WO1998001937A2 - A connection means between a frequency converter and its load - Google Patents
A connection means between a frequency converter and its load Download PDFInfo
- Publication number
- WO1998001937A2 WO1998001937A2 PCT/FI1997/000438 FI9700438W WO9801937A2 WO 1998001937 A2 WO1998001937 A2 WO 1998001937A2 FI 9700438 W FI9700438 W FI 9700438W WO 9801937 A2 WO9801937 A2 WO 9801937A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- connecting means
- conductors
- voltage
- load
- impulse
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/005—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection avoiding undesired transient conditions
-
- 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
- H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
- H02P29/50—Reduction of harmonics
Definitions
- FC frequency converters
- the voltage impulse is by nature an impulse wave, which when reflected at the motor winding terminals can lead even to doubling of the voltage between phases and to ground due to the often several times higher characteristic impedance of the winding compared to that of the cable between the FC and the motor
- the usual winding type is a so called random winding, characterized by round copper wire and that the turns in the coils are located randomly
- the coil voltage becomes decisive the voltage difference between the first and last turn of a coil, or correspondingly the coil pair voltage
- the load of an FC may also be comprised of some other electrical apparatus than a motor, for example a transformer, but the problems remain With the new FC types on the market, the turn voltage and especially the coil voltage and coil pair voltage have in some drive cases grown too high for the conventional windings and insulations, sometimes causing winding failures.
- Technical solutions to reduce the steepness of the voltage impulses have been presented, e.g. using chokes or filters, but these solutions have either been too complicated or they have had a negative influence on the properties of the FC, e g. its efficiency.
- the only remaining possibility has often been to enhance the insulation of the windings, which in turn leads to, e.g , special motor constructions and a considerable increase in costs.
- the invention presented herein is characterized by the fact that the rise time of the voltage impulse, arriving at the winding of the electrical apparatus constituting the load of the FC, can be lengthened such that the critical voltage stresses mentioned can be kept below the limits allowed for the conventional windings.
- a specially advantageous characteristic of the invention is the fact that the efficiency of the FC remains high, and extra losses are not created.
- the central idea with this invention is the realization that if the FC voltage impulse is forced to arrive at the winding of the electric apparatus stepwise, keeping, however, the maximum voltage at the earlier value at the most, the average rate of rise of the voltage will be slower and the total rise time of the impulse longer.
- This stepwise arrival of the impulse is carried out in one embodiment of the invention by dividing the cable or any other conductor between the FC and the electric apparatus into two or more successive parts, characterized by different wave impedances
- this will be achieved by dividing the cable or any other conductor into two or more parallel cables over a part of its length.
- Another way, characteristic of the invention, of changing the wave impedance of the cable or any other conductor is to change the dielectric constant of its insulation (as is known, the wave impedance of the cable is almost inversely proportional to the square root of the dielectric constant, see the equations presented below)
- the third characteristic way of changing the wave impedance is to change the inductance of the cable or other conductor per length unit, e g by varying the outer diameter of the conductor
- the invention is further characterized in that the parallel cables or any other conductors can show different propagation times for the impulses, in detailed embodiments of the invention this can be done by using parallel cables of different lengths, or the propagation velocity of the impulse wave is different in the parallel cables
- one embodiment of the invention is characterized by making the longer cable(s) essentially smaller in cross-section, enabling e g the longer cables to be bent on the same cable tray on which the mam cable is situated
- Fig A presents first the conventional cable arrangement between FC (1) and motor (2)
- Fig B describes how a voltage impulse (4) from FC (1 ) is propagating along the cable (3) (the propagating velocity is generally known to be in the order of 100 - 150 m/ ⁇ s) and is reflected at the terminals (2) of the motor winding to even double value (5), if the wave impedance of the motor is large in comparison to the cable wave impedance (this will happen, if the motor is a fairly low power motor, and the cable length exceeds the so called critical cable length - this is half the distance the impulse propagates during a time equal to the rise time)
- the rate of rise increases, proportional to the voltage reflection
- Fig C presents a cable arrangement according to the invention
- a voltage impulse (voltage u, rise time e g 200 ns) propagating along a single cable (6) first meets the junction where the cable divides into parallel branches (two in this example)
- the impulse propagates along the both branches (7) and (8) toward the motor, with an amplitude 2/3 u, rise time unchanged 200 ns
- the impulse propagating along the shorter cable (7) first meets the junction of the motor winding and the second cable (8)
- the reflection occurring here is not significant, assuming that the motor (2) wave impedance is great as in Fig B
- a wave with an amplitude of 2/3 u and rise time 200 ns begins to propagate into the motor winding
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
- Insulated Conductors (AREA)
- Control Of Electric Motors In General (AREA)
Abstract
The invention concerns a connecting means (3, 6, 7, 8) comprised of cables and/or other known types of conductors between a frequency converter (1) and its load (2), the latter being a motor or another electric apparatus. According to the invention the connecting means is constituted by two or more parts connected in series such that at least at one point the two successive parts (6, 7, 8) show different wave impedances.
Description
A CONNECTION MEANS BETWEEN A FREQUENCY CONVERTER AND ITS LOAD
The rotation speed of ac motors is increasingly often adjusted using frequency converters (FC) and the efficiency of the FCs has been improved through the use of high-speed components, for example IGBT-type transistors, to quite high levels At the same time, the rate of rise and/or fall of the voltage impulse has become very high and is even in the order of 20000 V/μs A consequence of this has been that the steep voltage impulse when arriving at the motor winding causes increased voltage stresses in several parts of the winding
- The voltage impulse is by nature an impulse wave, which when reflected at the motor winding terminals can lead even to doubling of the voltage between phases and to ground due to the often several times higher characteristic impedance of the winding compared to that of the cable between the FC and the motor
- When propagating into the motor winding the voltage impulse brings about increased voltages between the coil turns of the winding, as is generally known This voltage increase gets higher with shorter rise or fall times of the voltage impulse
- In low-voltage drives (voltage below 1000 V) the usual winding type is a so called random winding, characterized by round copper wire and that the turns in the coils are located randomly In this arrangement the coil voltage becomes decisive the voltage difference between the first and last turn of a coil, or correspondingly the coil pair voltage These voltages grow like the turn voltage
The load of an FC may also be comprised of some other electrical apparatus than a motor, for example a transformer, but the problems remain
With the new FC types on the market, the turn voltage and especially the coil voltage and coil pair voltage have in some drive cases grown too high for the conventional windings and insulations, sometimes causing winding failures. Technical solutions to reduce the steepness of the voltage impulses have been presented, e.g. using chokes or filters, but these solutions have either been too complicated or they have had a negative influence on the properties of the FC, e g. its efficiency. The only remaining possibility has often been to enhance the insulation of the windings, which in turn leads to, e.g , special motor constructions and a considerable increase in costs.
The invention presented herein is characterized by the fact that the rise time of the voltage impulse, arriving at the winding of the electrical apparatus constituting the load of the FC, can be lengthened such that the critical voltage stresses mentioned can be kept below the limits allowed for the conventional windings. A specially advantageous characteristic of the invention is the fact that the efficiency of the FC remains high, and extra losses are not created.
The economic significance of the invention is very great, since it makes the use of conventional windings possible in most FC drives, wherefore expensive special motors are not needed, and users do not need a large selection of spare motors of different constructions.
The central idea with this invention is the realization that if the FC voltage impulse is forced to arrive at the winding of the electric apparatus stepwise, keeping, however, the maximum voltage at the earlier value at the most, the average rate of rise of the voltage will be slower and the total rise time of the impulse longer. This stepwise arrival of the impulse is carried out in one embodiment of the invention by dividing the cable or any other conductor between the FC and the electric apparatus into two or more successive parts, characterized by different wave impedances
In one characteristic embodiment of the invention this will be achieved by dividing the cable or any other conductor into two or more parallel cables over a part of its length.
