Repulsion motor

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The repulsion motor is a special design of a single-phase asynchronous motor in which the position of the brushes can be adjusted for speed and torque adjustment. In the stator , a distributed single-phase winding is arranged, the anchor is like a direct current machine run. The rotor circuit is short-circuited via the brushes and the brushes can be rotated mechanically between the short-circuit and no-load position in order to set the speed and torque.

Repulsion motors are used, among other things, when high, shock-free starting torques are required. They were used z. B. in early electric locomotives like the French E 3301 . Due to the mechanically complex structure of the adjustable brushes, they are increasingly being replaced by robust and inexpensive three-phase asynchronous machines in combination with electronic frequency converters with space vector modulation . Thanks to the space vector modulation, three-phase asynchronous motors can start up smoothly at high load torques .

Repulsion motor

Basics

Repulsion motor standard symbol

The repulsion motor got its name because of its operating behavior. Repulsion comes from Latin and is derived from the term repulsus , which means something like repulsion . For many years repulsion motors were the only single-phase AC motors that were used as high-performance drives , e.g. B. in electric locomotives were suitable. Towards the end of the 19th century, the electrification of the railroad had a number of insoluble problems:

  • The speed of DC motors could be controlled well, but DC voltage could not be transmitted economically over long distances.
  • Three-phase motors were robust and reliable, but their speed could not be controlled. In addition, the construction of the pantographs was very problematic and costly.
  • Single-phase AC motors still had very poor efficiency levels, and there were also problems with field distortion at the main poles.

The repulsion motor seemed ideally suited to solving all these problems. In the 20th century, the single-phase series motors were technically improved and the repulsion motor was hardly installed in electric railways . It was literally replaced as a rail engine by the single-phase series motor.

historical overview

Historic 10-pole Déri repulsion motor of the Midi E 3301 electric locomotive
  • 1887 Elilu Thompson invents the forerunner of the repulsion motor.
  • 1892 E. Arnold designed the first repulsion motor, which, however, could not be operated continuously (too strong brush fire ).
  • 1894 Maschinenfabrik Oerlikon builds a repulsion motor with a short circuit device and a combined brush lifting device.
  • 1897 The engine developed by the Oerlikon machine factory is manufactured by Wagner Elektro Mfg. Co produced with great success in the USA .
  • 1898 Miksa Déri uses the advantages of the repulsion motor known as the "Wagner motor" and designs an induction motor that starts up as a repulsion motor .
  • 1904 the Viennese engineers Gabriel Winter and Friedrich Eichberg develop a combination of repulsion motor with a series motor, the Winter-Eichberg motor, at the AEG company in Berlin .
  • 1905 Miksa Déri develops a repulsion motor with two sets of brushes, the Déri motor , and introduces it to the professional world.
  • 1913 the Rhaetian Railway procures seven locomotives equipped with repulsion engines ( RhB Ge 2/4 ), two of which are still largely in their original condition today.

Types of repulsion motors

A large number of commutator motors for single-phase alternating current have already been developed. From the multitude of these developments , two types of repulsion motors have proven themselves and established themselves in practice. There are repulsion motors with a single brush set and repulsion motors with a double brush set (Déri motor).

Déri motors allow the speed to be set more finely , and they are also somewhat more efficient than repulsion motors with a simple brush set. However, due to the higher commutator wear and the increased wear of the carbon brushes, maintenance costs for the Déri motor are almost twice as high as for the repulsion motor with a simple brush set. Larger Déri motors can be converted into repulsion motors with a simple set of brushes; this is usually not possible with smaller Déri motors.

construction

Like every electric motor , the repulsion motor consists of the stator ( stator ) and the runner ( rotor ). The stator is also known as the primary armature and the rotor as the secondary armature. The stator of the repulsion motor is constructed in a similar way to that of the single-phase induction motor. In the stator core, there is a single-phase winding in mostly evenly spaced slots. Two thirds of the slots are occupied by the working winding (U - V), which is also known as the network winding. The remaining third of the grooves either remain free or are only partially wound.

The winding of the rotor is constructed like a direct current winding. The rotor is therefore very similar to a DC armature. The rotor winding is connected to a commutator ( commutator ). The carbon brushes sliding on the commutator , which are not connected to the mains , are short-circuited. This brush bridge is designed so that it can be moved. This means that the carbon brushes can be adjusted together. Since the armature circuit is self-contained, the current cannot be supplied to the armature winding directly from the outside.

The reversal of current is more difficult with the repulsion motor than with DC motors. Therefore the lamella tension , that is the tension between two adjacent lamellas, is chosen to be lower. For this reason, the number of lamellas increases. This in turn leads to an increase in the number of commutators.

