is effected when the power drops to 30% of the full load power value, which avoids the rapid switching of back and forth between the wye and delta connections due to spurious load fluctuations or oscillations.
From the foregoing detailed discussion it can thus be seen that the present invention pro-vides a new and improved control system which includes a power transducer for sensing the power applied to a motor load so as to cause reconnecting the primary windings of the electric motor into a wye conne~tion at light loads to effect energy savings. Further, the control system includes a differential comparator circuit for generating an actuating signal which causes operation of a switching device so as to establish alternately a~d selectively a wye-connection and a delta-connection between the induction motor and the electric power source.
While there has been illustrated and des~
cribed what is at present to be a preferred em-bodiment of the present invention, it will be under-stood by those skilled in the art that various changes and modifications may be made and equiva-lence may be substituted for elements thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the central scope thereof. There-fore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A control system for coupling the primary windings of an AC induction motor to a source of three-phase electric power, comprising:
a wye-delta starter for coupling the primary windings to the power source in order to apply power to the induction motor and which, in response to starting, connects the primary windings into a wye-connection to limit the inrush current normally occurring at start-up;
power sensing means for generating a control signal which is directly proportional to the power applied to the induction motor;
and differential comparator means responsive to said control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching the wye-delta starter between a first condition, wherein the primary windings are connected in a wye-connection, and a second condition wherein the primary windings are connected in a delta-connection, the first condition being established, to effect energy savings, during light loads when the power applied to the induction motor is below the preselected power input level, whereas the second condition is established during heavier loads when the power applied to the motor is above the preselected power input level.
a wye-delta starter for coupling the primary windings to the power source in order to apply power to the induction motor and which, in response to starting, connects the primary windings into a wye-connection to limit the inrush current normally occurring at start-up;
power sensing means for generating a control signal which is directly proportional to the power applied to the induction motor;
and differential comparator means responsive to said control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching the wye-delta starter between a first condition, wherein the primary windings are connected in a wye-connection, and a second condition wherein the primary windings are connected in a delta-connection, the first condition being established, to effect energy savings, during light loads when the power applied to the induction motor is below the preselected power input level, whereas the second condition is established during heavier loads when the power applied to the motor is above the preselected power input level.
2. A control system as claimed in Claim 1, wherein said power sensing means comprises a power transducer having its inputs coupled to the output of a wye-box for sensing voltage and to the output of a current transformer for detecting current, said power transducer having an output on which the control signal is generated; wherein said differential comparator means comprises an operational amplifier, to the inverting input of which is applied the adjustable reference signal and to the non-inverting input of which amplifier is applied the control signal, the actuating signal being produced at the output of the operational amplifier; and wherein said operational amplifier includes a feedback potentiometer interconnected between its output and its non-inverting input for providing a hysteresis adjustment.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US12995880A | 1980-03-13 | 1980-03-13 | |
| US129,958 | 1980-03-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179010A true CA1179010A (en) | 1984-12-04 |
Family
ID=22442384
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000372163A Expired CA1179010A (en) | 1980-03-13 | 1981-03-03 | Control system for ac induction motors |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS56141795A (en) |
| AU (1) | AU6807681A (en) |
| CA (1) | CA1179010A (en) |
| DE (1) | DE3108349A1 (en) |
| ES (1) | ES500287A0 (en) |
| FR (1) | FR2478399A1 (en) |
| GB (1) | GB2071938B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3347792A1 (en) * | 1983-02-22 | 1985-04-04 | Hemag Maschinenbau, Ing. A. & F. Manasek Ohg, 6900 Heidelberg | Method and device for controlling the drive motor of a wood-processing machine |
| DE3306061C2 (en) * | 1983-02-22 | 1985-04-04 | Hemag Maschinenbau, Ing. A. & F. Manasek Ohg, 6900 Heidelberg | Device for controlling the drive motor of a woodworking machine |
| DE4018146A1 (en) * | 1990-06-06 | 1991-12-12 | Alber Karin | Electronically-regulated electric drive - has star-delta switching device in supply path of asynchronous motor |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE536043A (en) * | 1952-05-10 | |||
| GB754066A (en) * | 1953-09-15 | 1956-08-01 | Licencia Talalmanyokat | Automatic load-dependent y-delta change-over system for electric induction motors |
| FR1272762A (en) * | 1959-10-31 | 1961-09-29 | Device for automatic switching from the star assembly of an electric motor to delta assembly, and vice versa depending on the load of the electric motor | |
| GB2009538B (en) * | 1977-11-23 | 1982-09-02 | Taylor P A | Apparatus for controlling the speed and torque of a pumpjack motor |
-
1981
- 1981-02-24 GB GB8105779A patent/GB2071938B/en not_active Expired
- 1981-03-03 CA CA000372163A patent/CA1179010A/en not_active Expired
- 1981-03-04 AU AU68076/81A patent/AU6807681A/en not_active Abandoned
- 1981-03-05 DE DE3108349A patent/DE3108349A1/en not_active Withdrawn
- 1981-03-12 ES ES500287A patent/ES500287A0/en active Granted
- 1981-03-12 FR FR8104966A patent/FR2478399A1/en not_active Withdrawn
- 1981-03-13 JP JP3639981A patent/JPS56141795A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS56141795A (en) | 1981-11-05 |
| GB2071938A (en) | 1981-09-23 |
| ES8203176A1 (en) | 1982-02-16 |
| ES500287A0 (en) | 1982-02-16 |
| FR2478399A1 (en) | 1981-09-18 |
| AU6807681A (en) | 1981-09-17 |
| DE3108349A1 (en) | 1982-01-21 |
| GB2071938B (en) | 1984-01-04 |
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| MKEX | Expiry |