DBL GROUP- An overview
1.1 Vision
The vision is to be the largest supplier in the world for quality apparels at competitive price, with production facilities spread across continents and have a visible contrubution to the GDP of Bangladesh.
1.2 Mission
Vision 2020 aims to sustain the confidence which has been endowed on them by the society and grow further as a distinctive DBL Group for its customers, employees, associates and stakeholders.
1.3 Company History
Mymun Textiles Ltd. is a sister concern of DBL GROUP. DBL Group is vertically integrated knit garments manufacturing & exporting composite industry. DBL Group started its business in 1991 with a garments factory named Dulal Brothers Ltd. They have now grown into a respected and trusted name in Bangladesh for thier manufacturing operations with an ever contributing workforce of about 12,000. They have state-of-the-art apparel manufacturing facilities with very strong backward linkage industries of yarn spinning, fabric knitting-dyeing-finishing, printing and packaging. They are supplying quality apparels across the world to the best of the retailers.
They have now embarked on a growth plan that is expected to truly transform their organization. In the next five years their home textiles, ceramics, pharmaceuticals, and leather industry will be in operation.
1.4 Board and Management:
Board of Directors
A. Wahed, Chairman
M. A. Jabbar, Managing Director
M. A. Rahim, Director
M. A. Quader, Director
Management Team
The Management Team is comprised of higher level professionals for smooth and successful running of the day-to-day business operation. Some of the key personnel are:
Md. Ishaque, FCMA – Advisor – Corporate Management
Syed Naser Bukhtear Ahmed – Advisor – Corporate Management
Engr. A.N.M. Anwarul Azim – Director Technical – Planning & Development
Dr. Delwar Hussain -Director- Medical & Health Care Service
Naser Khan – Executive Director – Garments unit
Abdul Matin, FCA – General Manager – Finance & Accounts
Gazi Md. Mohsin, FCMA – General Manager – Cost, Budget & Material Management
Md. Muzaffar Hossain – General Manager – Administration & Logistics
Sadek Ahmed (Pallab) – General Manager – Dyeing & Finishing Unit
Md. Sadequr Rahman – General Manager – Knitting unit
Md. Shamimul Haque – General Manager – Spinning Unit
1.5 Social Commitment:
A. Matin Jinnat Foundation
Matin Jinnat Foundation is a charitable trust named after the parents of the founding Directors of DBL Group. The trust has been formed to look after the welfare of the poor people. Service to the poor is provided by way of donations, charity, school, clinic, orphanage, etc. The foundation firmly believes that setting-up new industries and creating employment opportunities is the best form of serving the society.
B. Access to Medicines
They have a pharmacy at their manufacturing facility for their employees. They are able to get medicines at subsidized prices for themselves as well as their family. Free medicines are given to employees having financial constraint.
C. Protecting the People
They have provided Personal Protective Equipments to their employees for use in their job. Machines are also equipped with safety guards.
D. Protecting the Environment
They have a 4,000 cubic mtrs capacity Biological type Effluent Treatment Plant. This had been taken as a benchmark by Department Of Environment-Bangladesh for other ETPs in the country. Another ETP of 7,500 cubic mtrs is under construction.
They are using energy efficient USA/Europe/Japan machineries. The dyeing machines have individual heat recovery unit resulting in lower power consumption and energy saving by 15%. Water consumption saving is of about 20% compared to normal dyeing machines. Heat recovery from Captive Power Plant of 5MW capacity is providing energy saving of about 15%. Waste materials from production processes are recycled.
E. Children’s Hope
They are associated with Children’s Hope, Bangladesh as a Corporate Donor. They are active for development of poor children in the field of Education, Vocational Training, Health training, etc. and also takes part in various social humanitarian activities
Power Plant apparatus
2.1 Introduction:
The electric power system can be divided into the following regions:
- Generating stations
- Transmission system
- Receiving station
- Distribution system
- Load points
In all these regions need switchgear. Switchgear is a general term covering a wide range of equipment concerned with switching and protection. All equipment associated with the fault clearing processes are converted by the term ‘Switchgear.’ Switchgear is an essential part of a power system and also that of any electric circuit. Switchgear includes switches, fuses, circuit breakers, isolators, relays, control panels, lightning arresters, current transformers and various associated equipments. Switchgear is necessary at every switching point in AC power system. Between the generating station and final load point, there are several voltage levels.
2.2 Power Plant equipment:
In every power plant there are generally various types of indoor and outdoor equipments. The equipments are either indoor or outdoor, depending upon the voltage rating and local conditions. Generally indoor equipment may be preferred for voltages up to 33kv. For voltage of 33kv and above, outdoor switchgear is generally preferred. The outdoor equipment is installed under the sky.
The main equipment of a power plant is generator. It has two part, engine or prime mover and other is alternator, which produced the generated power. All of the system control from the control room. Control room is the brain of a power plant. Many types of control panel are arranges in the control room. Any things of power plant can control from this room.
