ENGINEERING ARTICLES

Thursday, October 24, 2013

POWER LOSS IN SERVICE MAINS

By Engr. Aneel Kumar October 24, 2013 No comments:

Service main is the path between the utility company and consumer. Service mains used are the cables, almost PVC cables are used. Power loss through the PVC cables is an important factor, through which it is analysed and estimated that how much percentage of the power is utilised by the customer, how much power is wasted through the cables?

In this chapter power loss through secondary distribution system, PVC cables, and behaviour of the utility companies towards the consumers is thoroughly described.

Secondary distribution is taken into account so as to clarify the nature of the network and power rating of the circuit. Transformers (Step Down), conductors, structures, insulators and other fittings and fixtures are the component of the secondary system.

A Service main is the wire or path between the secondary distribution system and consumer. Service mains almost used in the distribution system are PVC cable. Manufacturing, conductor size, current rating and power loss through these cables is measured and calculated.

It is important to know the utility laws incorporated from time to time, so as to make the reliable system. During these rules and regulations effects over the consumers are essential to consider.

POWER QUALITY ISSUES WITH RENEWABLE ENERGY

By Engr. Aneel Kumar October 24, 2013 No comments:

In renewable energy sources Power quality of distribution system can also be affected by non-linear loads.Non-linear loads are a source of harmonic currents.Renewable energy sources do not directly supplies AC power to the consumers.Renewable sources generate DC power which is then converted to AC with the help of electronic based inverters. Those electronic circuits associated with control and interconnection of renewable energy sources will inject harmonics in the system to which these are connected.

HYBRID SYSTEM AND ITS MERITS

By Engr. Aneel Kumar October 24, 2013 No comments:

Solar photovoltaic (PV) cells and wind mill dependent on climatic change to work and generate electrical energy. Therefore, when these energy sources working alone they are not good power supply. Emerging of solar and wind sources are more valued in electrical energy generation. Such a type of system is called Hybrid system.Thus a hybrid power system of renewable source with grid supply improves the stability of system. With hybrid system there are period of time when neither of sources produce energy. In separate systems energy storage is necessary to overcome this situation and provide energy during such periods.

Power electronic devices such as inverter and others are play very important role in the hybrid power system. The energy which extracted is used to charge batteries. The inverter is interconnected with consumer loads and to the electrical power grid. Hybrid system is the operation of two or more than two sources which utilize to the single load.

Merits of hybrid power system

>>Uninterrupted power can be provided to the customers.

>>No environmental harm will result in hybrid power system.

>>Hybrid system can be accessible to the far away customers at low-cost as compared to the hydraulic energy which are used for residential purposes, which can be reserved in the dams during the dynamic, to be utilized at height.

>>The continuation cost of hybrid generation system is not as much as compare to the usual generation system.

HARMONICS AND ITS CAUSES

By Engr. Aneel Kumar October 24, 2013 No comments:

Equipments are designed for operation at a fixed frequency called fundamental frequency.Harmonics are waveforms of the frequencies which are integral multiples of fundamental frequency. As per the calculations of the harmonics they are defined in the odd and even harmonics. However odd harmonics are important to know. Odd harmonics are defined as below:

If Fundamental Frequency is 50Hz, then

3rd Harmonic = 3 x 50Hz =150Hz,

5th Harmonic = 5 x 50Hz =250Hz and

7th harmonics= 7 x 50Hz = 350Hz.

Harmonics are cause by non-linear loads and in which current is not comparative to the applied voltage. Electronic devices are major source of harmonics. With a non-linear load, no one can easily forecast the link among voltage and current but for it you have an exact for each device.

RENEWABLE ENERGY SOURCES

By Engr. Aneel Kumar October 24, 2013 No comments:

Renewable energy sources are available free of cost, smooth during operationandclean source of energy. Renewable energy sourceshavelow operating and maintenance costand can be easily built.Solar and wind energy are almost widely used as the main renewable energy resource.Wind mills can be installed in bulk and later connected to national grid on commercial basis. On the other hand wind mills can also be installed by individual consumers to meet their loads. Solar cells can be used in homes and offices to generate electricity. Future aspects of solar and wind sources are bright and can play an important role in the world.

POWER QUALITY

By Engr. Aneel Kumar October 24, 2013 No comments:

It can be distinct as “Power problems existing in voltage, current or frequency variation that result in failure of consumer’sequipment”. There are a lot of ways inside power supply can be of poor power quality. It is vital to know the different types of power quality variations that can cause troubles with receptive loads. Some important power quality problems are following.

v Disturbance in supply

v Voltage dip

v Voltage swells

v Poor power factor

v Harmonics

These affect the performance of the power system components and results in huge capital loss. The most important problem of the power quality in waveform distortion is harmonics.

ESSENTIAL ELEMENTS OF A CABLE CONDITION MONITORING PROGRAM

By Engr. Aneel Kumar October 24, 2013 No comments:

In this section of the report, nine essential elements that constitute an effective cable condition monitoring (CM) program are presented.

These elements are as follows:

1. Selection of cables to be monitored

2. Development of database for monitored cables

3. Characterize and monitor service environments

4. Identify stressors and expected aging mechanisms

5. Select CM techniques suitable to monitored cables

6. Establish baseline condition of monitored cables

7. Perform test & inspection activities for periodic CM of cables

8. Periodic review & incorporation of plant & industry experience

9. Periodic review & assessment of monitored cables condition

Each element will be described in detail in the following subsections. The purpose for each of the individual elements of the cable CM program will be presented along with how the element fits into the overall cable CM program. Guidance will be provided for implementation of the important features or activities associated with the program element. Finally, the expected results or outcomes of each program element will be described. The guidance will also provide information needed to integrate each element into the overall cable CM program.

OPTIMUM LOADING OF HYBRID SUPPLY SYSTEM FOR RESIDENTIAL CUSTOMER

By Engr. Aneel Kumar October 24, 2013 No comments:

1. Introduction

The hybrid power system is a comprehensive electrical power supply system that can be easily configured to meet a broad range of power needs. Hybrid systems, like the name implies, combine two or more modes of electricity generation together, usually using renewable technologies such as solar photovoltaic (PV) and wind turbines. Hybrid systems provide a high level of energy security through the mix of generation methods, and often will incorporate a storage system (battery, fuel cell) or gird tied supply system to ensure maximum supply reliability and security.

There are three basic elements to this system - the power source, the battery, and the power management center. Power sources are wind turbine, solar energy and grid connection. The battery allows autonomous operation by compensating for the difference between power production and utilization. The power management center regulates power production from each of the sources, controls power use by classifying loads, and protects the battery from service extremes. Figure 1 shows a simple arrangement for a hybrid system comprising of solar and wind generations, connection to the existing utility network. Power can be taken from utility or can be feed back to utility.

Figure 1 Hybrid supply system concept

In general, Hybrid Power Systems have to meet different requirements depending on the appliances served, the consumer behavior, the consumer’s demands on the power quality and the energy sources available locally. While mobile phone antennas need to be supplied with almost constant power of high quality, small villages have a fluctuating and usually growing energy demand while short term power outages are not critical.

To realize cost efficient power supply with the required power quality an individual system design considering all site specific aspects is essential.

2. Solar Energy

The Solar Modules (Photovoltaic Cell) generate DC electricity when ever sun light falls in solar cells. The Solar Modules should be titled in an optimum angle for the particular location face due to south, and should not be shaded at any time in a day. Motorized control can be used to rotate solar panels in the direction of sun and ensure maximum sun light.

