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