WO1995035532A1

WO1995035532A1 - Circuit arrangement for decreasing the energy consumption and for protecting of a variable loaded asynchronous motor

Info

Publication number: WO1995035532A1
Application number: PCT/HU1995/000024
Authority: WO
Inventors: Zoltán KARDOS
Original assignee: Energestor Kereskedelmi És Szolgáltató Kft.
Priority date: 1994-06-17
Filing date: 1995-06-16
Publication date: 1995-12-28
Also published as: HU9401800D0; AU2749995A

Abstract

The invention relates to a circuit arrangement for decreasing the energy consumption and for protecting of a variable loaded asynchronous motor, which comprises a sensor stage sensing at least one electric parameter of the asynchronous motor, furthermore a processing and adjusting unit connecting to the output of the sensor stage, further a star-delta switch-over stage being in control connection with the output of the processing and adjusting unit, and a power supply for powering said electronic stages and units. The sensor stage comprises a current sensor (1) connected in one of the phase conductors (PL) of the asynchronous motor (M) and an input interface circuit (2) connecting to the current sensor (1); a processing and adjusting unit (3) connected in releasable manner to a programming circuit (6) and comprising a semiconductor storage means (3.2) being connected to a microprocessor (3.1), the outputs of which are connected both to control inputs of an output circuit (4) comprising a star-delta switch-over stage and to control inputs of a remote display; and a powering circuit (5) comprising the power supply (5.2) contains a synchronous signal generator (5.3) connected to the input interface circuit (2) and a pulse deficiency detector (5.4) connected to a control input of the microprocessor (3.1).

Description

Circuit Arrangement for Decreasing the Energy Consumption and for Protecting of a Variable Loaded Asynchronous Motor

Field of the Invention

The invention relates to a circuit arrangement for decreasing the energy consumption and for protecting of a variable loaded asynchronous motor, which comprises a sen¬ sor stage sensing at least one electric parameter of the asynchronous motor, further¬ more a processing and adjusting unit connecting to the output of the sensor, further a star-delta switch-over stage being in control connection with the output of the proc- essing and adjusting unit. The proposed circuit arrangement ensures the generally used automatic start of the variable loaded asynchronous electric motor by means of star-delta switch-over; the automatic running with energy saving depending on the load during operation; simultaneously keeping continuously the power factor of the motor above the value of cosφ = 0,8 and last but not least the protection of the motor against thermal and mechanical overload. It ensures furthermore the protection of the motor in the case of phase loss as well as the energy saving operation during the pe¬ riod of idle running. In the case of an idle running of long period the automatical stopping is also ensured, if requested. In addition to the above, in the case of the motors running without inspection, the circuit arrangement according to the invention ensures the possibility of the phase return of the stopped motor resulting from the phase loss or overload, or the possibility of the automatic restarting after elapsing the cooling period.

Prior Art

The book of Laszlό Csordas, titled "Handbook of Planning and Assembling for Heavy-current", (published by Mύszaki Konyvkiado, Budapest, 1966) describes the improving of power factor, which is a known problem in the professional field. It is well-known for the experts that the most natural way of improvement of the power factor (cosφ) is to decrease the idle energy demand. By means of decreasing the load, the power factor of the induction motors and asynchronous motors become worse. Therefore, on the one hand, the use of the overdimensioned motors is not required, on the other hand the idle running of the motors should be decreased. If the motor of delta connection runs with a half or a third load, during this period the energy saving star-delta switch-over is required, as the idle power is proportional with the square of the voltage. In the case of the star-delta switch-over - the above-mentioned energy saving connection - when the motor in delta-connection is switched over to star- connection generally during decrease the load by 40 percent, - means lower voltage on the coils of the motor, so the idle power decreases as well. According to the said document, in addition to the above mentioned fact, the solution of decreasing the en¬ ergy consumption and the power factor of the asynchronous motor, furtheron the star-delta switch-over executed by hand or automatically, depends on the experts.

As a consequence, the start-up using with automatic star-delta swith-over is already well-known for start-up the asynchronous motor, for this purpose, fully developed automatics are available in the market. The aim of the known methods is to develop an apparatus for automatic starting up up the motor independent of the subjective judgement of the operator. These apparatuses make the switching over from star- connection into delta-connection after the determined running-up period.

