ELECTRICAL SYSTEM OF AIR CONDITIONER

 ELECTRICAL CIRCUIT AND PARTS OF AIR CONDITIONER

In electrical system of air conditioner different types of electrical components are used.The different components of electric system  of air conditioner is given below, that is shown in figure: 

Circuit diagram air conditioner

a) Compressor motor
b) Fan motor
c) Starting capacitor
d) Running capacitor
e) Thermal overload protection
f) Main thermostate or temperature controller
g) Starting relay
h) Unit control switches
e) Fan capacitor
f) Motor compressor units
g) Connecting wire

The detail and working of above electrical components are given below:

1.Compressor motor and fan motor: In air conditioner unit two motors are used.These motors are single phase squirrel cage rotor, type induction motors.

The motor used for compressor motor is mainly capacitor start and capacitor run induction motor and the motor used for evaporator and condenser fan is capacitor start type induction motor.The speed of fan is controlled by induction regulator.

2.Starting capacitor: The starting capacitor provide starting torque to compressor motor and motor starts easily.It is connected to series in circuit.It is generally electrolytic capacitor.

3.Running capacitor: It is purely different from starting capacitor.It is heavy duly oil filled capacitor.It is always connected to series with compressor motor.

It improves the running characteristics of motor and also increases the starting torque of motor.It also increases the power factor, thus current taken by motor decreases (current is inversely proportional to power factor at constant voltage).Thus electrical energy consumption by motor decrease and makes the system economical.

4.Starting relay: This is single phase relay and works on single phase supply.The starting relay coil is always connected in series with running winding of motor.At the time of starting, motor takes high current from supply, thus the contact of relay closed and starting winding of motor and starting capacitor connected with each other and motor starts working.

When the motor speed increase, the value of current in running winding decrease.Thus the contact of relay become open and starting capacitor disconnect from circuit and running capacitor always connected to motor.

The starting relays are two types:

1. Voltage type relay
2. Current type relay

5.Thermal overload protection: This device protect the compressor motor from overloading.So, this is know as overload protection.This is always situated in compressor terminal cover.

When the compressor motor overloaded, current and temperature increase.So at this time if suitable protection is not available motor may be burn.When the motor overloaded the thermal overload protector disconnect the motor from supply and protect the motor.

6.Thermostate or temperature controller: This works on desire room temperature.When the room temperature increases, it closes the compressor circuit and compressor motor starts working.

When the temperature decrease, it break the compressor circuit and compressor motor does not work.Thus it control the room temperature.

7.Unit control switch:This switch is situated at the cabinet.This switch may be knob or rotary type.This switch has four conditions, that is marked by OFF-FAN-COOL-OPEN. 

Conclusion: Thus final conclusion is that, the knowledge of electric circuit diagram and component of air conditioner is necessary.Because it helps at the time of maintenance and repairing of air conditioner.

Important link:

What is air conditioning?Concept of air conditioner

TRANSFORMER OIL

TRANSFORMER OIL AND ITS PROPERTIES?DETERIORATION OF INSULATING OIL?

PRECAUTION AT A TIME OF TAKING OIL SAMPLE?

TRANSFORMER OIL: This is a synthetic mineral oil.It is prepare from fractional distillation of crude petrol.This is also known as mineral oil, insulating oil, switch gear oil etc.

Transformer oil

This is used for cooling,insulating, arc suppression in different electrical equipment like transformer, circuit breakers, switch gears etc.

PROPERTIES OF TRANSFORMER OIL: 

The properties of transformer oil is given below,

1.High specific resistance: They should be high specific resistance.Due to this insulating capacity of oil increases.

The minimum specific resistance at 90°C = 13*10¹² ohm–cm

The minimum specific resistance at 27°C = 500*10¹² ohm–cm

→ On increasing temperature the resistance of insulator decreases.

2.High dielectric strength: The dielectric strength of transformer oil means the maximum voltage at which transformer oil works without breakdown.