Figure 2 Solar system components

3. Wind Energy

Wind is the natural phenomenon related to the movement of air masses caused by the primarily by the differential solar heating of the earth’s surface. Seasonal variation in the energy received from the sun affects the strength and direction of the wind. The wind turbine capture the wind kinetic energy in a rotor consisting of two or more blades mechanically coupled to an electrical generator. The turbine is mounted on a tall tower to enhance the energy capture.

Figure 3 Wind system components

4. Grid Power

Electrical power is generated in bulk amount and transmitted to power grid and then distributed to the consumers. Its performance affects the consumers ‘appliances and also the economy of the power system. Existing system near the consumers is a three phase four wire system.

5. Literature Review

Parita G Dilwadi and Chintan R Mehta (March 2012) Calculated the cost of production of energy and it is also conclude that initial cost of the Wind solar hybrid system is high but it produces energy at least cost.

(1) M. Partovi and M.Mohammadian (March 2013) Study about Economic model of the FC-PV hybrid supply system and also estimate the daily optimal strategy for the hybrid system and to minimize the operation cost.

(2) F.D Surianu I. Borlea D.Jagoria Oprea and B Lustrea (March 2012) studies shows the broad utilization of the renewable energy resources, and also shows the comparison of renewable energy resources (3)

6. Objectives of the research

The objectives of the research project are to perform the operational studies for hybrid supply system and planning studies to optimum loading in the hybrid supply system, enhance reliability and Uninterrupted power supply (UPS) for residential customer.

Main objectives of the research are

Ø Modeling and simulation of Solar, Wind and grid tied hybrid system

Ø Analysis of optimum loading of hybrid supply system

Ø Economical analysis of optimization for hybrid system

7. Expected outcome of the research project

Following are the expected outcomes of research project:

Ø Un interrupted power supply when grid is not connected

Ø Optimum loading for hybrid supply system (Solar, Wind and Grid)

Ø Initial cost of solar and wind system is high but in hybrid connection it produces electricity at least cost

Ø It has many advantages that it produces no pollution and requires less maintenance.

8. Scope of the research Project

Now a days, world is facing the energy crisis the most optimist fact is that the main energy resources (Oil and natural Gas) are exhausted in 2050. In this scenario the only solution is finding and using new energy resources. Solar and wind energies are the solution in this scenario but the solar energy and wind energy highly depending on the climate conditions and also expensive but the combination of these technologies can be considered as hybrid supply system with high reliability to satisfy the electrical load of the residential customer.

Methodology Statement:

Methodology planning for this proposal topic is to optimum loading and economic analysis of hybrid supply system and Simulation as per the data collected from a house in defense Hyderabad where hybrid supply system is installed. However methodology for this proposal is divided into the following steps.

· Study of hybrid supply system:

First step of the project is to know how about hybrid supply system. Wind energy solar energy and grid connection.

· Survey of field

For the purpose of the data collection, we make a field survey of that house where hybrid supply system is installed Survey consists load of the customer and behavior of the load. Economic considerations and economical impacts over the customer

· Analysis

Collected data and simulation results will help to analyze the parameters of the hybrid supply system.
Analysis of cost and economic contribution of the hybrid supply system.

WIND TURBINES

By Engr. Aneel Kumar October 20, 2013 No comments:

Wind turbines are classified according to the interaction of the blades with the wind, orientation of the rotor axis with respect to the ground and to the tower (upwind, downwind), and innovative or unusual types of machines. The interaction of the blades with the wind is by drag or lift or a combination of the two.

For a drag device, the wind pushes against the blade or sail forcing the rotor to turn on its axis, and drag devices are inherently limited in efficiency since the speed of the device or blades cannot be greater than the wind speed. The maximum theoretical efficiency is 15%. Another major problem is that drag devices have a lot of material in the blades. Although a number of different drag devices (Figure 1.4) have been built, there are essentially no commercial (economically viable) drag devices in production for the generation of electricity.

Most lift devices use airfoils for blades (Figure 1.5), similar to propellers or airplane wings; however, other concepts are Magnus (rotating cylinders) and Savonius wind turbines (Figure 1.6). A Savonius rotor is not strictly a drag device, but it has the same characteristic of large blade area to intercept area.

This means more material and problems with the force of the wind on the rotor at high wind speeds, even if the rotor is not turning. An advantage of the Savonius wind turbine is the ease of construction.

Using lift, the blades can move faster than the wind and are more efficient in terms of aerodynamics and use of material, a ratio of around 100 to 1 compared to a drag device. The tip speed ratio is the speed of the tip of the blade divided by the wind speed, and lift devices typically have tip speed ratios around seven. There have even been one-bladed wind turbines, which save on material; however, most modern wind turbines have two or three blades.

The power coefficient is the power out or power produced by the wind turbine divided by the power in the wind. From conservation of energy and momentum, the maximum theoretical efficiency of a rotor is 59%. The capacity factor is the average power divided by the rated power. The average power is generally calculated by knowing the energy production divided by the hours in that time period (usually a year or can be calculated for a month or a quarter). For example, if the annual energy production is 4500 MWh for a wind turbine rated at 1.5 MW, then the average power = energy/hours = 4500/8760 = 0.5 MW and the capacity factor would be 0.5 MW/1.5 MW = 0.33 = 33%. So the capacity factor is like an average efficiency. A power curve shows the power produced as a function of wind speed (Figure 1.7).

Because there is a large scatter in the measured power versus wind speed, the method of bins (usually 1 m/s bid width suffices) is used.

Wind turbines are further classified by the orientation of the rotor axis with respect to the ground: horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT). The rotors on HAWTs need to be kept perpendicular to the wind, and yaw is this rotation of the unit about the tower axis. For upwind units yaw is by a tail for small wind turbines—a motor on large wind turbines, and for downwind units—yaw may be by coning (passive yaw) or a motor.

VAWT have the advantage of accepting the wind from any direction. Two examples of VAWTs are the Darrieus and giromill. The Darrieus shape is similar to the curve of a moving jump rope; however, the Darrieus is not self-starting, as the blades should be moving faster than the wind to generate power. The giromill can have articulated blades which change angle so it can be self-starting. Another advantage of VAWTs is that the speed increaser and generator can be at ground level. A disadvantage is that taller towers are a problem for VAWTs, especially for wind farm size units. Today there are no commercial, large-scale VAWTs for wind farms, although there are a number of development projects and new companies for small VAWTs. Some companies claim they can scale to MW size for wind farms.

The total system consists of the wind turbine and the load, which is also called a wind energy conversion system (WECS). A typical large wind turbine consists of the rotor (blades and hub), speed increaser (gear box), conversion system, controls and the tower (Figure 1.8). The most common configuration for large wind turbines is three blades, full span pitch control (motors in hub), upwind with yaw motor, speed increaser (gear box), and doubly fed induction generator (allows wider range of rpm for better aerodynamic efficiency). The nacelle is the covering or enclosure of the speed increaser and generator.

The output of the wind turbine, rotational kinetic energy, can be converted to mechanical, electrical, or thermal energy. Generally it is electrical energy. The generators can be synchronous or induction connected directly to the grid, or a variable frequency alternator (permanent magnet alternator) or direct current generator connected indirectly to the grid through an inverter. Most small wind turbines are direct drive and no speed increaser and operate at variable rpm. Wind turbines without a gearbox are direct drive units. Enercon has built large wind turbines with huge generators and no speed increaser, which have higher aerodynamic efficiency due to variable rpm operation of the rotor.

However, there are some energy losses in the conversion of variable frequency to the constant frequency (50 or 60 Hz) needed for the utility grid.