HU-PS 183 804 describes automatic start-up and switch off of a welding apparatus especially of welding generators. The method and the circuit arrangement for realiz¬ ing the method is known from said document, solving the switch off of the generator operating in idle running after the determined elapsed idle timing. The realization of starting up the electric motor by means of star-delta switch-over, after touching the welding electrode is taken place by closing of a control circuit of the oscillator sys- tem of high-frequency connected parallel with the operating circuit of the welding apparatus. After the welding period, detecing the impedance change of the breaking arc, the timing of the stopping automatic unit starts, and if the welding circuit does not close again, then after elapsing a predetermined period set the welding apparatus will be stopped. Though, this technical solution eliminates the starting up and stop- ping problems, however neither energy saving nor protection for the motor is re¬ sulted.

Summary of the Invention

The aim of the invention is to develop a circuit arrangement suitable for realizing more tasks, i.e. on the one hand, it is suitable for star-delta switch-over automatical starting up the variable loaded asynchronous motor; for automatical running thereof with energy saving depending on the load during operation; for keeping the power factor above the set value; for protection against phase loss and the thermal and me¬ chanical overload of the motor; and for automatical cut-off in the case of idle opera- tion. The aim of the invention is furthermore to realize the simple circuit arrangement having simple operation, supervision and last but not least well-reliability.

The invention is based on the recognition that the line power consumption (I|) per phase of an asynchronous motor from the idle value to the nominal load value (I,, is proportional with the mechanical axle load. The rate of the current values above the rated value (I_n) relating to the nominal value determines the grade of the overload of the motor (Vl_n) as well, and by this value relation all the loading operational value and the value exceeding the loading value can be determined. In the professional field the idle operation is to be understood by the value proportion of L/I_n : 0,20-0,38; while overload operation is to be understood by the value proportion of I]/I_n : 1,05- 6,00. These operational and overload line currents change depending on the power of the motor, so suitable matching current sensor is required for using these parameters. Thus, said varying values with the circuit arrangement change within the operation range.

The aimed task is solved by a circuit arrangement for decreasing the energy con¬ sumption and for protecting of a variable loaded asynchronous motor, comprising a sensor stage sensing at least one electric parameter of the asynchronous motor, fur¬ thermore a processing and adjusting unit connecting to the output of the sensor stage, further a star-delta switch-over stage being in control connection with the output of the processing and adjusting unit, and a power supply for powering said electronic stages and units. In the sense of the invention the the sensor stage comprises a current sensor connected in one of the phase conductors of the asynchronous motor and an input interface circuit connecting to the current sensor; a processing and adjusting unit connected in releasable manner to a programming circuit and comprising a semi- conductor storage means being connected to a microprocessor, the outputs of which are connected both to control inputs of an output circuit comprising a star-delta switch-over stage and to control inputs of a remote display; and a powering circuit comprising the power supply contains a synchronous signal generator connected to the input interface circuit and a pulse deficiency detector connected to a control input of the microprocessor.

In a preferred embodiment the input interface circuit comprises an impedance matching transformer converting the input signal of the current sensor into a prede¬ termined nominal level; a bridge rectifier connected to the output of the impedance matching transformer; and an analog to digital converter /A-D converter/ connected to the output of the bridge rectifier.

It is advantageous, if the circuit arrangement comprises a current transformer operat¬ ing as a current sensor.

It is favourable, if the semiconductor storage means connected to the microprocessor contains the operational program of the microprocessor as well as the the nominal value parameters and switch-over parameters entered during programming.

It is also advantageous, if the push-buttons starting up and stopping the asynchronous motor are connected to the control inputs of the microprocessor.

In addition to the above it is advantageous if further control inputs of the microproc¬ essor are connected through insulation means to remote control means.

In the sense of the invention favourably the insulation means are optocouplers.

Furthermore, it is advantageous if the programming circuit comprises push-buttons connecting to programming inputs of the microprocessor.

Further to the above, it is favourable if the programming circuit contains an alpha- numerical display.

It is also advantageous, if in the processing and adjusting unit the control output of the microprocessor is connected to an input of an output interface circuit through a decoder.

