Snubber circuit

What is a snubber circuit?

Snubber circuits are used for semiconductor switching devices such as transistors, SCRs, etc.
When a switching device changes its state from ON-state to OFF-state, the impedandce of the device abruptly jumps to a very high level, blocking the current. But the current still tends to keep flowing through the switch, which induces a high voltage across the switch. The faster the current decreases, the higher the induced voltage becomes. It may reach to sufficiently high level to destroy the switch. If the switch is unable to withstand the high induced voltage, it will be destroyed, and can no more block the current as an OFF-state switch. To avoid this, an auxiliary network is connected across the switch that prevents the induced voltage from going too high. The network is called a snubber.
Conversely, when a switching device changes its state from OFF-state to ON-state, the impedance of the device abruptly goes down to nearly zero, allowing current to flow freely. The problem in this case is that the current does not start to flow uniformly through the switch. This is because the switch does not recover its conductivity over the whole its cross-sectional area simultaneously. Some part of the area may be first open, and the current flow is concentrated to this relatively small portion of the switch, which may cause overheating and eventually failure. Thus some semiconductor switches should be protected from too fast increase of current. This is another function of a snubber.
In view of above discussion, the snubber circuit is someting like a "bumper." It alleviates rise of voltage when the switch is turning OFF, and alleviates rise of current when the switch is turning ON, to a safe level.

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11 march 2009, chattting brings people so close

It was a usual evening when i came online as every day . Usually I dont go visible in Yahoo messenger but that day i became visible and suddenly got a Hi .... from a friend whom I already deleted once when I got frustrated with the chatting routine and the consequences and removed all those buddies whom i  dint knew very well.. So, it was a surprising experience..Now, We started talking (She was a girl). The chatting started with general talk and went on and we shared each others cell numbers and got it saved in iur mobs. 

Now we started talking on cell and it was always long and magnetic (no one of us could withdraw oneself) ...It became an addiction and it became an addition to the daily routine to msg and miss call on eaqch other's cell number......

all the things above are not so peculiar but what will you do ..........

If YOU listen "I LOVE YOU" from someone whom you dont know much and even after knowing that you are engaged with someone else....the person says I felt it for the first time and its YOU.......

Power Factor Correction

Depending upon the rate structure of your electric utility, you may be able to save a substantial amount of money on your electric bill. Pay-back period for an equipment purchase including installation cost may be less than six months to a year. Utility rate structures that account for reactive power consumption, by either a KVA or var demand usage, or a power factor penalty are the ones that can provide this pay-back. Other ancillary benefits to be gained by correcting power factor are, lower energy losses, better voltage regulation and released system capacity. This page explains the fundamentals of power factor and how NEPSI's shunt capacitor banks can benefit you.All electric equipment requires "vars" - a term used by electric power engineers to describe the reactive or magnetizing power required by the inductive characteristics of electrical equipment. These inductive characteristics are more pronounced in motors and transformers, and therefore, can be quite significant in industrial facilities. The flow of vars, or reactive power, through a watt-hour meter will not effect the meter reading, but the flow of vars through the power system will result in energy losses on both the utility and the industrial facility. Some utilities charge for these vars in the form of a penalty, or KVA demand charge, to justify the cost for lost energy and the additional conductor and transformer capacity required to carry the vars. In addition to energy losses, var flow can also cause excessive voltage drop, which may have to be corrected by either the application of shunt capacitors, or other more expensive equipment, such as load-tap changing transformers, synchronous motors, and synchronous condensers.
Figure 1 - Power Factor Triangle

The power triangle shown in figure 1, is the simplest way to understand the effects of reactive power. The figure illustrates the relationship of active (real) and reactive (imaginary or magnetizing) power. The active power (represented by the horizontal leg) is the actual power, or watts that produces real work. This component, is the energy transfer component, which represents fuel burned at the power plant. The reactive power, or magnetizing power, (represented by the vertical leg of the upper or lower triangle) is the power required to produce the magnetic fields to enable the real work to be done. Without magnetizing power, transformers, conductors, motors, and even resistors and capacitors would not be able to operate. Reactive power is normally supplied by generators, capacitors and synchronous motors. The longest leg of the triangle (on the upper or lower triangle), labeled total power, represents the vector sum of the reactive power and real power components. Mathematically, this is equal to:


Electric power engineers often call total power, kVA, MVA, apparent power, or complex power. Some utilities measure this total power, (usually averaged over a 15 minute load period) and charge a monthly fee or tariff for the highest fifteen minute average load reading in the month. This tariff is usually added to the energy charge or kilowatt-hour charge. This type of billing is often called kva demand billing and can be quite costly to an industrial facility. NEPSI's shunt capacitors can save your company money by decreasing your reactive power component supplied by the utility to near zero vars.