Another way, characteristic of the invention, of changing the wave impedance of the cable or any other conductor is to change the dielectric constant of its insulation (as is known, the wave impedance of the cable is almost inversely proportional to the square root of the dielectric constant, see the equations presented below) The third characteristic way of changing the wave impedance is to change the inductance of the cable or other conductor per length unit, e g by varying the outer diameter of the conductor
The invention is further characterized in that the parallel cables or any other conductors can show different propagation times for the impulses, in detailed embodiments of the invention this can be done by using parallel cables of different lengths, or the propagation velocity of the impulse wave is different in the parallel cables The propagation velocity depends on the same parameters as the wave impedance (Propagation velocity v = Λ/( 1/lc), wave impedance Z = V(l/c), where 1 = inductance ja c = capacitance per unit length)
Parallel cables have already earlier been used in FC drives and generally in electric drives but the cables have always been made essentially uniform in length and of the same material over the entire distance between the FC and the electric apparatus, thus, no increase in the voltage impulse rise or fall time such as described for the invention will occur
One consequence of dividing the cable or other conductor to parallel conductors is the fact that the cross sections of the cables need not be identical or balanced in order to provide the same current densities This is possible, because only one of the cables or conductors can be made the current carrying conductor, the others acting as 'impulse rise time lengtheners' Thus, one embodiment of the invention is characterized by making the longer cable(s) essentially smaller in cross-section, enabling e g the longer cables to be bent on the same cable tray on which the mam cable is situated
In the presentation above the term 'cable' alone has sometimes been used to describe the
connecting means between the FC and the electric apparatus However, any conductor (as far as possible in practical life) can be used as the conducting means, without any effect on the application of the invention
In the following the increase in the rise time of the voltage impulse will be described, using a simple example, when a motor winding acts as the FC load For simplicity, the connecting means is called 'cable', which in practice is the conventional connecting means Fig A presents first the conventional cable arrangement between FC (1) and motor (2) Fig B describes how a voltage impulse (4) from FC (1 ) is propagating along the cable (3) (the propagating velocity is generally known to be in the order of 100 - 150 m/μs) and is reflected at the terminals (2) of the motor winding to even double value (5), if the wave impedance of the motor is large in comparison to the cable wave impedance (this will happen, if the motor is a fairly low power motor, and the cable length exceeds the so called critical cable length - this is half the distance the impulse propagates during a time equal to the rise time) At the motor terminals, the rate of rise increases, proportional to the voltage reflection
Fig C presents a cable arrangement according to the invention A voltage impulse (voltage u, rise time e g 200 ns) propagating along a single cable (6) first meets the junction where the cable divides into parallel branches (two in this example) Next, the impulse propagates along the both branches (7) and (8) toward the motor, with an amplitude 2/3 u, rise time unchanged 200 ns The impulse propagating along the shorter cable (7) first meets the junction of the motor winding and the second cable (8) The reflection occurring here is not significant, assuming that the motor (2) wave impedance is great as in Fig B A wave with an amplitude of 2/3 u and rise time 200 ns begins to propagate into the motor winding
Assuming that the cable (8) is longer than the cable (7) just enough to bring the wave to the motor 200 ns later than along cable (7), the voltage will continue to rise with the same rate and the same voltage step at the motor terminals As a result the voltage rises to a value of 4/3 u, during a total time of 400 ns Even if the voltage maximum can reach almost the same value as in Fig B, due to reflections at various junctions, the resulting
total rise time will more than double or the rate of rise will be reduced to less than half the original value If the difference in cable lengths is made bigger, the rise of the voltage more clearly changes stepwise and the total rise time grows longer still The same will happen, if more parallel cables will be used, or if successive groups of parallel cables have different numbers of parallel cables
Assuming that the two parallel cables are equally long and the impulse propagating time in both cables is the same, a voltage impulse of 2/3 u will arrive along both cables simultaneously, with a rise time of 200 ns The result at the motor winding terminals is a voltage rise to 4/3 u within 200 ns Reflections arriving later from junction 1 eventually bring the voltage to the level of 2 u, however, this happens in at least two steps, meaning that again the total rise time will be considerably longer than the original It is probable, that the first step 4/3 u of the voltage during 200 ns will be determining as regards the turn and coil voltages, thus these voltages will be lowered in the proportion of 4/3 to 2
The functioning model characteristic of the invention and described in the example does not change, if instead of parallel cables the wave impedance of the cable or any other connecting means changes at the junction, or if instead of using cables of different lengths the impulse propagating velocity deviates in some cable(s) from those of the other cables of the same group
Claims
1. A connecting means (3, 6, 7, 8) comprised of cables and/or other known types of conductors between a frequency converter (1) and its load (2), the latter being a motor or another electric apparatus, characterized in that the connecting means is constituted by two or more parts connected in series such that at least at one point the two successive parts (6, 7, 8) show different wave impedances.
