Repulsion motor

When Repulsionsmotor is a special version of a Einphasenasynchronmotors with the purpose of speed and torque setting, the brush can be adjusted in its position. In the stator, a distributed phase winding is arranged, the anchor is executed as in the case of a DC machine. The rotor circuit is short-circuited by the brushes and the brushes can be mechanically rotated between the short circuit and open circuit position, so as to adjust the speed and torque.

Repulsion are used, among other things, when high, shock-free starting torques are required. For use they were, for example, in early electric locomotives like the French e 3,301th The mechanically complicated design of the adjustable brush they are increasingly being replaced with space vector modulation by robust and cost -phase asynchronous machines in combination with electronic frequency converters. Due to the space vector modulation, a shock -free starting at high load torque is also possible with three-phase asynchronous motors.

Basics

The Repulsionsmotor got its name due to its operational behavior. Repulsion comes from Latin and is derived from the term " repulsus ", which means the recoil of means. Many years had Repulsion the single -phase AC motors as high-performance drives, eg were eligible in electric locomotives. Towards the end of the 19th century there was a series of unsolvable problems in the electrification of the railway.

• DC motors could be good though regulate the speed, but DC did not transfer economically over long distances
• AC motors were robust and reliable, but could not settle into their speed is. In addition, the design of the pantograph was very problematic and costly
• Single-phase AC motors were still very poor efficiency, and there were problems with field distortion at the main poles

For the solution of all these problems the Repulsionsmotor seemed ideal. When they wanted the single-phase series motors could improve technically in the 20th century, the Repulsionsmotor in electric railways was as good as no longer installed, he was ousted as rail engine literally by the single-phase series motor.

Historical Overview

Types of Repulsion

It has already developed a variety of Stromwendermotoren for single phase. From the variety of these developments, two Repulsionsmotorarten have proved and enforced in practice.

• Repulsionsmotor with easy brush set
• Repulsionsmotor dual brush set ( Deri - motor)

Deri engines allow a finely stepped speed adjustment, they also have a slightly higher efficiency than Repulsion with easy brush set. However, almost twice as high maintenance costs to be estimated as in Repulsionsmotor with easy brush set for the Deri - engine due to the higher collector wear and increased wear of the carbon brushes. Larger Deri engines can convert to Repulsion with easy brush set, with smaller Deri engines this is not usually possible.

Construction

The Repulsionsmotor is like any electric motor from the stator (stator) and rotor (rotor). The stator is also referred to as the primary armature and the secondary rotor and the armature. The stand of the Repulsionsmotors is similar in structure to that of the Einphaseninduktionsmotors. In a single-phase stator core is usually evenly spaced slots. Two thirds of the grooves of the main winding (U - V) is, also referred to as a network winding. The remaining third of the grooves is either free or is only partially wound.

The winding of the rotor is constructed as a DC winding. The rotor is thus very similar to a DC armature. The rotor winding is connected to a commutator ( commutator ). The sliding on the commutator carbon brushes, which are not connected to the network are short-circuited. This brush rocker is constructed to be displaceable. Thus, the carbon brushes can be adjusted together. Since the armature is closed in itself, the power can not be supplied directly to the armature winding from the outside.

Repulsionsmotor the commutation is more difficult than with DC motors. Therefore the lamellar voltage, which is lower the tension set between two adjacent slats. For this reason, the number of segments increases. This in turn leads to an increase of the commutator.

When Repulsionsmotor with easy brush set, there are two-pole and four-pole motors. In the two- pole Repulsionsmotor with simple brush set brushes are offset on the adjustable brush bridge by 180 ° and can, for speed control, theoretically shifted by 90 ° to the right or left from the neutral zone. In the four-pole Repulsionsmotor with easy brush set brushes are offset on the adjustable brush rocker at 90 ° and can therefore theoretically in steps of 45 ° (right / left) from the start position ( neutral zone ) to be moved.

With larger motors, the Bürstenverstellvorrichtung is coupled with the switch, which connects the working coil to the network. The switch is mechanically connected to the brush bridge, that the power is only turned on when the brush bridge has reached a position in which the motor can generate a sufficient starting torque. This is necessary to protect the collector from excessive sparking. In order to eliminate the brush fire during the operation, larger motors have a brush-lifting device with integrated short-circuit device. Here, after the starting of the motor, the brushes are lifted and short-circuited rotor windings in itself. However, in this position, the speed can not be changed.

When Deri engine sitting on the commutator shorted two brush sets, each consisting of a fixed and a movable brush. The two stationary brushes are arranged so that they are in the direction of the excitation axis. The moving brushes can be individually adjusted so that one obtains the same operating conditions ( rotation direction change and speed adjustment ) as in Repulsionsmotor with easy brush set. Because of the two individually adjustable brush the theoretical displacement angle is always twice as large as in the simple Repulsionsmotor. This gives a finely stepped speed adjustment.

The rotor and the stator are not electrically connected to each other in Repulsion.

Operation

Taking the network coil into an AC voltage, a current flows through the coil and produces a magnetic alternating field. This stand alternating field passes through the rotor and induces a voltage in the rotor coils. Through the brushes of the bridge circuit is closed, armature current flows.

The height of the rotor current and the position of the rotor field are dependent on the position of the brush bridge. The inductive coupling ( transformer coupling ) between the stator and rotor works with Repulsion is basically the same as with other induction motors. Therefore Repulsion may be connected to an alternating current.

