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# 1phase induction motors

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### 1phase induction motors

1. 1. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus            Theory “ 1ph Motors” Its basically used in home appliances, shops, offices etc. It is true that 1ph motors are less efficient than 3ph motors. 3ph power is normally not available except in large commercial and industrial use. 1phase motors are less efficient than 3phase motors. 1phase motors are not self starting. Alternating magnetic flux cannot move the rotor because of no rotational torque. Single phase motors produced only alternating flux which is not rotating type. The field polarity reverses after each half cycle but the field does not rotate. Consequently, alternating flux cannot produce rotation in a stationary squirrel-cage rotor. However, if the rotor of a single phase motor is rotated in one direction by some mechanical means, it will continue to run in the direction of rotation. The rotor quickly accelerates until it reaches a speed slightly below the synchronous speed. Once the motor is running at this speed, it will continue to rotate even though 1ph current is flowing through the stator winding. Types of single phase motors: Single phase motors are generally built in the fractional horsepower range. As a 1ph I.M. has no inherent starting torque and therefore special means must be used to make it self starting.  There are 4 types / methods: Single phase Induction Motor a) Split Phase Type b) Capacitor Type c) Shaded pole type  A.C. Series motor or Universal motor  Repulsion Motors I. Repulsion start induction run motor II. Repulsion Induction motor  Synchronous Motors A. Reluctance motor B. Hysteresis motor Single phase Induction motor: 1phase motors works only on 1phase power supply.  1ph motor is similar to a 3phase squirrel cage induction motor except that the stator has distributed 1ph winding. Basic Construction of 1phase I.M. : Rotor:- A rotating cylindrical part is called as Rotor.  Stator:- A stationary part is called as Stator. → The single phase stator winding produces a magnetic field that pulsates in strength in a sinusoidal manner. Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in
2. 2. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus → The field polarity reverses after each half cycle but the field does not rotate. → Consequently, the alternating flux cannot produce rotation in a stationary squirrel cage rotor. → If the rotor of 1phase motor rotates by applying some mechanical force then rotor rotates and quickly accelerates upto below the synchronous speed. → When it reached synchronous speed then motor runs continuously after receiving 1phase. → Hence, 1phase motor is not self starting. → To make a single phase motor self-starting then we have to produce a revolving stator magnetic field. → This can be achieved by converting a single phase supply into two phase supply through additional winding. → After getting sufficient speed, this additional winding removed depending upon type of motor. → Single phase motor can be classified as, 1) Split phase motors – started by starting winding/ auxiliary winding 2) Capacitor motors – started by starting winding and capacitor. 3) Shaded pole motors – motion of magnetic field produced by means of a shading coil around a portion of the structure. 1) Split phase Induction motors:- Introduction: 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 starting winding is located 90 degree electrical from the main winding.  This main winding operates during the brief period when the motor starts up.  Starting winding has high resistance and relatively small reactance.  Main winding has low resistance and relatively high reactance.  Consequently, there is 25 to 30 degree phase shift between two windings. Construction of Split Phase Induction Motor:→ Stator – it is made up of silicon steel. Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in
3. 3. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus → → → → → → Stator having slots in which two windings are kept. There are two windings called running (Main) winding & Starting winding. Running Winding is with high reactance & low resistance. Starting winding is with high resistance & low reactance. Rotor :- It is a cylindrical structure having bars in the slots. Rotor is made up of silicon steel and rotor windings are round copper bars embedded in the rotor slots and permanently short circuited. → Centrifugal switch is connected in series with starting winding. → Starting winding is located 90 degree electrical from the main winding and operates only during the brief period when the motor starts up. Working of Split Phase Motor:→ When an a.c. supply is given to the motor then current splits into two parts say I m and I S → I m is flowing through main winding and I S is flowing through starting winding. → I m is lags by greater angle due to more inductive & I S is lags by smaller angle due to less inductive. → Since, main winding is made highly inductive while the starting winding highly