prepaid by : PRAJAPATI DIVY D. ( ) PRAJAPATI ANANT M. ( ) VANI KIRAN V. ( ) PROJECT GUIDE MR. JIGNESH PATEL FACULTY, ELECTRICAL DEPT, SCET (DEGREE), KALOL.

Cross cutting of the DC motor Direct current (DC)motors

Back-emf (E) and Force (F) definition  If armature winding is connected to the supply voltage, the electrical current appears. Because of existing magnetic field (induction B), tangential force arise according to equation (2).  Because of force F (2), torque is generated and push the rotor to rotate.  When the rotor rotating in magnetic field, the voltage E, equ1, is induced in armature winding opposed to the voltage U. This voltage is called as “back-EMF” (back electromotor force).This voltage is proportional to rotor speed v, see equ1).  If supplied (armature) voltage in steady state (constant rotor speed) is greater than back-emf, U>E, we are talking about motor work,(motoring) or motor mode of operation; otherwise, U<E we are talking about generator work. (2) (1) DC motors- Introduction

Construction of DC motor  The rotor is made of sliced iron (alternated current in the rotor coils)!!.  Rotor winding consists of one or more solenoid (coils) where each of them is connected to collector segment (slice), se picture bellow)  Stator is aimed for a excitation (electromagnetic or permanent magnets) a) Description of DC motor components Covering of housing shaft bearing frame stator collector brushes and girder armature

Stator:  Immobile part, made mainly of massive iron (yoke). It doesn’t be laminated.  Main magnetic poles (electromagnets) are fixed on stator and assure magnetic fields (B) in the air-gap. The amount of magnetic field can be changed only if electromagnetic excitation is used.  If permanent magnet is used for excitation, the amount of excitation can not be changed! Excitation coils pole’s shoes hausing b) Description of DC motor components

Rotor (Armature):  Moving part, made off laminated iron (because of alternating current in armature winding)  Rotor has slotings with coils in it. Rotor’s winding consits of one or more coils where each of it is connected to collector. shaft Fe laminated Armature winding collector bearing c) Description of DC motor components

brush with girder collector rotor’s winding d) Description of DC motor components Rotor (Armature):

Collector with brushes (mechanical commutator!!), we wil see that later! Slices (segments) on collector) brush brush girder Armature winding (coils) e) Description of DC motor components Rotor (collector):

To rotor’s coil isolator collector’s segment Coil connection to collector’s segment brush  Collector’s segment is connected to rotor’s coil (as presented in the picture below).  Current flow from external source, over brush with girder and over collector’s slice enter into a coil (at the position of the neutral zone, where there are no induced voltage in this coil)! Collector’s segment f) Description of DC motor components

Construction of torque and back-EMF (voltage E) g) Description of DC motor components - Magnetic field (permanent magnets) - two brushes - two collector’s segment - one coil in magnetic field

Forces under poles “S” and “N” results in equivalent torques on the coil under “S” pole and “N” pole. Current direction in the coil under pole S change its direction when the coil reach the position under N pole. This is the reason why we say that the current in armature winding, when looking from outside the motor, is ALTERNATE current!!! a) How DC motor works Current enter in the motor from source over collector and brushes in armature winding. Result is motor work. collector = mechanical rectifier u i t u t brush colector slice brush

b) How DC motor works Because magnetic field act on the arm which is changed according to sinusoidal low, then torque is changed in the same way.

Red  Magnet or electromagnet with “N” pole Green  Magnet or electromagnet with “S” pole Stator may consist from more permanent magnets (multipole DC motor) Rotor coils are connected to collector (brown colour ), 3 pair of poles Brushes are dark-gray. Distance between collector slices is black. ANIMATION PICTURE Slots with coils in it