Performance

When Repulsionsmotor there in terms of the operating performance of three different brush settings:

• Idle position
• Operating position

Idle position

Here is the short-circuited brushes bridge in the neutral zone. The connecting line of the brush is perpendicular to the axis of the stator field. Although the magnetic field passes through the rotor winding in the idling position, no voltage is induced and therefore no rotor current flowing in a coil because no voltage can be induced, if the axis of which is perpendicular to a magnetic alternating field. This neutral position is also called start-up position. From the network, only a small idle current is drawn from the stator winding.

The Repulsionsmotor thus behaves in the neutral position as the single-phase starter motor.

When Deri engine stand in the start position, the movable brush right next to the stationary brushes, each brush bridge (A or B next to next to A1 B1).

If you move the brush from the neutral position, so you can reach the short-circuit zone ( short position). The short position is reached when two-pole motor with dual brush set brushes with a rotation of 180 ° and the two-pole motor with easy brush set brushes with a rotation of 90 °. Here then are the brush in the direction of the stator field.

In the short position, the Repulsionsmotor behaves like a short-circuited transformer. In runners, a very large current now flows. The force generated by the stator field and the rotor field acts in the direction of the wave. The motor effect stops and the motor is in spite of the large rotor current from no torque, the rotor remains stationary. If you were the runners leave some time in the short-circuit zone, then the engine will be damaged due to the high rotor currents. So that this can not happen in the operation, reaching the short position is prevented by a mechanical stop. Also, the engine starting from the short position is avoided to prevent the large inrush currents.

Operating position

If the brush is rotated from the short position or from the start position to the right or left to the operating position, have rotor field and the stator field different layers. In the armature coils a voltage is induced, which is normally 10 to 15 volts. The voltage is at most at 60 volts. About the brush bridge flows in the rotor circuit rotor current one, it creates a magnetic field runner. Since the two fields are eager to accept the same direction, the rotor turns, depending on the brush adjustment around the right or left.

When you move the brush rocker from the start position, there is a shift of the rotor currents corresponding to the motor control. A shift of the brush rocker to the left causes a clockwise rotation of the rotor. In order to obtain a change in direction to the left, the brush bridge must be turned opposes. The magnetic axis of the rotor behaves when Repulsionsmotor different from the magnetic axis of the induction motor, it is stationary in space. The magnetic axis can be changed only by the adjustable brushes.

When the rotor rotates, is cut from the coil sides of the rotor winding, the magnetic field of the rotor. Through this cutting the Statormagnetfeldlinien produced in the rotor voltage, which counteracts the armature current. This caused decrease of both the rotor current and the stator current. The fall of the current, the torque is smaller. If the motor is idling, the speed increases with decreasing torque on more and more. In contrast, the speed of the rotor goes back under load. The magnitude of the torque and its direction are thus dependent on the position of the brushes. In the operating position the brush rotor field and the stator field have another one convenient location. This also has both fields are very strong. Therefore, the extract has a large Repulsionsmotor moment in the operating position.

This performance is called a series-wound character, it is for all single-phase Stromwendermotoren a typical performance.

The power factor is strongly dependent on the speed at Repulsion. Less than the synchronous speed, the power factor becomes better; over synchronous speed he is getting worse. Is changed, the power factor by short-circuit currents caused by the carbon brushes at bridging the rotor coils. Since it comes with over synchronous speed in huge sparks between the brushes and collector ( brush fire ), larger super-synchronous speeds during operation should be avoided.

When Deri engine only a brush bridge is adjusted as a rule, the other brush bridge is allowed to stand in the neutral zone. This dual leadership of the collector to obtain a much better approximation of the field excitation curve at the optimal sinusoidal shape. Thus, the efficiency of the Deri engines increase.

Braking

When Repulsionsmotor can be achieved by a suitable brush adjustment any braking achieve. If the motor when running in the opposite direction, he works as a brake for the driven machine. Depending on the wiring of the motor operates either as a counter- current brake or regenerative braking. The regenerative braking is possible even at low speed. Thus, the motor acts as a generator and feeds energy back into the grid.

Internal structure ( schema table )

The rotor of the Repulsionsmotors attempts at oblique brush position to the position with the least mutual induction, the neutral position, move back. After sufficient angle of rotation of the commutator shifts the short-circuit point, thus the rotor rotates continuously.

Pros and Cons

• High torque
• Bumpless start
• Simple speed control and direction of rotation
• Low Beschaltungsaufwand
• Robust
• Finely speed control is possible, for example, when Deri engine

• 3 to 4 times higher inrush currents than in the single-phase series motor
• Tends idle runaway
• Low efficiency
• Strong reactive current load in the network
• Wear of carbon brushes and the collector ( high-maintenance )
• Strong brush fire

Areas of application

Wherever a shock-free but powerful restart is required, the Repulsionsmotor can be used. The use in small and medium power range is quite reasonable. In the high power range of the engine could not be maintained due to its disadvantages, in particular the high maintenance costs.

Is used among other things in the Repulsionsmotor mills, printing machines, textile manufacturing, cranes, grinders, honey extractors and in automation technology.

Standards and regulations

• EN 60 034 Part 1 General requirements for rotating electrical machines
• EN 60 034 Part 8 Terminal markings and direction of rotation for electrical machines
• DIN IEC 34 Part 7 types rotating electrical machines