In addition to the above it is also advantageous, if the output circuit comprises a delta-connection relay and a star-connection relay as a star-delta switch-over stage.

It is favourable in the sense of invention if the output interface circuit of the process¬ ing and adjusting unit is connected to a contactor of a main switch coupling the asyn¬ chronous motor to the electric network.

Further to the above, it is advantageous if the relays are of solid-state relays.

In the sense of the invention it is advantageous if the remote display comprises relays indicating overload, phase loss, current sensing failure, processing and adjusting unit failure, and contacts of said relays are led to indicating lamps serving as optical indi¬ cating elements.

Finally it is advantageous, if the relays are bypassed with light emitting diodes indi¬ cating the operational state of said relays.

The main advantage of the apparatus according to the invention is that the controlled motor is run by means of energy saving star-connection in the case of increasing axle load obtaining the load of 40-58 percent, than in the case of further load increase, it will be switched over to delta-connected operation. In the case of decreasing load obtaining the load range of 58-40 percent, after a determinable time of grace the motor will be switched again into energy saving star-connected operation.

In the energy saving operation the winding voltage of the motor coil decreases in the rate of 1/3, the rate of induction decreases in the same proportion, while the idle power demand drops to its fraction. Similarly, the iron and copper losses decrease as well. As a consequence, during the whole operational period the power factor of the motor increases above the value of 0,8 even in the range of the idle basis load. In the case of low mechanical load the specific wattous energy demand of the motor is es¬ sentially lower in star-connected operation as in delta-connected operation at the same load, owing to this fact, in the case of application of the circuit arrangement ac¬ cording to the invention considerable extent of wattous energy savings come into being in addition to the improvement of power factor and the decrease of the idle cur¬ rent demand.

Further advantage is in that the power factor during the whole working period ex¬ ceeds the value of 0,8, due to this in the case of using the apparatus according to the invention no synchronous condenser is requested for improving the power factor, so the apparatus according to the invention can be considered as a natural power-factor condenser unit.

Further advantage of the apparatus according to the invention is its feature that it en¬ ables, owing to the nature of the program edited into the microprocessor, to realize the whole protection of the motor controlled by itself. The protection involves the sphere of phase loss, the mechanical and thermal overload and of short-circuit pro¬ tection. Brief Description of the Drawings

The invention is described in details with the aid of the enclosed drawings presenting some embodiments of the circuit arrangement according to the invention by way of example, in which:

Fig. 1 is a block diagram of a possible embodiment of the circuit arrangement according to the invention,

Fig. 2 illustrates the circuit diagram of the current sensor and the input interface circuit of the circuit arrangement according to the invention,

Fig. 3 is the circuit diagram of a possible example of the processing and adjust- ing unit of the circuit arrangement according to the invention,

Fig. 4 illustrates the circuit diagram of the set up of the output circuit of the cir¬ cuit arrangement according to the invention,

Fig. 5 shows a possible set up of the programming circuit,

Fig. 6 is the circuit diagram of a possible embodiment of the power supply stage of the circuit arrangement according to the invention,

Fig. 7 illustrates the electric connection diagram of the circuit arrangement ac¬ cording to the invention, while

Fig. 8 explains the current and timing value in its diagram, which are taken into consideration by the microprocessor during the operation while forming the output commands.

