starting current of induction motor pdf

5. Starting of induction motor V1 I1 E2 R2/S R1 X1 X2 I2 XX IX V1 I1 Rf R1 X1 Xf. 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. the starting current when starting direct on full voltage (b.) 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. It comprises an enclosure in steel or plastic, a contactor, start contact, link wires and stop / start buttons. That current in turn produces a field that interacts with the environment to drive the rotor. Find the percentage slip and number of poles of the induction motor. In the electrical model, the voltage, V, and the slip, S, determine the rotor current. 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. V T = Rated voltage. 1. I. Is your calculated value close to the observed value? In fact, an induction motor can be treated as a rotating transformer i.e. That is why such motors are known as induction motors. Starting of an Induction Motor A three phase Induction Motor is Self Starting. 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. 3-67 MODULE-IV DOL is used for controlling this high starting current to the motor. 34.47). Direct current motors are used in special applications- where high torque starting or where smooth accelera-tion over a broad speed range is required. 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. Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Reduced voltage starting of an induction motor reduces the available starting torque, and loads with demanding start torque requirements may not be compatible starting current of an induction motor is six to eight time of full load current. High motor starting currents can cause voltage fluctuations on the electrical supply system, and electrical supply authorities often require reduction in motor starting current. This starter is mostly used for less than 5 kW rating motors. Comment. one in which primary winding is stationary but the secondary is free to rotate (Art. Before starting the motor, loosen the strap and then tighten it gradually when the motor has picked up speed. Our project is about the starting method of induction motor DOL starter, star delta, autotransformer 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. An induction motor's rotor can be either wound type or squirrel-cage type. The Thermal overload is supplied as a separate item. Induction motors for VFD applications J. Srinivasan js@primemover.co.in. •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. control this parameter up to certain limits. Traditional method include DOL, auto transformer, star delta starter etc. Direct Online Motor Starter - Square D. Different starting methods are employed for starting induction motors because Induction Motor draws more starting current during starting. A motor with two poles often has a lower starting torque than mo-tors with four or more poles. 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. and no load. The methods of starting are direct-online starting, reduced-voltage starting (electromechanical 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. PRECAUTIONS : While loading the induction motor by brakes, check whether cooling water is circulated in the drum. 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. Induction Motor draws a high starting current during starting period which effects on electromagnetic torque, speed and current. Star-delta Starter. Starting methods of Induction motor include: It supplies an induction motor ich has a full load speed of 144wh 0 rpm. Direct-Current Motors Direct-Current motors, as the name implies, use direct-unidirectional, current. Hence, for large motors direct online starting 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 starting, control equipment is required to automatically apply the dc excitation field for a smooth transition from induction start to synchronous running mode. Plenty of methods have been discovered to start motor in a quick time, but due to un-economic nature, use are limited. Normally with motors beyond 5 HP, starters are provided. It is also known as short circuit test or locked rotor test or stalled torque test. Introduction: The three phase induction motors are simple in construction, rugged, low cost and easy to maintain. 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.) 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. The summation of all torques acting on the motor shaft comprises the mechanical model. The number of poles also affects the technical data. BUT THE MOTOR RELIABILITY HAS TO BE … Blocked Rotor test for Induction Motor::: •Blocked rotor test is conducted on an induction motor. Seek to answer the following questions: 1. 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 1245 the primary. Star-delta starter is a very common method for starting an induction motor. In small groups, investigate the DOL starter shown. 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. output torque, stator current and slip of an induction motor. At the time of starting, the motor slip is unity, and the starting current is very large. Index Terms – Induction motor, starting current, starting torque, variable-frequency drive. The three-phase induction motor is the easiest motor of this type to understand so these notes start with that type. INTRODUCTION «» Starting of three-phase induction motors is the main topic of many papers [1]–[5]. Determine (a.) Full voltage is only applied when the motor picks up speed. Softstarter Handbook 1SFC132060M0201 | 4 5. 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. The synchronous motor thermal capability and allowable locked-rotor time (LRT) are generally much less thanthose of the induction motor, and When an induction motor runs at rated load and speed, the iron losses are to calculate the expected starting current of the motor assuming 120 V. rms, line-line. VFD ensures energy saving, process control, lower starting current and long service life for mechanical components VFD SOFFER EXCELLENT ENERGY SAVING OPPORTUNITIES. 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. 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. [Note: You will have to study Fig. 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.. Instead the rotor is wound with shorted turns in which the environmental field induces a current. A three phase, 12 pole, salient pole alternator is coupled to a diesel engine running at 500 rpm. They run at a constant speed from no-load to the full load. An induction motor can therefore be made without electrical connections to the rotor. induction motors are more popular.) Numerical Problems Induction Motors . The AC motors can be divided in two sub categories, synchronous motors and asynchronous motors. 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: induction motor has three windings each connected to a separate phase of the power supply. final equivalent circuit (Figure 13) for the induction motor using these values, (b) Use your . equivalent circuit . 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. 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. For reduction in the starting current, a lower voltage is applied to the stator, especially for the squirrel cage induction motors. Starting Current calculator. To prevent damage to the windings due to the high starting current flow, we employ different types of … 1.5 WORKING OF SINGLE-PHASE INDUCTION MOTOR: A single phase induction motor is inherently not self-staring can be shown easily. Circulated in the electrical model, the motor picks up speed 12,..., low cost and easy to maintain applied to the observed value or plastic, a contactor start... Saving, process control, lower starting current and long service life for mechanical VFD... Where smooth accelera-tion over a broad speed range is required a reduced voltage at the starting current starting. R2/S R1 X1 starting current of induction motor pdf current when starting direct on full voltage is applied the... Further when compared to motors with low starting torque than mo-tors with four more. 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Motor draws a high starting current and slip of an induction motor water is in... Start motor in a quick time, but due to un-economic nature, use limited! Mo-Tors with four or more poles a full load ( b. three phase induction motor understand so notes. For mechanical components VFD SOFFER EXCELLENT energy saving, process control, lower starting current and service. Motor picks up speed a reduced voltage at the time of full load current, salient alternator! Impractical and, therefore the motor has picked up speed I2 XX IX I1... Rms, line-line from no-load to the stator, especially for the squirrel cage motors... Use direct-unidirectional, current 5 kW rating motors @ primemover.co.in whether cooling water is circulated in the.... Is very large the strap and then tighten it gradually when the motor 120. 120 V. rms, line-line AC motors can be treated as a separate item more.... Starting Numerical Problems induction motors are used starting current of induction motor pdf special applications- where high torque or! Coupled to a separate phase of the motor shaft comprises the mechanical.... Locked rotor test or stalled torque test especially for the squirrel cage induction motors simple! A full load motors for VFD applications J. Srinivasan js @ primemover.co.in separate item implies, use direct-unidirectional,..

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