In the Mymun Textiles Ltd., there are three generators, which are controlled by PLC (Programmable Logic Controller). Every thing of this power plant controlled and measured by this PLC. Charge air compressor, Lube oil pump & motor, Heat exchanger, LT and HT etc. are the other equipments of Mymun Textiles Ltd. power plant.
2.2.1 Generator:
“Energy can neither be created nor be destroyed”. We can only change its forms, using appropriate energy – conversion processes. Energy conversion takes place between well known pairs of forms of Energy; Electrical ? Chemical, Electrical ? Thermal, Electrical ? Optical, Electrical ? Sound and Electrical ? Mechanical are the common forms with numerous varieties of engineering – applications.
Purpose of electro – mechanical conversion device is to change the form of energy. Here, for simpler discussion, only rotary system will be dealt with. When it is converting mechanical input to electrical output the device is “generating”. With electrical input, when mechanical output is obtained, the device is “motoring”.
An electrical generator is a machine which converts mechanical energy (or power) into electrical energy (or power). The conversion is based on the principle of the production of dynamically (or motionally) induced e.m.f. When a conductor cuts magnetic flux, dynamically induced e.m.f. is produced in it according to Faraday’s Laws of Electromagnetic induction. This e.m.f. causes of current to flow if the conductor circuit is closed.
Faraday summed up the above facts into two laws known as Faraday’s Laws of Electromagnetic Induction.
First law, it states:
Whenever a conductor cuts magnetic flux, an e.m.f. is induced in that conductor.
Second law, it states:
The magnitude of the induced e.m.f. is equal to the rate of change of flux – linkages.
The Basic two parts of an AC generator is,
- Prime mover or engine, and
- Alternator
Prime mover or engine use for rotating of magnetic field and alternator which mainly generates the energy or power. By using of engine, rotor (magnetic field) rotates and alternator (stator) produces energy by cutting the flux of magnetic field.
In the figure shows a single – turn rectangular copper coil ABCD rotating its own axis in a magnetic field provided by either permanent magnet is or electromagnet. The two ends of the coil are joined to two slip – rings ‘a’ and ‘b’ which are insulated each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip – rings. Their function is to collect the current induced in the coil and convey it to the external load resistance R. The rotating coil may be called ‘armature’ and the magnets as ‘field magnets’.
Working principle of generator:
Imagine the coil to be rotating in clock-wise direction. As the coil assume successive positions in the field, the flux linked with it changes. Hence, an e.m.f. is induced in it which is proportional to the rate of change of flux linkages. When the plane of the coil is at right angles to lines of flux, when it is in position, 1, then flux linked with the coil is maximum but rate of change of flux linkages is minimum.
In a generator, the electrical power that is produced constantly changes. At first, the generated electric current moves in one direction (as from left to right). Then, when the coil reaches a position where it is parallel to the magnetic lines of force, no current at all is produced. As the coil continues to rotate, it cuts through magnetic lines of force in the opposite direction, and the electrical current generated travels in the opposite direction (as from right to left). The ends of the coil are attached to metal slip rings that collect the electrical current. Each slip ring, in turn, is attached to a metal brush, which transfers the current to an external circuit.
Thus, a spinning coil in a fixed magnetic field will produce an alternating current, one that travels first in one direction and then in the opposite. The rate at which the current switches back and forth is known as its frequency. Ordinary household current alternates at a frequency of 50 times per second (or 50 hertz).
The efficiency of an AC generator can be increased by substituting an armature for the wire coil. An armature consists of a cylinder-shaped iron core with a long piece of wire wrapped around it. The longer the piece of wire, the greater the electrical current that can be generated by the armature.
An AC generator can be modified to produce direct current (DC) electricity also. This change requires a commutator. A commutator is simply a slip ring that has been cut in half, with both halves insulated from each other. The brushes attached to each half of the commutator are arranged so that at the moment the direction of the current in the coil reverses, they slip from one half of the commutator to the other. The current that flows into the external circuit, therefore, is always traveling in the same direction. This results in a steadier current.
In the MTL, there use WAUKESHA generator for power generation. It is V – type gas engine generator. The engine of this generator mainly use in the marine vehicle. The engine of this generator runs by natural gas. This engine used for rotating the rotor in 1000 rpm. So, the magnet of the rotor producing magnetic flux which is cutting by the stator conductor of the alternator and producing electrical energy.
Fig: WAUKESHA Gas Generator
Technical Data:
01. Alternator Model No. MTG-846C
02.Serial No. CB115391
03.Enginator Model VHP-7104GSID
04.Serial No. C-94885-901/2
05.Voltage 400V
06.Pressure of Gas 10PSI
07.Temparature of cool water 28-40 degree C
08.Temparature of Lube Oil 81-85 degree C
09.Power 1100KW
Fig: Working with Generator
2.2.2 Types of AC Generators:
There are two types of generators:
I. The stationary field, rotating armature
II. The rotating field, stationary armature.
Small AC generators usually have a stationary field and a rotating armature (Figure 2.5).