The minimum dielectric strength of transformer oil before use = 30 kV

The minimum dielectric strength of transformer oil after use = 20 kV

The maximum dielectric strength of new transformer oil = 55 kV

3.High flash point: The flash point of transformer is defined as the minimum temperature at which oil form vapour near its surface and it ignite or produce spark, when it comes near fire.So, the transformer oil should be high flash point.

The minimum value of flash point of transformer oil is 140°C.

4.High fire point: The minimum temperature at which transformer oil catch fire is known as fire point of transformer oil.

According to Indian standard the fire point of transformer oil 25% more than the flash point of transformer oil.

5.High pour point: The minimum temperature at which oil remains in liquid condition is know pour point of oil.

If the pour point of transformer oil will low, Then in winter or hilly area the maximum possibility of freezing the transformer oil.This effects the heat transferring of transformer by transformer oil.

So, the pour point of transformer oil should be -10°C (according to Indian standard).

6.No chemical impurities: The transformer oil should be free from chemical impurities.Because due to presence of chemical impurities it forms sludge that settle down in bottom of the transformer body.The transformer oil should be chemically inert.

7.Moisture less: It should be free from moisture.Because due to presence of moisture the insulating property of oil decrease and it also start the rusting of transformer body.It also effect the insulation of transformer winding.

8.Low viscosity: The transformer oil should have low viscosity.Due to low viscosity of oil it flow easily in transformer body, that is very effective for transformer cooling.

9.Free from dirt and dust: It should be free from dirt and dust.Due to presence of dirt and dust viscosity of transformer oil increases and it effects the heat transferring of transformer by transfer oil and also due to presence of dirt and dust in transformer oil sludge formation in transformer takes place.

10.Suitable permittivity: The permittivity value show the insulating permittivity of material, means higher the value of permittivity higher the insulating property of material and vice versa.So, the transformer oil should have suitable value of permittivity.

The permittivity of transformer oil should be 2.1 to 2.2.

DETERIORATION OF INSULATING OIL:

The decreases of dielectric strength of transformer oil is known as deterioration of transformer oil.

OR

When the standard value of transformer oil decrease, then it is known as deterioration of transformer oil.

The deterioration of transformer oil takes place due to following reasons:

1.Physical Deterioration: When dust, dirt and water mix with oil, then it is known as physical deterioration.The reason of physical deterioration is given below:

• The tank of oil remains open.
• The oil drum does not close properly.
• The installation of electric equipment near the moisture.
• The storage of oil is not proper.

2.Chemical Deterioration: The oxidization of oil is known as chemical deterioration.The reason of chemical deterioration of transformer oil is given below:

• Over load condition of transformer.
• Earth fault at transformer
• Short circuiting fault at transformer.

→When the hot oil comes in contact with water and oxygen, then oxidation of oil takes place.

3.Gaseous Deterioration: When the temperature of oil increase it vapourizes.This is known as gaseous deterioration of oil.Due to this flash point of oil decrease and oil can catch fire easily.

PRECAUTION AT A TIME OF TAKING OIL SAMPLE:

The precaution at a time of taking oil sample is given below:

• The oil sample should be taken from drain cock, that is situated bottom of the transformer oil tank. 

  

  Drain coke

• Drain coke should be clean by clean and dry cloth before taking oil sample.
• The sample of oil should be taken by the transformer when the transformer is on load condition.
• The oil sample should be taken in glass tube or bottle.The sample should not be taken in metal, rubber or plastic tube.
• The glass tube should be clean and dry.
• After taking sample, the oil filled bottle or tube should be covered properly.
• The cover of glass tube or bottle should not be made of rubber.
• The oil sample should be taken in sunny day.

→After taking sample, marking is should be done on oil filled bottle or tube with date and time.

Conclusion: The final conclusion is that transformer oil play a important role in transformer functioning.If we keep the above point regarding transformer oil in mind, then life of transformer increase and it works properly for a long time.

Important links:

What is transformer?Ratio of transformer?Different term in rating of transformer?

Different types of transformer?

