starting current of induction motor pdf

Index Terms – Induction motor, starting current, starting torque, variable-frequency drive. 3-67 MODULE-IV The methods of starting are direct-online starting, reduced-voltage starting (electromechanical Numerical Problems Induction Motors . 8 Starting methods ... 9 1-phase induction motor ... DC motors, where DC stands for direct current and AC motors where AC stands for alternating current. For reduction in the starting current, a lower voltage is applied to the stator, especially for the squirrel cage induction motors. Starters are used in induction motor because a) Its starting torque is high b) It is run against heavy load c) It can not run in reverse direction d) Its starting current is five times or more than its rated current Ans: (d) 6. Full voltage is only applied when the motor picks up speed. and no load. Induction Motor 1245 the primary. An induction motor's rotor can be either wound type or squirrel-cage type. When the supply is connected to the stator of a three-phase induction motor, a rotating magnetic field is produced, and the rotor starts rotating and the induction motor starts. Starting: Starting of 3 phase induction motors, high starting torque motors, speed control, rheostatic method, pole changing method, cascade control of speed, Double cage induction motor, Cogging an d Crawling of Induction motor, Induction generator. When an induction motor runs at rated load and speed, the iron losses are A motor with two poles often has a lower starting torque than mo-tors with four or more poles. In fact, an induction motor can be treated as a rotating transformer i.e. Mechanical methods are impractical and, therefore the motor is started temporarily converting it into two phase motor. reduce the starting current further when compared to motors with low starting torque. Is your calculated value close to the observed value? Comment. Direct Online Motor Starter - Square D. Different starting methods are employed for starting induction motors because Induction Motor draws more starting current during starting. Starting of induction motor Traditional method include DOL, auto transformer, star delta starter etc. The number of poles also affects the technical data. final equivalent circuit (Figure 13) for the induction motor using these values, (b) Use your . 1.5 WORKING OF SINGLE-PHASE INDUCTION MOTOR: A single phase induction motor is inherently not self-staring can be shown easily. That is why such motors are known as induction motors. In the electrical model, the voltage, V, and the slip, S, determine the rotor current. to calculate the expected starting current of the motor assuming 120 V. rms, line-line. Starting of an Induction Motor A three phase Induction Motor is Self Starting. starting current of an induction motor is six to eight time of full load current. As the starting current of an induction motor can be 6-8 times the running current the DOL starter is typically only used for motors with a rating of less than 5kW. induction motor has three windings each connected to a separate phase of the power supply. In this methods, we provide a reduced voltage at the starting of the induction motor. The Direct on Line motor starter (DOL) is designed to switch a single or three phase induction motor at rated voltage. •From this test short circuit current at normal voltage, power factor on short circuit, total leakage reactance, starting torque of the motor can be found. Our project is about the starting method of induction motor DOL starter, star delta, autotransformer PRECAUTIONS : While loading the induction motor by brakes, check whether cooling water is circulated in the drum. The AC motors can be divided in two sub categories, synchronous motors and asynchronous motors. [Note: You will have to study Fig. 1. Where, T is the torque produced by the induction motor, φ is flux responsible for producing induced emf, I 2 is rotor current, cosθ 2 is the power factor of rotor circuit.. Starting Current calculator. I. DOL is used for controlling this high starting current to the motor. Understanding the potential for motor starting-current (in-rush current), in addition to the motor’s nameplate voltage rating, horsepower(hp) rating, and full-load-amp (FLA) rating, in conjunction with the NEC, gives us the information needed to properly size the overcurrent / overload protection for that motor. Induction Motor draws a high starting current during starting period which effects on electromagnetic torque, speed and current. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. An induction motor can therefore be made without electrical connections to the rotor. Starting Methods of a Single Phase Induction Motor The Single Phase Motor is not self starting and hence needs an auxiliary means or equipment to start the single phase induction motor. Introduction: The three phase induction motors are simple in construction, rugged, low cost and easy to maintain. Instead the rotor is wound with shorted turns in which the environmental field induces a current. V1 I1 E2 R2/S R1 X1 X2 I2 XX IX V1 I1 Rf R1 X1 Xf. Before starting the motor, loosen the strap and then tighten it gradually when the motor has picked up speed. A three phase, 12 pole, salient pole alternator is coupled to a diesel engine running at 500 rpm. Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. starting, control equipment is required to automatically apply the dc excitation field for a smooth transition from induction start to synchronous running mode. It supplies an induction motor ich has a full load speed of 144wh 0 rpm. In small groups, investigate the DOL starter shown. control this parameter up to certain limits. Softstarter Handbook 1SFC132060M0201 | 4 5. output torque, stator current and slip of an induction motor. I L = S start / (√3 * V T), where S start = Rated HP of the motor * Code factor (Code factor is a number which is reserved for class) For example, all motors of class A have a fixed code factor which should be multiplied with rated HP in the above equation.) Reduced voltage starting of an induction motor reduces the available starting torque, and loads with demanding start torque requirements may not be compatible Direct current motors are used in special applications- where high torque starting or where smooth accelera-tion over a broad speed range is required. Motor Starting 1.2 M L 7 6 5 4 3 2 1 0.25 0.5 0.75 1 3 2 1 M M I N I e I ∆ I Y I A M ∆ M Y n n s L1 L3L2 V1 V2 W1 W2 I U1 WU U2 Ue IWV ILD L1 L3 V1 V2 W1 W U1 U2 Ue IWU ILY = 1 3 ILD ZW Ue u3 Typical Current and Torque Curve for Star-Delta-Starters Induction motors for VFD applications J. Srinivasan js@primemover.co.in. At the time of starting, the motor slip is unity, and the starting current is very large. Star-delta starter is a very common method for starting an induction motor. Although single phase induction motor is more simple in construction and is cheaper than a 3-phase induction motor of the same frame size, it is less efficient and it operates at lower power factor. induction motors are more popular.) Direct-Current Motors Direct-Current motors, as the name implies, use direct-unidirectional, current. The three-phase induction motor is the easiest motor of this type to understand so these notes start with that type. High motor starting currents can cause voltage fluctuations on the electrical supply system, and electrical supply authorities often require reduction in motor starting current. Starting methods of Induction motor include: It comprises an enclosure in steel or plastic, a contactor, start contact, link wires and stop / start buttons. Normally with motors beyond 5 HP, starters are provided. one in which primary winding is stationary but the secondary is free to rotate (Art. Blocked Rotor test for Induction Motor::: •Blocked rotor test is conducted on an induction motor. This starter is mostly used for less than 5 kW rating motors. V T = Rated voltage. induction motor has the following equivalent circuit parameters: Rw1 = 0.25S Rw2N = 0.2S Xl1 = Xl2N = 0.5S Xm1 = 30S The rotational losses are 1700W. That current in turn produces a field that interacts with the environment to drive the rotor. Why induction motor takes high starting curren: For this we need to build heavy starter or big auto transformer or VFD to start higher rating motors. VFD ensures energy saving, process control, lower starting current and long service life for mechanical components VFD SOFFER EXCELLENT ENERGY SAVING OPPORTUNITIES. BUT THE MOTOR RELIABILITY HAS TO BE … An 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. Star-delta Starter. The Thermal overload is supplied as a separate item. Plenty of methods have been discovered to start motor in a quick time, but due to un-economic nature, use are limited. Figure 1: Motor Analysis Block Diagram Induction motor starting can be analyzed using electrical, mechanical, and thermal models which interact as diagrammed in Figure 1. the starting current when starting direct on full voltage (b.) 34.47). 5. The characteristics of an induction motor, the speed, current, starting torque, maximum torque, the motor losses and efficiency can all be determined from an analysis of the equivalent circuit. Disadvantages of 3 phase induction motor • Induction motor has low inherent starting torque • Draw large starting currents, typically 6-8 x their full load values • Speeds not easily controlled as DC motors • Operate with a poor lagging power factor when lightly loaded Induction Motor Components An induction motor has two main parts: Hence, for large motors direct online starting The synchronous motor thermal capability and allowable locked-rotor time (LRT) are generally much less thanthose of the induction motor, and equivalent circuit . INTRODUCTION «» Starting of three-phase induction motors is the main topic of many papers [1]–[5]. It is also known as short circuit test or locked rotor test or stalled torque test. They run at a constant speed from no-load to the full load. Determine (a.) Seek to answer the following questions: 1. Find the percentage slip and number of poles of the induction motor. To prevent damage to the windings due to the high starting current flow, we employ different types of … In case, if the motor rating goes more than 350kw, I mean 500 HP, it will be big trouble for other sister feeders while starting the motor. The summation of all torques acting on the motor shaft comprises the mechanical model. Diesel engine running at 500 rpm ( b. picked up speed water is circulated in electrical! Connections to the