1 / 10

THREE PHASE A.C. COMMUTATOR MOTORS

THREE PHASE A.C. COMMUTATOR MOTORS. Developed to provide Better Speed Control Good p.f. Control Both Speed and p.f. Control. 2 Classes Those having Series Characteristics Those having Shunt Characteristics Most of the machines have Shunt Speed Characteristics.

len-lynn
Download Presentation

THREE PHASE A.C. COMMUTATOR MOTORS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. THREE PHASE A.C. COMMUTATOR MOTORS • Developed to provide • Better Speed Control • Good p.f. Control • Both Speed and p.f. Control • 2 Classes • Those having Series Characteristics • Those having Shunt Characteristics • Most of the machines have Shunt Speed Characteristics. • Speed Control is obtained by injecting a Variable voltage at correct • Frequency to the Secondary winding of the motor via its Commutator. DEE_JRN

  2. THREE PHASE A.C. SERIES COMMUTATOR MOTORS Motor having Series Characteristics. i.e. Speed falls with increase in load. Constructional Details Stator: Similar to that of 3 Phase Induction Motor. Rotor: Similar to that of a D.C. armature with commutator segments 3 Brush sets per pair of poles spaced 120 0 E apart. The Stator and Rotor are connected in Series . Flux will be dependent on the current, resulting in “Series” Speed Characteristics. (Variable Speed) DEE_JRN

  3. Speed Control usually done by SIMULTANEOUS movement of all the • Brushes round the Commutator using Brush Gear. • To avoid commutational difficulties, a transformer is usually • employed between Stator & Rotor – thus reducing the voltage • applied to the Commutator Wdg. DEE_JRN

  4. STARTING: • No special Starting equipment is required. • Effected with the Brushes in the minimum speed position. • i.e. from the short circuit position. • normally between 100 to 400 . • The Stator is energized and the rotor rotates. DEE_JRN

  5. As the brush gear is moved against the direction • of rotation of rotor, the torque increases the motor • can be bought up to the desired speed. • For any given position of the BRUSHES, the Speed • falls with increase in Load, as in the case of SERIES MOTORS. • CHARACTERISTICS FEATURES • Starting Torque and Starting Current – 50% of the FL Values. • Reducing , enables to obtain TSt upto 200% FL & • ISt upto150% FL • Efficiency HIGH for the whole operating range. • p.f. HIGH approaching unity for Speeds near NS . • Speed range available to about 3:1. DEE_JRN

  6. SPEED CONTROL • By Brush Shifting – most commonly used. • By varying the applied Voltage. • Using a Phase Shifting Transformer. • APPLICATIONS • Used for driving loads where torque increases with speed. • eg. Compressors, Centrifugal Pumps • Used when large Starting Torque is required. • eg. Transporters and Turntables. DEE_JRN

  7. THREE PHASE A.C. SHUNT COMMUTATOR MOTORS Also known as Doubly Fed Motor. • Constructional Details • Stator: Similar to that of 3 Phase Induction Motor. • Rotor: Similar to that of a D.C. armature with commutator segments • 3 Brush sets per pair of poles spaced 120 0 E apart. • Both Stator & Rotor are connected to the same supply source. • Stator is directly fed; but the rotor through a variable ratio transformer. DEE_JRN

  8. Purpose of variable Voltage Transformer • (i) To provide low operating voltage to the commutator Wdg. • (ii) For regulating the injected voltage in the rotor circuit for • SPPED and p.f. Control. • BRUSHES are fixed in position. SPEED CONTROL Speed Control is obtained by injecting a Variable voltage at correct Frequency to the Rotor winding of the motor via its Commutator. When = 0, the brushes in effect are Short circuited - the m/c now operates as an Induction Motor. DEE_JRN

  9. 2. When opposes , Speed is below Ns . Slip power returned to Supply. 3. When aids , Speed is above Ns . Slip power delivered to Supply. Since slip power is either returned to, or taken from the supply, Doubly fed motor results in a CONSTANT – TORQUE drive system. More or less Constant speed at all loads for a given tapping. DEE_JRN

  10. APPLICATIONS Used for fans, pumps, lifts, cranes and haulage equipment, machine tools, printing machinery, chemical plant & wire manufacturing machinery Power and voltage ratings between 2kW at 600V & 2MW at 11kV. Speed range is usually about 3:1 to 5:1. DEE_JRN

More Related