This relation applies equally well to all rotating machines, regardless of the type of machine. A typical alternator is shown in figure 33, view a. Eeeb344 electromechanical devices chapter 5 chapter 5. Generator working principle and explain about ac and dc. Generator losses in dc generators, as in most electrical devices, certain forces act to decrease the efficiency. A portion of the input energy gets lost in the machine. Basic construction details about design of dc motor or generator.
But in order to understand efficiency well, we must know losses which fortunately are less compared to dc motor. In the case of shunt generators, it is practically constant. Efficiency is a very important specification of any type of electrical machine. Losses in dc machine the losses that occur in a dc machine is divided into five basic categories. In a typical generator, a prime mover such as a steam turbine supplies mechanical power to the generator, which is converted to electrical power and delivered to the electrical system.
The dc machines are classified into two types such as dc generator as well as dc motor. There are several tests to judge the performance of a dc machine. Generator is a machine that converts mechanical energy into electrical energy. The losses in a dc machine affect its cost, rating, and performance. This video demonstrates how the power output and efficiency can be calculated for a dc shunt generator. Losses and efficiency of dc machine electrical academia.
Whole of the input power can not be converted into the output power in a practical machine due to various losses that take place within the machine. In case of generator p a input power rotational losses output powerefficiency rotational losses p. Stray load loss is difficult to calculate accurately and therefore it is taken as 1 % of the output of a dc machine. Armature copper loss is given by ia2 ra, where ia is the armature current and ra is the resistance of the armature. Three most important characteristic of shunt wound dc generators are discussed below. A dc machine is an electromechanical energy alteration device. Once the losses of the machine are known, its efficiency at any desired load can be determined in advance.
Losses and efficiency of dc machines electric equipment. Generator losses copper,hysteresis, eddy current and. Direct current machines are energy transfer devices. Thus, there are three basic classification dc generators 1 permanentmagnet field 2 separatelyexcited field and 3 selfexcited field. Most synchronous generators that have brushless exciters also use slip rings and brushes as an auxiliary source of field dc current in emergencies.
There are four internal losses that contribute to lower efficiency of a dc generator. A dc generator converts mechanical power into electrical power and a dc motor converts electrical power into mechanical power. Further under highly saturated conditions of teeth, flux leaks through the frame and end shields causing eddy current loss in them. To understand the factors on which various losses depend upon. Calculating power output and efficiency for a dc shunt. The smaller the losses, the greater is the efficiency of the machine.
Dc motors and generators have the same basic construction, differing primarily in the energy conversion. Magnetic losses include hysteresis loss and eddy current loss. Dc generators industrial wiki odesie by tech transfer. How to flash a generator when output is lost due to loss. The losses in the synchronous machine are similar to those of the transformer and other types of rotating machines.
The losses that occur in a dc machine is divided into five basic categories. The current rating is based on the size of the conductor and the amount of heat that can be dissipated in the generator. Efficiency of dc generator maximum efficiency circuit globe. There are three methods of excitation, and thus three main types of dc generators. To know what are the various power losses which take place in a d. Other members of the family are the direct current dc motor or generator, the induction motor or generator, and a number of derivatives of all these. Laminations of core are generally made of a case iron b carbon c silicon steel d stainless steel d. This energy conversion is based on the principle of production of dynamically induced emf. The efficiency of a dc machine depends upon the losses. Like any coil, the armature has some amount of resistance and inductive reactance. The efficiency of a rotating machine is frequently determined by measuring the losses, using. Whether the machine operates as a motor or as a generator, the losses can be summed as.
This relationship is sometimes incorrectly stated as maximum. Pdf the power ratings of the drive systems used in cyclic duty applications such as flyingdie and cuttolength shears are dictated by the thermal. Like all electrical machines, synchronous machines have copper, steel, rotational, and stray losses. Measurement of stray load loss of dc machines scholars mine. The equivalent circuit of a synchronous generator the voltage ea is the internal generated voltage produced in one phase of a synchronous generator. The final result is the electrical output of the generator. The working principle of a dc machine is when electric current flows through a coil within a magnetic field, and then the magnetic force generates a torque which rotates the dc motor. It works based on principle of faraday law of electromagnetic induction.
Field switch allows connecting and disconnecting the output of the excitation system to the field winding of the generator. Dc generator a dc generator is an electrical machine which converts mechanical energy into direct current electricity. Permanent magnet dc generators field coils excited by permanent magnets. How to flash a generator when output is lost due to loss of excitation. State the term that applies to voltage variation from noload to fullload conditions and how it is expressed as a percentage. Efficiency of dc generator and types of losses in dc generator. These losses are about 30% of the total full load losses. External characteristic of separately excited dc generator the external characteristic of the separately excited dc generator is obtained by subtracting the drops due to ohmic loss ia ra in the armature from generated voltage eg. Electric motors experience losses during the conversion of electrical power to mechanical power. Introduction in 1949,1 a single phase offset mho relay was introduced for the high speed detection of loss of excitation in synchronous generators. Internal losses that reduce efficiency of a dc generator. Equation 1 shows that the efficiency of a dc generator is maximum when those losses proportional to the square of the load current are equal to the constant losses of the dc generator.
