EET 3064 ELECTRICAL MACHINES CHAPTER 3 INDUCTION MOTOR

EET 306/4 ELECTRICAL MACHINES CHAPTER 3 INDUCTION MOTOR (SINGLE PHASE) By: BAHARUDDIN BIN ISMAIL Email: baha@unimap. edu. my SCHOOL OF ELECTRICAL SYSTEM ENGINEERING

SINGLE PHASE INDUCTION MOTOR DESCRIBE & EXPLAIN: Single phase induction motors, 1) Theory and performance 2) Starting methods - Split-phase windings - Capacitor-type windings - Shaded stator poles 3) Starting and running performance

THEORY AND PERFORMANCE

SINGLE PHASE INDUCTION MOTOR The most familiar of all electrics motors because they are used in home appliance and portable machine tools such as used for the washing machines, clocks, drills, compressors, pumps, and so on.

SINGLE PHASE INDUCTION MOTOR (1 Φ and 3 Φ) Induction motor construction; Consist of two main parts : (a) STATOR : core, slot, winding (b) ROTOR : core, slot, winding or bar Two types of ROTOR : (1) Squirrel-Cage rotor or cage rotor (SCIM) *The physical stator of an induction motor = synchronous machine

SINGLE PHASE INDUCTION MOTOR Stator Core Stator Slot + Winding Rotor Core Rotor Slot + Winding/Bar Sketching of STATOR & ROTOR

SINGLE PHASE INDUCTION MOTOR Stator Construction

SINGLE PHASE INDUCTION MOTOR SCIM Construction

SINGLE PHASE INDUCTION MOTOR Single phase motor stator has a laminated iron core with two windings arranged perpendicularly. - Main winding = to create a set of N and S poles - Auxiliary winding = starting winding

SINGLE PHASE INDUCTION MOTOR The progressive steps in winding a 4 -pole, 36 -slot stator

SINGLE PHASE INDUCTION MOTOR $ Four Poles of the main winding are inserted in the slots Four Poles of the auxiliary winding straddle the main winding

SINGLE PHASE INDUCTION MOTOR -Each pole of the main winding consists of a group of four concentric coils, connected in series -Adjacent poles are connected so as to produce alternate N, S polarity

SINGLE PHASE INDUCTION MOTOR - The empty slot in the centre of each pole (shown as a vertical dash line) and the partially filled slot of it are used to lodge the auxiliary winding. - Mmf produce by main winding. * Position of the auxiliary with respect to the main winding.

SINGLE PHASE INDUCTION MOTOR *What do you understand about this figure? What is the relationship with the previous figure/concept?

SINGLE PHASE INDUCTION MOTOR Basic Induction Motor Concept: The development of induced torque in an induction motor. ii. The concept of rotor slip iii. The electrical frequency on the rotor i.

SINGLE PHASE INDUCTION MOTOR i. The development of induced torque in an induction motor. Ø The speed of the magnetic field’s rotation is given by, Where, = Synchronous Speed (r/min) = frequency of the source (Hz) = Number of Poles

SINGLE PHASE INDUCTION MOTOR Ø The voltage induced in a given rotor bar is given by the equation, Where, = Velocity of the bar relative to the magnetic field = Magnetic flux density vector = length of conductor in the magnetic field

SINGLE PHASE INDUCTION MOTOR Ø The induced torque in the machine is given by, Where, = Constant = Rotor Magnetic field = Stator magnetic field Note: At normal operation, both the rotor and stator magnetic fields together at synchronous speed and rotate , while rotor itself turns at a slower speed.

SINGLE PHASE INDUCTION MOTOR The concept of rotor slip. Ø Two (2) terms are commonly used to define the relative motion of the rotor and the magnetic fields. Ø First is slip speed, defined as the different between synchronous speed and rotor speed. ii. Where, = Slip speed of the machine = Speed of the magnetic field = Mechanical shaft speed of rotor/motor

SINGLE PHASE INDUCTION MOTOR The concept of rotor slip (Cont…). Ø Second term used to describe the relative motion is slip, which is the relative speed expressed on a per-unit or a percentage basis. Slip is define as, ………………(1) ii. ………………. (2) ………………. (3) (radians per second)

SINGLE PHASE INDUCTION MOTOR ii. The concept of rotor slip (Cont…). * Notice that the rotor turns at , S=0, while if the rotor is stationary, S=1. * All normal motor speeds fall somewhere between those two limits. * It possible to express the mechanical speed of the rotor shaft in terms of synchronous speed and slip. …………………. . (1) …………………. . (2)

SINGLE PHASE INDUCTION MOTOR iii. The electrical frequency on the rotor. At Ø , , For any speed in between, the rotor frequency is directly proportional to the different between speed of the magnetic field and speed of the rotor. Ø Since slip of rotor is defined as, Ø

SINGLE PHASE INDUCTION MOTOR iii. The electrical frequency on the rotor (Cont…). Ø The rotor frequency can be expressed as, …………. (1) …………. (2) …………. (3) …………. (4)

SINGLE PHASE INDUCTION MOTOR Question: 1) 4 -pole, 50 -Hz. Calculate motor speed when an induction motor has a full load slip 3. 4 %. 2) 208 -V, 10 -hp, 4 -pole, 50 -Hz, induction motor has 5% full load slip. (a) what of this motor? (b) what of this motor at the rated load? (c) what of this motor at the rated load?