The power triangle and the equation above show, that as the reactive power component is decreased by adding shunt capacitors, the total power will also decrease. This is shown by the decreased length of the dashed lines in the power triangle as the reactive power component approaches zero. Therefore, adding capacitors, which will supply reactive power locally, can reduce your total power and monthly kva demand charge.

The angle "phi" in the power triangle is called the power factor angle and is mathematically equal to:

The ratio of the real power to the total power in the equation above (or the cos of phi) is called power factor. As the angle gets larger (caused by increasing reactive power) the power factor gets smaller. In fact, the power factor can vary from 0 to 1, and can be either inductive (lagging) or capacitive (leading). Capacitive loads are drawn down, and inductive loads are drawn up on the power triangle. Most industrials normally operate on the upper triangle (inductive or lagging triangle). As an industrial adds capacitors, the length of reactive (inductive) power leg is shortened by the number of capacitive kvar that were added. If the number of capacitive kvar added exceeds the industrials inductive kvar load, operation occurs on the lower triangle. This is commonly referred to as over compensation.

Utilities charge for reactive power in a countless number of ways. Some utilities charge for kvar demand, while others charge a strait fee for a power factor less than their target. To fully understand the benefits of NEPSI's shunt capacitor and harmonic filters, you must acquire your electric billing rate structure. This rate structure will describe how cost for poor power factor are added to your monthly bills. If you need assistance in calculating your pay-back periods, feel free to contact our nearest factory trained sales representatives or just call Northeast Power Systems, Inc.

Table 1, which contains kilowatt multipliers, can be used to calculate the amount of kvar required to raise your "original power factor" to your "desired power factor". For example, a facility has a peak kilowatt demand of 5000 kW with a power factor of 0.80. The facilities engineer wants to raise its power factor from 0.80 to 0.95. The kW multiplier obtained from table 1 is 0.421. Multiplying this value times the facilities kilowatt demand yields 2105 kvar (0.421 X 5000 = 2105). Therefore, a 2105 kvar capacitor bank would raise the facility's power factor from 0.80 to 0.95.

Table - 1 Kilowatt Multipliers


In addition to the above table, the following web page can be used to calculate the required amount of vars based upon an initial power, desired power factor, and kw demand (Calculation of Required kvar to Raise Power Factor).

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Top 100 Engineering Institutes In India

Top 100 Engineering Institutes In India

Just a list I stumbled upon!! might help you if you've just completed your 10+2 or are planning to pursue your higher education in India..... please note, this list is not my personal opinion!!