SWITCHGEAR AND MOTOR CONTROL CENTRES

By Engr. Aneel Kumar October 13, 2013 No comments:

The terms ‘switchgear’ and ‘motor control centres’ are used in general to describe combinations of enclosures, bus bars, circuit breakers, power contactors, power fuses, protective relays, controls and indicating devices. The standards used in Europe often refer to IEC60050 for definitions of general terms. Particular IEC standards tend to give additional definitions that relate to the equipment being described, e.g. IEC60439 and IEC60947 for low voltage equipment, IEC60056, IEC60298 and IEC60694 for high voltage equipment. An earlier standard IEC60277 has been withdrawn. These standards tend to prefer the general terms ‘switchgear’ and ‘control gear’. Control gear may be used in the same context as ‘motor control centres’ which is a more popular and specific term used in the oil industry.

In general switchgear may be more closely associated with switchboards that contain circuit breaker or contactor cubicles for power distribution to other switchboards and motor control centres, and which receive their power from generators or incoming lines or cables. Motor control centres tend to be assemblies that contain outgoing cubicles specifically for supplying and controlling power to motors. However, motor control centres may contain outgoing cubicles for interconnection to other switchboards or motor control centres, and circuit breakers for their incomers and bus bar sectioning. Switchboards may be a combination of switchgear and motor control centres. For example a main high voltage switchboard for an offshore platform will have switchgear for the generators, bus bar sectioning and outgoing transformer feeders. It will have motor control centre cubicles for the high voltage motors. IEC60439 applies to low voltage equipment that is described as ‘factory built assemblies’, or FBAs, of switchgear and control gear.

Switchgear tends to be operated infrequently, whereas motor control centres operate frequently as required by the process that uses the motor. Apart from the incomers and bus bar section circuit breakers, the motor control centres are designed with contactors and fuses (or some types of moulded case circuit breakers in low voltage equipment) that will interrupt fault currents within a fraction of a cycle of AC current. Circuit breakers need several cycles of fault current to flow before interruption is complete. Consequently the components within a circuit breaker must withstand the higher forces and heat produced when several complete cycles of fault current flow.

Switchgear is available up to at least 400 kV, whereas motor control centres are only designed for voltages up to approximately 15 kV because this is the normal limit for high voltage motors.

DC UPS

By Engr. Aneel Kumar October 08, 2013 No comments:

A DC uninterruptible power supply is basically a battery bank and a charger. However, it differs from a simple battery and charger system that may be associated with starting diesel engines, or similar rugged functions, because the output voltage must be maintained within a close tolerance of the nominal DC voltage.

DC uninterruptible power supplies are used for:

• Closing and tripping of circuit breakers and contactors in switchboards.

• Switchboard indicating lamps.

• Radio communication equipment.

• Emergency generator control panels.

• Start-up and shut-down lubricating oil pumps and auxiliary systems for gas turbines, large pumps and compressors.

When specifying the battery and charger system the following points should be considered.

• Rated voltage and current.

• Rated ampere-hour capacity.

• Rate of discharge

• Type of cell i.e. lead-acid or nickel-cadmium

• Ventilated batteries. Some types of cells can be non-venting but this greatly influences the charging process.

• Type of charger e.g. rectifier or thyristor.

• Boost, float and trickle charging requirements.

• Duty and standby units, and their interlocking and control philosophy.

• Volt-drop considerations in the DC outgoing cables.

• Overload and short-circuit protection.

• Tolerance on the DC output voltage during all load and charging conditions.

• Ambient temperature and appropriate derating factors for the cells and the charger.

UNINTERRUPTIBLE POWER SUPPLIES

By Engr. Aneel Kumar October 08, 2013 No comments:

Static inverters are used to convert DC voltage into AC voltage. The simplest forms of inverters produce an output waveform that is rectangular, as a result of the simple switching, rectangular waveform can be used to feed some types of AC equipment e.g. incandescent lamps, domestic equipment such as kitchen mixers and kettles. Equipment that contains electronic devices may not function properly if their supply waveform is non-sinusoidal.

Their timing circuits and pulse generating systems may be disturbed by the shape of the waveform or its derivative.

Harmonics in the voltage waveform may create harmonic currents in the equipment that could give rise to excessive heat dissipation and ultimately damage may be caused.

All but the smaller ratings of inverters used in the oil industry require a sinusoidal output waveform. The quality of the waveform is typically defined as, being that no greater than 5% total harmonic distortions should be present. In order to achieve a sinusoidal output it is necessary to include a filter in the output circuit. The output of the inverter usually has a double wound transformer so that the required line voltage is obtained. The filter is placed on the load side of the transformer; its leakage reactance of the transformer contributes to the filtering process.

Inverters are fed from a battery bank that has sufficient cells to optimize the output voltage of the inverter and the performance of the rectifier or charger. The inverter is shown in Figure below, which provides an uninterruptible supply (UPS) that also has an off-load bypass supply.

Some of the equipment in a plant requires a source of power that is extremely reliable and does not become interrupted during an emergency. For example if all the main generators on a production platform trip for some emergency reason then it is necessary to maintain supplies to vital services such as communications, public address, emergency lighting, navigational panels, fire and gas systems. Many of these loads can tolerate a short break and can be supplied by the emergency diesel generator once it is ready for service. Some loads cannot tolerate an interruption at all e.g. data processing systems, instrument panels, safety shut-down systems.

Inverters can be arranged to operate in various ways to provide an uninterruptible supply.

CONSTRUCTION OF DC MOTOR

By Engr. Aneel Kumar October 08, 2013 No comments:

DC motors consist of one set of coils, called armature winding, inside another set of coils or a set of permanent magnets, called the stator. Applying a voltage to the coils produces a torque in the armature, resulting in motion.

Stator

The stator is the stationary outside part of a motor.

The stator of a permanent magnet dc motor is composed of two or more permanent magnet pole pieces.

The magnetic field can alternatively be created by an electromagnet. In this case, a DC coil (field winding) is wound around a magnetic material that forms part of the stator.

Rotor

The rotor is the inner part which rotates.

The rotor is composed of windings (called armature windings) which are connected to the external circuit through a mechanical commutator.

Both stator and rotor are made of ferromagnetic materials. The two are separated by air-gap.

Winding

A winding is made up of series or parallel connection of coils.

Armature winding - The winding through which the voltage is applied or induced.

Field winding - The winding through which a current is passed to produce flux (for the electromagnet)

Windings are usually made of copper.

PROTECTION SYSTEMS OF HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The turbine-generator unit and related equipment are protected against mechanical, electrical, hydraulic, and thermal damage that may occur as a result of abnormal conditions within the plant or on the power system to which the plant is connected. Abnormal conditions are detected automatically by means of protective relays and other devices and measures are taken to isolate the faulty equipment as quickly as possible while maintaining the maximum amount of equipment in service. Typical protective devices include electrical fault detecting relays, temperature, pressure, level, speed, and fire sensors, and vibration monitors associated with the turbine, generator, and related auxiliaries. The protective devices operate in various isolation and unit shutdown sequences, depending on the severity of the fault.

The type and extent of protection will vary depending on the size of the unit, manufacturer’s recommendations, owner’s practices, and industry standards.

HYDROELECTRIC POWER PLANT AUXILIARY EQUIPMENT

By Engr. Aneel Kumar October 03, 2013 No comments:

A number of auxiliary systems and related controls are provided throughout the hydroelectric plant to support the operation of the generating units. These include the following:

1. Switchyard systems.

2. Alternating current (AC) station service. Depending on the size and criticality of the plant, multiple sources are often supplied, with emergency backup provided by a diesel generator.