The repulsion motor with a simple brush set has two-pole and four-pole motors. In the case of the two-pole repulsion motor with a simple set of brushes, the brushes are offset by 180 ° on the adjustable brush bridge and can theoretically be moved 90 ° to the right or left out of the neutral zone for speed control. In the four-pole repulsion motor with a simple set of brushes, the brushes are offset by 90 ° on the adjustable brush bridge and can therefore theoretically be moved 45 ° (right / left) from the start-up position (neutral zone ).

Two-pole derimotor
Four-pole deri motor

With larger motors, the brush adjustment device is coupled to the switch that connects the working winding with the mains. The switch is mechanically connected to the brush bridge in such a way that the mains is only switched on when the brush bridge has reached a position in which the motor can develop sufficient starting torque. This is necessary to protect the collector from excessive brush fire . In order to eliminate the brush fire during operation, larger motors have a brush lifting device with an integrated short-circuit device . Here, after the motor has started, the brushes are lifted and the rotor windings are short-circuited. However, the speed cannot be changed in this position .

In the Déri motor, there are two short-circuited brush sets on the commutator, each consisting of an immovable and a movable brush. The two immovable brushes are arranged so that they are in the direction of the excitation axis. The moving brushes can be adjusted individually so that the same operating conditions ( change in direction of rotation and speed adjustment) are obtained as with the repulsion motor with a simple set of brushes . Due to the two individually adjustable brushes, the theoretical displacement angle is twice as large as with the simple repulsion motor. This gives you a finer speed setting.

The rotor and the stator are not galvanically connected to each other in repulsion motors .

Mode of action

If the mains winding is connected to an alternating voltage, a current flows through the coil and an alternating magnetic field is created. This alternating stator field penetrates the rotor and induces a voltage in the armature coils. The circuit is closed via the brush bridge, a rotor current flows.

The height of the rotor current and also the position of the rotor field depend on the position of the brush bridge. The inductive coupling ( transformer coupling ) between the stator and the rotor works in principle in the same way with repulsion motors as with other induction motors. Therefore repulsion motors may only be connected to AC voltage .

Operating behavior

The repulsion motor has three different brush settings with regard to the operating behavior:

Idle position
  • Idle position
  • Short-circuit position
  • Operating position

Idle position

The short-circuited brush bridge is in the neutral zone. The line connecting the brushes is perpendicular to the axis of the stator field. Although the magnetic field penetrates the rotor winding, no voltage is induced in the idle position and thus no rotor current flows, because no voltage can be induced in a coil if its axis is perpendicular to an alternating magnetic field . This idle position is also called the start-up position. Only a small no-load current is drawn from the network by the stator winding.

The repulsion motor behaves like the single-phase starter motor in the idle position.

In the start-up position of the Déri motor, the movable brushes are directly next to the immovable brushes, the respective brush bridge (A next to A1 or B next to B1).

Short-circuit position

Short-circuit position

If you move the brushes out of the idle position, you reach the short-circuit zone (short-circuit position). The short-circuit position is reached with a two-pole motor with a double set of brushes when the brush is rotated by 180 ° and with a four-pole motor with a single set of brushes when the brush is rotated by 90 °. The brushes are then in the direction of the stator field.

In the short-circuit position, the repulsion motor behaves like a short-circuited transformer . A very large current now flows in the rotor . The force generated by the stator field and rotor field acts in the direction of the shaft. The motor action ceases and the motor does not deliver any torque despite the large rotor current, the rotor remains stationary. If the rotor were to be left in the short-circuit zone for a longer period of time, the motor would be damaged due to the high rotor currents. A mechanical stop prevents this from happening during operation. In addition, to avoid the large inrush currents to start the engine prevented from shorting position.

Operating position

Operating position in clockwise rotation
Operating position in left-hand rotation

If the brushes are turned from the short-circuit position or from the start-up position to the right or left into the operating position, the rotor field and the stator field have different positions. A voltage is induced in the rotor windings, which is normally between 10 and 15 volts . The maximum voltage is 60 volts. A rotor current flows through the brush bridge in the rotor circuit, creating a rotor magnetic field. Since the two fields strive to assume the same direction, the rotor rotates to the right or left depending on the brush adjustment.

When moving the brush bridge from the start-up position, the rotor currents are shifted according to the motor rule. Moving the brush bridge to the left causes the rotor to turn to the right. To change the direction of rotation to the left, the brush bridge must be turned in the opposite direction. The magnetic axis of the rotor behaves differently in the repulsion motor than the magnetic axis in the asynchronous motor, it stands still in space. The magnetic axis can only be changed by adjusting the brushes.

