electrical &electronic engineering site
my total courses
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important books
SOME IMPORTANT BOOK LIST
1INTRODUCTORY CIRCUIT ANALYSIS-BOYLESTAD
2.PRINCIPLES OF ELECTRONICS-V.K MEHTA
3.FIELD AND WAVE ELECTRO MAGNETIC FIELD.-DAVID.K CHANG
4.CONTINUOUS AND DISCRETE SIGNAL AND SYSTEM-SAMIR S. SOLMAN
5.ENGINEERING MECHANICS-R .S .KHURMI
6ELECTRO TECHNOLOGY-B.L THEREZA
7.AULTERNATING CURRENT CIRCUIT-RUSSELM.KERCHNER
8.ELECTROMECHINARY FUNDAMENTALS-STEPHEN J.CHAPMAN
9.ELEMENT OF POWER SYSTEM ANALYSIS-WILLIAM D.STEVENSON
10.INTRODUCTORY METHODS OF FUNDAMENTAL ANALYSIS-S.S,SASTRY
assingment
my recent assingment which i did on 24/05/07
Screwdriver:The screwdriver is a device specifically designed to insert and tighten, or to loosen and remove, screws. The screwdriver comprises a head or tip which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver. A typical hand screwdriver comprises an approximately cylindrical handle of a size and shape to be held by a human hand, and an axial shaft fixed to the handle, the tip of which is shaped to fit a particular type of screw. The handle and shaft allow the screwdriver to be positioned and supported and, when rotated, to apply torque. Screwdrivers are made in a variety of shapes, and the tip can be rotated manually or by an electric or other motor.
A screw has a head with a contour such that an appropriate screwdriver tip can be engaged in it in such a way that the application of sufficient torque to the screwdriver will cause the screw to rotate.
Side-Cutting Pliers
These side-cutting pliers feature a smooth streamlined design. They slide more easily in and out of any tool bag. They feature sure-gripping, cross-hatched knurled jaws.
9" High-Leverage Side-Cutting Pliers
High leverage design. Rivet is closer to the cutting edge for 46% greater cutting and gripping power than other plier designs. Streamlined design with sure-gripping, cross-hatched knurled jaws.
Journeyman™ High-Leverage Side-Cutting Pliers - Connector Crimping
Crimping die behind hinge for superior leverage crimping non-insulated connectors, lugs and terminals. High-leverage design. Rivet is closer to the cutting edge for 46% greater cutting and gripping power than other plier designs. Streamlined design with sure-gripping, cross-hatched knurled jaws. Induction-hardened cutting knives for long life.
Journeyman™ High-Leverage Side-Cutting Pliers - Fish Tape Pulling
Quickly and easily pulls 1/8" or 1/4" flat steel fish tape without damaging the tape. High-leverage design. Rivet is closer to the cutting edge for 46% greater cutting and gripping power than other plier designs. Streamlined design with sure-gripping, cross-hatched knurled jawsDiagonal Pliers
8" High-Leverage Diagonal-Cutting Pliers - Angled Head
These high-leverage diagonal-cutting pliers are heavy-duty with a head angled for easier work in confined spaces. Standard bevel cutting knives with plastic-dipped handles. For use on non-ferrous wire only. Not for hard wire.
Journeyman™ High-Leverage Diagonal-Cutting Pliers
High-leverage design. Rivet is closer to the cutting edge for 36% greater cutting power than other plier designs. Short jaws and beveled cutting edges permit close cutting of wire. Induction-hardened cutting knives for long life.
These inexpensive pliers shear wire up to No. 14 AWG with unique flush-cutting action that minimizes fly-off. The design greatly reduces cutting effort. Compact head is easy to manipulate in confined areas.
8" High-Leverage Diagonal-Cutting Pliers
High-leverage design. Rivet is closer to the cutting edge for 36% greater cutting power than standard heavy-duty diagonal cutters. Plastic dipped handles, hand-form style
5" Electronics Midget Diagonal-Cutting Pliers
Sharp pointed-nose for precise tip cutting and trimming printed circuit boards. Spring-loaded for self-opening action. Hot-riveted joint ensures smooth action and no handle wobble.
5" Electronics Diagonal-Cutting - Pointed Nose, Narrow Jaws
This narrow jaw and hinge diagonal cutter reaches into confined spaces to permit full-flush cutting. Features a fully polished head and neck and coil spring
#########Long-Nose Pliers
6" & 7" Standard Long-Nose Pliers
6" & 7" Standard Long-Nose Pliers - Side-Cutting
Induction hardened cutting knives for long life. Heavier design for greater cutting power, extended handles provide added reach and leverage. Curved handles provide greater tool control.
8" Heavy-Duty Long-Nose Pliers - Side-Cutting
Induction hardened cutting knives for long life. Heavier design for greater cutting power, extended handles provide added reach and leverage. Curved handles provide greater tool control.