3. Direct current (DC) station service. It is normally provided by one or more battery banks, for supply of protection, control, emergency lighting, and exciter field flashing.

4. Lubrication systems, particularly for supply to generator and turbine bearings and bushings.

5. Drainage pumps, for removing leakage water from the plant.

6. Air compressors, for supply to the governors, generator brakes, and other systems.

7. Cooling water systems, for supply to the generator air coolers, generator and turbine bearings, and step-up transformer.

8. Fire detection and extinguishing systems.

9. Intake gate or isolation valve systems.

10. Draft tube gate systems.

11. Reservoir and tailrace water level monitoring.

12. Synchronous condenser equipment, for dewatering the draft tube to allow the runner to spin in air during synchronous condenser operation. In this case, the generator acts as a synchronous motor, supplying or absorbing reactive power.

13. Service water systems.

14. Overhead crane.

15. Heating, ventilation, and air conditioning.

16. Environmental systems.

CONTROL SYSTEMS USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

A general hierarchy of control is illustrated in Table 5.1. Manual controls, normally installed adjacent to the device being controlled, are used during testing and maintenance, and as a backup to the automatic control systems. Figure 5.5 illustrates the relationship of control locations and typical functions available at each location. Automatic sequences implemented for starting, synchronizing, and shutdown of hydroelectric units are used.

Modern hydroelectric plants and plants undergoing rehabilitation and life extension are incorporating higher levels of computer automation. The relative simplicity of hydroelectric plant control allows most plants to be operated in an unattended mode from off-site control centers. The current trend is to apply automated condition monitoring systems for hydroelectric plant equipment.

Condition monitoring systems, coupled with expert system computer programs, allow plant owners and operators to more fully utilize the capacity of plant equipment and water resources, make better maintenance and replacement decisions, and maximize the value of installed assets.

EXCITATION SYSTEM USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The excitation system fulfills two main functions:

1. It produces DC voltage (and power) to force current to flow in the field windings of the generator.

There is a direct relationship between the generator terminal voltage and the quantity of current flowing in the field windings.

2. It provides a means for regulating the terminal voltage of the generator to match a desired set point and to provide damping for power system oscillations.

Another system used for smaller high-speed units is a brushless exciter with a rotating AC generator and rotating rectifiers.

Modern static exciters have the advantage of providing extremely fast response times and high field ceiling voltages for forcing rapid changes in the generator terminal voltage during system faults. This is necessary to overcome the inherent large time constant in the response between terminal voltage and field voltage (referred to as T’do’, typically in the range of 5–10 s). Rapid terminal voltage forcing is necessary to maintain transient stability of the power system during and immediately after system faults. Power system stabilizers are also applied to static exciters to cause the generator terminal voltage to vary in phase with the speed deviations of the machine, for damping power system dynamic oscillations.

Various auxiliary devices are applied to the static exciter to allow remote setting of the generator voltage and to limit the field current within rotor thermal and under excited limits. Field flashing equipment is provided to build up generator terminal voltage during starting to the point at which the thyrsistor can begin gating. Power for field flashing is provided either from the station battery or alternating current (AC) station service.

GOVERNOR SYSTEM USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The governor system is the key element of the unit speed and power control system. It consists of control and actuating equipment for regulating the flow of water through the turbine, for starting and stopping the unit, and for regulating the speed and power output of the turbine generator. The governor system includes set point and sensing equipment for speed, power and actuator position, compensation circuits, and hydraulic power actuators which convert governor control signals to mechanical movement of the wicket gates (Francis and Kaplan turbines), runner blades (Kaplan turbine), and nozzle jets (Pelton turbine). The hydraulic power actuator system includes high-pressure oil pumps, pressure tanks, oil sump, actuating valves, and servomotors.

Older governors are of the mechanical-hydraulic type, consisting of ball head speed sensing, mechanical dashpot and compensation, gate limit, and speed droop adjustments. Modern governors are of the electro-hydraulic type where the majority of the sensing, compensation, and control functions are performed by electronic or microprocessor circuits. Compensation circuits utilize proportional plus integral (PI) or proportional plus integral plus derivative (PID) controllers to compensate for the phase lags in the penstock–turbine–generator–governor control loop. PID settings are normally adjusted to ensure that the hydroelectric unit remains stable when serving an isolated electrical load. These settings ensure that the unit contributes to the damping of system frequency disturbances when connected to an integrated power system. Various techniques are available for modeling and tuning the governor.

A number of auxiliary devices are provided for remote setting of power, speed, and actuator limits and for electrical protection, control, alarming, and indication. Various solenoids are installed in the hydraulic actuators for controlling the manual and automatic start-up and shutdown of the turbine generator unit.

GENERATOR TERMINAL EQUIPMENT USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The generator output is connected to terminal equipment via cable, bus bar, or isolated phase bus. The terminal equipment comprises current transformers (CTs), voltage transformers (VTs), and surge suppression devices. The CTs and VTs are used for unit protection, metering and synchronizing, and for governor and excitation system functions. The surge protection devices, consisting of surge arresters and capacitors, protect the generator and low-voltage windings of the step-up transformer from lightning and switching-induced surges.

GENERATOR SWITCHGEAR USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The generator circuit breaker and associated isolating disconnect switches are used to connect and disconnect the generator to and from the power system. The generator circuit breaker may be located on either the low-voltage or high-voltage side of the generator step-up transformer. In some cases, the generator is connected to the system by means of circuit breakers located in the switchyard of the generating plant. The generator circuit breaker may be of the oil filled, air magnetic, air blast, or compressed gas insulated type, depending on the specific application. The circuit breaker is closed as part of the generator synchronizing sequence and is opened (tripped) either by operator control, as part of the automatic unit stopping sequence, or by operation of protective relay devices in the event of unit fault conditions.

GENERATOR STEP UP TRANSFORMER

By Engr. Aneel Kumar October 03, 2013 No comments:

The generator transformer steps up the generator terminal voltage to the voltage of the power system or plant switchyard. Generator transformers are generally specified and operated in accordance with international standards for power transformers, with the additional consideration that the transformer will be operated close to its maximum rating for the majority of its operating life. Various types of cooling systems are specified depending on the transformer rating and physical constraints of the specific application.

In some applications, dual low-voltage windings are provided to connect two generating units to a single bank of step-up transformers. Also, transformer tertiary windings are sometimes provided to serve the AC station service requirements of the power plant.

FLOW CONTROL EQUIPMENT USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The flow through the turbine is controlled by wicket gates on reaction turbines and by needle nozzles on impulse turbines. A turbine inlet valve or penstock intake gate is provided for isolation of the turbine during shutdown and maintenance.

Spillways and additional control valves and outlet tunnels are provided in the dam structure to pass flows that normally cannot be routed through the turbines.

GENERATOR USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The majority of hydroelectric installations utilize salient pole synchronous generators. Salient pole machines are used because the hydraulic turbine operates at low speeds, requiring a relatively large number of field poles to produce the rated frequency. A rotor with salient poles is mechanically better suited for low-speed operation, compared to round rotor machines, which are applied in horizontal axis high-speed turbo-generators.

Generally, hydroelectric generators are rated on a continuous-duty basis to deliver net kVA output at a rated speed, frequency, voltage, and power factor and under specified service conditions including the temperature of the cooling medium (air or direct water). Industry standards specify the allowable temperature rise of generator components (above the coolant temperature) that are dependent on the voltage rating and class of insulation of the windings. The generator capability curve (Figure 5.3) describes the maximum real and reactive power output limits at rated voltage within which the generator rating will not be exceeded with respect to stator and rotor heating and other limits.

