The subject of power systems has assumed considerable importance in recent years and growing demand for a compact work has resulted in this book. A new. Download Principles of Power System By V.K. Mehta, Rohit Mehta – “Principles of Power System” is a comprehensive textbook for students of engineering. Principles of Power System by V. K. Mehta, , available at Book Depository with free delivery worldwide.
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Principles Of Power System book. Read 3 reviews from the world's largest community for readers. Principles Of Power System (Multicolor Edition) by V K Mehta And Rohit Mehta. Book Summary: In the present edition, a chapter has been updated according to . Book Details. In the present edition, chapter have been updated according to the latest syllabus. A notable feature is the inclusion of chapter on " Neutral.
This reactive power can be provided by the generators themselves, through the adjustment of generator excitation, but it is often cheaper to provide it through capacitors, hence capacitors are often placed near inductive loads to reduce current demand on the power system i.
Power factor correction may be applied at a central substation, through the use of so-called "synchronous condensers" synchronous machines which act as condensers which are variable in VAR value, through the adjustment of machine excitation or adjacent to large loads, through the use of so-called "static condensers" condensers which are fixed in VAR value. Reactors consume reactive power and are used to regulate voltage on long transmission lines.
In light load conditions, where the loading on transmission lines is well below the surge impedance loading , the efficiency of the power system may actually be improved by switching in reactors.
Reactors installed in series in a power system also limit rushes of current flow, small reactors are therefore almost always installed in series with capacitors to limit the current rush associated with switching in a capacitor.
Series reactors can also be used to limit fault currents. Capacitors and reactors are switched by circuit breakers, which results in moderately large steps in reactive power.
A solution comes in the form of static VAR compensators and static synchronous compensators. Briefly, static VAR compensators work by switching in capacitors using thyristors as opposed to circuit breakers allowing capacitors to be switched-in and switched-out within a single cycle. This provides a far more refined response than circuit breaker switched capacitors. Static synchronous compensators take a step further by achieving reactive power adjustments using only power electronics.
Power electronics[ edit ] Power electronics are semiconductor based devices that are able to switch quantities of power ranging from a few hundred watts to several hundred megawatts. Despite their relatively simple function, their speed of operation typically in the order of nanoseconds  means they are capable of a wide range of tasks that would be difficult or impossible with conventional technology.
The classic function of power electronics is rectification , or the conversion of AC-to-DC power, power electronics are therefore found in almost every digital device that is supplied from an AC source either as an adapter that plugs into the wall see photo in Basics of Electric Power section or as component internal to the device.
HVDC is used because it proves to be more economical than similar high voltage AC systems for very long distances hundreds to thousands of kilometres. HVDC is also desirable for interconnects because it allows frequency independence thus improving system stability.
Power electronics are also essential for any power source that is required to produce an AC output but that by its nature produces a DC output.
They are therefore used by many photovoltaic installations both industrial and residential. Power electronics also feature in a wide range of more exotic uses. They are at the heart of all modern electric and hybrid vehicles—where they are used for both motor control and as part of the brushless DC motor. Power electronics are also found in practically all modern petrol-powered vehicles, this is because the power provided by the car's batteries alone is insufficient to provide ignition, air-conditioning, internal lighting, radio and dashboard displays for the life of the car.
So the batteries must be recharged while driving using DC power from the engine—a feat that is typically accomplished using power electronics. Whereas conventional technology would be unsuitable for a modern electric car, commutators can and have been used in petrol-powered cars, the switch to alternators in combination with power electronics has occurred because of the improved durability of brushless machinery.
In the middle twentieth century, rectifier locomotives were popular, these used power electronics to convert AC power from the railway network for use by a DC motor.
The use of power electronics to assist with the motor control and with starter circuits cannot be overestimated and, in addition to rectification, is responsible for power electronics appearing in a wide range of industrial machinery.
Power electronics even appear in modern residential air conditioners. Power electronics are also at the heart of the variable speed wind turbine. Conventional wind turbines require significant engineering to ensure they operate at some ratio of the system frequency, however by using power electronics this requirement can be eliminated leading to quieter, more flexible and at the moment more costly wind turbines.
A final example of one of the more exotic uses of power electronics comes from the previous section where the fast-switching times of power electronics were used to provide more refined reactive compensation to the power system.
Main article: power system protection Power systems contain protective devices to prevent injury or damage during failures. The quintessential protective device is the fuse. When the current through a fuse exceeds a certain threshold, the fuse element melts, producing an arc across the resulting gap that is then extinguished, interrupting the circuit. Given that fuses can be built as the weak point of a system, fuses are ideal for protecting circuitry from damage.
Fuses however have two problems: First, after they have functioned, fuses must be replaced as they cannot be reset. This can prove inconvenient if the fuse is at a remote site or a spare fuse is not on hand.
And second, fuses are typically inadequate as the sole safety device in most power systems as they allow current flows well in excess of that that would prove lethal to a human or animal. The first problem is resolved by the use of circuit breakers —devices that can be reset after they have broken current flow.
These devices combine the mechanism that initiates the trip by sensing excess current as well as the mechanism that breaks the current flow in a single unit.
