2014 OIL & NATURAL GAS

CORPORATION LIMITED

Aakash M. Shah Electrical Engg. Department (6th semester)

Babaria Inst. of Technology,Varnama

[TRAINIG REPORT] The report about the design of receiving substations of 11KV, working and

design of Central A.C. plant, A.C. workshop, Illumination and Power

distribution in the ONGC Vadodara Basin.

Electrical Engg. Department (6th semester)

BABARIA INSTITUTE OF

TECHNOLOGY, VARNAMA

INDEX

I. Introduction on the ONGC

II. Electricity distribution in the ONGC

Vadodara Basin

III. Detailed Information on Central A.C. plant &

its workshop of ONGC Vadodara Basin

IV. Detailed Information on ILLUMINATION of

ONGC Vadodara Basin

A brief History of ONGC is as under:

From 1947 – 1960 During pre-independence, the Assam Oil Company in the North-Eastern

and Attock Oil company in North-Western part of undivided India were the only oil companies

producing oil in the country. The major part of Indian sedimentary basins was deemed to be unfit

for development of oil and gas resources.

After independence, the Government realized the importance of oil and gas for rapid industrial

development and its strategic role in defence. Consequently, while

framing the Industrial Policy Statement of 1948, the development of

the hydrocarbon industry in the country was considered to be of

utmost necessity.

Until 1955, private oil companies mainly carried out exploration of

hydrocarbon resources of India. Assam Oil Company was producing

oil at Digboi, Assam (discovered in 1889) and the Oil India Ltd. (a 50%

joint venture between Government of India and Burmah Oil Company)

was engaged in developing two fields Naharkatiya and Moran in

Assam. In West Bengal, the Indo-Stanvac Petroleum project (a joint

venture between Government of India and Standard Vacuum Oil

Company of USA) was engaged in exploration work. The vast

sedimentary tract in other parts of India and adjoining offshore

remained largely unexplored.

In 1955, Government of India decided to develop the oil and natural gas resources in the various

regions of the country as part of Public Sector development. With

this objective, an Oil and Natural Gas Directorate was set up in

1955 under the then Ministry of Natural Resources and Scientific

Research. The department was constituted with a nucleus of

geoscientists from the Geological survey of India.

A delegation under the leadership of Mr. K D Malviya, the then

Minister of Natural Resources, visited several countries to study the

oil industry and to facilitate the training of Indian professionals for

exploring potential oil and gas reserves. Foreign experts from USA, West Germany, Romania and

erstwhile USSR visited India and helped the government with their expertise. Finally, the visiting

Soviet experts drew up a detailed plan for geological and geophysical surveys and drilling

operations to be carried out in the 2ndFive Year Plan (1956-57 to 1960-61).

In April 1956, the Government of India adopted the Industrial Policy Resolution, which placed

mineral oil industry amongst the Schedule 'A' industries, the future development of which was to

be the sole and exclusive responsibility of the state.

Soon, after the formation of the Oil and Natural Gas

Directorate, it became apparent that it would not be possible

for the Directorate with limited financial and administrative

powers to function efficiently. So in August, 1956, the

Directorate was raised to the status of a commission with

enhanced powers, although it continued to be under the

government. In October 1959, the Commission was converted

into a statutory body by an act of Parliament, which enhanced

powers of the commission further. The main functions of the

Oil and Natural Gas Commission subject to the provisions of the Act, were "to plan, promote,

organize and implement programmes for development of Petroleum Resources and the production

and sale of petroleum and petroleum products produced by it, and to perform such other functions

as the Central Government may, from time to time, assign to it". The act further outlined the

activities and steps to be taken by ONGC in fulfilling its mandate.

1961 – 1990

Since its inception, ONGC has been instrumental in transforming the country's limited upstream

sector into a large viable playing field, with its activities spread throughout India and significantly

in overseas territories. In the inland areas, ONGC not only found new resources in Assam but also

established new oil province in Cambay basin (Gujarat), while

adding new petroliferous areas in the Assam-Arakan Fold Belt

and East coast basins (both inland and offshore).ONGC went

offshore in early 70's and discovered a giant oil field in the form

of Bombay High, now known as Mumbai High. This discovery,

along with subsequent discoveries of huge oil and gas fields in

Western offshore changed the oil scenario of the country.

Subsequently, over 5 billion tonnes of hydrocarbons, which

were present in the country, were discovered. The most

important contribution of ONGC, however, is its self-reliance and development of core competence

in E&P activities at a globally competitive level.

After 1990

The liberalized economic policy, adopted by the Government of India in July 1991, sought to

deregulate and de-license the core sectors (including petroleum sector) with partial disinvestments

of government equity in Public Sector Undertakings and other measures. As a consequence thereof,

ONGC was re-organized as a limited Company under the Company's Act, 1956 in February 1994.

During March 1999, ONGC, Indian Oil Corporation (IOC) - a downstream giant and Gas

Authority of India Limited (GAIL) - the only gas marketing company, agreed to have cross holding

in each other's stock. This paved the way for long-term strategic alliances both for the domestic and

overseas business opportunities in the energy value chain, amongst themselves. Consequent to this

the Government sold off 10 per cent of its share holding in ONGC to IOC and 2.5 per cent to GAIL.

With this, the Government holding in ONGC came down to 84.11 per cent.

In the year 2002-03, after taking over MRPL from the A V Birla Group, ONGC diversified into the

downstream sector. ONGC has also entered the global field through its

subsidiary, ONGC Videsh Ltd. (OVL). ONGC has made major

investments in Vietnam, Sakhalin, Columbia, Venezuela, Sudan, etc. and

earned its first hydrocarbon overseas revenue from its investment in

Vietnam.

Global Ranking

ONGC is world's no. 3 E&P Company as per prestigious Platts ranking and is 22nd among Platts

Top 250 global companiesRanked 21st among global Oil and Gas Operations industry in Forbes

Global 2000 list of the World's biggest companies for 2014; Ranked 176 in the overall list - based on

Sales (US$ 29.6 billion), Profits (US$ 4.5 billion), Assets (US$ 53.8 billion) and Market Value (US$

46.4 billion).Only Indian energy major in Fortune's Most Admired List 2014 under 'Mining, Crude

Oil Production' category (No. 7 worldwide - Up 3 places from previous year)Stands at 369 in

Fortune Global 500 for year 2013Ranked 39 among the world's 105 largest listed companies in

'transparency in corporate reporting' by Transparency International making it the most transparent

company in IndiaRanked 386 in the Newsweek Green Rankings 2012 Global 500 Companies

Perspective Plan 2030 (PP2030)

PP2030 charts the roadmap for ONGC's growth over the next two decades. It aims to double

ONGC's production over the plan period with 4-5 per cent growth against the present growth rate

of 2 percent. In physical terms the aspirations under Perspective Plan 2030 aims for -Production of

130 mmtoe of oil and oil equivalent gas (O + OEG) per year and accretion of over 1,300 mmtoe of

proven reserves.Grow ONGC Videsh Limited (OVL) six fold to 60 mmtoe of international O+OEG

production per year by 2030.

Electricity Distribution

General layout of power system

Power system is generally divided into 3 parts:

Generation

Transmission

Distribution

In the generating stations the electric supply is generated at 11KV & then after

stepping up the voltage at Extra High Voltage and transmitted to the customers. After

transmission process this supply voltage gets stepped down as per the requirement with

the help of transformers and through the substations supply gets locally distributed.

Similarly, in the ONGC Vadodara Onshore basin the electricity is distributed. ONGC

Vadodara Onshore basin has three substations; namely substation 1, substation 2,

substation3, from which the substation 1 is having four ways to get the supply accordingly

two ways of the are from the tarsali substation, one way is from the lalbaug substation by

changing the supply connections with the help of GANG switch (mounted on the pole)

and another one is from the diesel generators i.e. DG sets available at every substations

situated in the ONGC Vadodara basin region. The explanation about all the three

substations briefly given:

Substation 1

In the substation 1 the supply is coming through the Tarsali substation, where

voltage is being stepped down to the 66kV & 11KV. This 11KV supply enters into the S/S-1

through Oil Circuit Breaker as rated by below values shown in the tabular form:

OIL CIRCUIT BREAKER RATING

FOR INCOMING FEEDER

VOLTAGE 11000V

CURRENT 400A

MVA RATING 250MVA

EXCITATION

VOLTAGE

30V

FOR OUTGOING FEEDER

VOLTAGE 11000V

CURRENT 800A

MVA

RATING

350MVA

CT RATIO 200/5A

NOTE THAT: HERE THE RELAY CONNECTIONS ARE SET FOR OVERCURRENT

RELAY ON 3.75 A & EARTH FAULT RELAY ON 0.5 A FOR OCB ONLY.

Now the supply enters through 2x3CORE 225sq.mm XPLE cable to the a 11KV

switchgear panel located at HT room, where six circuit breakers are connected for

protection purpose. Out of six, five circuit breakers are SF6 circuit breakers and sixth one is

Vacuum Circuit Breaker. Their ratings are shown below in the tabular forms located at the

11KV HT room.

THE TABULAR FORM OF SF6 CIRCUIT BREAKER RATINGS:

Out of these five SF6 C.B.s, 1st one is connected at the incoming supply of 11KV

coming through the Oil Circuit Breaker, 2nd & 3rd one are connected to the POWER

TRANSFORMERS 1&2, 4th one is connected to the supply going to the C/W, 5th one is

connected to the supply going to the S/S-2 & 6th one is connected to the supply going to the

S/S-3 as shown in the fig.

RATING OF SF6 CICUIT BREAKER

TYPE GMH

NUMBER 1321/87

FOR MAIN CIRCUIT

RATED VOLTAGE 11000V

RATED CURRENT 830A

FREQUENCY 50Hz

FOR AUXILLARY CIRCUIT

EXCITATION VOLTAGE 30V D.C.

FREQENCY 50Hz

Now the supply given to the POWER TRANSFORMERS 1 the ratings are shown

below in the tabular form:

RATINGS OF THE POWER TRANSFORMER-1

REFERENCE AMBIENT TEMPRATURE-323K

AVERAGE WINDING TEMPRATURE-363K

KVA RATING 1000KVA

NO LOAD

VOLTAGE

11000V H.V.SIDE

433V L.V.SIDE

CURRENT 52.49A H.V.SIDE

1333A L.V.SIDE

PHASES 3 (FOR BOTH THE SIDES)

INSULATION CLASS ‘F’

TYPE OF COOLING AN

FREQENCY 50Hz

% IMPEDENCE 4.87%

VECTOR GROUP Dyn11

INSULATION LEVEL 75KVP

WEIGHT 3400KG

YEAR OF MANUFACTURE 1987

COMPANY NAME VOLTAMP LTD.

CONNECTION & VECTOR DESIGN:

Now, this POWER TRANSFORMER steps down the 11KV supply to 433V & provide

this supply to the old capacitor bank, RTI shed, NEGI Bhavan, GS building TBG power,

C&M power, AMF panel 1&2 & two of them made spares as shown in the figure.

Now, the ratings & vector design of the POWER TRANSFORMER-2 are given

below:

RATINGS OF THE POWER TRANSFORMER-2

REFERENCE AMBIENT TEMPRATURE-323K

AVERAGE WINDING TEMPRATURE-363K

KVA RATING 1000KVA

NO LOAD

VOLTAGE

11000V H.V.SIDE

433V L.V.SIDE

CURRENT 52.49A H.V.SIDE

1333A L.V.SIDE

PHASES 3 (FOR BOTH THE SIDES)

INSULATION CLASS ‘F’

TYPE OF COOLING AN

FREQENCY 50Hz

% IMPEDENCE 4.90%

VECTOR GROUP Dyn11

INSULATION LEVEL 75KVP

WEIGHT 3400KG

YEAR OF MANUFACTURE 1987

COMPANY NAME VOLTAMP LTD.

CONNECTION & VECTOR DESIGN:

Similarly, POWER TRANSFORMER 2 works as the POWER TRANSFORMER 1, it

provides the stepped down 433V to new capacitor panel, FP-near CWC gate MS building,

O/G RS new emergency, FP for semi-permanent quartos, old B&C type near store & last

one is kept as spare. After the section of the power transformers there is a change over

panel room where two DIESELGENERATORS are placed of the 310KVA, their rating table

is given below:

RATINGS OF THE DIESEL GENERATORS AT S/S1

KVA RATING 500KVA&310KVA

RPM 1500

VOLTAGE 415V

CURRENTS 431A

EXCITATION VOLTAGE 70V (D.C.)

EXCITATION CURRENT 2A(D.C.)

ROTATION REVERSIBLE

INSULATION TYPE ‘F’

ELECTRICITY TYPE AC

FREQENCY 50Hz

NO. OF PHASES 3

POWER FACTOR 0.8

CONNECTION TYPE Y

With the help of these generators in case of emergency these generators are able give

supply to C&M office, Regional store, building cewells C2&C3, street lights of A-type,

water tank new etc. as shown in the fig. given below:

Substation 2 & 3

Substation 2&3 is also having almost same type of design, only few differences exist

here. Now, in the substation 2 the supply is coming through the substation 1, it moves

forward to the POWER TRANSFORMER of the substation 2. The ratings of the POWER

TRANSFORMER is given below in the tabular form:

RATINGS OF THE POWER TRANSFORMER-1

REFERENCE AMBIENT TEMPRATURE-323K

AVERAGE WINDING TEMPRATURE-363K

KVA RATING 1000KVA

NO LOAD

VOLTAGE

11000V H.V.SIDE

433V L.V.SIDE

CURRENT 52.49A H.V.SIDE

1333A L.V.SIDE

PHASES 3 (FOR BOTH THE SIDES)

INSULATION CLASS ‘F’

TYPE OF COOLING AN

FREQENCY 50Hz

% IMPEDENCE 5.17%

VECTOR GROUP Dyn11

INSULATION LEVEL 75KVP

WEIGHT 3400KG

YEAR OF MANUFACTURE 1987

COMPANY NAME VOLTAMP LTD.

CONNECTION & VECTOR DESIGN:

From this power transformer the supply goes stepped down from 11KV to 433V. The

officers club, 1-6 D-type bungalow, officers club A/C, SBI bank A/C supply, shopping

centres & CWC building etc. are the places which get the electricity from this S/S-2. This

substation is having another facility to supply the power same as the S/S-1 i.e. diesel

generators which are being used in the emergency case. The connection diagram is shown

below:

From the above figure it is seen that whenever the supply is provided by the diesel

generators then the AMF switches are being connected to these emergency panels &

provides them supply primarily.

Similarly, in the S/S3 the coming from the substation 1 &2 are first given to the three

POWER TRANSFORMERS of the S/S-3 as shown in the figure given below:

The ratings of the power transformer 1,2,3 are given below in the tabular form

THE RATINGS OF THE POWER TRANSFORMER 1,2,3 OF S/S3

KVA RATING 1000

NO LOAD VOLTAGE 110000V(H.V.) , 433V (L.V.)