The types of losses are generally classified as one of five types magnetic, mechanical, copper, brush, or stray. Generator the various losses occurring in a generator can be subdivided as follows. Residual magnetism in the generator exciter field allows the generator to build up voltage during startup. The faradays law states that whenever a conductor is placed in a varying magnetic field, emf is induced and. The various losses are electrical or copper losses i 2 r losses, core losses or iron losses, brush losses, mechanical losses, stray load losses. Losses in dc machine types of losses circuit globe. The combination of these make up what is known as the internal resistance, which causes a loss in an ac generator. Swinburnes test is the simplest indirect method of testing dc machines. These forces, as they affect the armature, are considered as losses and may be defined as follows.
Losses in dc dc generator and effency free download as word doc. The diagram visualizes the amount of power that has been lost in various types of losses and the amount of power which has been actually converted into the output. These machines can function as either a motor or a generator. To better understand the operation and construction of dc.
Lossofexciation protection for synchronous generators. Q a shortshunt compound generator has armature, shunt fi eld and series fi eld resistances of 0. The most convenient method to understand these losses in a dc generator or a dc motor is using the power flow diagram. Losses in dc dc generator and effency electromagnetic induction. Armature copper loss i a 2 r a where, i a is armature current and r a is armature resistance. Types of dc generators diagrams included electrical4u. The synchronous electrical generator also called alternator belongs to the family of electric rotating machines. Investigation on generator loss of excitation protection. The various losses are electrical or copper losses i2r losses, core losses or iron. Thus, for a dc generator, input power is in the form of mechanical and the output power is in the form of electrical. Applications of dc generators nowadays cheap and economical rectifiers and filters grant a new life to dc generators and give them a great importance in all fields around us and it also leads to diversity so there are many types of dc generators which we illustrated and which has many applications and thats. Dc machine construction, working, types, emf equation.
Principal of electrical machinery and optimization of. Magnetic or open circuit characteristic of shunt wound dc generator this curve is drawn between shunt field currenti sh and the no load voltage e 0. Voltage rating of a machine is based on the insulation type and design of the machine. This article outlines basic construction and working of a dc generator. Pdf evaluation of losses in dc machines a statistical approach. Dc generators are classified based on how their fields are excited i. Power and torque in synchronous generators the real output power of the synchronous generator is p v i v i out t l a 3 cos 3 cos the reactive output power of the synchronous generator is q vi viout t l a 3 sin 3 sin recall that the power factor angle is the angle between v and.
Explain the effect of motor reaction in a dc generator. When we talk about efficiency, losses comes into the picture. The losses can be divided into three types in a dc machine generator or motor. Field winding copper loss i f 2 r f where, i f is field current and r f is field resistance. Copper loss is the power lost as heat in the windings. Electrical machines lab 1 griet eee 1 department of electrical and electronics engineering electrical machinel d. It summarizes the advantages and disadvantages of different schemes and serves as a reference for selecting the loss of excitation protection scheme. C laboratory manual gokaraju rangaraju institute of engineering. Generators electrical engineering multiple choice questions and answer pdf free download interview questions objective type questions lab viva.
Core or iron losses listed in hysteresis losses and eddy current losses. In this method, the dc machine generator or motor is run as a motor at noload and losses of the machine are determined. Note that in a selfexcited dc generator, the field losses would be included in the copper losses, whereas in a separately excited dc generator the field losses would constitute a separate electrical input that would also be added to the losses of the machine. The losses in a dc machine generator or motor may be divided into three classes viz copper losses iron or core losses and mechanical losses. These losses are about 25% theoretically, but practically it is constant.
Losses in an ac generator the load current flows through the armature in all ac generators. No load condition operative condition of the generator when it is at nominal speed and voltage in terminals, and is not connected to the electric power system. Dc generator theory dc generators dc generator ratings a dc generator contains four ratings. When supplying a load of 8 kw at a terminal voltage of 250 v the input power supplied by the driving motor is 10. For many years the standard practice, in calculation of conventional efficiency of d. The copper losses are proportional to the square of the current flowing through the winding. Separately excited dc generators field coils excited by some external source. Principal of electrical machinery and optimization of electrical power. Dc generator efficiency can be calculated by finding the total losses in it. Applications of dc generators that surround us everywhere. For a given excitation current or field current, the emf generated at no load e 0 varies in proportionally with the. Thus, in order to design rotating dc machines with higher efficiency, it is important to study the losses occurring in them.
Generator a copper losses b magnetic losses c mechanical losses. In a dc machine, there are only two windings, armature and field winding. In all machines, the whole of input energy does not get convertered into output energy. If the machine is not connected to a load no armature current flowing, the terminal voltage will be. C generators are classified according to the way in which a magnetic field is developed in the stator of the machine. The core losses are 200 w, and the mechanical losses are 240 w at full load.
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