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Industrial Star Delta Starter for a 3-Phase Induction Motor
Contents of CourseIntroduction to Induction MotorConstruction of Induction Motor3D Simulation showing working of induction MotorWhat are issues arises while starting of induction MotorDirect Online start DOL of induction MotorAdvantages and disadvantages of DOLWhat are different types of starting techniquesReviewing Induction motor starting curveStar Delta StarterPurpose of Start Delta StarterAdvantages & Disadvantages of Star Delta StarterUnderstanding Control Circuit of Star Delta StarterComponent of Star Delta StarterUnderstanding Power Circuit of Star Delta StarterReading Schematic drawings of Star Delta StarterComparing Different Curves of starting current when use different startersIntroduction Of Induction MotorAn induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor. An induction motor’s rotor can be either wound type or squirrel-cage type. Three Phase induction motor is self started, because flux is moving at synchronous speed. Where as single phase induction motor is not self start, capacitor is used to produce rotating field. Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFD) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump and compressor load applications. Squirrel-cage induction motors are very widely used in both fixed-speed and variable-frequency drive applications. Cutaway view through stator of induction motor, showing rotor with internal air circulation vanes.A 3 Phase Induction motor consists of a stator. It contains 3 phase winding connected to the 3 phase AC supply. The arrangement of the winding is to produce a rotating magnetic field. The rotor of the Induction motor contains cylindrical core with parallel slots that contain conductors. Industrial Star Delta Starter for a 3-Phase Induction Motor What Problems Can Encounter During Motor Starting?During the motor self starting period, torque increases and a large amount of current flows in the rotor. To achieve this the stator draws a large amount of current and by the time the motor reaches its full speed A large amount of current is drawn and coils get heated up, damaging the motor. Hence there is a need to control the motor starting. One way is to reduce the applied voltage, which in turn reduces the torqueStarting current of induction motorStarting current of induction motor is as high as 5 to 7 times the normal full load current. Therefore different starting of induction motor, methods such as (star delta starter, auto transformer starter and other starting methods) are employed in order to reduce the high starting currents of induction motor. PURPOSE OF STARTERIf a rated stator voltage is applied to the motor at the time of starting, then the motorwill draw heavy starting current. This will lead to excess i2R losses in the winding which will overheat the motor. Secondly due to a heavy current drawn from the AC supply voltage will reduce. The heavy starting current may damage the motor windings. In order to avoid these problems, we can use some kind of a starter to start theinduction motor safely. To avoid this situation, we use star delta starter. At the time of start, motor connections (statorconnections) are made in star mode so impressed voltage is reduced by 1/3 (Phase voltage = Linevoltage/3) which reduces the starting current. Some of the techniques used to reduce the starting current of a squirrel induction motor: Soft starting (voltage control)Variable Frequency Drives (Voltage and frequency control)Star/Delta Starting. Stator impedance and/or resistance starting. Autotransformer StartingDirect Online STARTER BASIC POWER CIRCUITADVANTAGES OF DOL STARTER1. Most Economical and Cheapest Starter .2. Simple to establish, operate and maintain .3. Simple Control Circuitry .4. Easy to understand and troubleshoot.5. It provides 100% torque at the time of starting.6. Only one set of cable is required from starter to motor.7. Motor is connected in delta at motor terminals. DISADVANTAGES OF DOL STARTER1. Starting current:- It does not reduce the starting current of the motor.2. High Starting Current:- Very High Starting Current (Typically 6 to 8 times the FLC of the motor).3. Mechanically Harsh:- Thermal Stress on the motor, thereby reducing its life.4. Voltage Dip:- There is a big voltage dip in the electrical installation because of high in-rush currentaffecting other customers connected to the same lines and th
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