CURRENT 52.49A(H.V.) , 1333.33A(L.V.)

PHASES 3

FREQUENCY 50Hz

COOLING AN

INSULATION CLASS ‘H’

MAX. AMB. TEMP. 323K

MAX.TEMP. RISE OIL/WNDG 388K

%IMPEDENCE 4.97%

PROTECTION CLASS IP-23

TYPE OF INSTALLATION INDOOR

YEAR OF MANUFACTURE 2010

CORE & WINDING WEIGHT 3140KG.

TOTAL WEIGHT 4100KG.

Now, again this substation is also having the DG set their rating table is given below:

RATINGS OF THE DIESEL GENERATORS AT S/S3

KVA RATING 500KVA&310KVA

&1000KVA

RPM 1500

VOLTAGE 415V

CURRENTS 431A

EXCITATION VOLTAGE 70V (D.C.)

EXCITATION CURRENT 2A(D.C.)

ROTATION REVERSIBLE

INSULATION TYPE ‘F’

ELECTRICITY TYPE AC

FREQENCY 50Hz

NO. OF PHASES 3

POWER FACTOR 0.8

CONNECTION TYPE Y

They are also used in the case of emergency to provide the supply to LT07 panel &

RCC main panel as shown in the fig

Arrangement of the diesel generators withLT panel & RCC main panel

Central A.C. plant & its workshop

AIR CINDITIONING

Air conditioning (often referred to as aircon, AC or A/C) is the process of altering the

properties of air (primarily temperature and humidity) to more favourable conditions,

typically with the aim of distributing the conditioned air to an occupied space to improve

comfort. In the most general sense, air conditioning can refer to any form of technology,

heating, cooling, de-humidification,

humidification, cleaning, ventilation, or air

movement that modifies the condition of air.

In common use, an air conditioner is a

device (most commonly a home

appliance or automobile system) that lowers

the air temperature. The cooling is typically

done using a simple refrigeration cycle, but

sometimes evaporation is used, commonly for

comfort cooling in buildings and motor

vehicles. In construction, a complete system of

heating, ventilation and air conditioning is

referred to as "HVAC".

Air conditioning can also be provided by a simple process called free cooling which

uses pumps to circulate a coolant (typically water or a glycol mix) from a cold source,

which in turn acts as a heat sink for the energy that is removed from the cooled space. Free

cooling systems can have very high efficiencies, and are sometimes combined with seasonal

thermal energy storage (STES) so the cold of winter can be used for summer air

conditioning. Common storage media are deep aquifers or a natural underground rock

mass accessed via a cluster of small-diameter, heat exchanger equipped boreholes. Some

systems with small storage are hybrids, using free cooling early in the cooling season, and

later employing a heat pump to chill the circulation coming from the storage. The heat

pump is added-in because the temperature of the storage gradually increases during the

cooling season, thereby declining in effectiveness. Free cooling and hybrid systems

are mature technology.

HISTORY

The basic concept behind air conditioning is said to have been applied in ancient

Egypt, where reeds were hung in windows and were moistened with trickling water.

The evaporation of water cooled the air blowing through the window, though this

process also made the air more humid (also beneficial in a dry desert climate). In Ancient

Rome, water from aqueducts was circulated through the walls of certain houses to cool

them.

Other techniques in medieval Persia involved the use of cisterns and wind towers to

cool buildings during the hot season. Modern air conditioning emerged from advances

in chemistry during the 19th century, and the first large-scale electrical air conditioning was

invented and used in 1902 by Willis Carrier. The introduction of residential air conditioning

in the 1920s helped enable the great migration to the Sun Belt in the US.

St George's Hall in Liverpool England, built between 1841 and 1854, was, in 2005,

awarded a Blue Plaque by the Heritage Group of the CIBSE recognising it as the World's

First Air Conditioned Building.

Mechanical cooling

The 2nd-century Chinese inventor Ding Huan (fl 180) of

the Han Dynasty invented a rotary fan for air conditioning,

with seven wheels 3 m (9.8 ft) in diameter and manually

powered. In 747, Emperor Xuanzong (r. 712–762) of the Tang

Dynasty (618–907) had the Cool Hall (Liang Tian) built in the

imperial palace, which the Tang Yulin describes as

having water-powered fan wheels for air conditioning as well

as rising jet streams of water from fountains. During the

subsequent Song Dynasty (960–1279), written sources

mentioned the air-conditioning rotary fan as even more widely

used.

In the 17th century, Cornelis Drebbel demonstrated

"Turning Summer into Winter" for James I of England by adding salt to water.

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge

University, conducted an experiment to explore the principle of evaporation as a means to

rapidly cool an object. Franklin and Hadley confirmed that evaporation of highly volatile

liquids such as alcohol and ether could be used to drive down the temperature of an object

past the freezing point of water. They conducted their experiment with the bulb of a

mercury thermometer as their object and with a bellows used to "quicken" the evaporation;

they lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the

ambient temperature was 18 °C (64 °F). Franklin noted that, soon after they passed the

freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the

thermometer's bulb and that the ice mass was about a quarter-inch thick when they

stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded, "From this

experiment one may see the possibility of freezing a man to death on a warm summer's

day".

In 1820, English scientist and inventor Michael Faraday discovered that compressing

and liquefying ammonia could chill air when the liquefied ammonia was allowed to

evaporate.

In 1842, Florida physician John Gorrie used compressor technology to create ice,

which he used to cool air for his patients in his hospital in Apalachicola, Florida.[9] He

hoped eventually to use his ice-making machine to regulate the temperature of buildings.

He even envisioned centralized air conditioning that could cool entire cities.[10] Though his

prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-

making machine. His hopes for its success vanished soon afterwards when his chief

financial backer died; Gorrie did not get the money he needed to develop the machine.

According to his biographer, Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor,

for his failure, suspecting that Tudor had launched asmear campaign against his invention.

Dr. Gorrie died impoverished in 1855, and the idea of air conditioning went away for 50

years.Since prehistoric times, snow and ice were used for cooling. The business of

harvesting ice during winter and storing for use in summer became popular towards the

late 19th century. This practice was replaced by mechanical ice-making machine.

James Harrison's first mechanical ice-making machine began operation in 1851 on

the banks of the Barwon River at Rocky Point in Geelong (Australia). His first commercial

ice-making machine followed in 1854, and his patent for an ether vapor-compression

refrigeration system was granted in 1855. This novel system used a compressor to force the

refrigeration gas to pass through a condenser, where it cooled down and liquefied. The

liquefied gas then circulated through the refrigeration coils and vaporised again, cooling

down the surrounding system. The machine employed a

5 m (16 ft.) flywheel and produced 3,000 kilograms

(6,600 lb) of ice per day.

Electromechanical cooling

In 1902, the first modern electrical air conditioning

unit was invented by Willis Carrier in Buffalo, New York.

After graduating from Cornell University, Carrier, a native

of Angola, New York, found a job at the Buffalo Forge

Company. While there, Carrier began experimenting with

air conditioning as a way to solve an application problem

for the Sackett-Wilhelms Lithographing and Publishing

Company in Brooklyn, New York, and the first "air

conditioner", designed and built in Buffalo by Carrier,

began working on 17 July 1902.