Standards also provide guidance on short-circuit capabilities and continuous and short-timer current unbalance requirements.

Synchronous generators require direct current (DC) field excitation to the rotor, provided by the excitation system. The generator saturation curve (Figure 5.4) describes the relationship of terminal voltage, stator current, and field current.

While the generator may be vertical or horizontal, the majority of new installations are vertical.

The basic components of a vertical generator are the stator (frame, magnetic core, and windings), rotor (shaft, thrust block, spider, rim, and field poles with windings), thrust bearing, one or two guide bearings, upper and lower brackets for the support of bearings and other components, and sole plates which are bolted to the foundation. Other components may include a direct connected exciter, speed signal generator, rotor brakes, rotor jacks, and ventilation systems with surface air coolers.

The stator core is composed of stacked steel laminations attached to the stator frame. The stator winding may consist of single-turn or multiturn coils or half-turn bars, connected in series to form a three phase circuit. Double layer windings, consisting of two coils per slot, are most common. One or more circuits are connected in parallel to form a complete phase winding. The stator winding is normally connected in wye configuration, with the neutral grounded through one of a number of alternative methods that depend on the amount of phase-to-ground fault current that is permitted to flow.

Generator output voltages range from approximately 480 VAC to 22 kVAC line-to line, depending on the MVA rating of the unit. Temperature detectors are installed between coils in a number of stator slots.

The rotor is normally comprised of a spider frame attached to the shaft, a rim constructed of solid steel or laminated rings, and field poles attached to the rim. The rotor construction will vary significantly depending on the shaft and bearing system, unit speed, ventilation type, rotor dimensions, and characteristics of the driving hydraulic turbine. Damper windings or amortisseurs in the form of copper or brass rods are embedded in the pole faces for damping rotor speed oscillations.

TURBINE USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

The type of turbine selected for a particular application is influenced by the head and flow rate. There are two classifications of hydraulic turbines: impulse and reaction.

The impulse turbine is used for high heads—approximately 300 m or greater. High-velocity jets of water strike spoon-shaped buckets on the runner which is at atmospheric pressure. Impulse turbines may be mounted horizontally or vertically and include perpendicular jets (known as a Pelton Jet type), diagonal jets (known as a Turgo Jettype), or cross-flow types.

In a reaction turbine, the water passes from a spiral casing through stationary radial guide vanes, through control gates and onto the runner blades at pressures above atmospheric. There are two categories of reaction turbine—Francis and propeller.

In the Francis turbine, installed at heads up to approximately 360 m, the water impacts the runner blades tangentially and exits axially. The propeller turbine uses a propeller-type runner and is used at low heads—below approximately 45 m.

The propeller runner may use fixed blades or variable pitch blades—known as a Kaplan or double regulated type—that allows control of the blade angle to maximize turbine efficiency at various hydraulic heads and generation levels.

Francis and propeller turbines may also be arranged in a slant, tubular, bulb, and rim generator configurations. Water discharged from the turbine is directed into a draft tube where it exits to a tailrace channel, lower reservoir, or directly to the river.

FLOW CONTROL EQUIPMENT USED IN HYDROELECTRIC POWER PLANT

By Engr. Aneel Kumar October 03, 2013 No comments:

HYDROELECTRIC PLANT FEATURES

By Engr. Aneel Kumar October 03, 2013 No comments:

Figures 5.1 and 5.2 illustrate the main components of a hydroelectric generating unit. The generating unit may have its shaft oriented in a vertical, horizontal, or inclined direction depending on the physical conditions of the site and the type of turbine applied. Figure 5.1 shows a typical vertical shaft Francis turbine unit and Figure 5.2 shows a horizontal shaft propeller turbine unit.

Turbine Used In Hydroelectric Power Plant

The type of turbine selected for a particular application is influenced by the head and flow rate. There are two classifications of hydraulic turbines: impulse and reaction.

The impulse turbine is used for high heads—approximately 300 m or greater. High-velocity jets of water strike spoon-shaped buckets on the runner which is at atmospheric pressure. Impulse turbines may be mounted horizontally or vertically and include perpendicular jets (known as a Pelton Jet type), diagonal jets (known as a Turgo Jettype), or cross-flow types.

In a reaction turbine, the water passes from a spiral casing through stationary radial guide vanes, through control gates and onto the runner blades at pressures above atmospheric. There are two categories of reaction turbine—Francis and propeller.

Flow Control Equipment Used In Hydroelectric Power Plant

The flow through the turbine is controlled by wicket gates on reaction turbines and by needle nozzles on impulse turbines. A turbine inlet valve or penstock intake gate is provided for isolation of the turbine during shutdown and maintenance.

Spillways and additional control valves and outlet tunnels are provided in the dam structure to pass flows that normally cannot be routed through the turbines.

Generator Used In Hydroelectric Power Plant

Synchronous generators and induction generators are used to convert the mechanical energy output of the turbine to electrical energy. Induction generators are used in small hydroelectric applications (less than 5 MVA) due to their lower cost which results from elimination of the exciter, voltage regulator, and synchronizer associated with synchronous generators. The induction generator draws its excitation current from the electrical system and thus cannot be used in an isolated power system.

The majority of hydroelectric installations utilize salient pole synchronous generators. Salient pole machines are used because the hydraulic turbine operates at low speeds, requiring a relatively large number of field poles to produce the rated frequency. A rotor with salient poles is mechanically better suited for low-speed operation, compared to round rotor machines, which are applied in horizontal axis high-speed turbo-generators.

Generally, hydroelectric generators are rated on a continuous-duty basis to deliver net kVA output at a rated speed, frequency, voltage, and power factor and under specified service conditions including the temperature of the cooling medium (air or direct water). Industry standards specify the allowable temperature rise of generator components (above the coolant temperature) that are dependent on the voltage rating and class of insulation of the windings. The generator capability curve (Figure 5.3) describes the maximum real and reactive power output limits at rated voltage within which the generator rating will not be exceeded with respect to stator and rotor heating and other limits.

The thrust bearing supports the mass of both the generator and turbine plus the hydraulic thrust imposed on the turbine runner and is located either above the rotor (suspended unit) or below the rotor (umbrella unit). Thrust bearings are constructed of oil-lubricated, segmented, babbitt-lined shoes. One or two oil-lubricated generator guide bearings are used to restrain the radial movement of the shaft.

Fire protection systems are normally installed to detect combustion products in the generator enclosure, initiate rapid de-energization of the generator, and release extinguishing material. Carbon dioxide and water are commonly used as the fire quenching medium.

Excessive unit vibrations may result from mechanical or magnetic unbalance. Vibration monitoring devices such as proximity probes to detect shaft run out are provided to initiate alarms and unit shutdown.

The choice of generator inertia is an important consideration in the design of a hydroelectric plant. The speed rise of the turbine-generator unit under load rejection conditions, caused by the instantaneous disconnection of electrical load, is inversely proportional to the combined inertia of the generator and turbine. Turbine inertia is normally about 5% of the generator inertia. During the design of the plant, unit inertia, effective wicket gate or nozzle closing and opening times, and penstock dimensions are optimized to control the pressure fluctuations in the penstock and speed variations of the turbine-generator during load rejection and load acceptance. Speed variations may be reduced by increasing the generator inertia at added cost. Inertia can be added by increasing the mass of the generator, adjusting the rotor diameter, or by adding a flywheel. The unit inertia also has a significant effect on the transient stability of the electrical system, as this factor influences the rate at which energy can be moved in or out of the generator to control the rotor angle acceleration during system fault conditions.