Description of the Preferred Embodiments

Figure 1 shows a block diagram of a possible embodiment of the circuit arrangement according to the invention, distinguishing six main units. In the electric connection diagram of Figure 7 can be seen that the primary side of the current transformer, de- pending on the rated current I] and on the power of the asynchronous motor M, is connected to the phase conductor PL of the asynchronous motor M. In the shown ex¬ ample the current transformer serves as a current sensor 1 of the circuit arrangement. The secondary side of the current transformer is connected to the primary side of the impedance matching transformer 2.1 of the input interface circuit 2. The secondary side of the impedance matching transformer 2.1 connects to the input of the bridge rectifier 2.2, onto the output of which parallel with an analog to digital converter /A- D converter/ 2.3 in the usually way a filter capacitor and a resistance setting the volt¬ age division are connected. The analog to digital converter /A-D converter/ 2.3, which can be shown in details in the Figure 2, can be realized for example by way of an integrated circuit of ADC 0841 type. The principle of the operation of the circuit, its practical, dimensional and setting particulars can be found in the circuit product booklet, so they are not described detailed in the present description. The output of the input interface circuit 2 is connected to the processing and adjusting unit 3. The processing and adjusting unit 3 - it can be seen in details in Figure 3 - contains a mi¬ croprocessor 3.1 realized for example by the microprocessor of 87C51 type, to which for example a semiconductor storage means 3.2 comprising the integrated circuit of 93C06 is connected in the usual way. The outputs of the optocouplers 3.3, 3.4 and 3.5 are connected to the control inputs of the microprocessor 3.1. The START push- button 3.6 is connected to the output of the optocoupler 3.3, while the STOP push¬ button 3.7 is connected to the output of the optocoupler 3.4, the other poles of the push-buttons 3.6, 3.7 are connected commoned to the supply voltage. The optocou¬ plers 3.3, 3.4, 3.5 operate as insulation means, which are in connection with the re¬ mote control means ensuring the start and the stop of the circuit arrangement as well as indicating the phase loss of the power supply of the asynchronous motor M in the way of ensuring the galvanic separation. In Figure 3 the circuit elements necessary for the operation of the microprocessor 3.1 are shown without reference numbers, their functions and dimensions are described in details by the product booklet or da¬ tasheet of the microprocessor 3.1. The microprocessor 3.1 - see in Fig. 1 - is in con- nection with the programming circuit 6 through the plug-in connector 3.8 , wherein the programming circuit 6 contains alphanumerical display 6.1 and push-buttons 6.2. The programming circuit 6, more exactly the alphanumerical display 6.1 matches fa¬ vourably to the type of the microprocessor 3.1. In the case of the mentioned micro¬ processor of 87C51 type a liquid crystalline alphanumerical display 6.1 of LM16155 type can be used. Its connection to the microprocessor 3.1 considering the operation is described in the product booklet of the microprocessor, the diagram of connection can be schematically represented in Figure 5. Here can be seen four push-buttons 6.2 which serve for selecting the parameters appearing on the alphanumerical display 6.1 as well as for obtaining the parameter's data. - 8 -

The outputs of the microprocessor 3.1 serving for output of the processing and adjust¬ ing unit 3 are connected in the present case to an output interface circuit 4.2 through the decoder 4.1 of the output circuit 4. The decoder 4.1 can be realized for example by the integrated circuit of 74HCT164 type, the outputs of which, characterizing the circuit, join to the output interface circuit 4.2 comprising the integrated circuit of ULN28803A type. The outputs of the output interface circuit 4.2 are connected among others to a delta-connection relay 4.3 of the star-delta switch-over stage, to a delta-connection relay 4.5 and to a relay 4.4 of a contactor 7.1 of a main switch of the asynchronous motor M. In this case the relays 4.3, 4.4 and 4.5 are solid-state relays, and their outputs are of usually connected star-connection, delta-connection, main switch being in connection with the actuating coil of the contactor 7.3, 7.2, 7.1. The other outputs of the output interface circuit 4.2 according to the shown embodiment are connected to the control input of the the relay 4.6 indicating the overload, the re¬ lay 4.7 indicating the phase loss, the relay 4.8 indicating the failure of the current sensor, the relay 4.9 indicating the failure of the processing and adjusting unit 3. The contacts of the relays 4.6 to 4.9 are in connection with the power voltage and the in¬ dicating lamps LI to L4, which are connected to the circuit as optical indicating ele¬ ments. With the relays 4.3 to 4.9 each a light emitting diode is connected parallel, which indicates the momentary operation and state of the asynchronous motor M and the relays direct on the spot of the relays 4.3 to 4.9. The output of the output interface circuit 4.2 is connected furthermore to the light emitting diode LD10, which serves for indicating the idle range of the asynchronous motor M. In the presented case the light emitting diodes LD1 to LD3 are of green, the light emitting diodes LD4 to LD7 are of red colour, while the light emitting diode LD 10 is of yellow colour, by means of these colours referring to the faultless or the fault operation of the asynchronous motor M. The main part of the circuit arrangement is formed furthermore by the powering circuit 5 comprising a power supply 5.2 of stabilized low-voltage which can be connected to the network by means of key operated switch 5.1. The power supply 5.2 can be realized for example by means of integrated circuit of type 7805 according to its known circuit diagram. The secondary side of the transformer form¬ ing the part of the power supply 5.2 is connected to the input of the synchronous sig¬ nal generator 5.3 as well as to the input of the pulse deficiency detector 5.4. The syn¬ chronous signal generator 5.3 - can be seen in Fig. 6 in details - comprises an opera¬ tional amplifier of type LM339 and a D-flip-flop of type 74HCT74, the output of which is connected to the input of the synchronous signal of the analog to digital converter /A-D converter/ 2.3 of the input interface circuit 2. The pulse deficiency detector 5.4 comprises also the operational amplifier of type LM339 formed by known way as an integrating stage, the output of which is connected also to the commoned point of the opto-coupler 3.4 and the STOP push-button 3.7.

