ELECTRIC MOTORS

Prepared by-Kushal goelRushikesh solase

1. The heart of every electric vehicle is its electric motor

2. It is the most efficient mechanical devices on the Planet

3. Electric motor emits zero pollutants

INTRODUCTION

DEFINITIONAn electric motor is a device which is used to convert electrical energy into mechanical energy

CONSTRUCTIONAll electric motors by definition have a fixed stator or stationary part, and a rotor or moveable part

Why an Electric Motor?• Electric motors are inherently powerful

you can move a mountain. Nearly all traction motors deliver near peak torque at zero rpm. That’s why electric traction motors have powered our trolley cars, subways, and diesel-electric railroad locomotives

• Electric motors are inherently efficient

RATING• Electric motors are rated at their point

of maximum efficiency• Which may be capable of 2–4 times their

continuous rating but only for a few minutes

• For example, the FB1-4001A motor is rated as 30 hp continuous at 144V and 100 hp peak

• The 5-minute rating of the FB1-4001A motor is 48 hp at 144V

Horsepower Relation• Each 1,000 lbs. of vehicle weight after

conversion requires 6–8 hp. This is the continuous rating of the motor

• The available horsepower of a motor increases with voltage

• for example, the FB1-4001A motor is rated at 18 hp continuous at 72V but is rated at 30 hp continuous at 144V

• As the voltage is increased the rpm increases. Therefore Horsepower is a function of rpm and torque.

Horsepower Relation Continue..

• Highway speeds require greater horsepower

• The horsepower required at 70 mph is four times the horsepower required at 35 mph

Type of electric motor used as prime mover

• DC Electric Motor

• AC Electric Motor

DC MOTOR

DC MOTOR

DC MOTOR PARTS Armature-• The armature is the main current-

carrying part of a motor that normally rotates and produces torque via the action of current flow in its coils.

• The armature usually consists of a shaft surrounded by laminated sheet steel pieces called the armature core.

• The laminations reduce eddy current losses

• There are grooves or slots parallel to the shaft around the outside of the core

Commutator-The commutator is the smart part of the motor that permits constant rotation by reversing the direction of current in the windings

Field Poles - In a real motor the lines of flux are produced by an electromagnet created by winding turns of wire around its poles or pole pieces. A pole is normally built up of laminated sheet steel pieces, which reduce eddy current losses; as with armatures, steel has been replaced by more efficient metals in the newer models. The pole pieces are usually curved where they surround the armature to produce a more uniform magnetic field

Brushes

Typically consisting of rectangular-shaped pieces of graphite or carbon, brushes are held in place by springs whose tension can be adjusted. The brush holder is an insulated material that electrically isolates the brush itself from the motor frame. A small flexible copper wire embedded in the brush (called a pigtail) provides current to the brush.Smaller brushes can be connected together internally to support greater current flows

Motor Case, Frame, or Yoke

The function of this part is not only to provide support for the mechanical elements, but also to provide a magnetic path for the lines of flux to complete their circuit—just like the lines of flux around a bar magnet.

DC Motor Operation

• In a dc motor, the stator poles are supplied by dc excitation current, which produces a dc magnetic field. • The rotor is supplied by dc current through the brushes, commutator and coils. • The interaction of the magnetic field and rotor current generates a force that drives the motor

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Shaft

Brush

Coppersegment

Insulation

RotorWinding

N S

Ir_dcIr_dc/2

Rotation

Ir_dc/2

Ir_dc

12

3

4

5

6

7

8

Polewinding

• The magnetic field lines enter into the rotor from the north pole (N) and exit toward the south pole (S).

• The poles generate a magnetic field that is perpendicular to the current carrying conductors.

• The interaction between the field and the current produces a Lorentz force

• The force is perpendicular to both the magnetic field and conductor

• Direction of force is given by fleming’s left hand rule

MIDDLE FINGER=Conventional Current

Direction

FORE FINGER=Magnetic Field Direction

THUMB=Direction of Rotation (Lorentz Force)

Fleming's Left Hand Rule

• The generated force turns the rotor until the coil reaches the neutral point between the poles.

• However, inertia drives the motor beyond the neutral zone where the direction of the magnetic field reverses.

• To avoid the reversal of the force direction, the commutator changes the current direction, which maintains the counterclockwise rotation.

DC Motor Types

1. Series2. Shunt3. Compound

BEHAVIOURS OF DIFFERENT DC MOTOR

“The superior AC system will replace the entrenched but inferior DC one.”

—George Westinghouse (from Tesla: Man Out of Time)

AC MOTOR

Inventor of AC motor is : Nikola Tesla

1982: Tesla envisions rotating fields

1883: Tesla develops poly-phase AC induction

motor

1887: Tesla develops brushless AC motor

1888: Tesla patented for a rotating transformer.

INTRODUCTIONAC motors works on Alternating current(AC).AC is an electrical current whose magnitude and direction vary cyclically

Application of AC Motor AC Motor which encounters most often in our everyday life, the great majority of our homes, offices, and factories are fed by alternating current (AC).

• CD/DVD players• Toys• Household appliances • Locomotives• Pipeline compressors

TransformerConstruction:

• A transformer consists of two copper coils wound on a ferromagnetic core• The primary is normally connected to a source of alternating electric current. The secondary is normally connected to the load.

Working Of Transformer

When a changing current is applied to the primary coil, a changing magnetic field common to both coils results in the transfer of electrical energy to the second coil.

There are two types of transformer: 1) Step-Up transformer 2) Step-Down transformer

A/C Motor ConstructionAn outside stationary stator having coils supplied with AC current to produce a rotating magnetic field An inside rotor which is attached to the output shaft.

Types of A/C Motor1) The synchronous motorrotates at the supply frequency 2) The induction motor turns slightly slower. 3) Single-phase motors run on only one of the three phases of current operate on the domestic electricity supply. 4) Multi (Commonly three phase) motors Run on three of the phases of current produced by power stations.Mainly used for high power applications

Single-Phase AC Induction Motor

• At startup you have no net torque (or more correctly, balanced opposing torques) operating on its motionless rotor conductors.• It cause problem of starting, we have two apply force by hand to give initial twist.• To avoid this if we introduce a second winding that is physically at right angles to the main stator winding, it induce a rotor current out of phase with the main rotor current that is sufficient to start the motor.

• To maximize the electrical phase difference between the two windings, the resistance of the starting winding is much higher and its induction is much lower than the running winding.• The most common split-phase induction motor is one that uses a capacitor-start

Polyphase AC Induction Motor

Polyphase A C motor

Phase Diagram

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