Generator Terminal Equipment Used In Hydroelectric Power Plant

The generator output is connected to terminal equipment via cable, bus bar, or isolated phase bus. The terminal equipment comprises current transformers (CTs), voltage transformers (VTs), and surge suppression devices. The CTs and VTs are used for unit protection, metering and synchronizing, and for governor and excitation system functions. The surge protection devices, consisting of surge arresters and capacitors, protect the generator and low-voltage windings of the step-up transformer from lightning and switching-induced surges.

Generator Switchgear Used In Hydroelectric Power Plant

The generator circuit breaker and associated isolating disconnect switches are used to connect and disconnect the generator to and from the power system. The generator circuit breaker may be located on either the low-voltage or high-voltage side of the generator step-up transformer. In some cases, the generator is connected to the system by means of circuit breakers located in the switchyard of the generating plant. The generator circuit breaker may be of the oil filled, air magnetic, air blast, or compressed gas insulated type, depending on the specific application. The circuit breaker is closed as part of the generator synchronizing sequence and is opened (tripped) either by operator control, as part of the automatic unit stopping sequence, or by operation of protective relay devices in the event of unit fault conditions.

Generator Step-Up Transformer Used In Hydroelectric Power Plant

The generator transformer steps up the generator terminal voltage to the voltage of the power system or plant switchyard. Generator transformers are generally specified and operated in accordance with international standards for power transformers, with the additional consideration that the transformer will be operated close to its maximum rating for the majority of its operating life. Various types of cooling systems are specified depending on the transformer rating and physical constraints of the specific application.

In some applications, dual low-voltage windings are provided to connect two generating units to a single bank of step-up transformers. Also, transformer tertiary windings are sometimes provided to serve the AC station service requirements of the power plant.

Excitation System Used In Hydroelectric Power Plant

The excitation system fulfills two main functions:

1. It produces DC voltage (and power) to force current to flow in the field windings of the generator.

There is a direct relationship between the generator terminal voltage and the quantity of current flowing in the field windings.

2. It provides a means for regulating the terminal voltage of the generator to match a desired set point and to provide damping for power system oscillations.

Another system used for smaller high-speed units is a brushless exciter with a rotating AC generator and rotating rectifiers.

Modern static exciters have the advantage of providing extremely fast response times and high field ceiling voltages for forcing rapid changes in the generator terminal voltage during system faults. This is necessary to overcome the inherent large time constant in the response between terminal voltage and field voltage (referred to as T’do’, typically in the range of 5–10 s). Rapid terminal voltage forcing is necessary to maintain transient stability of the power system during and immediately after system faults. Power system stabilizers are also applied to static exciters to cause the generator terminal voltage to vary in phase with the speed deviations of the machine, for damping power system dynamic oscillations.

Various auxiliary devices are applied to the static exciter to allow remote setting of the generator voltage and to limit the field current within rotor thermal and under excited limits. Field flashing equipment is provided to build up generator terminal voltage during starting to the point at which the thyrsistor can begin gating. Power for field flashing is provided either from the station battery or alternating current (AC) station service.

Governor System Used In Hydroelectric Power Plant

The governor system is the key element of the unit speed and power control system. It consists of control and actuating equipment for regulating the flow of water through the turbine, for starting and stopping the unit, and for regulating the speed and power output of the turbine generator. The governor system includes set point and sensing equipment for speed, power and actuator position, compensation circuits, and hydraulic power actuators which convert governor control signals to mechanical movement of the wicket gates (Francis and Kaplan turbines), runner blades (Kaplan turbine), and nozzle jets (Pelton turbine). The hydraulic power actuator system includes high-pressure oil pumps, pressure tanks, oil sump, actuating valves, and servomotors.

Older governors are of the mechanical-hydraulic type, consisting of ball head speed sensing, mechanical dashpot and compensation, gate limit, and speed droop adjustments. Modern governors are of the electro-hydraulic type where the majority of the sensing, compensation, and control functions are performed by electronic or microprocessor circuits. Compensation circuits utilize proportional plus integral (PI) or proportional plus integral plus derivative (PID) controllers to compensate for the phase lags in the penstock–turbine–generator–governor control loop. PID settings are normally adjusted to ensure that the hydroelectric unit remains stable when serving an isolated electrical load. These settings ensure that the unit contributes to the damping of system frequency disturbances when connected to an integrated power system. Various techniques are available for modeling and tuning the governor.

A number of auxiliary devices are provided for remote setting of power, speed, and actuator limits and for electrical protection, control, alarming, and indication. Various solenoids are installed in the hydraulic actuators for controlling the manual and automatic start-up and shutdown of the turbine generator unit.

Control Systems Used In Hydroelectric Power Plant

A general hierarchy of control is illustrated in Table 5.1. Manual controls, normally installed adjacent to the device being controlled, are used during testing and maintenance, and as a backup to the automatic control systems. Figure 5.5 illustrates the relationship of control locations and typical functions available at each location. Automatic sequences implemented for starting, synchronizing, and shutdown of hydroelectric units are used.

Modern hydroelectric plants and plants undergoing rehabilitation and life extension are incorporating higher levels of computer automation. The relative simplicity of hydroelectric plant control allows most plants to be operated in an unattended mode from off-site control centers. The current trend is to apply automated condition monitoring systems for hydroelectric plant equipment.

Condition monitoring systems, coupled with expert system computer programs, allow plant owners and operators to more fully utilize the capacity of plant equipment and water resources, make better maintenance and replacement decisions, and maximize the value of installed assets.

Protection Systems Used In Hydroelectric Power Plant

The turbine-generator unit and related equipment are protected against mechanical, electrical, hydraulic, and thermal damage that may occur as a result of abnormal conditions within the plant or on the power system to which the plant is connected. Abnormal conditions are detected automatically by means of protective relays and other devices and measures are taken to isolate the faulty equipment as quickly as possible while maintaining the maximum amount of equipment in service. Typical protective devices include electrical fault detecting relays, temperature, pressure, level, speed, and fire sensors, and vibration monitors associated with the turbine, generator, and related auxiliaries. The protective devices operate in various isolation and unit shutdown sequences, depending on the severity of the fault.

The type and extent of protection will vary depending on the size of the unit, manufacturer’s recommendations, owner’s practices, and industry standards.

Plant Auxiliary Equipment Used In Hydroelectric Power Plant

A number of auxiliary systems and related controls are provided throughout the hydroelectric plant to support the operation of the generating units. These include the following:

1. Switchyard systems.

2. Alternating current (AC) station service. Depending on the size and criticality of the plant, multiple sources are often supplied, with emergency backup provided by a diesel generator.

3. Direct current (DC) station service. It is normally provided by one or more battery banks, for supply of protection, control, emergency lighting, and exciter field flashing.

4. Lubrication systems, particularly for supply to generator and turbine bearings and bushings.

5. Drainage pumps, for removing leakage water from the plant.

6. Air compressors, for supply to the governors, generator brakes, and other systems.

7. Cooling water systems, for supply to the generator air coolers, generator and turbine bearings, and step-up transformer.

8. Fire detection and extinguishing systems.

9. Intake gate or isolation valve systems.

10. Draft tube gate systems.

11. Reservoir and tailrace water level monitoring.

12. Synchronous condenser equipment, for dewatering the draft tube to allow the runner to spin in air during synchronous condenser operation. In this case, the generator acts as a synchronous motor, supplying or absorbing reactive power.

13. Service water systems.

14. Overhead crane.

15. Heating, ventilation, and air conditioning.

16. Environmental systems.

PLANNING OF HYDROELECTRIC FACILITIES

By Engr. Aneel Kumar September 29, 2013 No comments:

1) Siting

Hydroelectric plants are located in geographic areas where they will make economic use of hydraulic energy sources. Hydraulic energy is available wherever there is a flow of liquid and accumulated head.

Head represents potential energy and is the vertical distance through which the fluid falls in the energy conversion process. The majority of sites utilize the head developed by freshwater; however, other liquids such as saltwater and treated sewage have been utilized. The siting of a prospective hydroelectric plant requires careful evaluation of technical, economic, environmental, and social factors. A significant portion of the project cost may be required for mitigation of environmental effects on fish and wildlife and relocation of infrastructure and population from flooded areas.

2) Hydroelectric Plant Schemes

There are three main types of hydroelectric plant arrangements, classified according to the method of controlling the hydraulic flow at the site:

1. Run-of-the-river plants, having small amounts of water storage and thus little control of the flow through the plant

2. Storage plants, having the ability to store water and thus control the flow through the plant on a daily or seasonal basis

3. Pumped storage plants, in which the direction of rotation of the turbines is reversed during off-peak hours, pumping water from a lower reservoir to an upper reservoir, thus “storing energy” for later production of electricity during peak hours

3) Selection of Plant Capacity, Energy, and Other Design Features

The generating capacity of a hydroelectric plant is a function of the head and flow rate of water discharged through the hydraulic turbines, as shown in the following equation:

P = 9.8 η QH

Where

P is the power (kW)

η is the plant efficiency

Q is the discharge flow rate (m3/s)

H is the head (m)

Flow rate and head are influenced by reservoir inflow, storage characteristics, plant and equipment design features, and flow restrictions imposed by irrigation, minimum downstream releases, or flood control requirements. Historical daily, seasonal, maximum (flood), and minimum (drought) flow conditions are carefully studied in the planning stages of a new development. Plant capacity, energy, and physical features such as the dam and spillway structures are optimized through complex economic studies that consider the hydrological data, planned reservoir operation, performance characteristics of plant equipment, construction costs, the value of capacity and energy, and financial discount rates. The costs of substation, transmission, telecommunications, and off-site control facilities are also important considerations in the economic analysis. If the plant has storage capability, then societal benefits from flood control may be included in the economic analysis.

Another important planning consideration is the selection of the number and size of generating units installed to achieve the desired plant capacity and energy, taking into account installed unit costs, unit availability, and efficiencies at various unit power.

HYDROELECTRIC POWER GENERATION

By Engr. Aneel Kumar September 29, 2013 No comments:

Hydroelectric power generation involves the storage of a hydraulic fluid, water, conversion of the hydraulic (potential) energy of the fluid into mechanical (kinetic) energy in a hydraulic turbine, and conversion of the mechanical energy to electrical energy in an electric generator.

The first hydroelectric power plants came into service in the 1880s and now comprise approximately 20% (875 GW) of the worlds installed generation capacity (World Energy Council, 2010). Hydroelectricity is an important source of renewable energy and provides significant flexibility in base loading, peaking, and energy storage applications. While initial capital costs are high, the inherent simplicity of hydroelectric plants, coupled with their low operating and maintenance costs, long service life, and high reliability, makes them a very cost-effective and flexible source of electricity generation.

Especially valuable is their operating characteristic of fast response for start-up, loading, unloading, and following of system load variations. Other useful features include their ability to start without the availability of power system voltage (black start capability), ability to transfer rapidly from generation mode to synchronous-condenser mode, and pumped storage application.

Hydroelectric units have been installed in capacities ranging from a few kilowatts to nearly 1 GW. Multiunit plant sizes range from a few kilowatts to a maximum of 22.5 GW.

ELECTRICAL ENGINEERING PROGRAM EDUCATIONAL OBJECTIVES

By Engr. Aneel Kumar September 17, 2013 No comments:

Successfully practice electrical engineering to serve state and regional industries, government agencies, or national and international industries.

Work professionally in one or more of the following areas: analog electronics, digital electronics, communication systems, signal processing, control systems, and computer-based systems.

Achieve personal and professional success with awareness and commitment to their ethical and social responsibilities, both as individuals and in team environments.

Maintain and improve their technical competence through lifelong learning, including entering and succeeding in an advanced degree program in a field such as engineering, science, or business.
Electrical Engineering Student Outcomes

Student outcomes are statements that describe what students are expected to know and are able to do by the time of graduation, the achievement of which indicates that the student is equipped to achieve the program objectives.

The generalized outcomes for the electrical engineering program are given below.

To Understand - to understand the mathematical and physical foundations of electrical engineering and how these are used in electronic devices and systems. An understanding that engineering knowledge should be applied in an ethically responsible manner for the good of society.

To Question - to critically evaluate alternate assumptions, approaches, procedures, tradeoffs, and results related to engineering problems.

To Design - to design a variety of electronic and/or computer-based components and systems for applications including signal processing, communications, computer networks, and control systems.

To Lead - to lead a small team of student engineers performing a laboratory exercise or design project; to participate in the various roles in a team and understand how they contribute to accomplishing the task at hand.

To Communicate - to use written and oral communications to document work and present project results.

SELF INDUCTANCE

By Engr. Aneel Kumar September 13, 2013 No comments:

A current-carrying coil produces a magnetic field that links its own turns. If the current in the coil changes the amount of magnetic flux linking the coil changes and, by Faraday’s law, an emf is produced in the coil. This emf is called a self-induced emf.

Let the coil have N turns. Assume that the same amount of magnetic flux F links each turn of the coil. The net flux linking the coil is then NF. This net flux is proportional to the magnetic field, which, in turn, is proportional to the current I in the coil. Thus we can write NF µ I. This proportionality can be turned into an equation by introducing a constant. Call this constant L, the self-inductance (or simply inductance) of the coil:

As with mutual inductance, the unit of self-inductance is the henry.

The self-induced emf can now be calculated using Faraday’s law:

The above formula is the emf due to self-induction.

Example

Find the formula for the self-inductance of a solenoid of N turns, length l, and cross-sectional area A.

Assume that the solenoid carries a current I. Then the magnetic flux in the solenoid is

MUTUAL INDUCTANCE

By Engr. Aneel Kumar September 13, 2013 No comments:

Suppose we hook up an AC generator to a solenoid so that the wire in the solenoid carries AC. Call this solenoid the primary coil. Next place a second solenoid connected to an AC voltmeter near the primary coil so that it is coaxial with the primary coil. Call this second solenoid the secondary coil. As shown in figure.

The alternating current in the primary coil produces an alternating magnetic field whose lines of flux link the secondary coil (like thread passing through the eye of a needle). Hence the secondary coil encloses a changing magnetic field. By Faraday’s law of induction this changing magnetic flux induces an emf in the secondary coil. This effect in which changing current in one circuit induces an emf in another circuit is called mutual induction.

Let the primary coil have N1 turns and the secondary coil have N₂ turns. Assume that the same amount of magnetic flux F₂from the primary coil links each turn of the secondary coil. The net flux linking the secondary coil is then N₂F₂. This net flux is proportional to the magnetic field, which, in turn, is proportional to the current I1 in the primary coil. Thus we can write N₂F₂µI₁. This proportionality can be turned into an equation by introducing a constant. Call this constant M, the mutual inductance of the two coils:

The unit of inductance is WB/A=Henry (H) named after Joseph Henry.