Journeyman™ 6" & 7" Standard Long-Nose Pliers
The Journeyman™ line of hand tools has expanded with the addition of two new long-nose pliers with side-cutting knives. Both tools, a six inch and seven inch version, feature state-of- the-art, dual-material handles, that provide a better grip without sacrificing tool strength or durability.
Journeyman™ 8" Heavy-Duty Long-Nose Pliers - Side-Cutting
This Journeyman™ plier has the feature state-of- the-art, dual-material handles, that provides a better grip without sacrificing tool strength or durability. The soft, outer-surface handle material combines comfort with a firm grip, while the harder, inner-surface handle material is designed for extra toughness and durability in harsh work environments.
Klein Tools’ long reach long nose pliers allow you to work efficiently and comfortably around obstructions. The knurled jaw provides precision gripping and sure looping of wire. These pliers are made of custom forged, hardened, and tempered steel for maximum strength and holding power with little effort.
Hammer
A hammer is a tool meant to deliver blows to an object. The most common uses are for driving nails, fitting parts, and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure. Usual features are a handle and a head, with most of the weight in the head. The basic design is hand-operated, but there are also many mechanically operated models for heavier uses.The hammer is a basic tool of many professions, and can also be used as a weapon. Either way, it is perhaps the oldest human tool, perhaps even older than the earliest Homo speciesHYPERLINK "/wiki/Wikipedia:Citing_sources"[citation needed].
Basic design and variations
The essential part of a hammer is the head, a compact solid mass that is able to deliver the blows to the intended target without itself deforming
The opposite side of the head may have a second striking surface; or a claw or wedge to pull nails, or may be shaped like a ball as in the ball-peen hammer and the cow hammer. Some upholstery hammers have a magnetized appendage, to pick up tacks. In the hatchet the hammer head is secondary to the cutting edge of the tool.
Slip joint pliers
These versatile pliers have both serrated teeth and coarse contoured teeth to grip objects of different shapes. The jaws can be adjusted ("slipped") to handle objects of various sizes.
Using Slip-Joint Pliers
Use the narrow jaw setting to grip small objects. For larger objects, increase the width of the jaw opening by spreading the handles and then sliding the slotted handle along the pivot post. Close the handles to lock the setting.
Use pliers to turn a nut only in an emergency. Pliers can round over the corners, making the nut difficult to remove. Don't use light pliers for heavy-duty work; you might damage them.
An alternative to slip-joint pliers is curved thin-nose slip-joint pliers. These have a narrower head than standard slip-joint pliers, allowing a better view of the work. The jaws have both flat and curved areas to grasp objects of different shapes. Like all slip-joint pliers, this tool can be adjusted to handle objects of various sizes. These pliers are most commonly available in 6- and 8-inch sizes.
Wood Saw:
A small wood saw with a 12 inch blade has rough teeth but is capable of cutting to any depth and is much easier to use on larger pieces of wood. This again is an essential item.
Hacksaw
A hacksaw is a saw for cutting metal or bones. Some of them have pistol grips which keep the hacksaw firm and easy to grip. It is a fine-tooth saw with a blade under tension in a frame.
Small hand-held hacksaws consist of a metal arch with a handle, that fits around a narrow, rigid blade. The blade has many small saw teeth along one side. The blade can either be attached such that the teeth face away from the handle, resulting in sawing action by pushing, or be attached such that the teeth face toward the handle, resulting in sawing action by pulling. On the push stroke, the arch will bend a little, releasing the tension on the blade. The blade is normally quite brittle, so care needs to be taken to prevent brittle fracture of the blade. A panel hacksaw eliminates the frame, so that the saw can cut into panels of sheet metal without the length of cut being restricted by the frame. Junior hacksaws are the small variant, while larger mechanical hacksaws are used to cut working pieces from bulk metal.
Twist drill
The twist drill bit is the type produced in largest quantity today. It can be used to create holes in metal, plastic, wood and stone.
The twist drill bit was invented by Steven A. MorseHYPERLINK "http://www.morsecuttingtools.com/company/about.html"[1] of East Bridgewater, Massachusetts in 1861. He received U.S. Patent 38,119HYPERLINK "http://www.pat2pdf.org/pat2pdf/foo.pl?number=38119" for his invention on 7 April 1863. The original method of manufacture was to cut two grooves in opposite sides of a round bar, then to twist the bar to produce the helical flutes. This gave the tool its name. Nowadays, the drill bit is usually made by rotating the bar while moving it past a grinding wheel to cut the flutes in the same manner as cutting helical gears.Tools recognizable as twist drill bits are currently produced in diameters covering the range at least from 0.05 mm to 100 mm. Lengths up to about 1000 mm are available for use in powered hand tools.