Willis Carrier

Designed to improve manufacturing process control in a printing plant, Carrier's invention

controlled not only temperature but also humidity

Carrier used his knowledge of the heating of objects with steam and reversed the

process. Instead of sending air through hot coils, he sent it through cold coils (ones filled

with cold water).

The air blowing over the cold coils cooled, and one could thereby control the amount

of moisture the colder air could hold. In turn, the humidity in the room could be controlled.

The low heat and humidity helped maintain consistent paper dimensions and ink

alignment. Later, Carrier's technology was applied to increase productivity in the

workplace, and The Carrier Air Conditioning Company of Americawas formed to meet

rising demand. Over time, air conditioning came to be used to improve comfort in homes

and automobiles as well. Residential sales expanded dramatically in the 1950s.

Refrigerant development

The first air conditioners and refrigerators employed toxic or flammable gases, such

as ammonia, methyl chloride, or propane, that could result in fatal accidents when they

leaked. Thomas created the first non-flammable, non-toxic chlorofluorocarbon gas, Freon,

in 1928.

"Freon" is a trademark name owned by DuPont for any Chlorofluorocarbon (CFC),

Hydro chlorofluorocarbon (HCFC), or Hydro fluorocarbon (HFC) refrigerant, the name of

each including a number indicating molecular composition (R-11, R-12, R-22, R-134A). The

blend most used in direct-expansion home and building comfort cooling is an HCFC

known as R-22. It was to be phased out for use in new equipment by 2010, and is to be

completely discontinued by 2020.

R-12 was the most common blend used in automobiles in the US until 1994, when

most designs changed to R-134A. R-11 and R-12 are no longer manufactured in the US for

this type of application, the only source for air-conditioning repair purposes being the

cleaned and purified gas recovered from other air-conditioner systems. Several non-ozone-

depleting refrigerants have been developed as alternatives, including R-410A, invented by

AlliedSignal (now part of Honeywell) in Buffalo, and sold under the Genetron (R) AZ-20

name. It was first commercially used by Carrier under the brand name Puron.

Innovation in air-conditioning technologies continues, with much recent emphasis

placed on energy efficiency and on improving indoor air quality. Reducing climate-change

impact is an important area of innovation because, in addition to greenhouse-gas emissions

associated with energy use, CFCs, HCFCs, and HFCs are, themselves, potent greenhouse

gases when leaked to the atmosphere. For example, R-22 (also known as HCFC-22) has

a global warming potential about 1,800 times higher than CO2.[13] As an alternative to

conventional refrigerants, natural alternatives, such as carbon dioxide (CO2. R-744), have

been proposed.

Refrigeration cycle

In the refrigeration cycle, a heat

pump transfers heat from a lower-

temperature heat source into a higher-

temperature heat sink. Heat would naturally

flow in the opposite direction. This is the most

common type of air conditioning.

A refrigerator works in much the same way,

as it pumps the heat out of the interior and

into the room in which it stands.

Simple stylized diagram of the refrigeration cycle:

1) condensing coil, 2) expansion valve,

3) evaporator coil, 4) compressor

This cycle takes advantage of the way phase changes work, where latent heat is released at

a constant temperature during a liquid/gasphase change, and where varying

the pressure of a pure substance also varies its condensation/boiling point.

The most common refrigeration cycle uses an electric motor to drive a compressor.

In an automobile, the compressor is driven by a belt over a pulley, the belt being driven by

the engine's crankshaft (similar to the driving of the pulleys for the alternator, power

steering, etc.). Although some newer vehicles, including hybrid and electric, use an electric

compressor as opposed to belt driven. Whether in a car or building, both use electric fan

motors for air circulation. Since evaporation occurs when heat is absorbed, and

condensation occurs when heat is released, air conditioners use a compressor to

cause pressure changes between two compartments, and actively condense and pump

a refrigerant around. A refrigerant is pumped into the evaporator coil, located in the

compartment to be cooled, where the low pressure causes the refrigerant to evaporate into

a vapour, taking heat with it. At the opposite side of the cycle is the condenser, which is

located outside of the cooled compartment, where the refrigerant vapour is compressed

and forced through another heat exchange coil, condensing the refrigerant into a liquid,

thus releasing the heat previously absorbed from the cooled space.

By placing the condenser (where the heat is rejected) inside a compartment, and the

evaporator (which absorbs heat) in the ambient environment (such as outside), or merely

running a normal air conditioner's refrigerant in the opposite direction, the overall effect is

the opposite, and the compartment is heated. This is usually called a heat pump, and is

capable of heating a home to comfortable temperatures (25 °C; 77 °F), even when the

outside air is below the freezing point of water (0 °C; 32 °F).

Cylinder unloaders are a method of load control used mainly in commercial air

conditioning systems. On a semi-hermetic (or open) compressor, the heads can be fitted

with unloaders which remove a portion of the load from the compressor so that it can run

better when full cooling is not needed. Unloaders can be electrical or mechanical.

Energy

In a thermodynamically closed system, any power dissipated into the system that is

being maintained at a set temperature (which is a standard mode of operation for modern

air conditioners) requires that the rate of energy removal by the air conditioner increase.

This increase has the effect that, for each unit of energy input into the system (say to

power a light bulb in the closed system), the air conditioner removes that energy. In order

to do so, the air conditioner must increase its power consumption by the inverse of its

"efficiency" (coefficient of performance) times the amount of power dissipated into the

system. As an example, assume that inside the closed system a 100 W heating element is

activated, and the air conditioner has an coefficient of performance of 200%. The air

conditioner's power consumption will increase by 50 W to compensate for this, thus

making the 100 W heating element cost a total of 150 W of power.

It is typical for air conditioners to operate at "efficiencies" of significantly greater

than 100%.However, it may be noted that the input electrical energy is of higher

thermodynamic quality (lower entropy) than the output thermal energy (heat energy).

Air conditioner equipment power in the U.S. is often described in terms of "tons of

refrigeration". A ton of refrigeration is approximately equal to the cooling power of

one short ton(2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is

defined as 12,000 BTU per hour, or 3517 watts. Residential central air systems are usually

from 1 to 5 tons (3 to 20 kilowatts (kW)) in capacity.

In an automobile, the A/C system will use around 4 horsepower (3 kW) of the

engine's power.

Seasonal energy efficiency ratio

For residential homes, some countries set minimum requirements for energy

efficiency. In the United States, the efficiency of air conditioners is often (but not always)

rated by the seasonal energy efficiency ratio (SEER). The higher the SEER rating, the more

energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during

its normal annual usage divided by the total electric energy input in watt hours (W·h)

during the same period.

SEER = BTU ÷ (W·h) this can also be rewritten as: SEER = (BTU / h) ÷ W,

where "W" is the average electrical power in Watts, and (BTU/h) is the rated cooling

power.

For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, would consume

5000/10 = 500 Watts of power on average.

The electrical energy consumed per year can be calculated as the average power

multiplied by the annual operating time:

500 W × 1000 h = 500,000 W·h = 500 kWh

Assuming 1000 hours of operation during a typical cooling season (i.e., 8 hours per

day for 125 days per year).

Another method that yields the same result, is to calculate the total annual cooling

output:

5000 BTU/h × 1000 h = 5,000,000 BTU

Then, for a SEER of 10, the annual electrical energy usage would be:

5,000,000 BTU ÷ 10 = 500,000 W·h = 500 kWh

SEER is related to the coefficient of performance (COP) commonly used

in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency

rating for the equipment at a particular pair of external and internal temperatures, while

SEER is calculated over a whole range of external temperatures (i.e., the temperature

distribution for the geographical location of the SEER test). SEER is unusual in that it is

composed of an Imperial unit divided by an SI unit. The COP is a ratio with the same

metric units of energy (joules) in both the numerator and denominator. They cancel out,

leaving a dimensionless quantity. Formulas for the approximate conversion between SEER

and EER or COP are available from the Pacific Gas and Electric Company:

(1) SEER = EER ÷ 0.9

(2) SEER = COP × 3.792

(3) EER = COP × 3.413

From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means

that 3.43 units of heat energy are pumped per unit of work energy.