When the rotor rotates, the magnetic field of the rotor is cut by the coil sides of the rotor winding . This cutting of the stator magnetic field lines creates a voltage in the rotor that counteracts the rotor current. As a result, both the rotor current and the stator current decrease. As the current drops, the torque becomes smaller. If the engine is idling, the speed increases more and more as the torque decreases. On the other hand, the speed of the rotor decreases under load. The size of the torque and its direction are therefore dependent on the position of the brushes. When the brushes are in the operating position, the rotor field and the stator field are in a favorable position relative to one another. In addition, both fields are very strong here. This is why the repulsion motor has a large pull-out torque in the operating position.

Operating characteristic with a fixed brush position

This operating behavior is called a series connection , it is a typical operating behavior for all single-phase commutator motors.

In repulsion motors, the power factor is strongly dependent on the speed. At subsynchronous speed the power factor is better; at over synchronous speed it gets worse. The power factor is changed by short-circuit currents that arise when the rotor coils are bridged by the carbon brushes. Since there is strong spark formation between the brush and collector (brush fire) at oversynchronous speeds, greater oversynchronous speeds should be avoided as far as possible during operation.

With the Déri motor, only one brush bridge is usually adjusted, the other brush bridge is left in the neutral zone. This double guidance of the collector results in a significantly better adjustment of the field exciter curve to the optimal sinusoidal shape . This increases the efficiency of the Déri motors.

braking

With the repulsion motor, any braking can be achieved by means of a suitable adjustment of the brushes. If the motor is driven in the opposite direction while running, it works as a brake for the driven machine. Depending on the interconnection, the motor works either as a countercurrent brake or as a regenerative brake . Regenerative braking is also possible at low speeds. As a result, the motor acts as a generator and feeds energy back into the grid .

Internal structure (schematic)

With the brush position inclined, the rotor of the repulsion motor tries to move back into the position with the lowest mutual induction, the idle position. After a sufficient angle of rotation, the commutator shifts the short-circuit point, so the rotor turns continuously.

Left: idle position
Right: operating position

Advantages and disadvantages

advantages
  • high tightening torque
  • smooth start
  • simple speed control and reversal of direction of rotation
  • low wiring effort
  • robust
  • Fine speed control possible, e.g. B. the Déri engine
disadvantage

Areas of application

The repulsion motor can be used wherever a smooth but powerful start-up is required. The use in the small and medium power range makes perfect sense. In the high-performance range, the engine could not hold its own due to its disadvantages, particularly the high maintenance requirements.

The repulsion motor is used, among other things, in spinning mills , printing machines , machines for textile production, crane systems , grinding machines , honey extractors and in automation technology .

Standards and regulations

  • EN 60 034 Part 1 General provisions for rotating electrical machines
  • EN 60 034 part 8 Terminal designations and direction of rotation for electrical machines
  • DIN IEC 34 Part 7 Types of rotating electrical machines

literature

  • Otto Lueger: Lexicon of the entire technology and its auxiliary sciences . tape 9 . Stuttgart, Leipzig.
  • Repulsion motor . Meyers Lexikononline 2.0. Bibliographisches Institut & FA Brockhaus A6, 2007.

Individual evidence

  1. ↑ a b c d e f g h i j k l Günter Boy, Horst Flachmann, Otto Mai: The master's degree in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg, 1983, ISBN 3-8023-0725-9 .
  2. ^ The dictionary of foreign words . German book community CA Koch's publishing house Darmstadt .
  3. ↑ PONS Latin-German dictionary for schools and studies . Klett-Verlag, ISBN 3-12-517552-6 .
  4. ^ Christoph Cramer: Project locomotive 205.
  5. ^ Kramer, Christoph in Eisenbahn & Nostalgie, Die Motorentechnik series . 1999 - 2007 (last accessed on February 29, 2012).
  6. ^ Rudolf Richter: Electrical machines. Fifth volume, commutator machines for single- and multi-phase alternating current rule sets, Springer Verlag Berlin-Heidelberg GmbH, Berlin 1950, pp. 136–144.
  7. ↑ a b c d e f g h i j k A. Senner: Electrical engineering. 4th edition. Verlag Europa-Lehrmittel, 1965.
  8. ↑ a b Herbert Kyser: The electric railways and their operating resources. Printed and published by Friedrich Vieweg and Son, Braunschweig 1907.
  9. ↑ Herbert Kyser: The electric power transmission. First volume, third edition, published by Julius Springer, Berlin 1930.
  10. ^ F. Niethammer: The electric railway systems of the present . Published by Albert Raustein, Zurich 1905.

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