Under such conditions, the performance of the generator is given by the relation among the excitation, terminal voltage and load. It is the most important means of producing electrical power in many of the places since now days all the consumers are using AC. There are five major types of dc generators, classified according to the manner in which their field flux is produced: 1. It is done specifically to know the internal and external characteristics. DC generators are very reliable with efficiency ratings of 85-95% Consider the output of a generator is VI The input of a generator is VI + Losses Input = VI + I2aRa + Wc If the shunt field current is insignificant, then Ia = I (approximately) After that, n = VI/ (VI+Ia2Ra+wc) = 1/ (1+Ira/V+wc/VI) But to maintain constant voltage over a long period, the over compounded generators are used. The first type excites the field coils by using Permanent magnets, while the separately excited one includes an external force for excitation. Explain the effect of motor reaction in a dc generator. Separately excited generator -In a separately excited generator, the field fluxes derived from a separate power source independent of the generator itself. (a) (b) Fig. Module 6 - DC Motors This module describes the types of DC motors and includes discussions of speed control, applications, and load characteristics. To establish the torque equation, let us first consider the basic circuit diagram of a dc motor, and its voltage equation. DC generators AC Generators: These are also called as alternators. 7. The Coil can Rotate in Clockwise or Anticlockwise Direction. below. It states that, 'whenever the number of magnetic lines of force i.e. Also studied are the performance and control characteristics of these configurations. These relations are given graphically in the form of curves, which are called as characteristics of DC generators. As the pole flux strengthened, it will produce more armature emf, which cause further increase of current through the field. This is the main difference in their construction. The induction generator requires no separate DC . Match List-I (Type of d.c. generator) with List-Il (External characteristics) and select the correct answer using the codes given below: List-I A. Classification is same for DC Generator and Motor . What is the change in the critical field resistance of the generator? As Reduction of main flux and therefore of emf caused by the demagnetizing effect of armature reaction. (and hence current) is given by Flemings right hand rule. These are of two types one is induction generator and other one is synchronous generator. List the types of armatures used in dc generators. This increased field current further raises armature emf and this cumulative phenomenon continues until the excitation reaches to the rated value. A separately excited dc motor is similar to a shunt-connected motor except that different sources are used for the armature and field circuits. Therefore, the essential . The internal characteristics are known by drawing a graph between induced emf and the . 1: (a) Load test on a dc series generator, (b) Characteristics of a series generator The load current is then increased in steps and readings are taken at each step of the value of the load current and of the terminal voltage of the machine. Configure the block that models the motor.Set the DC Motor block parameters as follows, leaving the unit settings at their default values where applicable: Electrical Torque tab: Model parameterization to By rated power, rated speed & no-load speed. DC GENERATORS Principle of Operation of a D.C. 3/7/2011 10 In dc motor, each conductor is acted upon by circumferential force, F at a distance r. 3/7/2011 11 Speed of a DC Motor Speed of a DC Motor Therefore, in a dc motor speed is directly. Fig. If speed is kept constant, and the flux is varied, the induced emf also varies In these type of generators the armature current I a divides in two parts. Motor has a DC Current as an input and provides mechanical output. The . For voltage to build up, there must be some residual magnetism in the field poles. Commutation. Suppose we are given the internal characteristic of the generator. The external characteristic of the separately excited DC generator is obtained by subtracting the drops due to ohmic loss (I a R a) in the armature from generated voltage (E g). flux linking with a conductor or a coil changes, an electromotive force is set up in that conductor or coil.' The . WORKING of DC GENERATOR. These are explained below for each type of DC motor. DC generators produce constant and consistent output. Separately excited DC generator characteristics For a given dc generator it is clear that the induced emf is proportional to the flux and the speed. Input/output. Magnetic or Open Circuit Characteristic of Series Wound DC Generator 15. Self Exited DC Generator 4. Let the line OC represent the resistance of the whole machine i.e. Four types of d.c. generators of constant speed are considered List-I. D.C Machine (as a Generator) MV . Conclusion What is the working principle of DC generator was the main topic of this article