The United States now requires that residential systems manufactured in 2006 have a

minimum SEER rating of 13 (although window-box systems are exempt from this law, so

their SEER is still around 10).

Design

Types

Window and through-wall

Room air conditioners come in two forms:

unitary and packaged terminal (PTAC) systems.

Unitary systems, the common one-room air

conditioners, sit in a window or wall opening, with

interior controls. Interior air is cooled as a fan blows it

over the evaporator. On the exterior the air is heated as

a second fan blows it over the condenser. In this

process, heat is drawn from the room and discharged

to the environment. A large house or building may

have several such units, permitting each room to be

cooled separately.

PTAC systems are also known as wall-split air conditioning systems or ductless

systems. These PTAC systems which are frequently used in hotels have two separate units

(terminal packages), the evaporative unit on the interior and the condensing unit on the

exterior, with tubing passing through the wall and connecting them.

This minimizes the interior system footprint and allows each room to be adjusted

independently. PTAC systems may be adapted to provide heating in cold weather, either

directly by using an electric strip, gas or other heater, or by reversing the refrigerant flow to

heat the interior and draw heat from the exterior air, converting the air conditioner into a

heat pump. While room air conditioning provides maximum flexibility, when used to cool

many rooms at a time it is generally more expensive than central air conditioning.

The first practical through the wall air conditioning unit was invented by engineers

at Chrysler Motors and offered for sale starting in 1935.

Split systems

Split-system air conditioners come in two forms:

central and mini-split. In both types, the inside-

environment (evaporative) heat exchanger and fan is

separated by some distance from the outside-

environment (condensing unit) heat exchanger and fan.

In central air conditioning, the inside heat-

exchanger is typically placed inside the central

furnace/AC unit of forced air heating system which is

then used in the summer to distribute chilled air

throughout a residence or commercial building.

A mini-split system typically supplied chilled air to only a single space, and thus

was sometimes referred to as split-system single-zone air conditioning. Today, however,

one split-system compressor can supply chilled air to up to eight indoor units. If the split

system contains a heat pump, as is often the case, the system may be easily switched

seasonally to supply heat instead of cold. Controls can be wall-mounted or handheld (the

size of the remote control for a television).

Ductless (split-system) air conditioning

Mini-split systems - today usually called ductless air conditioners — typically

produce 9,000–36,000 Btu (9,500–38,000 kJ) per hour of cooling. Most ductless systems are

similar to PTAC air conditioners in that they are often designed to cool a single room or

space.

But ductless air conditioning allows design and installation flexibility because the

inside wall space required is significantly reduced and the compressor and heat exchanger

can be located further away from the inside space, rather than merely on the other side of

the same unit as in a PTAC or window air conditioner. In addition, ductless systems will

offer much higher efficiency (up to 27.1 SEER on some systems).[citation needed] Today's

brands include Aircon, Carrier, Daikin, Klimaire, LG, Mitsubishi, Sanyo, Fujitsu and YMGI.

Most ductless (split system) air conditioners still typically provide cooling to a single

room or interior zone, just like a window air conditioner or PTAC; but more powerful

outside units are becoming more and more available, supporting cooling of ever-more

interior zones. Advantages of the ductless system include smaller size and flexibility for

zoning or heating and cooling individual rooms.

Flexible exterior hoses lead from the outside unit to the interior one(s); these are

often enclosed with metal to look like common drainpipes from the roof. Those enclosures

can be painted to match the colour of the house.

The primary disadvantage of ductless air conditioners is their cost. Such systems

cost about $1,500 to $2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about

30% more than central systems (not including ductwork) and may cost more than twice as

much as window units of similar capacity."

An additional possible disadvantage that may increase net cost is that ductless

systems may sometimes not be eligible for energy efficiency rebates offered by

many electric utility companies as part of an incentive program to reduce summer cooling

load on the electrical grid.

Central Air Conditioning

Central (ducted) air conditioning offers whole-house or large-commercial-space

cooling, and often offers moderate multi-zone temperature control capability by the

addition of air-louver-control boxes.

Evaporative coolers

In very dry climates, evaporative coolers, sometimes referred to as swamp coolers or

desert coolers, are popular for improving coolness during hot weather.

An evaporative cooler is a device that draws outside air through a wet pad, such as a

large sponge soaked with water. Thesensible heat of the

incoming air, as measured by a dry bulb thermometer,

is reduced. The total heat (sensible heat plus latent heat)

of the entering air is unchanged. Some of the sensible

heat of the entering air is converted to latent heat by the

evaporation of water in the wet cooler pads. If the

entering air is dry enough, the results can be quite

cooling; evaporative coolers tend to feel as if they are

not working during times of high humidity, when there

is not much dry air with which the coolers can work to make the air as cool as possible for

dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the

outside air to be channeled through cooler pads that cool the air before it reaches the inside

of a house through its air duct system; this cooled outside air must be allowed to push the

warmer air within the house out through an exhaust opening such as an open door or

window.

Heat pumps

"Heat pump" is a term for a type of air conditioner in which the refrigeration

cycle can be reversed, producing heating instead of cooling in the indoor environment.

They are also commonly referred to, and marketed as, a "reverse cycle air conditioner".

Using an air conditioner in this way to produce heat is significantly more energy efficient

than electric resistance heating. Some homeowners elect to have a heat pump system

installed, which is simply a central air conditioner with heat pump functionality (the

refrigeration cycle can be reversed in cold weather).

When the heat pump is in heating mode, the indoor evaporator coil switches roles

and becomes the condenser coil, producing heat. The outdoor condenser unit also switches

roles to serve as the evaporator, and discharges cold air (colder than the ambient outdoor

air).

Heat pumps are more popular in milder winter climates where the temperature is

frequently in the range of 40–55°F (4–13°C), because heat pumps become inefficient in more

extreme cold. This is due to the problem of ice forming on the outdoor unit's heat

exchanger coil, which blocks air flow over the coil. To compensate for this, the heat pump

system must temporarily switch back into the regular air conditioning mode to switch the

outdoor evaporator coil back to being the condenser coil, so that it can heat up and defrost.

A heat pump system will therefore have a form of electric resistance heating in the

indoor air path that is activated only in this mode in order to compensate for the temporary

indoor air cooling, which would otherwise be uncomfortable in the winter. The icing

problem becomes much more severe with lower outdoor temperatures, so heat pumps are

commonly installed in tandem with a more conventional form of heating, such as a natural

gas or oil furnace, which is used instead of the heat pump during harsher winter

temperatures. In this case, the heat pump is used efficiently during the milder

temperatures, and the system is switched to the conventional heat source when the outdoor

temperature is lower.it also works on the basis of carnot cycle.

Absorption heat pumps are actually a kind of air-source heat pump, but they do not

depend on electricity to power them. Instead, gas, solar power, or heated water is used as a

main power source. Additionally, refrigerant is not used at all in the process.[dubious –

discuss] An absorption pump absorbs ammonia into water.[further explanation

needed] Next, the water and ammonia mixture is depressurized to induce boiling, and the

ammonia is boiled off, resulting in cooling.