This arrangement is called a rotating field, stationary armature AC generator. The rotating field, stationary armature type AC generator is used when large power generation is involved. In this type of generator, a DC source is supplied to the rotating field coils, which produces a magnetic field around the rotating element. As the rotor is turned by the prime mover, the field will cut the conductors of the stationary armature, and an EMF will be induced into the armature windings. This type of AC generator has several advantages over the stationary field, rotating armature AC
Generator: (1) a load can be connected to the armature without moving contacts in the circuit, (2) It is much easier to insulate stator fields than rotating fields; and (3) much higher voltages and currents can be generated.
2.2.3 Three-Phase AC Generator:
The principles of a three-phase generator are basically the same as that of a single-phase generator, except that there are three equally-spaced windings and three output voltages that are all 120° out of phase with one another. Physically adjacent loops are separated by 60° of rotation; however, the loops are connected to the slip rings in such a manner that there are 120 electrical degrees between phases.
Figure 2.9 Stationary Armature 3 Phase Generator
The individual coils of each winding are combined and represented as a single coil. The significance of Figure 2.6 is that it shows that the three-phase generator has three separate armature windings that are 120 electrical degrees out of phase.
2.2.1.1 Prime mover (Engine)
A machine that transforms energy from thermal, electrical or pressure form to mechanical form; typically an engine. An engine is a machine designed to convert energy into useful mechanical motion. In common usage, an engine burns or otherwise consumes fuel, and is differentiated from an electric machine (i.e., electric motor) that derives power without changing the composition of matter. An engine may also serve as a “Prime mover”, a component that transforms the flow or changes in pressure of a fluid into mechanical energy. An automobile powered by an internal combustion engine may make use of various motors and pumps, but ultimately all such devices derive their power from the engine. In modern usage, the term is used to describe devices capable of performing mechanical work, as in the original steam engine. In most cases the work is produced by exerting a torque or linear force, which is used to operate other machinery which can generate electricity, pump water, or compress gas.
There are two mainly two types of engine –
a) internal combustion engine and
b) external combustion engine
The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. An externalcombustionengine (EC engine) is a heat engine where an internal working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger.
In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy. The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines.
Fig: V – Type engine
Applications
Internal combustion engines are most commonly used for mobile propulsion in vehicles and portable machinery. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel (mainly petroleum), these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives).
Where very low power-to-weight ratios are not required, internal combustion engines appear in the form of gas turbines. These applications include jet aircraft, helicopters, large ships and electric generators.
Four stroke Engine configurations
Operation
Four-strokecycle(orOttocycle)
1.Intake
2.Compression
3.Power
4.Exhaust
As their name implies, operation of four stroke internal combustion engines have four basic steps that repeat with every two revolutions of the engine:
Intake
Combustible mixtures are emplaced in the combustion chamber
Compression
The mixtures are placed under pressure
Power
The mixture is burnt and hot mixture is expanded, pressing on and moving parts of the engine and performing useful work.
Exhaust
The cooled combustion products are exhausted into the atmosphere
Fig: operation of four stroke internal combustion engines
Gasoline Ignition Process
Gasoline engine ignition systems generally rely on a combination of a lead-acid battery and an induction coil to provide a high-voltage electrical spark to ignite the air-fuel mix in the engine’s cylinders. This battery is recharged during operation using an electricity-generating device such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar (1.28 MPa), then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.
Combustion chambers
Internal combustion engines can contain any number of combustion chambers (cylinders), with numbers between one and twelve being common; though as many as 36 have been used. Having more cylinders in an engine yields two potential benefits: first, the engine can have a larger displacement with smaller individual reciprocating masses, that is, the mass of each piston can be less thus making a smoother-running engine since the engine tends to vibrate as a result of the pistons moving up and down. Doubling the number of the same size cylinders will double the torque and power. The downside to having more pistons is that the engine will tend to weigh more and generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and robs the engine of some of its power. For high-performance gasoline engines using current materials and technology—such as the engines found in modern automobiles, there seems to be a point around 10 or 12 cylinders after which the addition of cylinders becomes an overall detriment to performance and efficiency.
Ignition system
The ignition system of an internal combustion engines depends on the type of engine and the fuel used. Petrol engines are typically ignited by a precisely timed spark, and diesel engines by compression heating.
Fig:Ignition Circuit Diagram – Mechanically Timed Ignition
Fig: Basic Electronic Ignition System
Spark
The mixture is ignited by an electrical spark from a spark plug—the timing of which is very precisely controlled. Almost all gasoline engines are of this type. Diesel engines timing is precisely controlled by the pressure pump and injector.
Compression
Ignition occurs as the temperature of the fuel/air mixture is taken over its auto ignition temperature, due to heat generated by the compression of the air during the compression stroke. The vast majority of compression ignition engines are diesels in which the fuel is mixed with the air after the air has reached ignition temperature. In this case, the timing comes from the fuel injection system. Very small model engines for which simplicity and light weight is more important than fuel costs use easily ignited fuels (a mixture of kerosene, ether, and lubricant) and adjustable compression to control ignition timing for starting and running.