Some miniature circuit breakers operate solely on the basis of electromagnetism. In these miniature circuit breakers, the current is run through a solenoid, and, in the event of excess current flow, the magnetic pull of the solenoid is sufficient to force open the circuit breaker's contacts often indirectly through a tripping mechanism.
A better design, however, arises by inserting a bimetallic strip before the solenoid—this means that instead of always producing a magnetic force, the solenoid only produces a magnetic force when the current is strong enough to deform the bimetallic strip and complete the solenoid's circuit.
In higher powered applications, the protective relays that detect a fault and initiate a trip are separate from the circuit breaker. Early relays worked based upon electromagnetic principles similar to those mentioned in the previous paragraph, modern relays are application-specific computers that determine whether to trip based upon readings from the power system.
Different relays will initiate trips depending upon different protection schemes. For example, an overcurrent relay might initiate a trip if the current on any phase exceeds a certain threshold whereas a set of differential relays might initiate a trip if the sum of currents between them indicates there may be current leaking to earth.
The circuit breakers in higher powered applications are different too. Air is typically no longer sufficient to quench the arc that forms when the contacts are forced open so a variety of techniques are used.
One of the most popular techniques is to keep the chamber enclosing the contacts flooded with sulfur hexafluoride SF6 —a non-toxic gas that has sound arc-quenching properties. Other techniques are discussed in the reference. In any properly functioning electrical appliance, the current flowing into the appliance on the active line should equal the current flowing out of the appliance on the neutral line.
A residual current device works by monitoring the active and neutral lines and tripping the active line if it notices a difference. This is typically not a problem in most residential applications where standard wiring provides an active and neutral line for each appliance that's why your power plugs always have at least two tongs and the voltages are relatively low however these issues do limit the effectiveness of RCDs in other applications such as industry.
Even with the installation of an RCD, exposure to electricity can still prove lethal. SCADA systems[ edit ] In large electric power systems, supervisory control and data acquisition SCADA is used for tasks such as switching on generators, controlling generator output and switching in or out system elements for maintenance. The first supervisory control systems implemented consisted of a panel of lamps and switches at a central console near the controlled plant.
The lamps provided feedback on the state of the plant the data acquisition function and the switches allowed adjustments to the plant to be made the supervisory control function. Today, SCADA systems are much more sophisticated and, due to advances in communication systems, the consoles controlling the plant no longer need to be near the plant itself. Instead, it is now common for plants to be controlled with equipment similar if not identical to a desktop computer.
The ability to control such plants through computers has increased the need for security—there have already been reports of cyber-attacks on such systems causing significant disruptions to power systems.
This section introduces some common power system types and briefly explains their operation. Residential power systems[ edit ] Residential dwellings almost always take supply from the low voltage distribution lines or cables that run past the dwelling. These operate at voltages of between and volts phase-to-earth depending upon national standards. A few decades ago small dwellings would be fed a single phase using a dedicated two-core service cable one core for the active phase and one core for the neutral return.
The active line would then be run through a main isolating switch in the fuse box and then split into one or more circuits to feed lighting and appliances inside the house.
By convention, the lighting and appliance circuits are kept separate so the failure of an appliance does not leave the dwelling's occupants in the dark.
All circuits would be fused with an appropriate fuse based upon the wire size used for that circuit. Circuits would have both an active and neutral wire with both the lighting and power sockets being connected in parallel. Sockets would also be provided with a protective earth.
This would be made available to appliances to connect to any metallic casing. If this casing were to become live, the theory is the connection to earth would cause an RCD or fuse to trip—thus preventing the future electrocution of an occupant handling the appliance.
Earthing systems vary between regions, but in countries such as the United Kingdom and Australia both the protective earth and neutral line would be earthed together near the fuse box before the main isolating switch and the neutral earthed once again back at the distribution transformer. Some of the most significant ways modern residential power systems in developed countries tend to vary from older ones include: For convenience, miniature circuit breakers are now almost always used in the fuse box instead of fuses as these can easily be reset by occupants and, if of the thermomagnetic type, can respond more quickly to some types of fault.
For safety reasons, RCDs are now often installed on appliance circuits and, increasingly, even on lighting circuits. Whereas residential air conditioners of the past might have been fed from a dedicated circuit attached to a single phase, larger centralised air conditioners that require three-phase power are now becoming common in some countries.
Protective earths are now run with lighting circuits to allow for metallic lamp holders to be earthed.
Increasingly residential power systems are incorporating microgenerators , most notably, photovoltaic cells. Commercial power systems[ edit ] Commercial power systems such as shopping centers or high-rise buildings are larger in scale than residential systems. Electrical designs for larger commercial systems are usually studied for load flow, short-circuit fault levels, and voltage drop for steady-state loads and during starting of large motors.
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Principles of Power System V. Mehta and Rohit Mehta. ISBN Published by S. Chand Publisher, Used Condition: As New Soft cover. Save for Later. download Used Price: Bookseller Inventory Ask Seller a Question. Bibliographic Details Title: Principles of Power System Publisher: Chand Publisher Publication Date: Soft cover Book Condition: