What is Buchholz Relay ?

 Buchholz Relay principle 

The Buchholz Relay working principle of is very simple. Buchholz Relay function is based on very simple mechanical phenomenon. It is mechanically actuated. Whenever there will be a minor internal fault in the transformer such as an insulation faults between turns, break down of core of transformer, core heating, the transformer insulating oil will be decomposed in different hydrocarbon gases, CO2 and CO. The gases produced due to decomposition of transformer insulating oil will accumulate in the upper part the Buchholz Container which causes fall of oil level in it. Fall of oil level means lowering the position of float and thereby tilting the mercury switch. The contacts of this mercury switch are closed and an alarm circuit energized. Sometime due to oil leakage on the main tank air bubbles may be accumulated in the upper part the Buchholz Container which may also cause fall of oil level in it and alarm circuit will be energized. By collecting the accumulated gases from the gas release pockets on the top of the relay and by analyzing them one can predict the type of fault in the transformer.

More severe types of faults, such as short circuit between phases or to earth and faults in the tap changing equipment, are accompanied by a surge of oil which strikes the baffle plate and causes the mercury switch of the lower element to close. This switch energized the trip circuit of the Circuit Breakers associated with the transformer and immediately isolate the faulty transformer from the rest of the electrical power system by inter tripping the Circuit Breakers associated with both LV and HV sides of the transformer. This is how Buchholz Relay functions.

Construction of Buchholz Relay

Buchholz Relay in transformer is an oil container housed the connecting pipe from main tank to conservator tank. It has mainly two elements. The upper element consists of a float. The float is attached to a hinge in such a way that it can move up and down depending upon the oil level in the Buchholz Relay Container. One mercury switch is fixed on the float. The alignment of mercury switch hence depends upon the position of the float.

The lower element consists of a baffle plate and mercury switch. This plate is fitted on a hinge just in front of the inlet (main tank side ) of Buchholz Relay in transformer in such a way that when oil enters in the relay from that inlet in high pressure the alignment of the baffle plate along with the mercury switch attached to it, will change. In addition to these main elements a Buchholz Relay has gas release pockets on top. The electrical leads from both mercury switches are taken out through a molded terminal block.

Buchholz Relay Operation – Certain Precaution

The Buchholz Relay operation may be actuated without any fault in the transformer. For instance, when oil is added to a transformer, air may get in together with oil, accumulated under the relay cover and thus cause a false Buchholz Relay operation. That is why mechanical lock is provided in that relay so that one can lock the movement of mercury switches when oil is topping up in the transformer. This mechanical locking also helps to prevent unnecessary movement of breakable glass bulb of mercury switches during transportation of the Buchholz Relays.

The lower float may also falsely operate if the oil velocity in the connection pipe through, not due to internal fault, is sufficient to trip over the float. This can occurs in the event of external short circuit when over currents flowing through the winding cause overheated the copper and the oil and cause the oil to expand.

TRANSDUCERS

In general terms, the transduction process involves the transformation of oneform of energy into another form. This process consists of sensing withspecificity the input energy from the measurand by means of a “sensing element” and then transforming it into another form by a “transductionelement.”

The sensor-transduction element combination shown in Fig. 5.1 will henceforth be referred to as the “transducer.” Measurand relates to the quantity, property, or state that the transducer seeks to translate into an electrical output.

As an example, consider a “walkie-talkie” intercom set where the loudspeaker also functions as a microphone. At the input end, the loudspeaker functions as an acousto electric transducer and at the output end as an electro acoustic transducer. Moreover, in the reverse direction, the functions of the loudspeakers are interchanged, and for this reason we say that the loud-speaker is a bidirectional transducer and the transduction process is reversible.

Another example of reversible transduction is seen in piezoelectric materials; when an electric voltage is applied to the faces of a piezoelectric substrate, it produces a change in its physical dimensions; and conversely, when the material is physically deformed, an electric charge is generated on these faces.

In this transducer, the sensing and transduction functions cannot be separated as easily, and it represents a good example of a practical transducer used in the field of nondestructive testing (NDT) of materials and in medical ultrasound imaging of body tissues and organs. This is a bidirectional transducer, but most practical transducers are not bidirectional.

Transducers may be classified as self-generating or externally powered.

Fig 5.1. Sensor-Transduction Element Combination

 

Windows 7 - The Missing Manual

Windows has recently been going through a tough phase of its glorious legacy in the world of technology which it has dominated for the past few decades. Its internet Browser "internet explorer" is getting upstaged by other browsing engines like Mozilla Firefox and Google Chrome while it also went through that fiasco of Vista which really was shockingly bad.
So it was no surprise when I found myself holding onto XP and waiting for what else Microsoft would come up with. Trust the worlds richest man and he came up with the Windows 7. Though I wanted to do a head bang on it right away! the prospect of going through another technical manual which would have me scratching my head was not exactly tempting.
In computer book land, you either get lame introduction type material which leaves you with only the basics and at times actually makes you feel like a lost soul, or you get a thoroughly informative book that puts you into a short lived coma.

At this critical juncture of time enter Windows 7 - The Missing Manual.

The Missing Manual is a guide to everything that you need to know regarding Microsoft's newest adventure. One may ask how is it any different from the other manuals that continue to bore us to death. The answer lies in the fact that it does exactly the opposite of what the other manuals do i.e. it does not bore you. The language used by the author is a conversational one that everyone can comprehend making the material extremely simple to grasp.

