What is a single-phase repulsion motor? Also write several single-phase motor applications?

A motor is an electrical device that converts the electrical input into mechanical output, where the electrical input can be in the form of current or voltage and the mechanical output can be in the form of torque or force. The motor consists of two main parts, namely, the stator and the rotor, where the stator is a stationary part of the motor and the rotor is a rotating part of the motor. A motor that works on the repulsion principle is known as a repulsion motor, where repulsion occurs between two magnetic fields of the stator or rotor. Repulsion motor is a single-phase motor.

What is the repulsion type motor?

Definition: A repulsion motor is a single-phase electric motor that operates by supplying incoming AC (alternating current). The main application of the repulsion engine is electric trains. It starts as a repulsion motor and functions as an induction motor, where the starting torque must be high for the repulsion motor and with very good operating characteristics for the induction motor.

Construction of Repulsion Motor

It is a single-phase AC motor, consisting of a pole core that is the north pole and the south pole of a magnet. The construction of this motor is similar to the split-phase induction motor and the DC series motor. The rotor and the stator are the two main components of the motors that are inductively coupled. The field winding (either a distributed type winding or the stator) is similar to the main winding of the split-phase induction motor. Therefore, the flow is evenly distributed and the space between the stator and the rotor decreases and the reluctance also decreases, which in turn improves the power factor.

The rotor or armature is similar to the DC series motor, which is provided with a drum-type winding connected to the commutator, where the commutator is in turn connected to short-circuit carbon brushes. A brush holder mechanism provides a variable crankshaft to change the direction or alignment of the brushes along the axis. Therefore, the torque produced during this process helps to control speed. The energy in the repulsion motor is transferred by the action of the transformer or by the induction action (where the emf is transferred between the stator and the rotor).

Repulsion Motor Image Source- Google

Principle of work

The repulsion motor works on the principle of repulsion, where two poles of a magnet repel each other. The working principle of the repulsion motor can be explained from 3 cases of α, depending on the position of the magnet as follows.

Case (i): When α = 90 Degrees

 

Suppose that the 'C and D' brushes are aligned vertically at 90 degrees and the rotor is horizontally aligned along the d axis (field axis), which is the direction of the current flow. From the principle of Lenz's law, we know that the induced emf depends mainly on the flow of the stator and the current direction (which is based on the alignment of the brushes). Therefore, the net emf resulting from the brush from 'C to D' is '0', as shown in the diagram, which is represented as 'x' and '.', There is no current flow in the rotor, therefore Ir = 0. When no current passes through the rotor, so it acts as an open circuit transformer. Therefore, the stator current is = less. The direction of the magnetic field is in the direction of the brush axis, where the axis of the stator and rotor field has a 180-degree phase shift, the torque generated is '0' and the mutual induction induced in the motor is '0'.

Case (ii): When α = 0

 

The 'C and D' brushes are now oriented along the d axis and are short-circuited. Therefore, the net emf induced in the motor is very high, which generates the flow between the windings. The liquid emf can be represented as 'x' and '.', As shown in the figure. It is similar to a short-circuit transformer. Where the stator current and mutual induction are maximum, which means Ir = Is = maximum. From the figure, we can see that the fields of the stator and rotor are 180 degrees opposite in phase, which means that the generated torque will oppose so that the rotor cannot rotate.

Case (iii): When α = 45 When brushes 'C and D' are tilted at some angle (45 degrees) and the brushes are shorted. Let's assume that the rotor (brush axis) is fixed and the stator is rotated. The stator winding is represented as the number of 'Ns' of effective turns and the current passage is 'Is', the field produced by the stator is in the 'Is Ns' direction, which is the MMF of the stator, as shown in the figure. The MMF (magnetomotive force) is solved in two components (MMF1 and MMF2), where MMF1 is together with the brush direction (Is Nf) and MMF2 is perpendicular to the brush direction (Is Nt), which is the direction of the transformer, and 'α' is the angle between 'Is Nt' and 'Is Nf'. Therefore, the flow produced by this field in two components is 'Is Nf' and 'Is Nt'. The rotor-induced emf produces flow along the q axis.

The field produced by the rotor along the brush axis is mathematically represented as follows 

 É Nt = É Ns cos α ……… .. 1 

 Nt = Ns Cos α ………… 2 

 Nf = Ns Sin α ………… 3 

Repulsion Engine Classification 

There are three types of repulsion engines: Plywood Type It consists of an additional winding, that is, a compensation winding and an additional pair of brushes are placed between the brushes (short-circuited). The compensation winding and a pair of brushes are connected in series to improve the power and speed factors. A compensated type motor is used where high power is needed at the same speed. Compensated type repulsion motor offset type repulsion engine Induction type of onset of repulsion It starts with the coil repulsion and runs with the induction principle, where the speed is kept constant. It has a single stator and rotor similar to the DC armature and a switch, in which a centrifuge mechanism causes a short circuit in the switch bars and has higher torque (6 times) than the current in the load. The repulsion operation can be understood from the graph, that is, when the frequency of the synchronous speed increases, the percentage of the total torque load begins to decrease, where at one point the magnet poles experience a repulsive force and pass to the induction mode. Here we can see the load that is inversely proportional to the speed. Repulsion-Start-Induction-Motor Chart repulsion-start-induction-motor-graphic Repulsion type It works with the principle of repulsion and induction, which consists of a stator winding, 2 winding rotors (where one is a squirrel cage and the other is a direct current winding). These windings are shorted for the commutator and two brushes. Operates in a condition where the load can be adjustable and whose initial torque is 2.5  to 3. 

Repulsion type like repulsion Benefits 

The advantages are The high value of the initial torque Speed ​​is not limited By adjusting the value of 'α', we can adjust the torque, where we can increase the speed based on the torque adjustment. By adjusting the position brushes, we can control torque and speed easily. 

Disadvantages 

The disadvantages are Speed ​​varies with load variation The power factor is less, except at high speeds The cost is high High maintenance. 

Forms Applications are They are used where starting torque is required with high-speed equipment Coil reels: where we can adjust the speed flexibly and easily and the direction can also be changed by reversing the direction of the brush axis. 

1. Toys 

2. Elevators, etc. 

Since the magnetic axis 'T' and the brush axis coincide with the MMF rotor that is along the brush axis it is equal to the flow generated by the stator.