Once the motor is running at this speed, it will continue to rotate even though single-phase current is flowing through the stator winding. This method of starting is generally not convenient for large motors. Nor can it be employed fur a motor located at some inaccessible spot Figure 3hows single-phase induction motor having a squirrel cage rotor and a single phase distributed stator winding.
Such a motor inherently docs not develop any starting torque and, therefore, will not start to rotate if the stator winding is connected to single-phase a. However, if the rotor is started by auxiliary means, the motor will quickly attain me final speed.
This strange behavior of single-phase induction motor can be explained on the basis of double-field revolving theory. The currents which generated due to this field in rotor be in right side reverse to lift side , the total torque equal zero. Malik It was stated earlier that when the stator of a single-phase induction motor is con heeled to single-phase supply, the stator current produces a pulsating flux that is equivalent to two- constant-amplitude fluxes revolving in opposite directions at the synchronous speed double-field revolving theory.
Each of these fluxes induces currents in the rotor circuit and produces induction motor action. Therefore, a single-phase induction motor can to imagined to be consisting of two motors, having a common stator winding but with their respective rotors revolving in opposite directions. Each rotor has resistance and reactance half the actual rotor values.
Malik A-Split-Phase Induction Motor The stator of a split-phase induction motor is provided with an auxiliary or starting winding S in addition to the main or running winding M. The two windings are so resigned that the starting winding S has a high resistance and relatively small reactance while the main winding M has relatively low resistance and large reactance to be as inductance the current delay with voltage to make shifting current as shown in the schematic connections in Fig.
Consequently, a weak revolving field approximating to that of a 2-phase machine is produced which starts the motor. The starting torque is given by; where k is a constant whose magnitude depends upon the design of the motor. The motor then operates as a single-phase induction motor and continues to accelerate till it reaches the normal speed.
The normal speed of the motor is below the synchronous speed and depends upon the load on the motor. Malik Characteristics i The sinning torque is 2 times the full-loud torque mid lie starting current is 6 to 8 times the full-load current. If the starting period exceeds 5 seconds, the winding may burn out unless the motor is protected by built-in-thermal relay.
This motor is, therefore, suitable where starting periods are not frequent. The power rating of such motors generally lies between 60 W and W. Malik The capacitor-start motor is identical to a split-phase motor except that the starting winding has as many turns as the main winding. Malik possess the same running characteristics because the main windings are identical.
Consequently, for the same starting torque, the current in the starting winding is only about half that in a split-phase motor.
Therefore, the starting winding of a capacitor start motor heats up less quickly and is well suited to applications involving either frequent or prolonged starting periods. Two designs are generally used. This design eliminates the need of a centrifugal switch and at the same time improves the power factor and efficiency of the motor. The smaller capacitor C1 required for optimum running conditions is permanently connected in series with the starting winding.
The much larger capacitor C2 is connected in parallel with C1 for optimum starting and remains in the circuit during starting. Malik synchronous speed. The motor then runs as a single-phase induction motor. The motor then produces a constant torque and not a pulsating torque as in other single- phase motors. Malik The shaded-pole motor is very popular for ratings below 0. Wiring diagrams mainly shows the physical position of components and connections in the built circuit, and not necessarily in logic order.
It emphasizes around the layout in the wires. Schematics emphasize on what circuits work logically. To read a wiring diagram, is actually a program need to know what fundamental elements are included inside a wiring diagram, and which pictorial symbols are widely-used to represent them. The common elements inside a wiring diagram are ground, power, wire and connection, output devices, switches, resistors, logic gate, lights, etc.
A line represents a wire. Wires are utilized to connect the components together. All points along the wire are similar and connected. A black dot can be used to suggest the injunction of two lines. Main lines are represented by L1, L2, etc.
Usually different colors are employed to distinguish the wires. There should be a legend on the wiring diagram to tell you what each color means. Usually circuits exceeding two components have two basic kinds of connections: series and parallel. A series circuit is really a circuit through which components are connected along one particular path, hence the current flows through one aspect of arrive at the next one.
In a series circuit, voltages accumulate for those components connected inside the circuit, and currents are identical through all components. In a parallel circuit, each device is directly coupled to the power source, so each device receives the identical voltage. The current in a parallel circuit flows along each parallel branch and re-combines in the event the branches meet again.
A good wiring diagram should be technically correct and clear to read. Take care of all the info.
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