Rotational motion problems solutions northern highlands. A 50 hp, 240 vdc separately excited motor is operating at rpm. Problems 4 1 a 230 v dc shunt motor runs at 800 rpm and takes armature current of 50 a. Unit 16 electric motors washington state university.
Due to electrical and mechanical losses in the motor, the mechanical power out of the motor must be less than the electrical power in. Identify and utilize equations that represent motor performance to solve separately excited dc motor problems. A simple numerical just to get you guys understand the concepts. Find the percentage slip and number of poles of the induction motor. Introduction a series dc motor is a motor whose filed windings consists of a relatively few turns connected in series with the armature circuit. With drives and motors, there are a few common problems that application engineers tend to see the most.
The power input to a dc motor is simply the input current multiplied by the applied voltage. Specific electric loading, ac 28173 ndm specific magnetic loading. Synchronous motors are often directcoupled to the load and may share a common shaft and bearings with the load. A shunt generator delivers 450 a at 230 v and the resistance of the shunt field and armature are 50. The first problem is solved by the use of hairsprings attached to each end of the coil as shown in figure 2.
Soft foot occurs when the motor feet are bolted down out of level. Compare the rotation of this motor with that in figure 164. A three phase, 12 pole, salient pole alternator is coupled to a diesel engine running at 500 rpm. Previous question next question transcribed image text from this question. The frequency of routine service varies widely between applications. Even though you have a multiloop circuit so you need to write down the equations from the loop rule and the junction rule, you may not have to actually solve simultaneous equations. This conversion of ac into dc is accomplished through the use of a commutator. Tips for troubleshooting motor drives design world.
At fullload and rated voltage, the line current is 55a. When driven at 750 revmin the machine produces a total armature current of 400 a at a terminal voltage of 200 v. Under the steadystate conditions, the timederivatives of motor dynamic variables vanish e. It supplies an induction motor ich has a full load speed of 144wh 0 rpm. Mo tor motor characteristicscharacteri5tics of series mo. How to solve common electric motor problems and get great. These hairsprings can also be used to make the electrical connections to the coil.
The circuit connection diagrams of these four types of dc motors are shown in fig. Calculate the armature voltage at 1200 rpm if the field resistance rf 60. Write the complete solution for the circuit in the form. However, motors were a problem with alternating current. Electric motor failures can be due to mechanical component failure or electrical circuit failure. A 10 kw, 250 v shunt motor has an armature resistance of 0. Construction and principle of operation of singlephase transformer, emf equation, singlephase autotransformer. The motor shaft must turn along its full length to within 0. Overhead transmission lines and underground cables 9. If the line current is 37a,find the armature resistance.
The most obvious electrical loss is due to the armature resistance, p elec. To achieve long motor life in wet environments, like a dairy processing plant, standard motor construction and standard water. Possible causes could include a short on the motor output, grounding on the motor terminals, or an overloaded motor, among other causes. Power system analysis for solving problems with expanding. In all practical problems of electrical calculations, it is assumed that the temperature rise is within limits, so that electrical properties such as insulation and conduction properties of the. Under rated load conditions, the machine draws 60 a of armature current ia, runs at rpm wm, and the induced backemf voltage is 200v ea. Soft starters solve this problem through controlling the application of. In this lecture we shall consider mainly the separately excited and the shunt dc motors. In particular, if a coil rotates in the presence of a magnetic field, the induced emf varies sinusoidally with time and leads to an alternating current ac, and provides a source of ac.
Motors although the previous discussion pertains to both dc and ac motors, the two are very different. The flux of a dc motor can be changed by changing ish with help of a shunt field rheostat. Draw a circuit model of a separately excited dc motor. The conductors of the armature of a dc generator are connected to commutator segments. For the love of physics walter lewin may 16, 2011 duration. Below is an overview of the most common problems and the fixes to get your drive and motor working properly. Let us now solve some problems on shunt, separately excited and series motors. These same curved pole pieces are found in a motor. Inadequate mounting of the motor can lead to defects when it is not correctly levelled as part of the installation process. Experiment 7 series dc motor i objectives to determine the torquespeed characteristic curve. Dc motors, generators and energy conversion devices. Initially, ac motors were constructed like dc motors, but numerous problems were encountered due to changing magnetic fields.
Introduction to ac motors ac motors electronics textbook. Steinmetz contributed to solving these problems with his investigation of hysteresis losses in iron armatures. Mechanical problems such as worn bearings or a broken pinion could cause a mechanical overload. Connection of the field circuit and armature circuit for a separately exited motor,b series motor c shunt motor and d compound motor. To find out how to reverse the direction of rotation of a series dc motor.
Electric machines problem set 8 solutions october 24, 20. A 30 hp, 240 v, 1150 rpm dc shunt motor, operating at rated conditions, has an efficiency of 88. Large synchronous motors are usually started acrossthe line. Calculate the torque for the above condition maintaining the terminal voltage constant, the field current is adjusted until the motor is operating at steady state, supplying a mechanical load of 4160w at 1450 rpm. A 350 kw, 500v, 450rpm, 6pole, dc generator is built with an armature diameter of 0. After rearranging the steadystate forms of motor equations 1, the following expression for the motor steadystate curve is obtained. Problem 4 a separately excited dc motor has the following specifications. A 30 hp, 240 v, 1150 rpm dc shunt motor, operating. If the housing is not properly bolted to the rest of the assembly or the surroundings, uneven. This minimises the vibration, forces and loads that planetary rotation of one shaft in respect to the other would create.
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