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SINGLE-PHASE MOTORS

 

INTRODUCTION

Single-phase AC motors area unit the foremost common motors engineered. Every home, workshop, and vessel has them. Since there’s such a large form of these motors, it’s not possible to explain all of them. This chapter can describe the foremost common varieties found on Army watercraft. Figure 17-1 shows the fundamental schematic diagrams for the single-phase motors.

The basic diagram (view A) shows a circle with 2 leads labeled  T1 and T2. even as within the three-phase motor diagram, the motor shows the ability offer lines as being known with the T. for many shore facility applications, this is often the case. In several cases, the single-phase motors on board a ship are wired into the lighting distribution panels. The lighting distribution panels area unit the supply for single-phase power offer. the ability distribution panels area unit the supply of the three-phase power offer. For this reason, the single-phase motors area unit ordinarily connected to L1 and L2, as shown in Figure 17-2.

Figure 17-1 shows four single-phase motor diagrams. Diagram A shows the motor because it are seen on blueprints and general layouts. it’s involved solely with the general operation of the electrical distribution system. Diagrams B and C show a additional concerned internal wiring system indicating 2 inductors and 3 terminals. These diagrams area unit necessary to grasp the precise nature and performance of the single-phase motor. Refrigeration and manufacturer’s wiring schematics conjointly use diagrams B and C to make sure a positive troubleshooting application. Figure 17-3 shows a awfully basic one-line diagram — of the single-phase motor. Refer back to the present diagram because the operational needs of the single-phase motor area unit mentioned. The single-phase induction motor is far constant in construction because the three-phase motor. Some single-phase induction motors are known as cage motors as a result of the rotor’s similarity to a circular animal exercise wheel. As mentioned in Chapter sixteen, the cage contains the bars and shorting-rings that form up the rotor windings. The cage is additionally thought of the secondary windings of the motor (Figure 17-4).

INDUCTION MOTORS Despite the actual fact that the three-phase motor has additional phases than the single-phase motor, the singlephase motor may be a way more complicated machine. many extra elements area unit necessary to control the single-phase motor. Single-phase motors have solely 2 power supply offer lines connected. The single-phase motor will operate off either the A-B, B-C, C-A, A-N, B-N, or C-N power supply phases. The twowire power offer will offer solely a single-phase alternating supply (Figure 17-5). The individual single-phase current incoming within the mechanical device winding of the single-phase motor doesn’t have constant “revolving” result that the 3 individual phases of the three-phase power offer provides. The field of force developed by the single-phase current is made within the mechanical device windings and so is gone. a whole cycle should be completed before current is once more offered at the single-phase motor stat or. This prevents the event of the revolving field thus simply obtained with the threephase power offer. the matter with the singlephase motor is its inability to develop a revolving field of its own accord. while not a revolving field, force can not be developed, and also the rotor can ne’er flip. With just one mechanical device winding, the single-phase motor will solely manufacture associate oscillatory field of force.

Figure 17-6 shows a main winding separated into 2 coils. every winding is wound in a very completely different direction. The importance of the 2 completely different coil winding directions is to stress the applying of the left-hand rule for coils as expressed in previous chapters. By winding the wire in a very completely different direction, the polarity of the coil face nearest to the rotor will be modified. By exploitation one wire wrapped in 2 completely different directions, the polarity of each alternative coil will be modified.

When current flows within the main winding, the field of force is established throughout the windings (Figure 17-6). before long this flow stops and changes direction (Figure 17-7). With amendment|this alteration|this modification|this variation|this transformation} in current direction comes a change altogether the coil polarities. The field of force of the rotor is developed through induction within the same manner as delineated  for the three-phase induction motor rotor. The rotor bars and also the shorting rings have associate elicited electrical phenomenon created in them, and a current flow develops. This current flow establishes a field of force of associate opposite polarity of the stator directly across from it. sadly, there are not any overlapping 120-degree individual mechanical device windings during this single-phase motor.

Whenever current changes direction and a brand new field of force is established within the mechanical device, the elicited rotor field of force changes to the other polarity of the stator directly across from it. All the rotor will do is oscillate. while not some force to twist or flip the rotor, no force will be developed. an individual examining this motor can hear a definite hum. this is often known as associate AC hum. it’s typically detected coming back from transformers or single-phase motors that don’t seem to be turning. If the soldier physically turned the axis of rotation (not recommended) in either direction, the rotor would begin to maneuver. The speed would still increase till it reached its traditional in operation speed. NOTE: though sure motors, like fans, will be found to be started physically by turning the axis of rotation, this action isn’t suggested. Whenever a motor doesn’t begin of its own accord, it’s as a result of one thing is wrong. If the motor has associate electrical malfunction, it’s not knowing bit the electrical elements once current is applied.

As long because the rotor’s force field is slightly displaced from the force field within the stator coil, a torsion is developed. Slip can keep the rotor’s field slightly behind the stator’s field. The distinction in speed (relative motion) is critical to take care of the torsion. Relative motion is critical to induce the voltage into the rotor to take care of the rotor’s force field. If the soldier disconnects power and permits the rotor to prevent, he once more should offer the initial movement to start out the rotor. this can be not an appropriate condition for a motor. while not the utilization of a three-phase AC, a synthetic part displacement should be established. If the stator coil might solely develop another current, slightly out of part from the first current, a revolving field might be assimilated. this can be the matter encountered by single-phase induction motors. it’s additionally the world of greatest part failure and maintenance necessities, In fact, the precise names for induction motors represent the suggests that during which the revolving field is developed from a single-phase power supply. There area unit a large number of single-phase motor mixtures. This text can discuss solely 5 basic designs: Split-phase (resistance-start). Capacitor-start. Permanent-capacitor. Two-capacitor. Shaded-pole. Single-Phase Motor beginning additionally to the run or main winding, all induction single-phase motors area unit equipped with AN auxiliary or begin winding within the stator coil. The auxiliary or begin winding overlaps the most or run winding. This provides the revolving field necessary to show the rotor. The terms area unit employed in sets. The frost cluster is that the run and begin set. The second cluster is that the main and auxiliary winding set. every cluster includes a common terminal association. Run and begin Winding Set. The term “run winding” is employed to designate a winding that receives current all the time the motor is operative. it’s the outer winding, placed next to the motor housing. The term “run” is employed only the opposite winding may be a begin winding. A begin winding is in parallel with the run winding. the beginning winding receives current solely throughout the initial beginning amount. Then it becomes disconnected from the facility supply. the beginning winding is that the set of coils placed nearest to the rotor (Figure 17-8).

Main and Auxiliary Winding Set. The term “main winding” is employed to designate a winding that receives current all the time the motor is working. the most winding is found next to the motor housing. The term “main” is employed only the opposite winding is AN auxiliary winding. AN auxiliary winding receives current all the time the motor is working. it’s perpetually in parallel with the most winding. The auxiliary coils area unit placed nearest to the rotor. By making a winding with higher insulating properties and a motor housing with higher cooling qualities, the auxiliary winding will stay within the circuit as long because the main winding. This then will increase the motor’s running load capabilities. Common association. The auxiliary or begin winding is connected to the most or run winding through a association referred to as the common. The auxiliary or begin winding is in parallel with the most or run winding (Figure 17-9). each the windings within the motor use identical single-phase power supply. The common association between the set of windings is critical to finish the closed circuit.

You can watch the following video or read the written tutorial below.