The emf induced in the secondary coil may now be calculated using Faraday’s law:

The above formula is the emf due to mutual induction.

Example

The apparatus used in Experiment EM-11B consists of two coaxial solenoids. A solenoid is essentially just a coil of wire. For a long, tightly-wound solenoid of n turns per unit length carrying current I the magnetic field over its cross-section is nearly constant and given by

. Assume that the two solenoids have the same cross-sectional area A. Find a formula for the mutual inductance of the solenoids.

EFFICIENCY OF A TRANSFORMER

By Engr. Aneel Kumar September 12, 2013 No comments:

Since the equivalent circuit contains two winding resistances and a core-loss resistance then power is lost as heating energy inside the transformer. Hence the conversion of power through the transformer cannot be 100%, a small loss of efficiency occurs. This is usually less than about 2% for power transformers. Assume all resistances and reactances are referred to the secondary winding. The efficiency can be expressed as,

Where cosØ is the power factor of the load

Pc is the core-loss
Is is the secondary current
Vs is the secondary voltage
Es is the secondary emf.

This formula applies to single-phase transformers, or to one phase of a three-phase transformer.

OPERATING PRINCIPLES OF T RANSFORMERS

By Engr. Aneel Kumar September 12, 2013 No comments:

A single-phase power system transformer consists basically of two windings wound onto an iron core. The iron core concentrates the flux and restricts it to a defined path. It also creates the maximum possible amount of flux for a given excitation. In order to maximize the mutual coupling the two windings are wound concentrically on to the same part of the iron core. Figure 6.1 shows the typical winding arrangement of a single-phase transformer. This is called shell-type construction.

Not all the flux created by one winding couples with the other winding. Furthermore the flux which does not couple both windings does not flow completely round the iron core, some of it flows in the air close to the windings. The common flux in the iron circuit is called the mutual or magnetizing flux. The flux that escapes into the air and does not couple the windings is called the leakage flux. One winding is referred to as the primary winding and is connected to the source of supply voltage. The second winding is the secondary winding and is connected to the load. The primary may be either the low or the high voltage winding.

The magnetizing flux is determined by the applied voltage to the primary winding. In power transformers the current drawn from the supply to magnetize the core is only a fraction of one percent of the rated primary winding current. The core design and type of iron is specially chosen to minimize the magnetizing current.

When current is drawn from the secondary winding the effect on the magnetizing flux is to reduce it. However, the magnetizing flux density must be maintained and this is achieved by the primary winding drawing more current from the supply.

METHODS OF STARTING INDUCTION MOTORS

By Engr. Aneel Kumar September 07, 2013 No comments:

When the maximum kW rating of an induction motor is reached for direct-on-line starting, it becomes necessary to introduce an alternative method of starting the motor. There are several methods used in the oil industry. The object is to reduce the starting current drawn from the supply during all or part of the run-up period. There are two basic approaches that can be used:-

• Select special-purpose designs for the motor in which the winding arrangements are modified by external switching devices that are matched to the motor, e.g. star-delta motor and starter.

• Select conventional motors but use special external starting devices, e.g. Korndorfer starter, autotransformer starter, ‘soft-starter’ using a controlled rectifier-inverter system.

In all cases of reduced voltage starting, care must be taken to check that the motor will create sufficient torque at the reduced voltage to accelerate the load to the desired speed in as short a time as possible. Excessive run-up times must be avoided as. When the run-up time is expected to be high the manufacturer of the motor should be consulted regarding the possibility of damage and infringement of its guarantees. The following methods are the most commonly used, typically in the order shown below.

• Star-delta method.
• Korndorfer auto-transformer method.
• Soft-start power electronics method.
• Series reactor method.
• Part winding method.

Star-Delta Method Of Starting Induction Motors

A specially designed motor is used. The stator windings are arranged so that the start and finish of each phase winding in the stator is brought out to the main terminal box so that six terminals are available for connection to cables. Usually two three-core or four-core cables are used unless their conductor size becomes too large, in which case single-core cables would be used. The windings are connected externally in star for starting and delta for running. The external connections are made by using a special starter in the motor control centre which also provides control relays and current transformers that determine when the transfer from star to delta should take place.

Disadvantages of Star-Delta Method

• The windings are open-circuited during the transfer and this is not considered good practice, a delay should be incorporated to allow the flux in the motor to decay during the transfer.

• The starting current and torque are reduced to 33% of their value during the run-up period. This reduction may be too much for some applications.

• The running condition requires a delta winding connection and this has the disadvantage that harmonic currents can circulate in the windings.

Figure shows the basic circuit for a star-delta starter.

Korndorfer Auto-Transformer Method Of Starting Induction Motors

A standard design of motor is used. An external auto-transformer is connected between the main circuit breaker, or contactor, and the motor during the starting and run-up period. Figure 5.8 shows the connections that are commonly used in a balanced three-phase arrangement. The voltage ratio of the auto-transformer needs to be carefully selected. If it is too high then the full benefit is not achieved. If too low then insufficient torque will be created. The most effective ratio is usually found between 65% and 80%.

Disadvantage of Korndorfer Auto-Transformer Method

Two extra three-phase circuit breakers or contactors are necessary, thus making three in total for the motor circuit, which require space to be allocated. Retro-fitting a Korndorfer starter may therefore be difficult if space is scarce.

Figure shows the basic circuit for Korndorfer Auto-Transformer Method.

Soft-Start Power Electronics Method Of Starting Induction Motors

A standard design of motor is used. An external rectifier-inverter is connected between the main circuit breaker, or contactor, and the motor during the starting and run-up period. The starter varies the frequency and voltage magnitude of the applied three-phase supply to the motor. Upon starting the frequency and voltage are set to their lowest values, and thereafter they are slowly raised as the shaft speed increases. The intent is to operate the motor in its near-synchronous speed state for each frequency that the motor receives.

The rectifier-inverter equipment is expensive when compared with other switching and transformer methods, but it has several advantages:-

• The starting current can be limited to a value that is equal to or a little higher than the full-load current of the motor.

• The torque created in the motor during the whole run-up period can be in the order of the full-load value, and so the shape of the inherent torque-speed curve of the motor is not a critical issue for most standard designs of motors.

Series Reactor Method Of Starting Induction Motors

A standard design of motor is used. This is a simple method that requires the insertion of a series reactor during starting. The reactor is bypassed once the motor reaches its normal working speed.

Only one extra circuit breaker or contactor is required. The amount of reactance is calculated on the basis of the desired reduction of line current during starting, but the limiting factor is the reduced starting torque. The torque is reduced for two reasons, firstly because the total circuit impedance is increased and secondly the reactance-to-resistance ratio is increased.

Part Winding Method Of Starting Induction Motors

A special design of motor is used. The stator has two three-phase windings that are arranged in parallel and wound in the same slots. If the two windings are the same then on starting and during run-up one winding would provide half of the total torque at any speed. Hence one winding is used for starting and both for running. The method is not suited to small or high speed motors. With two equal windings the starting current and torque are half of their totals. This method is seldom used in the oil industry because of the preference for standard motors, and the availability of satisfactory alternative methods.

Thursday, October 24, 2013

Merits of hybrid power system

Sunday, October 20, 2013

Sunday, October 13, 2013

Tuesday, October 08, 2013

Stator

Rotor

Winding

Thursday, October 03, 2013

Sunday, September 29, 2013

Tuesday, September 17, 2013

Friday, September 13, 2013

Thursday, September 12, 2013

Saturday, September 07, 2013

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