SEMINARON

BRUSHLESSEXCITATION

CONTENTS

IntroductionNeeds of ExcitationWhy Excitation in D.C, Why not in A.C?Types of ExcitationMethod of maintenanceAdvantages of Brushless ExcitationApplicationConclusionRefference

INTRODUCTION

A new brushless excitation system is

described for a electrical motor having a

series resonant self commuted thyristor

inverter circuit.

Field excitation is provided by a

standard brushless excitationsystem

which consists of a rotating armature,

diode bridge and stationary field. The

brushless excitation system eliminates periodic brush and

collector ring maintenance and replacement.

NEEDS OF EXCITATIONNEEDS OF EXCITATION According to FLEMING’S RULE According to FLEMING’S RULE “When “When

a field magnet is excited and its armature a field magnet is excited and its armature conductors are supplied with current from conductors are supplied with current from the supply mains , they experience a force the supply mains , they experience a force tending to rotate the armature”.tending to rotate the armature”.

So for rotating the motor orSo for rotating the motor or generating the power from the generating the power from the generator we must require a generator we must require a excited magnetic field.excited magnetic field. The field excitation of motor The field excitation of motor or generator is always by D.Cor generator is always by D.C supply.supply.

WHY EXCITATION IN D.C , WHY WHY EXCITATION IN D.C , WHY NOT IN A.C ???NOT IN A.C ???

According to Weber & Ewing’s molecular TheoryAccording to Weber & Ewing’s molecular Theory

““The molecules of all substances are inherently The molecules of all substances are inherently magnets in themselves, each having a N & S pole”.magnets in themselves, each having a N & S pole”. In the unmagnetised material electronic spin In the unmagnetised material electronic spin

alignment is haphazard manner.alignment is haphazard manner. If we placed the unmagnetised material in a If we placed the unmagnetised material in a

magnetic field or we give the D.C supply then themagnetic field or we give the D.C supply then the Electronic spin start turn round their axis & Electronic spin start turn round their axis &

arrangearrange Parallel to the magnetic field.Parallel to the magnetic field. The arrangement of electronic spin results in N The arrangement of electronic spin results in N

polarity at one end & the P polarity at the other.polarity at one end & the P polarity at the other.

INTERNAL STRUCTURE…

BEFOREEXCITATION (UNMAGNETISED)

Continue…

AFTER EXCITATION (MAGNETISED)

effect of A.Ceffect of A.C…… If we placed the unmagnetised materialIf we placed the unmagnetised material across the A.C supply then the positive &across the A.C supply then the positive & negative electron spins are equal.negative electron spins are equal. Because in the A.C supply we found bothBecause in the A.C supply we found both positive & negative half cycle in a fractionpositive & negative half cycle in a fraction of time.of time. At a particular time the electron alignmentAt a particular time the electron alignment try to achieve both positive & negative try to achieve both positive & negative

electron spin. So they cancel each other & electron spin. So they cancel each other & results in there is no such pole for field.results in there is no such pole for field.

Continue…

POSITIVE SPIN

NEGATIVE SPIN

AFTER A.C EXCITATION

TYPES OF EXCITATIONTYPES OF EXCITATION

WITH BRUSH EXCITATIONWITH BRUSH EXCITATION The function of the brush is to collect current from The function of the brush is to collect current from

Commutator. Commutator. It is usually made of carbon or graphite and are inIt is usually made of carbon or graphite and are in

the shape of rectangular block.the shape of rectangular block. It requires collector ring, brushes or commutator.It requires collector ring, brushes or commutator.