RANK	Name of Institute	City
1	IIT Kanpur	Kanpur
2	IIT Kharagpur	Kharagpur
3	IIT Bombay	Mumbai
4	IIT Madras	Chennai
5	IIT Delhi	Delhi
6	BITS Pilani	Pilani
7	IIT Roorkee	Roorkee
8	IT-BHU	Varanasi
9	IIT-Guwahati	Guwahati
10	Coll. of Engg, Anna Univ.	Guindy
11	Jadavpur University , Faculty of Engg & Tech	Calcutta
12	Indian School of Mines	Dhanbad
13	NIT- W	Warangal
14	BIT, Mesra	Ranchi
15	NIT- Trichy	Trichy
16	Delhi College of Engg.	New Delhi
17	Punjab Engineering College	Chandigarh
18	NIT- K	Suratkal
19	Motilal Nehru National Inst. of Technology	Allahabad
20	Thapar Inst of Engineering & Technology	Patiala
21	Bengal Eng and ScienceUniversity , Shibpur	Howrah
22	MANIT	Bhopal
23	PSG College of Technology	Coimbatore
24	IIIT	Hyderabad
25	Harcourt Butler Technological Institute	Kanpur
26	Malviya National Institute of Technology	Jaipur
27	VNIT	Nagpur
28	NIT- Kozhikode	Kozhikode
29	Dhirubhai Ambani IICT	Gandhinagar
30	Osmania Univ. College of Engineering	Hyderabad
31	College of Engineering ,Andhra University	Vishakhapatnam
32	Netaji Subhas Institute ofTechnology	New Delhi
33	NIT- National Institute of Technology	Kurukshetra
34	NIT- National Institute of Technology	Rourkela
35	SVNIT	Surat
36	Govt. College of Engineering	Pune
37	Manipal Institute of Technology	Manipal
38	JNTU	Hyderabad
39	R.V. College of Engineering	Bangalore
40	NIT- Jamshedpur	Jamshedpur
41	University VisvesvarayaCollege of Engg.	Bangalore
42	VJTI	Mumbai
43	Vellore Institute of Technology	Vellore
44	Coimbatore Institute of Technology	Coimbatore
45	SSN College of Engineering	Chennai
46	IIIT	Allahabad
47	College of Engineering	Trivandrum
48	NIT Durgapur	Durgapur
49	SIT	Calcutta
50	Mumbai University Inst of Chemical Tech	Mumbai
51	Sardar Patel College of Engineering	Mumbai
52	P.E.S. Institute of Technology	Bangalore
53	Maharashtra Institute of Technology	Pune
54	Amrita Institute of Technology & Science	Coimbatore
55	National Institute ofEngineering	Mysore
56	B.M.S. College of Engineering	Bangalore
57	Laxminarayan Institute Of Tech.	Nagpur
58	Nirma Institute of Technology	Ahmedabad
59	IIIT	Pune
60	Amity School of Engineering	Noida
61	JNTU	Kakinada
62	S.J. College of Engineering	Mysore
63	Chaitanya Bharathi Inst. of Technology	Hyderabad
64	IIIT	Bangalore
65	SRM Institute of Science and Technology	Chennai
66	SASTRA	Thanjavur
67	Bangalore Institute of Technology	Bangalore
68	The Technological Inst. of Textile & Sciences	Bhiwani
69	III	Gwalior
70	JNTU	Anantpur
71	M.S. Ramaiah Institute of Technology	Bangalore
72	Gitam	Vishakhapatnam
73	NIT- Hamirpur	Hamirpur
74	NIT- Jalandhar	Jalandhar
75	SV University EngineeringCollege	Tirupati
76	NIT- Raipur	Raipur
77	Vasavi College of Engineering	Hyderabad
78	The ICFAI Inst of Science and Technology	Hyderabad
79	NIT- Patna	Patna
80	Cummins Colleges of Engg of Women	Pune
81	VIT	Pune
82	Shri Ramdeo Baba K.N.Engineering College	Nagpur
83	Muffakham Jah EngineeringCollege	Hyderabad
84	Karunya Institute of Technology	Coimbatore
85	D.J. Sanghvi	Mumbai
86	Sathyabhama EngineeringCollege	Chennai
87	Kongu Engineering College	Erode
88	Mepco Schlek EngineeringCollege	Sivakasi
89	Guru Nanak Dev EngineeringCollege	Ludhiana
90	Hindustan Inst of Engineering Technology	Chennai
91	SDM College of Engineering	Dharwad
92	R.V.R. & J.C. College Of Engg	Guntur
93	Jamia Millia Islamia	New Delhi
94	K.L. College of Engineering	Veddeswaram
95	Dharmsinh Desai Institute of Technology	Nadiad
96	S.G.S. Institute of Technology & Science	Indore
97	Jabalpur Engineering College	Jabalpur
98	Sree Chitra Thirunal Collegeof Engineering	Trivandrum
99	G.H. Patel College of Engg & Technology	Vallabh Vidyanagar
100	Kalinga Institute of Industrial Technology	Bhubaneshwar

Do you agree with this list??

Now Thats A Wedding Cake!!

Now Thats A Wedding Cake!!

This has to be the awesomest geek wedding cake ever!! It was aFlickr user's wedding cake, and it seems to have everything in theMario world represented nicely. It’s got Toad, Yoshi, Piranha plants, mushrooms, even the Chain Chomp guy. The castle on a planet was inspired from Super Mario Galaxy. The cake was created by Beth from Let Them Eat Cake in California.

Ever wondered why people never divorce with such style?? They should. You’re getting the hell away from each other after all which, according to me, is cause to celebrate!! Marry with aMario cake and divorce with a Zelda cake, that’s what I say. Or how about a Tetris cake, that can be thrown at each other.

Pure fun huh?? Go Geeks!!