2. A connecting means (7, 8) comprised of one or more types of parallel conductors between the frequency converter (1) and its load (2), the latter being a motor or another electric apparatus, characterized in that the voltage impulse propagating time in at least one of the parallel conductors (7, 8) deviates from that of the others
3. A connecting means (3, 6, 8) between frequency converter (1 ) and its load (2), the latter being a motor or another electric apparatus, characterized in that the connecting means includes parts connected in series according to both claim 1 and claim 2
4. A connecting means (3, 6, 7, 8) according to claim 1 or 3, characterized in that the first part (6) leaving the frequency converter ( 1 ) shows a higher wave impedance than the successive part (7, 8)
5. A connecting means (3, 6, 7, 8) according to claim 1 or 3, characterized in that the different wave impedances of the various parts (6, 7, 8) are achieved by using two or more parallel conductors (7, 8) at one or more parts of the connecting means (3)
6. A connecting means (7, 8, 6) according to claim 2 or 3, characterized in that the deviating propagation time has been accomplished by using a conductor of different length (7) than those conductors of the same group of parallel connected conductors, which show a different propagation time or times (8).
7. A connecting means (7, 8, 6) according to claim 2 or 3, characterized in that the deviating propagation time has been accomplished by using a conductor (7) of different propagation velocity of the impulse than those conductors of the same group of parallel connected conductors, which show a different propagation time or times (8)
8 A connecting means (3, 6, 7, 8) according to claim 1 or 3, characterized in that the different wave impedances of the various parts are accomplished by using in one or more parts (6) a conductor where the inductance and/or capacitance per unit length deviates from those of another part (7, 8) of the connecting means (3)
9 A connecting means (6, 7, 8) according to claim 7, characterized in that the different propagation velocity of the impulse has been accomplished by using a conductor (7) where the inductance and/or capacitance per unit length deviates from those of another part (8) of the connecting means
10 A connecting means (6, 7, 8) according to claim 2 or 3, characterized in that in a group of parallel conductors only those conductors having the same propagation time (8) are dimensioned to together correspond to the required current load, and that the others (7) are essentially smaller in cross-section
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU34450/97A AU3445097A (en) | 1996-07-08 | 1997-07-03 | A connection means between a frequency converter and its load |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI962778 | 1996-07-08 | ||
| FI962778A FI104394B (en) | 1996-07-08 | 1996-07-08 | Connector structure between drive and its load |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO1998001937A2 true WO1998001937A2 (en) | 1998-01-15 |
| WO1998001937A3 WO1998001937A3 (en) | 1998-02-26 |
Family
ID=8546350
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/FI1997/000438 WO1998001937A2 (en) | 1996-07-08 | 1997-07-03 | A connection means between a frequency converter and its load |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU3445097A (en) |
| FI (1) | FI104394B (en) |
| WO (1) | WO1998001937A2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001039347A1 (en) * | 1999-11-26 | 2001-05-31 | Siemens Aktiengesellschaft | Protective device against overpotential in the terminals of electrical equipment, caused by switching operations |
| CN106786227A (en) * | 2017-03-09 | 2017-05-31 | 东北电力大学 | A kind of rock tunnel(ling) machine service cable extension fixture and operating method |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0473192A2 (en) * | 1990-08-30 | 1992-03-04 | Mitsubishi Denki Kabushiki Kaisha | A circuit for reducing resonance voltage |
-
1996
- 1996-07-08 FI FI962778A patent/FI104394B/en active
-
1997
- 1997-07-03 AU AU34450/97A patent/AU3445097A/en not_active Abandoned
- 1997-07-03 WO PCT/FI1997/000438 patent/WO1998001937A2/en active Application Filing
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0473192A2 (en) * | 1990-08-30 | 1992-03-04 | Mitsubishi Denki Kabushiki Kaisha | A circuit for reducing resonance voltage |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2001039347A1 (en) * | 1999-11-26 | 2001-05-31 | Siemens Aktiengesellschaft | Protective device against overpotential in the terminals of electrical equipment, caused by switching operations |
| DE19957132C1 (en) * | 1999-11-26 | 2001-06-13 | Siemens Ag | Protective device against the overvoltages at terminals of electrical equipment caused by switching processes of a power supply |
| CN106786227A (en) * | 2017-03-09 | 2017-05-31 | 东北电力大学 | A kind of rock tunnel(ling) machine service cable extension fixture and operating method |
| CN106786227B (en) * | 2017-03-09 | 2018-09-07 | 东北电力大学 | A kind of rock tunnel(ling) machine service cable extends device and operating method |
Also Published As
| Publication number | Publication date |
|---|---|
| WO1998001937A3 (en) | 1998-02-26 |
| FI962778A0 (en) | 1996-07-08 |
| AU3445097A (en) | 1998-02-02 |
| FI962778A (en) | 1998-01-09 |
| FI104394B (en) | 2000-01-14 |
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