Some more expensive window air conditioning units have a true heat pump

function. However, a window unit that has a "heat" selection is not necessarily a heat pump

because some units use only electric resistance heat when heating is desired. A unit that has

true heat pump functionality will be indicated its specifications by the term "heat pump".

Refrigerants

Modern refrigerants have been developed to be more

environmentally safe than many of the

early chlorofluorocarbon-based refrigerants used in the

early- and mid-twentieth century. These include

as HCFCs (R-22, used in most homes today) and HFCs (R-

134a, used in most cars) have replaced most CFC use.

HCFCs, in turn, are being phased out under the Montreal

Protocol and replaced by hydro fluorocarbons (HFCs) such

as R-410A, which lack chlorine.

Carbon dioxide (R-744) is being rapidly[according to whom?] adopted as a

refrigerant in Europe and Japan. R-744 is an effective refrigerant with a global warming

potential of 1. It must use higher compression to produce an equivalent cooling

effect.[citation needed]

Historically, "Freon"—a trade name for a family of haloalkane refrigerants

manufactured by DuPont and other companies—refrigerants were commonly

used[when?] in air conditioners due to their superior stability and safety properties.

However, these chlorine-bearing refrigerants reach the upper atmosphere when they

escape. Once the refrigerant reaches the stratosphere, UV radiation from

the Sunhomolytically cleaves the chlorine-carbon bond, yielding a chlorine radical.

These chlorine atoms catalyse the breakdown of ozone intodiatomic oxygen,

depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each

chlorine radical remains active as a catalyst unless it binds with another chlorine radical,

forming a stable molecule and breaking the chain reaction. The use of CFC as a refrigerant

was once common, being used in the refrigerants R-11 and R-12. In most countries

[which?] the manufacture and use of CFCs has been banned or severely restricted due to

concerns about ozone depletion. In light of these environmental concerns, beginning on

November 14, 1994, the U.S. Environmental Protection Agency has restricted the sale,

possession and use of refrigerant to only licensed technicians, per Rules 608 and 609 of the

EPA rules and regulations.

Illumination

The ONGC is having different types of illuminations like CFLs, LEDs etc. The description

about the illumination is given below:

Florescent lamp:

A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapour gas-

discharge lamp that uses fluorescence to produce visible light. An electric current in the

gas excites mercury vapour which produces short-wave ultraviolet light that then causes

a phosphor coating on the inside of the bulb to glow. A fluorescent lamp converts electrical

energy into useful light much more efficiently than incandescent. The luminous efficacy of

a fluorescent light bulb can exceed 100 lumens per watt, several times the efficacy of an

incandescent bulb with comparable light output.

Fluorescent lamp fixtures are more costly than incandescent lamps because they require

a ballast to regulate the current through the lamp, but the lower energy cost typically

offsets the higher initial cost. Compact fluorescent lamps are now available in the same

popular sizes as incandescent and are used as an energy-saving alternative in homes.

Because they contain mercury, many fluorescent lamps are classified as hazardous waste.

The United States Environmental Protection Agency recommends that fluorescent lamps be

segregated from general waste for recycling or safe disposal.

A photo of florescent light

Construction A fluorescent lamp tube is filled with a gas containing low pressure mercury vapour

and argon, xenon, neon, or krypton. The pressure inside the lamp is around 0.3% of

atmospheric pressure.[17] The inner surface of the lamp is coated with a fluorescent (and

often slightly phosphorescent) coating made of varying blends of metallic and rare-

earth phosphor salts. The lamp's electrodes are typically made of coiled tungsten and

usually referred to as cathodes because of their prime function of emitting electrons. For

this, they are coated with a mixture of barium, strontium and calcium oxides chosen to

have a low thermionic emission temperature.

Fluorescent lamp tubes are typically straight and range in length from about 100

millimetres (3.9 in) for miniature lamps, to 2.43 meters (8.0 ft) for high-output lamps. Some

lamps have the tube bent into a circle, used for table lamps or other places where a more

compact light source is desired. Larger U-shaped lamps are used to provide the same

amount of light in a more compact area, and are used for special architectural

purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle

of two, four, or six, or a small diameter tube coiled into a spiral, to provide a high amount

of light output in little volume.

Light-emitting phosphors are applied as a paint-like coating to the inside of the tube.

The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting

point of glass to drive off remaining organic compounds and fuse the coating to the lamp

tube. Careful control of the grain size of the suspended phosphors is necessary; large

grains, 35 micrometres or larger, lead to weak

grainy coatings, whereas too many small particles

1 or 2 micrometres or smaller leads to poor light

maintenance and efficiency. Most phosphors

perform best with a particle size around 10

micrometres. The coating must be thick enough to

capture all the ultraviolet light produced by the

mercury arc, but not so thick that the phosphor

coating absorbs too much visible light. The first

phosphors were synthetic versions of naturally

occurring fluorescent minerals, with small

amounts of metals added as activators. Later other

compounds were discovered, allowing differing

colours of lamps to be made.

Construction of the Florescent

Advantage

Luminous efficacy

Fluorescent lamps convert more of the input power to visible light than incandescent

lamps, though as of 2013 LEDs are sometimes even more efficient and are more rapidly

increasing in efficiency. A typical 100 watt tungsten filament incandescent lamp may

convert only 5% of its power input to visible white light (400–700 nm wavelength), whereas

typical fluorescent lamps convert about 22% of the power input to visible white light.

Life Typically a fluorescent lamp will last between 10 to 20 times as long as an

equivalent incandescent lamp when operated several hours at a time. Under standard test

conditions general lighting lamps have 9,000 hours or longer service life. The higher initial

cost of a fluorescent lamp is usually more than compensated for by lower energy

consumption over its life.

Lower luminance Compared with an incandescent lamp, a fluorescent tube is a more diffuse and

physically larger light source. In suitably designed lamps, light can be more evenly

distributed without point source of glare such as seen from an undiffused incandescent

filament; the lamp is large compared to the typical distance between lamp and illuminated

surfaces.

Lower heat About two-thirds to three-quarters less heat is given off by fluorescent lamps

compared to an equivalent installation of incandescent lamps. This greatly reduces the size,

cost, and energy consumption devoted to air conditioning for office buildings that would

typically have many lights and few windows.

Disadvantages

Frequently switching may cause the decrement in the life of the specimen.

The disposal of phosphor and particularly the toxic mercury in the tubes is an

environmental issue. Governmental regulations in many areas require special

disposal of fluorescent lamps separate from general and household wastes.

For large commercial or industrial users of fluorescent lights, recycling

services are available in many nations, and may be required by regulation.

Flickering problems occur.

Fluorescent tubes are long, low-luminance sources compared with high

pressure arc lamps, incandescent lamps and leds. However, low luminous

intensity of the emitting surface is useful because it reduces glare. Lamp

fixture design must control light from a long tube instead of a compact globe.

The compact fluorescent lamp (CFL) replaces regular incandescent bulbs.

However, some CFLs will not fit some lamps, because the harp (heavy wire

shade support bracket) is shaped for the narrow neck of an incandescent

lamp, while CFLs tend to have a wide housing for their electronic ballast

close to the lamp's base.

Simple inductive fluorescent lamp ballasts have a power factor of less than

unity. Inductive ballasts include power factor correction capacitors. Simple

electronic ballasts may also have low power factor due to their rectifier input

stage.