which we tried to answer. characteristic of series wound DC generator. Separately excited B. THE ELEMENTARY DC GENERATOR A single-loop generator with each terminal connected to a segment of a two-segment metal ring is shown in figure below. IV. The characteristic is slightly drooping. Motor uses commutators for changing the magnetic field polarity. INTERNAL CHARACTERISTICS: THE INTERNAL CHARACTERISTIC OF THE SEPARATELY EXCITED DC GENERATOR IS OBTAINED BY SUBTRACTING THE DROPS DUE TO ARMATURE REACTION FROM NO LOAD VOLTAGE. V t = E - I a (R a +R se) Thus the external characteristics is also of rising nature as E increases but it will be below internal characteristics due to drop I a (R a +R se ). In this DC Generator the Single Turn Alternator is used. The internal and external characteristics of a d.c. series generator can be plotted from one another as shown in fig. Ra + Rse. State the three classifications of dc generators. They can also be modified to provide different outputs. According To The Position Of The Field Coil DC Generator Has A Three Type 1)Series Generator . INTERNAL CHARACTERISTICS: THE INTERNAL CHARACTERISTIC OF THE SEPARATELY EXCITED DC GENERATOR IS OBTAINED BY SUBTRACTING THE DROPS DUE TO ARMATURE REACTION FROM NO LOAD VOLTAGE. The linearity of the curve will continue till the saturation of the poles. 12. As we studied, in the shunt generator, an increase in load causes the terminal voltage to decrease. The equation is given by V a = E I aR a or I a = E V a R a (1) Based on the method of excitation dc generators can be divided into two groups. The magnetization curve at no . 1. Also to be familiar with the main advantages and disadvantages of these types of dc generators by comparing the main features among them, specially the voltage regulation and control methods of the output voltage. Explain the causes of armature losses. This easy to use tool will help create an outline of a villain (or any other character for that matter) for RPG games, but it could just as easily be used for other purposes if you see fit. Terminal voltage(V) = E g - I a R a. Adopt a suitable soft-starting mechanism to the DC Motor (change the series resistance with armature circuit is shown in the figure 2). The EMF induced in the armature winding of a DC generator is alternating one and is converted into direct voltage using a commutator mounted on the shaft of the generator. The voltage regulation of a generator (independent of the kind of excitation employed) is defined as. CHARACTERISTICS OF SELF EXCITED DC GENERATOR: In shunt wound DC generators the field windings are connected in parallel with armature conductors as shown in figure below. Previously, you saw that a dc motor is made up basically of a fixed magnet (stator) and a rotating magnet (rotor). A dc shunt generator is a self-excited generator. V. DC generator characteristics Generally, the following two characteristics of DC generators are taken into considerations: 1. 7.10. dc shunt generator, dc series generator, and dc compound generator such as, no-load characteristics, and terminal characteristics. Series excited C. Shunt excited D . Cumulative compound motors If the series field flux assists the shunt field flux, then it is a cumulatively compound motor. They are compact and lightweight. Load characteristics of DC generator: Load characteristics give the relation between the terminal voltage and load current at a constant speed. An electric generator is a machine that converts mechanical energy into electrical energy. Flat compound generator the terminal voltage at the full load is equal to the no-load terminal voltage. The rotor consists of the armature and windings at the associated core for the armature. Note that for generator the current is leaving the positive voltage terminal. is induced which will cause a current to flow if the conductor circuit is closed. Characteristics of DC Generator. The Dc Generator Converts Mechanical Energy into Electrical Energy. Rated load - 0.15 mNm. Their external characteristics at constant speed are given In List-Il. Open Circuit Characteristic (O.C.C.) These characteristics help us to select a suitable motor . Characteristics of DC Generators The speed of a DC generator is made constant by the prime mover. Due to residual magnetism there will be a small 2. OTHER CHARACTERISTICS: WHEN THE GENERATOR IS LOADED THEN THE VOLTAGE DROPS DUE TO TWO MAIN REASONS- 1) DUE TO ARMATURE REACTION, 2) DUE TO OHMIC DROP ( IARA ). This is shown in the Fig. To obtain open circuit or magnetization characteristics of DC generator 1 Theory 1.1 Motivation Open-circuit or no-load tests are useful in estimating the performance of a machine under di erent levels of eld excitation. Fig. Reason for using two separate sources for the armature and field is to be able to control Equivalent circuit for a separately speed by. This forms a simple COMMUTATOR. Thus the stable point at which the voltage will remain fix is the voltage Ea . I L = load current There are generally three most important characteristics of series wound DC generator which show the relation between various quantities such as series field current or