resistive, the currents have reasonable phase angle  (   25 to   30 ) → Main windings creates flux m & Starting winding creates flux S → Both the flux having phase angle difference which set up r.m.f. → Due to r.m.f., rotor starts rotating. → Starting Torque = TS  k.I m .I s . sin  → When the rotor speed reaches 70-80% of the normal speed then centrifugal switch is operated. → Centrifugal switch disconnected electrically from the circuit. → Motor runs continue till power on. → Hence, it is also called as Resistance Start Induction Run Motor. D.O.R:- (Direction Of Rotation)  DOR can be changed by interchanging the connection of either starting winding or running winding but not both the winding. Application a. Small machine tools b. Duplicating machines c. Oil burners 2) Capacitor Motors:Capacitor motors started by two phase motor action through the use of an auxiliary winding and capacitor.  Capacitor Motor :1) Capacitor Start Motor 2) Capacitor Start – Capacitor Run Motor 3) Permanent Capacitor Motor Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in
4. 4. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus a) Capacitor Start Induction Motor:- Construction of Capacitor Start Induction Motor:→ Stator – it is made up of silicon steel and stator windings are enameled Cu. → Stator having slots in which two windings are kept. → There are two windings called running (Main) winding & Starting winding. → Running Winding is with high reactance & low resistance. → Starting winding is with high resistance & low reactance. → Rotor :- It is a cylindrical structure having bars in the slots. → Rotor is made up of silicon steel and rotor windings are round copper bars embedded in the rotor slots and permanently short circuited. → Capacitor is connected in series with starting winding. Working of Capacitor Start Induction Motor:→ This motor is similar to Split phase induction motor except that the starting winding has as many turns as the main winding. → Capacitor (C) is connected in series with the starting winding. → Capacitor value will be selected that I S leads I m by about 80 degree. → Starting Torque = TS  k.I m .I s . sin  → Starting torque is more than Split phase Induction Motor. → When the rotor speed reaches 70-80% of the normal speed then centrifugal switch is operated. → Centrifugal switch disconnected electrically from the circuit. → Motor runs continue till power on. D.O.R:- (Direction Of Rotation)  DOR can be changed by making starting winding as running winding and vice versa. Application:- Capacitor start Induction Motors are used where high torque required. 1) Refrigerator 2) Drilling machine Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in
5. 5. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus 3) Lathe machine 4) Pumps 5) Printing press 6) Compressor 7) Large fans 8) High-inertia Loads b) Capacitor Start – Capacitor Run Induction Motor:→ This motor is identical to a capacitor start motor except that starting winding is not opened after starting. → So that both the windings remain connected to the supply when running as well as at starting. → There are two designs. Constructions of both the designs are same as Capacitor start but difference is as follows. i. Design – 1 (Permanent Capacitor Motor)   A single capacitor C is used for both starting and running winding. This design eliminates the need of a centrifugal switch and at the same time improves the power factor and efficiency of the motor. D.O.R. – DOR can be changed by making starting winding as running and vice versa. Application:Permanent Capacitor Induction Motors are used Where low torque is required Ceiling Fan, Table fan etc ii. Design – 2 ( Capacitor Start Capacitor Run Induction Motor) Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in
6. 6. Vijay Balu Raskar – Electrical Maintenance – Polyphase Circuit Junior Science College ( Std – XI ) - Syllabus      Two capacitor C1 and C 2 are used in the starting winding. C1 is very small capacitor and permanently connected in the circuit. C1 helps for optimum running conditions. C 2 is very large capacitor connected in parallel with C1 C 2 helps for optimum running conditions and remains in the circuit during starting.  When motor reaches about 75% of synchronous speed then C 2 will disconnected  Motor runs continue till power is ON. D.O.R. – DOR can be change by making starting winding as running winding and vice versa. Application:Room Cooler, Refrigerator, Compressor etc c. Shaded Pole Motor:- → → → → The shaded pole motor is very popular for ratings below 0.05H.P. (app. 40W). Because of its simple construction. It has salient poles on the stator excited by single phase supply and squirrel cage rotor. A portion of each pole is surrounded by a short circuited turn of copper strip called Shading Coil and made up of copper (cu coil). → Because of small starting torque developed in the motor and relatively large power loss in the shading coil. Construction of Shaded Pole Motor: Stator:- it is made up of silicon steel stamping having salient poles. Suggestions or difficulties are most welcome at vijayraskar2003@yahoo.co.in