The geometry and sharpening of the cutting edges is crucial to the performance of the bit. Users often throw away small bits that become blunt, and replace them with new bits, because they are inexpensive and sharpening them well is difficult. For larger bits, special grinding jigs are available. A special tool grinder is available for sharpening or reshaping cutting surfaces on twist drills to optimize the drill for a particular material.Manufacturers can produce special versions of the twist drill bit, varying the geometry and the materials used, to suit particular machinery and particular materials to be cut. Twist drill bits are available in the widest choice of tooling materials. However, even for industrial users, most holes are still drilled with a conventional bit of high speed steel.The most common twist drill (the one sold in general hardware stores) has a point of 118 degrees. This is a suitable angle for a wide array of tasks, and will not cause the uninitiated operator undue stress by walking or digging in. A more aggressive (pointy) angle, such as 90 degrees, is suited for very soft plastics and other materials. The bit will generally be self-starting and cut very quickly. A shallower angle, such as 150 degrees, is suited for drilling steels and other tougher materials. This style bit requires a starter hole, but will not bind or suffer premature wear when a proper feed rate is set.
Drills with no point angle are used in situations where a blind, flat-bottomed hole is required. These style drills are very sensitive to changes in lip angle, and even a slight change can result in an inappropriately fast cutting drill bit that will suffer premature wear.
wrenchen
A wrench or spanner is a tool used to provide a mechanical advantage in applying torque to turn bolts, nuts or other hard-to-turn items.
In American English, wrench is the standard term, while spanner refers to a specialized wrench with a series of pins or tabs around the circumference. (These pins or tabs fit into the holes or notches cut into the object to be turned.) The most common shapes are called open-end wrench and box-end wrench.
TRANSFORMERS
The information in this chapter is on the construction, theory, operation, and the various uses of transformers. Safety precautions to be observed by a person working with transformers are also discussed.
A TRANSFORMER is a device that transfers electrical energy from one circuit to another by electromagnetic induction (transformer action). The electrical energy is always transferred without a change in frequency, but may involve changes in magnitudes of voltage and current. Because a transformer works on the principle of electromagnetic induction, it must be used with an input source voltage that varies in amplitude. There are many types of power that fit this description; for ease of explanation and understanding, transformer action will be explained using an ac voltage as the input source.
In a preceding chapter you learned that alternating current has certain advantages over direct current. One important advantage is that when ac is used, the voltage and current levels can be increased or decreased by means of a transformer.
As you know, the amount of power used by the load of an electrical circuit is equal to the current in the load times the voltage across the load, or P = EI. If, for example, the load in an electrical circuit requires an input of 2 amperes at 10 volts (20 watts) and the source is capable of delivering only 1 ampere at 20 volts, the circuit could not normally be used with this particular source. However, if a transformer is connected between the source and the load, the voltage can be decreased (stepped down) to 10 volts and the current increased (stepped up) to 2 amperes. Notice in the above case that the power remains the same. That is, 20 volts times 1 ampere equals the same power as 10 volts times 2 amperes.
NOW WE WILL DESCRIBE ABOUT CURRENT TRANSFORMER&POTENTIAL TRANS FORMER:
OUR TEACHER TANBIR SIR QUESTION THROUGH TO US THAT
WHAT IS CURRENT TRANSFORMER AND POTENTIAL TRANSFORMER?
AND THEIR WORKING PRINCIPLE?
WHATEVER FIRST WE EXPLAIN CURRENT TRANSFORMER:
Current Transformer Design and Theory
If it were possible to have no core or wire losses at all, the calculation for the ratio between primary and secondary; equals dividing the primary current by the turns on the secondary equals the secondary current , then take the secondary current and multiplied it by the number of ohms of the burden resistor across the secondary, which would equal the voltage output across the secondary burden resistor.
Note: The maximum input current of a CT can be increased by varying the ohms of the burden resistor. Lowering the ohms of the burden resistor will increase the maximum input of the CT, but it lowers the resolution. Also, the accuracy of the output voltage depends on the accuracy of the burden resistor. The burden resistor should never be used for more than 55 % of its wattage capacity, and thermal concerns of the surrounding materials should be considered to prevent over heating damage. For circuits requiring very accurate outputs, the CT should only be used up to 50 % of saturation line of the core.
A current transformer is designed to provide a current in its secondary which is accurately proportional to the current flowing in its primary.
Current transformers are commonly used in electricity meters to facilitate the measurement of large currents which would be difficult to measure more directly.
Care must be taken that the secondary of a current transformer is not disconnected from its load while current is flowing in the primary as in this circumstance a very high voltage would be produced across the secondary.
Current transformers are often constructed with a single primary turn either as an insulated cable passing through a toroidal core, or else as a bar to which circuit conductors are connected.
How Does a Current Transformer Work?