Ignition timing
For reciprocating engines, the point in the cycle at which the fuel-oxidizer mixture is ignited has a direct effect on the efficiency and output of the ICE. The thermodynamics of the idealized Carnot heat engine tells us that an ICE is most efficient if most of the burning takes place at a high temperature, resulting from compression—near top dead center. The speed of the flame front is directly affected by the compression ratio, fuel mixture temperature, and octane rating or cetane number of the fuel. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced ignition timing. It is important to have combustion spread by a thermal flame front (deflagration), not by a shock wave. Combustion propagation by a shock wave is called detonation and, in engines, is also known as pinging or Engine knocking.
Fuel systems
Fuels burn faster and more efficiently when they present a large surface area to the oxygen in air. Liquid fuels must be atomized to create a fuel-air mixture; traditionally this was done with a carburetor in petrol engines and with fuel injection in diesel engines. Most modern petrol engines now use fuel injection too – though the technology is quite different. While diesel must be injected at an exact point in that engine cycle, no such precision is needed in a petrol engine. However, the lack of lubricity in petrol means that the injectors themselves must be more sophisticated.
Fuel injection
Larger gasoline engines used in automobiles have mostly moved to fuel injection systems. Diesel engines have always used fuel injection system because the timing of the injection initiates and controls the combustion. Autogas (LPG) engines use either fuel injection systems or open- or closed-loop carburetors.
Superchargers and turbochargers
A supercharger is a “forced induction” system which uses a compressor powered by the shaft of the engine which forces air through the valves of the engine to achieve higher flow. When these systems are employed the maximum absolute pressure at the inlet valve is typically around 2 times atmospheric pressure or more.
Turbochargers are another type of forced induction system which has its compressor powered by a gas turbine running off the exhaust gases from the engine.
Turbochargers and superchargers are particularly useful at high altitudes and they are frequently used in aircraft engines.
Duct jet engines use the same basic system, but eschew the piston engine, and replace it with a burner instead.
Fig: A cutaway of a turbocharger
Oxidiser-Air inlet system
Some engines such as solid rockets have oxidisers already within the combustion chamber but in most cases for combustion to occur, a continuous supply of oxidiser must be supplied to the combustion chamber.
Parts of Engine
Fig: An illustration of several key components in a four-stroke engine.
For a four-stroke engine, key parts of the engine include the crankshaft (purple), connecting rod (orange), one or more camshafts (red and blue), and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines there are one or more cylinders (grey and green), and for each cylinder there is a spark plug (darker-grey, gasoline engines only), a piston (yellow), and a crankpin (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke. The downward stroke that occurs directly after the air-fuel mix passes from the carburetor or fuel injector to the cylinder (where it is ignited) is also known as a power stroke.
Valves
All four-stroke internal combustion engines employ valves to control the admittance of fuel and air into the combustion chamber. Two-stroke engines use ports in the cylinder bore, covered and uncovered by the piston, though there have been variations such as exhaust valves.
Piston engine valves
In piston engines, the valves are grouped into ‘inlet valves’ which admit the entrance of fuel and air and ‘outlet valves’ which allow the exhaust gases to escape. Each valve opens once per cycle and the ones that are subject to extreme accelerations are held closed by springs that are typically opened by rods running on a camshaft rotating with the engines’ crankshaft.
Control valves
Continuous combustion engines—as well as piston engines—usually have valves that open and close to admit the fuel and/or air at the startup and shutdown. Some valves feather to adjust the flow to control power or engine speed as well.
Exhaust systems
Internal combustion engines have to manage the exhaust of the cooled combustion gas from the engine. The exhaust system frequently contains devices to control pollution, both chemical and noise pollution. In addition, for cyclic combustion engines the exhaust system is frequently tuned to improve emptying of the combustion chamber.
For jet propulsion internal combustion engines, the ‘exhaust system’ takes the form of a high velocity nozzle, which generates thrust for the engine and forms a collimated jet of gas that gives the engine its name.
Fig: Exhaust system of Mymun Textiles Ltd.
Cooling systems
Combustion generates a great deal of heat, and some of these transfers to the walls of the engine. Failure will occur if the body of the engine is allowed to reach too high a temperature; either the engine will physically fail, or any lubricants used will degrade to the point that they no longer protect the engine.
Cooling systems usually employ air (air cooled) or liquid (usually water) cooling while some very hot engines using radiative cooling (especially some Rocket engines). Some high altitude rocket engines use ablative cooling where the walls gradually erode in a controlled fashion. Rockets in particular can use regenerative cooling which uses the fuel to cool the solid parts of the engine.
Fig: Radiator of Mymun Textiles Ltd.
Piston
A piston is a component of reciprocating engines. It is located in a cylinder and is made gas-tight by piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In two-stroke engines the piston also acts as a valve by covering and uncovering ports in the cylinder wall.
Crankshaft
Most reciprocating internal combustion engines end up turning a shaft. This means that the linear motion of a piston must be converted into rotation. This is typically achieved by a crankshaft.
Flywheels
The flywheel is a disk or wheel attached to the crank, forming an inertial mass that stores rotational energy. In engines with only a single cylinder the flywheel is essential to carry energy over from the power stroke into a subsequent compression stroke. Flywheels are present in most reciprocating engines to smooth out the power delivery over each rotation of the crank and in most automotive engines also mount a gear ring for a starter. The rotational inertia of the flywheel also allows a much slower minimum unloaded speed and also improves the smoothness at idle. The flywheel may also perform a part of the balancing of the system and so by itself be out of balance, although most engines will use a neutral balance for the flywheel, enabling it to be balanced in a separate operation. The flywheel is also used as a mounting for the clutch or a torque converter in most automotive applications.
Starter systems
All internal combustion engines require some form of system to get them into operation. Most piston engines use a starter motor powered by the same battery as runs the rest of the electric systems. Large jet engines and gas turbines are started with a compressed air motor that is geared to one of the engine’s driveshafts. Compressed air can be supplied from another engine, a unit on the ground or by the aircraft’s APU. Small internal combustion engines are often started by pull cords. Motorcycles of all sizes were traditionally kick-started, though all but the smallest are now electric-start. Large stationary and marine engines may be started by the timed injection of compressed air into the cylinders—or occasionally with cartridges. Jump starting refers to assistance from another battery (typically when the fitted battery is discharged), while bump starting refers to an alternative method of starting by the application of some external force, e.g. rolling down a hill.
Lubrication Systems
Internal combustions engines require lubrication in operation that moving parts slide smoothly over each other. Insufficient lubrication subjects the parts of the engine to metal-to-metal contact, friction, heat build-up, rapid wear often culminating in parts becoming friction welded together e.g. pistons in their cylinders. Big end bearings seizing up will sometimes lead to a connecting rod breaking and poking out through the crankcase.
Several different types of lubrication systems are used. Simple two-stroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow-speed stationary and marine engines were lubricated by gravity from small chambers similar to those used on steam engines at the time—with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power-to-weight ratio led to increased speeds, higher temperatures, and greater pressure on bearings which in turn required pressure-lubrication for crank bearings and connecting-rod journals. This was provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends which had the advantage of providing higher pressures as the engine speed increased.
Control systems
Most engines require one or more systems to start and shutdown the engine and to control parameters such as the power, speed, torque, pollution, combustion temperature, efficiency and to stabilize the engine from modes of operation that may induce self-damage such as pre-ignition. Such systems may be referred to as engine control units.
Many control systems today are digital, and are frequently termed FADEC (Full Authority Digital Electronic Control) systems.
2.2.1. 2 Alternators
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current. Most alternators use a rotating magnetic field but linear alternators are occasionally used. In principle, any AC electrical generator can be called an alternator, but usually the word refers to small rotating machines driven by automotive and other internal combustion engines.
Alternators are single-phase or polyphase. Variations include three-phase alternators used as single-phase units by insulating and not using one phase lead. Since the lead is unused, it is not brought out to a terminal. The power rating is reduced from that of the three-phase unit as limited by the amount of current carried by a coil. An alternator designed only for single-phase operation usually does not have coils in all of the armature slots because end coils contribute little to the output voltage and increase the coil impedance in the same proportion as any other coil.
Single-phase alternators are usually used in smaller systems (limited to 25kW or less) and produce AC power at utilization voltages. Terminal voltage is usually 120 volts. The electric load is connected across the terminals with protective fuses. One voltmeter and one ammeter measure the output in volts and amperes; respectively the two-wire alternator has two power terminals, one for each end of the armature coil.
Fig: Two-wire, single-phase alternator
The three-wire, single-phase alternator has three power terminals; one from each end of the armature coil and one from the midpoint. Terminal voltage is usually 120 volts from the midpoint to either end of the armature coil and 240 volts between the two ends. The load is connected between the two outside wires or between either outside wire and neutral, depending upon the voltage required by the load. Assuming alternator voltage to be 120/240 volts, load 1, 0 and load 2,0 would consist of 120-volt lamps and 120-volt single phase power equipment. Load 1, 2 would consist of 240-volt power equipment. Two voltmeters and two ammeters (or equivalent) are required to determine the load in kilovolt amperes (kVA).