DISADVANTAGES DISADVANTAGES It require maintenance, adjustment & inspections.It require maintenance, adjustment & inspections. It produces brush drop, spark, noise & friction loss.It produces brush drop, spark, noise & friction loss. It limits maximum speed of the machine.It limits maximum speed of the machine. The brushes assembly on a large machine is a costlyThe brushes assembly on a large machine is a costly

element.element.

e.g: WITH BRUSH EXCITATION

FIELD POLES

COMMUTATOR

BRUSHES

SHAFT

BRUSHLESS EXCITATIONBRUSHLESS EXCITATION While brushless excitation system eliminate the While brushless excitation system eliminate the need for brushes, commutator & slip-ring.need for brushes, commutator & slip-ring. It uses bridge rectifier circuit consists of SCR &It uses bridge rectifier circuit consists of SCR & diode.diode. The bridge rectifier circuit placed on the rotor.The bridge rectifier circuit placed on the rotor. The bridge rectifier circuit rotates with the speed The bridge rectifier circuit rotates with the speed of the rotor.of the rotor. The A.C supply given to the bridge rectifier byThe A.C supply given to the bridge rectifier by the principle of “Electromagnetic Induction”.the principle of “Electromagnetic Induction”. Bridge rectifier being represented by a Bridge rectifier being represented by a

transformation from A.C voltage to D.C voltage.transformation from A.C voltage to D.C voltage. The D.C output of the rotating rectifier is appliedThe D.C output of the rotating rectifier is applied to the D.C rotating field of the motorto the D.C rotating field of the motor

CIRCUIT DIAGRAM

ON SITE…

PRACTICAL LAYOUT

METHOD OF MAINTENANCEMETHOD OF MAINTENANCE It developed two specialized method of It developed two specialized method of Testers. Testers. 1.THE SYNCRITE MODULE TESTER1.THE SYNCRITE MODULE TESTER This tester is used to test the syncrite field application This tester is used to test the syncrite field application

module.module. By syncrite field application module we adjusted theBy syncrite field application module we adjusted the synchronizing speed.synchronizing speed. It also test for proper zener operation.It also test for proper zener operation.

2.DIODE WHEEL TESTER2.DIODE WHEEL TESTER It is used to test the diodes & SCRS mounted on It is used to test the diodes & SCRS mounted on the rotating assembly.the rotating assembly. It also checks proper SCR firing & checks for It also checks proper SCR firing & checks for grounded components. grounded components.

SYNCRITE MODULE TESTER

DIODE WHEEL TESTER

ADVANTAGESADVANTAGES

Life of motor using brushless excitation significantlyLife of motor using brushless excitation significantly

longer compared to a motor using brushes.longer compared to a motor using brushes. It reduces noise.It reduces noise. Loss should be reduced, i.e brush drop.Loss should be reduced, i.e brush drop. It reduces the maintenance and replacement.It reduces the maintenance and replacement. Less maintenance cost.Less maintenance cost. It reduces spark, wear & tear.It reduces spark, wear & tear.

APPLICATIONAPPLICATION

Brushless Excitation is broadly used inBrushless Excitation is broadly used in

the electrical machine. Such as….the electrical machine. Such as…. Alternator.Alternator. Hydro generator.Hydro generator. Turbine generator.Turbine generator. D.C generator.D.C generator. D.C motor.D.C motor.

CONCLUSIONCONCLUSION Though I discussed about the brushless Though I discussed about the brushless

excitation. It is widely used in the presentexcitation. It is widely used in the present

scenario. Such as alternator and large scenario. Such as alternator and large motor. So “excitation is the backbone of motor. So “excitation is the backbone of

Electrical Machine”.Electrical Machine”.

REFERENCEREFERENCE

http://en.wikipedia.org/wiki/Alternator http://en.wikipedia.org/wiki/Electric_motor http://www.basler.comhttp://www.basler.com   Thompson, Sylvanus P., Dynamo-Electric Machinery, Thompson, Sylvanus P., Dynamo-Electric Machinery,

A Manual for Students of Electrotechnics, Part 1, A Manual for Students of Electrotechnics, Part 1, Collier and Sons, New York, 1902Collier and Sons, New York, 1902

White, Thomas H.,"White, Thomas H.,"Alternator-Transmitter Development (1891-1920)". (1891-1920)". EarlyRadioHistory.us.EarlyRadioHistory.us.

S.M.L.Kabir, R.Shuttle worth, “Brushless Exciter S.M.L.Kabir, R.Shuttle worth, “Brushless Exciter Model”.Model”.

  

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