Fluorescent lamps are a non-linear load and generate harmonic currents in

the electrical power supply. The arc within the lamp may generate radio

frequency noise, which can be conducted through power wiring. Suppression

of radio interference is possible. Very good suppression is possible, but adds

to the cost of the fluorescent fixtures.

LED LAMPS

An LED lamp is a light-emitting diode (LED) product that is assembled into

a lamp (or light bulb) for use in lighting fixtures. LED lamps have a lifespan and electrical

efficiency that is several times better than incandescent lamps, and significantly better than

most fluorescent lamps, with some chips able to emit more than 100 lumens per watt. The

LED lamp market is projected to grow more than 12-fold over the next decade, from $2

billion in the beginning of 2014 to $25 billion in 2023, which is a compound annual growth

rate (CAGR) of 25%.[1]

Like incandescent lamps and unlike most fluorescent lamps (e.g. tubes and compact

fluorescent lamp (CFL)), LED lights come to full brightness without need for a warm-up

time; the life of fluorescent lighting is also reduced by frequent switching on and off. Initial

cost of LED is usually higher. Degradation of LED dye and packaging materials reduces

light output to some extent over time.

With research into organic LEDs (OLED) and polymer LEDs (PLED), cost per lumen

and output per device have been improving rapidly according to what has been

called Haitz's law, analogous to Moore's law for semiconductor devices.

Some LED lamps are made to be a directly compatible drop-in replacement for

incandescent or fluorescent lamps. An LED lamp packaging may show the lumen output,

power consumption in watts, color temperature in kelvins or description (e.g. "warm

white") and sometimes the equivalent wattage of an incandescent lamp of similar luminous

output.

LEDs do not emit light in all directions, and their directional characteristics affect the

design of lamps. The light output of single LEDs is less than that of incandescent

and compact fluorescent lamps; in most applications multiple LEDs are used to form a

lamp, although high-power versions (see below) are becoming available.

LED chips need controlled direct current (DC) electrical power; an appropriate

power supply is needed. LEDs are adversely affected by high temperature, so LED lamps

typically include heat dissipation elements such as heat sinks and cooling fins.

LED lamps are made that replace screw-in incandescent or compact fluorescent light

bulbs, mostly replacing incandescent bulbs rated from 5 to 60 watts. Such lamps are made

with standard light bulb connections and shapes, such as an Edison screw base,

an MR16 shape with a bi-pin base, or a GU5.3 (bi-pin cap) or GU10 (bayonet fitting) and are

made compatible with the voltage supplied to the sockets. They include circuitry to rectify

the AC power and convert the voltage to an appropriate value.

As of 2010 some LED lamps replaced higher wattage bulbs; for example, one

manufacturer claimed a 16-watt LED bulb was as bright as a 150 W halogen lamp.

A standard general-purpose incandescent bulb emits light at an efficiency of about

14 to 17 lumens/W depending on its size and voltage. According to the European Union

standard, an energy-efficient bulb that claims to be the equivalent of a 60 W tungsten bulb

must have a minimum light output of 806 lumens.

Some models of LED bulbs are compatible with dimmers as used for incandescent

lamps. LED lamps often have directional light characteristics. The lamps have declined in

cost to between US$10 to $50 each as of 2012. These bulbs are more power-efficient than

compact fluorescent bulbs and offer lifespans of 30,000 or more hours, reduced if operated

at a higher temperature than specified. Incandescent bulbs have a typical life of 1,000 hours,

and compact fluorescents about 8,000 hours.[citation needed The bulbs maintain output

light intensity well over their lifetimes. Energy Star specifications require the bulbs to

typically drop less than 10% after 6,000 or more hours of operation, and in the worst case

not more than 15%.LED lamps are available with a variety of colour properties. The

purchase price is higher than most other, but the higher efficiency may make total cost of

ownership (purchase price plus cost of electricity and changing bulbs) lower.

Comparison LED with other lights:

Incandescent lamps (light bulbs) generate light by passing electric current through a

resistive filament, thereby heating the filament to a very high temperature so that it

glows and emits visible light over a broad range of wavelengths. Incandescent sources

yield a "warm" yellow or white color quality depending on the filament operating

temperature. Incandescent lamps emit 98% of the energy input as heat. A 100 W light

bulb for 120 V operation emits about 1,180 lumens, about 11.8 lumens/W; for 230 V

bulbs the figures are 1340 lm and 13.4 lm/W. Incandescent lamps are relatively

inexpensive to make. The typical lifespan of an AC incandescent lamp is 750 to 1,000

hours. They work well with dimmers. Most older light fixtures are designed for the size

and shape of these traditional bulbs. In the U.S. the regular sockets are E26 and E11, and

E27 and E14 in some European countries.

Fluorescent lamps work by passing electricity through mercury vapor, which in turn

emits ultraviolet light. The ultraviolet light is then absorbed by a phosphor coating

inside the lamp, causing it to glow, or fluoresce. Conventional linear fluorescent lamps

have life spans around 20,000 and 30,000 hours based on 3 hours per cycle according to

lamps NLPIP reviewed in 2006. Induction fluorescent relies on electromagnetism rather

than the cathodes used to start conventional linear fluorescent. The newer rare earth

triphosphor blend linear fluorescent lamps made by Osram, Philips, Crompton and

others have a life expectancy greater than 40,000 hours, if coupled with a warm-start

electronic ballast.

The life expectancy depends on the number of on/off cycles, and is lower if the light

is cycled often. The ballast-lamp combined system efficacy for then current linear

fluorescent systems in 1998 as tested by NLPIP ranged from 80 to 90 lm/W. For

comparison, general household LED bulbs available in 2011 emit 64 lumens/W.

Compact fluorescent lamps' specified lifespan typically ranges from 6,000 hours to

15,000 hours.

Electricity prices vary state to state and are customer dependent. Generally commercial

(10.3 cent/kWh) and industrial (6.8 cent/kWh) electricity prices are lower than

residential (12.3 cent/kWh) due to fewer transmission losses.

In keeping with the long life claimed for LED lamps, long warranties are offered.

One manufacturer warrants lamps for professional use, depending upon type, for

periods of (defined) "normal use" ranging from 1 year or 2,000 hours (whichever comes

first) to 5 years or 20,000 hours. A typical domestic lamp is stated to have an "average

life" of 15,000 hours (15 years at 3 hours/day), and to support 50,000 switch cycles.

LIMITATIONS

Colour rendition is not identical to incandescent lamps. A measurement unit

called CRI is used to express how the light source's ability to render the eight colour sample

chips compare to a reference on a scale from 0 to 100. LEDs with CRI below 75 are not

recommended for use in indoor lighting.

LED efficiency and life span drop at higher temperatures, which limits the power

that can be used in lamps that physically replace existing filament and compact fluorescent

types. Thermal is a significant factor in design of solid state lighting equipment.

LED lamps are sensitive to excessive heat, like most solid state electronic

components. LED lamps should be checked for compatibility for use in totally enclosed

fixtures before installation since heat build-up could cause lamp failure and/or fire.

LED lamps may flicker. The extent of flicker is based on the quality of the DC power

supply built into the lamp structure, usually located in the lamp base.

Depending on the design of the lamp, the LED lamp may be sensitive to electrical

surges. This is generally not an issue with incandescents, but can be an issue with LED and

compact fluorescent bulbs. Power circuits that supply LED lamps should be protected from

electrical surges through the use of surge protection devices.

The long life of LEDs, expected to be about 50 times that of the most common

incandescent bulbs and significantly longer than fluorescent types, is advantageous for

users but will affect manufacturers as it reduces the market for replacements in the distant

future.