The circuit arrangement according to the invention is developed first of all for de- creasing the energy consumption of a variable loaded asynchronous motor as well as that of the protection. The decreasing of the wattous and idle energy consumption is realized so that the controlled asynchronous motor M is automatically started, then in the case of low and middle load range it is operated by means of star-connection, while in higher load range it is operated in delta-connection, and then after a prede- termined idle timing it is switched off. In the case of overload the asynchronous mo¬ tor M is also switched out after a predetermined period and a possible restart is al¬ lowed only after elapsing the cooling period prescribed for the asynchronous motor M. The current signal of the current sensor 1 connected to one of the phase conduc¬ tors PL of the asynchronous motor M, varying proportionally with the momentary axle load of the asynchronous motor M is connected to the primary side of the im¬ pedance matching transformer 2.1. The signal voltage according to the rate of 1 A/ IV appearing on the secondary output of the impedance matching transformer 2.1 is led through the bridge rectifier 2.2 to the A-D converter 2.3, which serves digital signal sequence proportional for controlling the microprocessor 3.1 by means of changing the load of the asynchronous motor M. In accordance with the characteristic curve, the microprocessor 3.1, as it can be seen on Fig. 8, processes the digital signals pro¬ portion with the load of the asynchronous motor M. By the aid of the programming circuit 6 the characteristically allowed current and timing values selected from the data store of the memory of the microprocessor 3.1 are stored in the semiconductor storage means. These stored data during operation the microprocessor 3.1 are con¬ tinuously compared to the data of A-D converter 2.3, then in the case of coincidences occuring on the course of variations, after elapsing the determined and set timing the microprocessor 3.1 commands on its outputs for realizing the necessary intervention.

On the diagram of Fig. 8 the current and timing data are indicated by way of exam- pie, which are taken into consideration by the microprocessor 3.1 during operation forming the output commands. The rated current I_n of the asynchronous motor M is considered as 100 percent of the examined current data. All the differences from this value are considered as 100 percent value by the microprocessor 3.1 wherein during the operation the following operation current values are distinguished: I_m minimum value, which refers to the fault of the current sensor 1;

I; idle current of the asynchronous motor M;

I_Λ"Δ switch-over current value in the case of increasing load;

I_SΔ"Λ switch-over current value in the case of decreasing load;

I_pΔ"Λ prompt switch-over current value in the case of overload;

IpΛ~Δ prompt switch-over current value according to the basic program in the case of program disturbance;

I_n Normal load limit current value of 100 percent;

I_ol first overload current value: I|/I_n=l,05;

I_o2 second overload current value : I₁/I_n=l,2;

I_o3 third current value: I₁/I_n=l,5.

The current values and the timing thereof are processed and adjusted by the micro¬ processor 3.1 furthermore the cooling period T_c depending on the overload is proc¬ essed by the microprocessor 3.1 as well, before elapsing the cooling period the asyn- chronous motor M cannot be restarted.

During the continuous processing of the indicated current- and timing relations, the control outputs of the microprocessor 3.1 through the decoder 4.1 and the input inter¬ face circuit 4.2 according to need continuously operate the relays 4.3 to 4.9 together with the optical displays as well as the light emitting diode LD10. An advantage of the proposed circuit arrangement is in that after editing the operational program the programming circuit 6 can be separated from the unit comprising the circuit ar¬ rangement by means of parting the plug-in connector 3.8 and the asynchronous motor M for example by the aid of the push-button 3.6 or by means of a remote control connected to the same point it can be started. After that the processing and adjusting unit 3 controls the asynchronous motor M in accordance with the current program of the microprocessor 3.1.