The flow of this book allows you to move from section to section without there being a "hard" interruption in between, the index and appendix are top notch for anyone choosing to pick helpful nuggets here and there. The bad aspect of other books are that the humour in them is so false that it actually irritates you rather than lightening your mood. Although the book will not make you roll all over the floor, it will bring a lot of smiles to your face making your read enjoyable.

If you want a comprehensive manual for Windows 7 that is useful for beginners through to advanced users then get the book that Microsoft forgot to put in your box.

If you would like to read a chapter of this comprehensive guide click here

For your chance to get a free iPad or Amazon Kindle do check out http://powerfulreviews.com thanks.

My New iPad: A User's Guide Book Review

Wallace Wang, best seller of My New Mac and My New iPhone for the No Starch Press publisher has written a new book detailing everything you need to know about the iPad in a book called "My New iPad: A User's Guide." No Starch Press provided a reviewer's copy of "My New iPad: A User's Guide" for this review.
"My New iPad: A User's Guide" includes seven chapters including: basic training; customizing your iPad; getting on the Internet; sharing data with your iPad; video, music, and eBooks; organizing yourself and additional tips. Each chapter is small and comes in easily consumable chunks of information that can instantly help new users complete a certain task with easy to follow step by step instructions.
The first chapter called "Basic Training" teaches you how to turn on and off the iPad, what the various buttons and slides perform and how to use and customize the virtual keyboard. Apple changed the Screen Location Lock since the book was published so information has changed since the publish date resulting in incorrect information.

"Customizing Your iPad" is the second chapter that details how to customize your home screen, set the date and time, restoring and resetting your iPad and installing and uninstalling iPad apps.

The third chapter called "Getting on the Internet" shows how to use the email client and web browser called Safari including some intermediate information such as how to use bookmarks and automatically fill out forms with Safari.

If you do not know how to transfer content to your iPad, chapter four is perfect for you. "Sharing Data with Your iPad" shows how to synchronize with iTunes to transfer media such as photos, movies, TV shows and even podcasts. The chapter further goes on to show steps to synch your eBooks, Audio Books, Contacts, Appointments, Mail, Notes, Bookmarks and even iTunes University Courses. The book is light on how to actually configure Yahoo! or Google services with your iPad however.

The next chapter focuses on content consumption on the iPad and it titled "Video, Music and eBooks". This chapter shows you how to watch your photos to listen to your music to watching YouTube videos.

Chapter six focuses on how to use the iPad to keep yourself organized using included iPad apps and is called "Organizing Yourself."

Finally, the last chapter called "Additional Tips" provides some additional miscellaneous tips including how to update the iOS or use foreign languages. This last chapter also includes a section called "Best iPad Apps" which includes some good apps but is dated. To keep up with the best iPad apps, you should watch for articles that continually are updated such as the Gizmos for Geeks Favorite iPad Apps monthly updated list.

I started and finished "My New iPad: A User's Guide" in one afternoon. The book is geared towards new users of not only the iPad device but of Apple's iOS devices including iPod Touch and iPhones and definitely not towards advanced user's of the iOS. For example, this book would be ideal for my parents since they have never used an iOS device, but I found the book way to simplistic to really become engaged.

Doug Felteau enjoys blogging about the latest gadgets and anything technology related and maintains a monthly article on Gizmos for Geeks listing the best iPad apps. An avid iPad user since the device was released, Doug has integrated the device and apps into his everyday life.

High Ohmic Series Resistance with Micro ammeter

High D.C. voltages are usually measured by connecting a very high resistance (few hundreds of mega ohms) in series with a micro ammeter. Only the current flowing through the large calibrated resistance R is measured by the moving coil micro ammeter. The voltage of the source is given by

Series resistance micrometer

The voltage drop in the meter is negligible, as the impedance of the meter is only few ohms com pared to few hundred mega-ohms of the series resistance R. A protective device like a paper gap, a neon glow tube, or a zener diode with a suitable series resistance is connected across the meter as a protection against high voltages in case the series resistance R fails or flashes over. The ohmic value of the series resistance R is chosen such that a current of one to ten microamperes is allowed for full-scale deflection. The resistance is constructed from a large number of wire wound resistors in series. The voltage drop in each resistor element is chosen to avoid surface flashovers and discharges. A value of less than 5 kv /cm in air or less than 20 kV/cm in good oil is permissible. The resistor chain is provided with corona free terminations. The material for resistive elements is usually a carbon-alloy with temperature coefficient less than 1T Carbon and other metallic film resistors are also used. A resistance chain built with ±1% carbon resistors located in airtight transformer oil filled P.V.C. tube, for 100 kV operations had very good temperature stability.

 The limitations in the series resistance design are:

•    Power dissipation and source loading

•    Temperature effects and long time stability

•    Voltage dependence of resistive elements, and

•    Sensitivity to mechanical stresses

Series resistance meters are built for 500kV D.C. with accuracy better than 0.2%.

Welding:

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld.

This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the work pieces to form a bond between them, without melting the work pieces

Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in many different environments, including open air, under water and in outer space. Regardless of location, however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock, eye damage, poisonous fumes, and overexposure to ultraviolet light.

Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join metals by heating and pounding them. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and resistance welding followed soon after.

Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding and electron beam welding in the latter half of the century. Today, the science continues to advance. Robot welding is becoming more commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality and properties.