ENGINEERING ARTICLES

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 ca...

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.

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 ...

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 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.

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.

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...

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 lo...

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 ...

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, an...

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 ...

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...

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 ap...

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.

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....

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 ...

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 necessar...

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 ...

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.

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.

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.

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.

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...

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 Jet type), 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 turb...

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.

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 Jet type), or cross-flow types. In a...