Claims

1. Circuit arrangement for decreasing the energy consumption and for protecting of a variable loaded asynchronous motor, comprising

a sensor stage sensing at least one electric parameter of the asynchronous motor,

a processing and adjusting unit connected to the output of the sensor stage,

a star-delta switch-over stage being in control connection with the output of the proc¬ essing and adjusting unit, and

a power supply for powering said electronic stages and units

characterized in that the sensor stage comprises

a current sensor (1) connected in one of the phase conductors (PL) of the asynchro¬ nous motor (M) and an input interface circuit (2) connected to the current sensor (1);

the processing and adjusting unit (3) connected in releasable manner to a program¬ ming circuit (6) and comprising a semiconductor storage means (3.2) being con- nected to a microprocessor (3.1), the outputs of which are connected both to control inputs of an output circuit (4) comprising a star-delta switch-over stage and to control inputs of a remote display; and

a powering circuit (5) comprising the power supply (5.2) contains a synchronous sig¬ nal generator (5.3) connected to the input interface circuit (2) and a pulse deficiency detector (5.4) connected to a control input of the microprocessor (3.1).

2. Circuit arrangement according to Claim 1, characterized in that the input interface circuit (2) comprises

an impedance matching transformer (2.1) converting the input signal of the current sensor (1) into a predetermined nominal level;

a bridge rectifier (2.2) connected to the output of the impedance matching trans¬ former (2.1); and an analog to digital converter /A-D converter/ (2.3) connected to the output of the bridge rectifier (2.2).

3. Circuit arrangement according to Claim 1 or Claim 2, characterized in that it comprises a current transformer operating as a current sensor (1).

4. Circuit arrangement according to Claim 1, characterized in that the semiconductor storage means (3.2) connected to the microprocessor (3.1) contains the operational program of the microprocessor (3.1) as well as the the nominal value parameters and switch-over parameters entered during programming.

5. Circuit arrangement according to the Claim 1 or Claim 4, characterized in that push-buttons (3.6, 3.7) starting-up and stopping the asynchronous motor (M) are connected to the control inputs of the microprocessor (3.1).

6. Circuit arrangement according to any of the Claims 1, 4, 5 characterized in that further control inputs of the microprocessor (3.1) are connected through insulation means to remote control means.

7. Circuit arrangement according to the Claim 6, characterized in that the insulation means are optocouplers (3.3 to 3.5).

8. Circuit arrangement according to any of the Claims 1, 4 to 7 characterized in that the programming circuit (6) comprises push-buttons (6.2) connected to programming inputs of the microprocessor (3.1).

9. Circuit arrangement according to the Claim 8, characterized in that the program¬ ming circuit (6) contains an alphanumerical display (6.1 ).

10. Circuit arrangement according to any of the Claims 1 to 9 characterized in that in the processing and adjusting unit (3) the control output of the microprocessor (3.1) is connected to an input of an output interface circuit (4.2) through a decoder (4.1).

11. Circuit arrangement according to any of the Claims 1 to 10 characterized in that the output circuit (4) comprises a delta-connection relay (4.5) and a star-connection relay (4.3) as a star-delta switch-over stage.

12. Circuit arrangement according to any of the Claims 1 to 11 characterized in that the output interface circuit (4.2) of the processing and adjusting unit (3) is connected to a contactor (7.1) of a main switch coupling the asynchronous motor (M) to the electric network.

13. Circuit arrangement according to the Claims 11 or 12 characterized in that the relays (4.3 to 4.5) are of solid-state relays.

14. Circuit arrangement according to the Claim 1 characterized in that the remote display comprises relays (4.6 to 4.9) indicating overload, phase loss, current sensor failure, processing and adjusting unit failure, and contacts of said relays (4.6 to 4.9) are led to indicating lamps (LI to L4) serving as optical indicating elements.

15. Circuit arrangement according to any of the Claims 1 to 14 characterized in that the relays (4.3 to 4.9) are bypassed with light emitting diodes (LD1-LD7) indicating the operational state of said relays (4.3 to 4.9).