SINGLE PHASE INDUCTION MOTOR Solution: 1)

SINGLE PHASE INDUCTION MOTOR Solution: 2) (a) (b) (c)

STARTING METHODS

SINGLE PHASE INDUCTION MOTOR Ø There are three techniques commonly used to start IM, and single phase induction motors are classified according to the methods used to produced their starting torque. Ø The starting techniques differ in cost and in the amount of starting torque produced. Ø Three major starting techniques are: a) Split-phase windings b) Capacitor-type windings c) Shaded stator poles

SINGLE PHASE INDUCTION MOTOR a) Split-phase windings

SINGLE PHASE INDUCTION MOTOR a) Split-phase windings (Cont…) q Split-phase motor have a moderate starting torque with a fairly low starting current. q Split-phase motor used for applications which do not require very high starting torque such as fans, blowers and pumps.

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings CAPACITOR-START MOTORS

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) CAPACITOR-START MOTORS q The starting torque of the motor can be more than 300% of it rated value. q They are used in applications where a high starting torque is absolutely required such as for compressors, air conditioners and other pieces of equipment that must start under a load.

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) PERMANENT SPLIT-CAPACITOR MOTORS

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) PERMANENT SPLIT-CAPACITOR MOTORS q q This motor have a lower starting torque than capacitor-start motors. At normal load, this motors are more efficient and have higher power factor and smoother torque than ordinary 1Φ induction motor.

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) CAPACITOR START-CAPACITOR RUN MOTORS

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) CAPACITOR START-CAPACITOR RUN MOTORS q If both the largest possible starting torque and best running conditions are needed, 2 capacitors can be used with the auxiliary winding. q The permanent capacitor is large enough to balance the current at normal motor loads, the can operate efficiently with high torque and pf. q The permanent capacitor in this motor is typically about 10% -20% of the starting capacitor.

SINGLE PHASE INDUCTION MOTOR b) Capacitor-type windings (Cont…) CAPACITOR START-CAPACITOR RUN MOTORS

SINGLE PHASE INDUCTION MOTOR c) Shaded stator poles

SINGLE PHASE INDUCTION MOTOR c) Shaded stator poles (Cont…) q Shaded-pole motors only have a main winding. q Shaded-pole motors produce less starting torque and they are much less efficient and have a much higher slip than any other type of induction motor starting system.

STARTING AND RUNNING PERFORMANCE

SINGLE PHASE INDUCTION MOTOR a) Comparison of 1Φ induction motor Ø Naturally, the best motor is also most expensive, and the worst motor is the least expensive. Ø Not all starting techniques are available in all motor size ranges. Ø Single phase induction motors can be ranked from best to worst in terms of their starting and running performance. a) Capacitor start-capacitor run motor b) Capacitor-start motor c) Permanent split-capacitor motor d) Split-phase motor e) Shaded-pole motor

SINGLE PHASE INDUCTION MOTOR b) Circuit model of a 1Φ induction motor Ø The equivalent circuit of single phase IM at standstill. Ø R 1 and X 1 are the resistance and reactance of stator winding, XM is the magnetizing reactance, and R 2 and X 2 are the referred values of the rotor’s resistance and reactance.

SINGLE PHASE INDUCTION MOTOR b) Circuit model of a 1Φ induction motor (Cont…) Ø The equivalent circuit with the effects of the forward and reverse magnetic fields separated.

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit. Ø The 1Φ equivalent circuit is similar to the 3Φ, except that there are both forward and reverse component of power and torque present.

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø A series combination of RF and j. XF is the Thevenin equivalent of the forward-field impedance elements, and therefore RF must consume the same power from a given current as R 2/S would.

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø To make the calculation simpler, need to define forward (ZF) and reverse (ZB) impedances and the current flow (I 1) in the induction motor’s stator winding.

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø The power flow diagram of a single phase induction motor.

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø The power flow diagram of a single phase induction motor. ü Stator power factor of the motor ü Input and output power of the motor ü The efficiency of the induction motor

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø The power flow diagram of a single phase induction motor. ü Air gap power forward magnetic field ü Air gap power for reverse magnetic field ü Total air gap in a 1Φ induction motor

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø The power flow diagram of a single phase induction motor. ü Induced torque and load torque in a 1Φ/3Φ induction motor & ü Rotor copper loss ü Forward and reverse rotor copper loss &

SINGLE PHASE INDUCTION MOTOR b) Circuit analysis with the 1Φ IM equivalent circuit (Cont…). Ø The power flow diagram of a single phase induction motor. ü Converted power for 1Φ/3Φ induction motor ü Since ü , the equation can be re-expressed as , so the equation can be expressed as

SINGLE PHASE INDUCTION MOTOR Question: 1) A 2/3 -hp, 110 -V, 6 -pole, 50 -Hz, split-phase induction motor has the following impedances: The core losses of this motor are 35 -W, (friction, windage and stray losses) are 16 -W. The motor operate at rated voltage & frequency with open starting winding. Motor slip is 7%. Find: a) Speed (rpm) f) Converted Power b) Stator current (A) g) Induced torque c) Stator PF h) Output power d) Input power i) Load torque e) Air gap Power j) Efficiency

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