A transformer is an electrical device that takes electricity of one voltage and changes it into another voltage. You'll see transformers at the top of utility poles and even changing the voltage in a toy train set.
Basically, a transformer changes electricity from high to low voltage using two properties of electricity. In an electric circuit, there is magnetism around it. Second, whenever a magnetic field changes (by moving or by changing strength) a voltage is made. Voltage is the measure of the strength or amount of electrons flowing through a wire.
If there's another wire close to an electric current that is changing strength, the current of electricity will also flow into that other wire as the magnetism changes.
A transformer takes in electricity at a higher voltage and lets it run through lots of coils wound around an iron core. Because the current is alternating, the magnetism in the core is also alternating. Also around the core is an output wire with fewer coils. The magnetism changing back and forth makes a current in the wire. Having fewer coils means less voltage. So the voltage is "stepped-dow
Transformers on the Electrical Grid
Let's look at the electricity that comes to your home. When electricity moves from a power plant it is put into a very high voltage to be able to travel long distances. The high voltage lines can be as high 155,000 to 765,000 volts to travel many hundreds of miles.
In order for your home or a store to use the electricity, it has to be at a lower voltage than on the long-distance lines. So, the electricity is "stepped-down to a lower level using a transformer. This lower voltage electricity is put into the local electric wires at a substation. The substation breaks the larger amount of power down into smaller pieces at lower voltage. It then is stepped down again and again.
Once smaller transformers take that voltage down to usually 7,200, the power leaves this substation.
In your neighborhood, a transformer on top of a utility pole, or one connected to underground wires, transforms the 7,200 volts into 220-240 volts. This is then sent into your home over three wires. The three wires go through the electric meter, which measures how much electricity you use. One of the three wires is the ground, and the other two are the positives.
Some of the electrical appliances in your home use the 220-240 volts. These are things like a water heater, stove and oven, or air conditioner. They have very special connections and plugs. Other devices, like your TV or computer only use one-half of the electricity -- 110-120 volts.
In a toy train set, the voltage is reduced even more from 110-120 and is changed from alternating current into direct current.
Some businesses use higher voltage power to run big machines. So, they don't need to have the voltage reduced as much.
POTENTIAL TRANSFORMER:
Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications.
The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two fuses.
A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer.
> A potential transformer is a type of transformer used by the electric
> ulitility companies for measuring the voltage on their high voltage
> power lines. These transformers are very well made, very robust,
> and have low losses. Two of these transformers used together can
> approach the performance of a pole or distribution transformer.
> Unfortunately, they can be hard to obtain.
Transformers can also be used in electrical instrumentation systems. Due to transformers' ability to step up or step down voltage and current, and the electrical isolation they provide, they can serve as a way of connecting electrical instrumentation to high-voltage, high current power systems. Suppose we wanted to accurately measure the voltage of a 13.8 kV power system (a very common power distribution voltage in American industry):
Direct measurement of high voltage by a voltmeter is a potential safety hazard.
Designing, installing, and maintaining a voltmeter capable of directly measuring 13,800 volts AC would be no easy task. The safety hazard alone of bringing 13.8 kV conductors into an instrument panel would be severe, not to mention the design of the voltmeter itself. However, by using a precision step-down transformer, we can reduce the 13.8 kV down to a safe level of voltage at a constant ratio, and isolate it from the instrument connections, adding an additional level of safety to the metering system:
Instrumentation application:"Potential transformer" precisely scales dangerous high voltage to a safe value applicable to a conventional voltmeter.
Now the voltmeter reads a precise fraction, or ratio, of the actual system voltage, its scale set to read as though it were measuring the voltage directly. The transformer keeps the instrument voltage at a safe level and electrically isolates it from the power system, so there is no direct connection between the power lines and the instrument or instrument wiring. When used in this capacity, the transformer is called a Potential Transformer, or simply PT.
Potential transformers are designed to provide as accurate a voltage step-down ratio as possible. To aid in precise voltage regulation, loading is kept to a minimum: the voltmeter is made to have high input impedance so as to draw as little current from the PT as possible. As you can see, a fuse has been connected in series with the PTs primary winding, for safety and ease of disconnecting the PT from the circuit.
A standard secondary voltage for a PT is 120 volts AC, for full-rated power line voltage. The standard voltmeter range to accompany a PT is 150 volts, full-scale. PTs with custom winding ratios can be manufactured to suit any application. This lends itself well to industry standardization of the actual voltmeter instruments themselves, since the PT will be sized to step the system voltage down to this standard instrument level.
REFR:
Lessons In Electric Circuits -- Volume II
Chapter 9
TRANSFORMERS
*AND DIFFERENCE WEB SITE
WWW.POTENTIALTRANSFOMER.INFO
AND CURRENT TRANSFORMER.INFO