Fig: Three-wire, single-phase alternator
Polyphase alternators are two, three, or six phases. Two-phase power is used in only a few localities. Six-phase is Primarily used for operation of rotary converters or large rectifiers. Three-phase alternators are the most widely used for power production. Polyphase alternators have capacities from 3 kW to 250,000 kW and voltage from 110 V to 13,800 V. Two general types of three-phases alternator windings are the delta winding used in three wire, three-phase alternators, and the star or wye winding used in four-wire, three-phase types. Three-wire, three-phase alternators have three sets of single-phase windings spaced 120 electrical degrees apart around the armature. One electrical degree is equivalent to one degree of arc in a two pole machine, 0.50 degree of arc in a four-pole machine, 0.33 degree of arc in a six-pole machine, and so on. The three single-phase windings are connected in series to form the delta connection, and
the terminals are connected to the junction point of each pair of armature coils (see illustration below – Three-wire, three-phase alternator). The total current in a delta-connected circuit is always equal to the vector sum of currents in two-phase windings. The instantaneous current flows out to the load through two windings and returns from the load through the third winding. Since the coils are similar physically and electrically, equal voltages are generated and applied to the terminals. Due to spacing of the coils about the armature, the maximum voltage between the pairs of terminals does not occur simultaneously.
Fig: Three-wire, three-phase alternator
The characteristics of three- wire, three-phase (or delta) alternators are:
- The amount of current through the alternator terminals is the algebraic sum of current through the alternator coils.
- The currents are not equal in magnitude or time.
- Connection between coils can be made either inside or outside the generator.
- In a 60-Hertz machine, each coil experiences maximum instantaneous voltage, first positive and then negative, 120 times each second. Disregarding voltage direction, the maximum instantaneous voltages occur on successive coils 0.003 seconds apart. Due to time differences between the voltages and resulting currents, the amount of current through the alternator terminals and the amount through the alternator coils are not equal in magnitude or time. The current through the alternator is 73 percent greater than through the coils. Coil and terminal voltages are the same magnitude. Three voltmeters and three ammeters (or equivalent) are required to measure the load on the alternator. The average value of the three currents times the average value of the three voltages plus 73 percent gives a close approximation of the alternator load in kilovolt-amperes. Two single-phase or one two element polyphase kilowatt-hour meter is required to measure the alternator output in kilowatt-hours.
The four-wire, three-phase alternator has three sets of armature coils spaced 120 electrical degrees apart about the armature, the same as the three-wire, three-phase alternator. One end of each of the three coils is connected to a common terminal (neutral). The other end of each coil is connected to separate terminals (phase terminals). Thus, the four-wire alternator has four terminals which connect to the three-phase conductors and the neutral of the power-plant bus. When each end of each coil is brought out to separate terminals, the connections between coils are made outside of the alternator, enabling installation of a more comprehensive protective relaying system.
Fig: Four-wire, three-phase alternator
The four-wire, three-phase alternator can be connected to a transformer instead of the power plant bus by using a wye-wye transformation. Irregular (double or triple) harmonics, which may be produced, can be suppressed by using a core-type transformer. A third or tertiary winding with a delta connection may also be used as a suppressor. A wye-delta transformer may be used if the power plant bus is three wires and the alternator is four wire wye connected.
Four-wire three-phase, dual voltage and frequency alternators are also used. These are supplied in sizes from 15 to 1500 kW, 127-220 volts, three-phase, 60 Hertz, or 230-400 volts, three phase, 50 Hertz. Dual stator coils are used on each phase. Coil ends are brought out to a terminal board for making connections. Voltage and frequency combinations are shown in below (Dual voltage and Frequency).
Fig: Dual voltage and Frequency
Most parts of the world have standardized on either 50 or 60 Hertz alternating current power. Sixty Hertz power is commonly used in the United States. Fifty Hertz power is used in many countries outside the United States. The ratio be-teen the 60-50 Hertz frequencies are 6:5. Electrical energy received at one frequency can be converted to a different frequency by using a frequency changer. If a large power requirement exists, it may be more economical to use a special alternator to produce power at the desired frequency.
The applicable equation is:
Where:
V = generated voltage
K = constant value number (speed)
= phase/phase angle
N = number of turns
f = line frequency
The generated voltage is proportional to the strength of the magnetic field, phase, and number of turns in series between terminals and the speed.
Generator Exciters AC and DC
Generators require direct current to energize its magnetic field. The DC field current is obtained from a separate source called an exciter. Either rotating or static-type exciters are used for AC power generation systems. There are two types of rotating exciters: brush and brushless. The primary difference between brush and brushless exciters is the method used to transfer the DC exciting current to the generator fields. Static excitation for the generator fields is provided in several forms including field-flash voltage from storage batteries and voltage from a system of solid-state components. DC generators are either separately excited or self-excited.
Excitation systems in current use include direct-connected or gear-connected shaft-driven DC generators, belt-driven or separate prime mover or motor-driven DC generators, and DC supplied through static rectifiers.
The brush-type exciter can be mounted on the same shaft as the AC generator armature or can be housed separately from, but adjacent to, the generator. When it is housed separately, the exciter is rotated by the AC generator through a drive belt.
The distinguishing feature of the brush-type generator is that stationary brushes are used to transfer the DC exciting current to the rotating generator field. Current transfer is made via rotating slip rings (collector rings) that are in contact with the brushes.
Each collector ring is a hardened-steel forging that is mounted on the exciter shaft. Two collector rings are used on each exciter; each ring is fully insulated from the shaft and each other. The inner ring is usually wired for negative polarity, the outer ring for positive polarity.
A rotating-rectifier exciter is one example of brushless field excitation. In rotating-rectifier exciters, the brushes and slip rings are replaced by a rotating, solid-state rectifier assembly. The exciter armature, generator rotating assembly, and rectifier assembly are mounted on a common shaft. The rectifier assembly rotates with, but is insulated from, the generator shaft as well as from each winding.
Static exciters contain no moving parts. A portion of the AC from each phase of generator output is fed back to the field windings, as DC excitations, through a system of transformers, rectifiers, and reactors. An external source of DC is necessary for initial excitation of the field windings. On engine driven generators, the initial excitation may be obtained from the storage batteries used to start the engine or from control voltage at the switchgear.
Fig: Cutaway of an Alternator
Alternator Data of MTL
The output power of the alternator of CPGL is 1100KW. It is four-wire, three-phase alternator. A wye-delta transformer in the power plant bus is three wires and the alternator is four wire wye connected. Data of the alternator is as follow –
Model- MTG 846C
EMI 68600700
KVA 1375
KW 1100
P.F. 0.8
VOLTS 240/415
AMPS 1913
OVERSPEED 125 0/0
ROTATION CCW
HZ 50
RPM 1000
PHASE 3
RATING PRIME
Fig: Parts of an Alternator
Fig: Alternator of MTL
2.2.2 Charge air compressor
A charge air cooler (also known as an intercooler) is used for cooling engine air after it has passed through a turbocharger, but before it enters the engine. The idea is to return the air to a lower temperature, for the optimum power for the combustion process within the engine.
Charge air coolers range in size depending on the engine. The smallest are most often referred to as intercoolers and are attached to automobile engines or truck engines. The largest are reserved for use on huge marine diesel engines, and can weigh over 2 tones.
Fig: Charge Air Cooler
For KVGS – 18G4.2 generator, air consumption is 15400 m3n/h or 20000 Kg/h. Charge air temperature, for normal 55°C. For normal stop/shutdown 62/64°C. This air mix with fuel and supply to the combustion chamber. The Fuel air ratio is 1: 13.2.
Fig: Air Compressor in MTL
Fig: Charge air cooling system for generator
Fig: Charge air compressor and air tank
2. 2. 3 Lube oil pump & motor
The engine lubrication system is designed to deliver clean oil at the correct temperature and pressure to every part of the engine. The oil is sucked out the sump into the pump, being the heart of the system, than forced through an oil filter and pressure feeded to the main bearings and to the oil pressure gauge. From the main bearings, the oil passes through feed-holes into drilled passages in the crankshaft and on to the big-end bearings of the connecting rod. The cylinder walls and piston-pin bearings are lubricated by oil fling dispersed by the rotating crankshaft. The excess being scraped off by the lower ring in the piston. A bleed or tributary from the main supply passage feeds each camshaft bearing. Another bleed supplies the timing chain or gears on the camshaft drive. The excess oil then drains back to the sump, where the heat is dispersed to the surrounding air.
Fig: Lube oil pump
Fig: Lube oil filter
Internal combustions engines require lubrication in operation that moving parts slide smoothly over each other. Insufficient lubrication subjects the parts of the engine to metal-to-metal contact, friction, heat build-up, rapid wear often culminating in parts becoming friction welded together e.g. pistons in their cylinders. Big end bearings seizing up will sometimes lead to a connecting rod breaking and poking out through the crankcase.
Several different types of lubrication systems are used. Simple two-stroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow-speed stationary and marine engines were lubricated by gravity from small chambers similar to those used on steam engines at the time—with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power-to-weight ratio led to increased speeds, higher temperatures, and greater pressure on bearings which in turn required pressure-lubrication for crank bearings and connecting-rod journals. This was provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends which had the advantage of providing higher pressures as the engine speed increased.
Fig: Lube oil system
Lube oil data for generator as follows,
Main pump capacity – 68m3/h
Priming pump capacity – 10m3/h
Pressure at normal – 4-5bar
Normal stop/shutdown pressure – 1.7bar
Alarm, pressure low – 2.5bar
Lube oil engine inlet,
Normal – 65°C
Normal stop/shutdown – 71/73°C
Specific Lube oil consumption – 0.4g/KWh
Lube oil consumption – 1.5Kg/h
2. 2. 4 Heat exchanger
A heatexchanger is a device built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, and natural gas processing. One common example of a heat exchanger is the radiator in a car, in which the heat source, being a hot engine-cooling fluid, water, transfers heat to air flowing through the radiator (i.e. the heat transfer medium).
Fig: Heat exchanger
Heat exchangers may be classified according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat from the heat (transfer) medium. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.
For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger’s performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence.
Plate heat exchanger
Fig: Plate heat exchanger
There are many types of heat exchanger. Shell type, tube type etc. Another type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly-separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. Advances in gasket and brazing technology have made the plate-type heat exchanger increasingly practical. In HVAC applications, large heat exchangers of this type are called plate-and-frame; when used in open loops, these heat exchangers are normally of the gasketed type to allow periodic disassembly, cleaning, and inspection. There are many types of permanently-bonded plate heat exchangers, such as dip-brazed and vacuum-brazed plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and in the configurations of those plates. Some plates may be stamped with “chevron” or other patterns, where others may have machined fins and/or grooves.
Fig: Plate heat exchanger
Fig: Plate heat exchanger in Mymun Textiles Ltd.
2. 2. 5 LT and HT
Most internal combustion engines are fluid cooled using either air (a gaseous fluid) or a liquid coolant run through a heat exchanger (radiator) cooled by air. Marine engines and some stationary engines have ready access to a large volume of water at a suitable temperature. The water may be used directly to cool the engine, but often has sediment, which can clog coolant passages, or chemicals, such as salt, that can chemically damage the engine. Thus, engine coolant may be run through a heat exchanger that is cooled by the body of water.
Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors. The industry term for the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using a liquid with different properties, such as propylene glycol or a combination of propylene glycol and ethylene glycol. Most “air-cooled” engines use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts and the oil itself. Most “liquid-cooled” engines use some air cooling, with the intake stroke of air cooling the combustion chamber. An exception is Wankel engines, where some parts of the combustion chamber are never cooled by intake, requiring extra effort for successful operation.
There are many demands on a cooling system. One key requirement is that an engine fails if just one part overheats. Therefore, it is vital that the cooling system keep all parts at suitably low temperatures. Liquid-cooled engines are able to vary the size of their passageways through the engine block so that coolant flow may be tailored to the needs of each area. Locations with either high peak temperatures (narrow islands around the combustion chamber) or high heat flow (around exhaust ports) may require generous cooling. This reduces the occurrence of hot spots, which are more difficult to avoid with air cooling. Air cooled engines may also vary their cooling capacity by using more closely-spaced cooling fins in that area, but this can make their manufacture difficult and expensive.
Fig: LT Tank
Only the fixed parts of the engine, such as the block and head, are cooled directly by the main coolant system. Moving parts such as the pistons, and to a lesser extent the crank and rods, must rely on the lubrication oil as a coolant, or to a very limited amount of conduction into the block and thence the main coolant. High performance engines frequently have additional oil, beyond the amount needed for lubrication, sprayed upwards onto the bottom of the piston just for extra cooling. Air-cooled motorcycles often rely heavily on oil-cooling in addition to air-cooling of the cylinder barrels.
Liquid-cooled engines usually have a circulation pump. The first engines relied on thermo-syphon cooling alone, where hot coolant left the top of the engine block and passed to the radiator, where it was cooled before returning to the bottom of the engine. Circulation was powered by convection alone.
Low temperature (LT) and High temperature (HT) water are circulating in the engine. The main function of this water is cooling the total system. LT is used for cooling lube oil by using plate heat exchanger. There are two LT tank in the MTL. Lube oil get heated from the engine and then flow to the heat exchanger. LT water and lube oil flow to the heat exchanger. For normal temperature of LT water, high temperatures lube oil being cool down.
Fig: LT water pump
In MTL, there are two LT water motor. There rated power are 22KW and connection type is star – delta. The function of this motor is circulating water to the LT tank. The hot LT water cools down by using radiator.
High temperature (HT) water is circulating inside of the engine. The main function of the HT water is cool down the engine cylinder. A mechanical type pump continuously circulating HT water inside the engine. For LT and HT pure water (distil water) are using.
2. 2. 6 Control panel
Control panels are consisting of CT, PT, Overload Relay, MCCB. MCB, Switches, Fuse etc. The main functions of control panels are controlling every equipment in the power plant.
Fig: Control Panel of MTL
In electrical engineering, a current transformer (CT) is used for measurement of electric currents. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry.
Fig: Control System
Fig: Various types of CT
Fig: Current Transformer
Potential transformers are instrument transformers. They have a large number of secondary turns and a fewer number of primary turns. They are used to increase the range of voltmeters in electrical substations and generating stations.
Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications.
A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer.
Fig: Potential Transformer
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called “protection relays”.
Fig: Relay
Magnetic circuit breakers use a solenoid (electromagnet) that’s pulling force increases with the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid. The circuit breaker contacts are held closed by a latch. As the current in the solenoid increases beyond the rating of the circuit breaker, the solenoid’s pull releases the latch which then allows the contacts to open by spring action. Some types of magnetic breakers incorporate a hydraulic time delay feature using a viscous fluid. The core is restrained by a spring until the current exceeds the breaker rating. During an overload, the speed of the solenoid motion is restricted by the fluid. The delay permits brief current surges beyond normal running current for motor starting, energizing equipment, etc. Sh