The SF6 circuit breaker

There are three different types of circuit breakers. These are air blast circuit breaker,

oil circuit breaker and vacuum circuit breaker. The different types of breakers are mainly

classified based on the arc interrupting medium. From the operating principle of the circuit

breaker it is known that an arc is struck whenever the movable contacts separate on

occurrence of a fault. If the dielectric strength of the arc can be increased then it

extinguishes easily and does not re strikes. Increase of dielectric strength can be best

achieved by de ionization of the particles between the contact medium. Interruption of arc

was well performed with the help of the three mentioned circuit breakers types. Modern

day high voltage circuit breaker needed an arc quenching medium which would serve the

purpose in a much better way and work smoothly. Thus SF6 or sulphur hexafluoride circuit

breakers came into existence. This type of circuit breaker uses SF6 gas as the arc extinction

medium. SF6 gas because of its excellent dielectric strength, arc quenching, chemical and

other physical properties has proved its superiority over other mediums such as oil, air or

vacuum. Several types of SF6 circuit breakers have been developed by different

manufacturers during last two decades for rated voltages 3.6 to 760 kV. Let us now discuss

the important properties of sulphur hexafluoride (SF6) gas.

Properties of Sulphur Hexafluoride Gas

Sulphur hexafluoride gas is prepared by burning coarsely crushed sulphur in

fluorine gas in a gas tight steel box. The box is provided with horizontal shelves each

bearing about 4 kg of sulphur. The gas obtained contains other fluorides which are

removed by purification. This gas can be transported in liquid form in cylinders. Before

filling the gas, breaker is evacuated to the pressure of about 4 mm of mercury so as to

remove moisture and air. The different properties of the SF6

gas are discussed below.

♣ Gas is colourless, odourless, non-toxic and non

inflammable.

♣ Density of the gas is five times of air and it is very inert

♣ It has high thermal conductivity and helps in better cooling

of current carrying parts.

♣ It is highly electronegative that is the ability of an atom to

attract and hold electrons. Due to this property the arc time

constant is very low in order of 1 microsecond.

♣ Rate of rise of dielectric strength is high. Its dielectric strength at atmospheric pressure is

2.35 times that of the air and 30 % less than that of oil.

♣ The gas is chemically stable and inert up to 500 ° C.

♣ Sulphur hexafluoride gas absorbs free electrons from the particles in between the breaker

contacts. Free electrons are converted to immobile negative ions.

♣ It is approximately 100 times more effective as an arc quenching medium as compared to

air.

♣ The gas has very low reactivity and does not attack metals, plastics, etc. The inertness of

the gas is helpful in switchgear.

Construction of SF6 Circuit Breaker

The construction of a SF6 circuit breaker is quite simple. SF6 circuit breaker mainly

consists of the following parts: Contacts, Arc chamber, Moving member, Fixed member,

Insulated rods, Arcing horns and Gas inlet and outlet. The operation is mainly depended

up on two things. These are – interrupter unit and the gas system.

Arc interrupter unit of SF6 Circuit Breaker This unit consists of moving and fixed contacts placed inside the arc interruption chamber.

This chamber contains the SF6 gas. The chamber is connected to the gas reservoir. The

contacts comprises of a set of current carrying fingers and an arcing probe. Both the fixed

and moving contact are hollow cylindrical structure. The fixed contact is connected to the

arc horn while moving contact is provided with side vents which allow high pressure gas

to flow into the main tank. Interrupting nozzles and blast shield surrounds the contacts

which controls arc displacement. The contact tips and the arc horn are coated with copper-

tungsten as arc resistant materials.

The gas system of SF6 Circuit Breaker Sulphur hexafluoride gas is costly so it reclaimed after every operation of the

breaker. Necessary auxiliary system is provided for this purpose. The low and high

pressure systems are provided with alarms and a set of switches which gives a warning the

moment the gas pressure drops below a certain value.

The pressure if drops further it will lead to decrease of dielectric strength and arc

quenching ability. The gas is stored in high pressure and low pressure chambers

respectively at 16 atmospheres (atm) and 3 atms. Lot of care is taken to prevent gas leakage.

The temperature is kept at 20 ° C.There are certain sf6 breakers which apply Puffer Piston

principle and their construction is done accordingly. With this kind of principle arc

extinction pressure is produced during an opening operation by means of a piston attached

to the moving contacts. The arc extinction takes place in the insulating nozzle. In this

method a current carrying path is there around the arcing contacts which permits large

value of currents to be accommodated. This type of breakers are made from 72-550 kV with

rated interrupting current of 20-63 kA and rated current of 1200- 12000 A.

Operating Principle of SF6 Circuit Breaker The arc extinction process in SF6 circuit breaker is quite similar with that in air blast

circuit breakers. We will discuss its principle of operation in detail. There are two reservoirs

in SF6 circuit breaker. One is highly compressed with the SF6 gas and another is kept at low

pressure. There are some little vents or valves in the high pressure SF6 chamber, which are

covered by the moving member during normal operating conditions. When any fault

occurs in the system, the fixed and moving contacts quickly separated from each other. This

rapid separation of two high voltage contacts initiates an electric arc. But the system is

arranged such a way that whenever the moving contact is going to separate then the vents

of high pressure SF6 chamber opens. So there will be inrush of SF6 gas towards the arc.

During the arcing period the gas is blown axially along the arc. The heat is removed from

the arc by axial convection and radial dissipation due to the gas. Arc diameter also

decreases and it becomes small at current zero. SF6 gas shows electro-negativity and after a

short arcing period it regains its dielectric strength rapidly after current zero. The arc

extinction can be improved by moderate rate of forced gas flow through the arc space. On

opening of a valve the gas flows from the reservoir into the interruption chamber at a

pressure of 14 kg/ cm2. The gas flows from high pressure zone to low pressure zone

through a convergent-divergent nozzle. Such high pressure flow of this gas absorbs free

electrons in the arc path. Negatively charged immobile ions are formed from this.

The medium in between the contacts sets up a strong dielectric strength and causes

quick arc extinction. The basic requirement in arc extinction is not primarily the dielectric

strength but rate of recovery of dielectric strength. In SF6 gas dielectric strength is regained

quickly. After the arc extinction the moving member sets to the initial a spring action.

Advantages of SF6 Circuit Breaker F6 circuit breakers have the following advantages over other types of breakers.

♣ The gas is not inflammable and is chemically stable. The decomposition products are also

non explosive.

♣ SF6 gas has excellent insulating and arc extinguishing properties.

♣The gas can interrupt large current owing its high dielectric strength (2-3 times that of air).

♣The breaker performs noiseless operation; no such sound like air blast breaker operation.

♣ Maintenance required is minimum.

♣ Compact and sealed body keeps the interior dry, prevents mixing of dust, moisture etc.

♣ Arc time is short and there is no carbon deposit during arcing.

♣ The breaker performance is unaffected by the change in atmospheric pressure.

Apart from these widespread advantages there are some problems associated with SF6 circuit

breakers. These are:

♣ SF6 gas is suffocating to some extent. In case of leakage the gas being heavier than air settles

in the surroundings and cause suffocation. Though it is non-poisonous.

♣ In case moisture creeps inside the breaker it cause harmful effects.

♣ SF6 gas is costly. However large scale production reduces the cost and special facilities are

needed for transportation of the gas.

The actual internal structure is shown in the figure given below:

Operation counter Antipumping relay

Interlocking key Closing spring Terminals

Opening coil Closing coil Motor Auxiliary switch