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. 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. In small groups, investigate the DOL starter shown. The Thermal overload is supplied as a separate item. 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. It is also known as short circuit test or locked rotor test or stalled torque test. Star-delta starter is a very common method for starting an induction motor. This starter is mostly used for less than 5 kW rating motors. Mechanical methods are impractical and, therefore the motor is started temporarily converting it into two phase motor. final equivalent circuit (Figure 13) for the induction motor using these values, (b) Use your . 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: 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. V T = Rated voltage. Blocked Rotor test for Induction Motor::: •Blocked rotor test is conducted on an induction motor. 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. The synchronous motor thermal capability and allowable locked-rotor time (LRT) are generally much less thanthose of the induction motor, and Hence, for large motors direct online starting 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. Starting of induction motor Starting Current calculator. reduce the starting current further when compared to motors with low starting torque. When an induction motor runs at rated load and speed, the iron losses are Induction motors for VFD applications J. Srinivasan 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.) Our project is about the starting method of induction motor DOL starter, star delta, autotransformer The AC motors can be divided in two sub categories, synchronous motors and asynchronous motors. Introduction: The three phase induction motors are simple in construction, rugged, low cost and easy to maintain. Direct current motors are used in special applications- where high torque starting or where smooth accelera-tion over a broad speed range is required. Find the percentage slip and number of poles of the induction motor. INTRODUCTION «» Starting of three-phase induction motors is the main topic of many papers [1]–[5]. equivalent circuit . Traditional method include DOL, auto transformer, star delta starter etc. The Direct on Line motor starter (DOL) is designed to switch a single or three phase induction motor at rated voltage. output torque, stator current and slip of an induction motor. A three phase, 12 pole, salient pole alternator is coupled to a diesel engine running at 500 rpm. Determine (a.) The number of poles also affects the technical data. 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. starting, control equipment is required to automatically apply the dc excitation field for a smooth transition from induction start to synchronous running mode. Induction Motor draws a high starting current during starting period which effects on electromagnetic torque, speed and current. 1. Before starting the motor, loosen the strap and then tighten it gradually when the motor has picked up speed. A motor with two poles often has a lower starting torque than mo-tors with four or more poles. That current in turn produces a field that interacts with the environment to drive the rotor. 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. Numerical Problems Induction 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: At the time of starting, the motor slip is unity, and the starting current is very large. The summation of all torques acting on the motor shaft comprises the mechanical model. starting current of an induction motor is six to eight time of full load current. Instead the rotor is wound with shorted turns in which the environmental field induces a 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. 5. I. induction motor has three windings each connected to a separate phase of the power supply. Starting of an Induction Motor A three phase Induction Motor is Self Starting. Normally with motors beyond 5 HP, starters are provided. 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. In fact, an induction motor can be treated as a rotating transformer i.e. Reduced voltage starting of an induction motor reduces the available starting torque, and loads with demanding start torque requirements may not be compatible induction motors are more popular.) control this parameter up to certain limits. PRECAUTIONS : While loading the induction motor by brakes, check whether cooling water is circulated in the drum. [Note: You will have to study Fig. VFD ensures energy saving, process control, lower starting current and long service life for mechanical components VFD SOFFER EXCELLENT ENERGY SAVING OPPORTUNITIES. Softstarter Handbook 1SFC132060M0201 | 4 5. An induction motor's rotor can be either wound type or squirrel-cage type. Plenty of methods have been discovered to start motor in a quick time, but due to un-economic nature, use are limited. one in which primary winding is stationary but the secondary is free to rotate (Art. the starting current when starting direct on full voltage (b.) An induction motor can therefore be made without electrical connections to the rotor. Is your calculated value close to the observed value? In this methods, we provide a reduced voltage at the starting of the induction motor. BUT THE MOTOR RELIABILITY HAS TO BE … and no load. 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. Induction Motor 1245 the primary. 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. 34.47). 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 Comment. High motor starting currents can cause voltage fluctuations on the electrical supply system, and electrical supply authorities often require reduction in motor starting current. It comprises an enclosure in steel or plastic, a contactor, start contact, link wires and stop / start buttons. The three-phase induction motor is the easiest motor of this type to understand so these notes start with that type. Full voltage is only applied when the motor picks up speed. 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 methods of starting are direct-online starting, reduced-voltage starting (electromechanical Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Star-delta Starter. V1 I1 E2 R2/S R1 X1 X2 I2 XX IX V1 I1 Rf R1 X1 Xf. For reduction in the starting current, a lower voltage is applied to the stator, especially for the squirrel cage induction motors. 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.. It supplies an induction motor ich has a full load speed of 144wh 0 rpm. To prevent damage to the windings due to the high starting current flow, we employ different types of … Seek to answer the following questions: 1. 3-67 MODULE-IV 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 the following equivalent circuit parameters: Rw1 = 0.25S Rw2N = 0.2S Xl1 = Xl2N = 0.5S Xm1 = 30S The rotational losses are 1700W. Direct-Current Motors Direct-Current motors, as the name implies, use direct-unidirectional, current. They run at a constant speed from no-load to the full load. 1.5 WORKING OF SINGLE-PHASE INDUCTION MOTOR: A single phase induction motor is inherently not self-staring can be shown easily. 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. Index Terms – Induction motor, starting current, starting torque, variable-frequency drive. to calculate the expected starting current of the motor assuming 120 V. rms, line-line. DOL is used for controlling this high starting current to the motor. Starting methods of Induction motor include: •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.