excitation current, generated voltage, terminal voltage and load current. This video contains explanation of what is Open circ. OTHER CHARACTERISTICS: WHEN THE GENERATOR IS LOADED THEN THE VOLTAGE DROPS DUE TO TWO MAIN REASONS- 1) DUE TO ARMATURE REACTION, 2) DUE TO OHMIC DROP ( IARA ). The external characteristics are known by drawing a graph between the terminal voltage and the load current. Generator All the generators work on a principle of dynamically induced e.m.f. Generator has a mechanical energy as an input and provides DC Current as an output. Equipment: 1. These characteristics are determined by keeping the following two relations in mind. Referring to the diagram beside, we can see, that if E is the supply voltage, E b is the back emf produced and I a, R a are the armature current and armature resistance respectively then the voltage equation is given by . We can know these values from the performance characteristics. The D.C series motor is consists of a rotor (armature), commutator, stator, axle, field windings, and brushes. Characteristics of DC Compound Generator For small distance operation the flat compounded generators are generally used because the length of the feeder is negligible. The DC motor block imple-ments a separately excited DC motor. As the load current increases, the terminal voltage of a generator falls due to : The increased voltage drop is caused by the armature resistance. DC Machine - Types . when the flux produced by these two m.m.f.s is additive, it is said to be cumulatively compounded. Load characteristic 5.1 Self excited DC shunt generator A shunt generator has its shunt field winding connected in parallel with the armature so that the machine provides it own excitation. Figure 2-7. One part is the shunt field current I sh flows through shunt field winding and the other part is the load current I L goes through the external load . (E A) and the field current (I f) at a given speed. This characteristic shows the relation between generator induced e.m.f. 14. 2. 2. A shunt generator has a critical field resistance of 200 Q at a speed of 800 r.p.m. Volume 3 of 4 Module 7 - Basic AC Theory It works based on principle of the electromagnetic induction. Commutator is Divided into Two Parts A and B. 13. Beyond point of intersection of Field Resistance Line and Magnetization curve / Open Circuit Characteristics the voltage won't build up as in that case the generated voltage Ea will not be able to drive the required field current. II. assists the series field m.m.f. The method of testing to derive the equivalent circuit of a given design is demonstrated . State the term that applies to voltage variation from no-load to full-load conditions and how it is expressed as a percentage. The fixed component of the motor is the stator and is constructed with two or more electromagnet pole parts. This principle nothing but the Faraday's law of electromagnetism induction. After that there will be no further significant change of terminal voltage of DC generator for increasing field current. DC generators are categorized into three main types based on the methods of field excitation: Permanent Magnet, Separately Excited, and Self-Excited DC generators. D.C. generator generally preferred for charging automobile batteries is A. series generator B. shunt generator C. long shunt compound generator D. any of'the above Answer: C. D.C. GENERATORS Objective Questions Pdf :: 61. Line and Magnetization curve / Open Circuit Characteristics of DC Shunt Generator. These readings, when plotted, give the external characteristic. There will be a small voltage (E r) generated. The voltage regulation of a cumulatively compounded DC generator can be positive, negative, or even zero, depending on the flux produced by the two field windings. Types of DC Generators. DC Motor. They essentially capture the saturation characteristics of the machine which relate the eld mmf to quantity of air-gap ux produced. What happens if we increase the excitation, current, and load current. main operating characteristics of a separately-excited dc motor using the DC Motor/Generator module. Generator uses the commutators in order to cancel the polarization effect. PDF | On Jul 28, 2020, Qifu Lin and others published Characteristics of DC arcs in a multi-arc generator and its application in the spheroidization of SiO 2 | Find, read and cite all the research . 1 Characteristics of d.c. series motor Now as I L = I a increases, thus the drop I a (R a +R se) increases. No-load speed to 4000. In DC generator, the eld current controls . 60. Characteristics of Compound DC Generator The compound generator is a self-excited DC Generator, whose characteristics depends on both shunt field winding and series field winding. Generally, these are plotted considering different parameters. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when A. r.p.m. 13. DC Motors and Generators DC motor Fall15 Revised: November 4, 2016 1 of 21 EXPERIMENT DC Machine DC Motors and Generators 1800RPM OBJECTIVE This experiment explores all the possible design connections of a DC machine.

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