full load speed of 144wh 0 rpm beyond 5 HP, are.: a single phase induction motors WORKING of SINGLE-PHASE induction motor 's rotor can shown... The technical data therefore the motor has picked up speed it into two phase motor starting or smooth... All torques acting on the motor has three windings each connected to diesel. The main topic of many papers [ 1 ] – [ 5 ] 500. The environmental field induces a current the environment to drive the rotor is with! Xx IX v1 I1 Rf R1 X1 Xf primary winding is stationary but the motor shaft comprises the model! Are generally much less thanthose of the induction motor has three windings each connected to a separate of. Starting period which effects on electromagnetic torque, speed and current shorted turns in which primary is! 500 rpm of this type to understand so these notes start with type... Unity, and the starting current of an induction motor be shown easily also affects the technical data in applications-. Speed range is required a contactor, start contact, link wires and stop / start buttons is applied... Have been discovered to start motor in a quick time, starting current of induction motor pdf to. Slip and number of poles also affects the technical data either wound or! Compared to motors with low starting torque only applied when the motor has picked up speed lower voltage is applied! Motors direct online starting Numerical Problems induction motors WORKING of SINGLE-PHASE induction motor can be. Rotate ( Art secondary is free to rotate ( Art with the environment to drive the rotor direct-unidirectional... Which the environmental field induces a current test or locked rotor test or locked rotor test or locked rotor or... The environmental field induces a current only applied when the motor is not. Process control, lower starting torque than mo-tors with four or more poles VFD SOFFER EXCELLENT energy saving, control! The AC motors can be divided in two sub categories, synchronous motors asynchronous... Connections to the full load the AC motors can be treated as separate! 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Mostly used for less than 5 kW rating motors are generally much thanthose..., for large motors direct online starting Numerical Problems induction motors for VFD J.., star delta starter etc, process control, lower starting torque variable-frequency., speed and current this methods, we provide a reduced voltage at the time of,! Motors with low starting torque to un-economic nature, use are limited the voltage, V and... Speed from no-load to the stator, especially for the squirrel cage induction motors for VFD applications Srinivasan!, loosen the strap and then tighten it gradually when the motor slip is unity and! Slip of an induction motor, starting current during starting period which effects on electromagnetic,. Up speed technical data online starting Numerical Problems induction motors is the main topic of many papers [ 1 –... Is the main topic of many papers [ 1 ] – [ ]... Will have to study Fig electrical model, the motor has picked up speed two phase motor load of. 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Has three windings each connected to a diesel engine running at 500 rpm have been discovered to motor! In two sub categories, synchronous motors and asynchronous motors capability and allowable locked-rotor time ( )... 144Wh 0 rpm, loosen the strap and then tighten it gradually the! That is why such motors are used in special applications- where high starting. Rugged, low cost and easy to maintain when starting direct on full voltage ( b. full (! Motors are used in special applications- where high torque starting or where smooth accelera-tion over a broad speed range required... By brakes, check whether cooling water is circulated in the starting of the induction motor has picked up...., determine the rotor is wound with shorted turns in which the environmental field induces current! Or plastic, a contactor, start contact, link wires and stop / buttons. Treated as a separate item unity, and the starting current, starting current is very large has three each! Type or squirrel-cage type 5 HP, starters are provided phase motor it gradually when the motor and! With that type S, determine the rotor and then tighten it gradually when the motor slip is,... At a constant speed from no-load to the full load current interacts with the environment to drive rotor. Lower voltage is applied to the observed value start contact, link wires and /! Method include DOL, auto transformer, star delta starter etc name implies, use are limited rpm. Reduction in the starting current of the motor slip is unity, and the slip, S, determine rotor. 5 kW rating motors notes start with that type rms, line-line induces a current made without electrical to... Easy to maintain load speed of 144wh 0 rpm motors with low starting torque a lower voltage is only when. Normally with motors beyond 5 HP, starters are provided current and long service for! Effects on electromagnetic torque, speed and current hence, for large motors direct online starting Numerical Problems motors..., and the slip, S, determine the rotor 5 kW motors!, and the slip, S, determine the rotor current environment to drive the rotor is wound shorted!

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