EFFECT OF ELECTRICAL QUANTITIES ON HUMAN BODY

WHAT IS THE EFFECT OF DIFFERENT ELECTRICAL QUANTITIES ON HUMAN BODY?

PRECAUTIONS AT THE TIME OF ELECTRICAL WORK?

Effect of dangerous currents on human body: The main reason of electric shock is the electric current that flows through human body.The severity of electric shock depends upon two given below factors:

1. Time of contact: The more is the time of contact of the body with electric current.The more severity of electric shock.
2. Nature of current (AC or DC): The AC current is more dangerous than DC for human body.

If we know the working voltage and resistance of human body.Then the value of current flow through human body can be find by the OHM'S Law.

Current flow through the body = Working voltage/resistance of the body

Value of current and its severity on human body:

1. 1 to 8 mA: In the value of current man can be bear.But he feels the electric shock and it is not dangerous.
2. 8 to 15 mA: In this value of current body receives painful shock, but the severity of shock depends upon the health.
3. 15 to 20 mA: In this value of current body receives painful shock and body cannot control muscle nerve.So, human body cannot bear this value of current.
4. 20 to 50 mA: In this value of current, contraction of all muscle nerve started.So, human feels difficult in breathing.
5. 50 to 100 mA: In this value of current, due to contraction of muscle nerve, human feels difficult in breathing and heart beat increase.So, in this condition death may be possible.
6. Above 100 mA: In this value of current body burns, due to contraction of muscle nerve, human feel difficult in breathing and heart beat increase.So, in this condition death may be possible.

Electric shock

The Effect of electric current on human body is described below:

1. Due to electric shock body becomes weak and feel laziness.
2. The human may be become impotent, due to damage of nerve system.
3. The human may be become fully or partially handicapped.
4. Due to burning, the face become ugly.
5. The human may be become deaf.
6. The human may be become blind.
7. Any parts of body may be break.
8. Full body may be burned and converted into ash.

EFFECT OF AC FREQUENCY ON HUMAN BODY:

We know that the time period of alternating current is inversely proportional to frequency.

T = 1/f

Means lower the frequency more the time period of alternating current and vice-verse.Thus time of one cycle of alternating current is more and at time of electric shock it flow through the human body long time as comparison to high frequency AC and the peak value of AC flow through the body for long time and will harm the body.Thus lower frequency harm the body severely as comparison to high frequency. 

ELECTRIC RESISTANCE OF HUMAN BODY:

The value of resistance of human body depends upon two factors.

1. Dryness
2. Wetness

The value of resistance of body in different condition is given below:

1. Fully wet body = 1 KΩ
2. Partially wet body = 5 KΩ
3. Average dry body = 50 KΩ
4. Fully dry body = 100 KΩ

According to OHM'S Law, the greater the value of resistance the less is the current.So,wet body feel more electric shock as comparison to dry body.

EFFECT OF DANGEROUS VOLTAGE ON HUMAN BODY:

We know that current is more dangerous than voltage for human body.We can find the dangerous voltage according to OHM'S Law.

Dangerous voltage for human body = Current*resistance of body

The value of dangerous voltage for children is 24V and for adults is 60V.

PRECAUTIONS: We know that electricity is very dangerous for human life.So, at the time of electric work the given below points keep in mind.

1. At the time of work done, if you feel uncomfortable or may be a small injury happens.Than take rest for some time.
2. If a man comes in contact with live wire.Than take a dry wood stick to break the contact between human and live wire.It is to good before doing this you stood on a wood or rubber sheet.
3. Every time should be alert at the time of work.
4. At the time of work do not be hasty.
5. At the time of work, working a zone should be earthed.
6. The communication should be good.
7. At the time of work safety dress is necessary.
8. If you have not knowledge about the work than doing not do it.
9. At the time of work do not talk with any person and fully focused on work.
10. Always used insulated tools at the time of work.

Conclusion: The conclusion is that electricity is very dangerous for human life.But it can be avoided by taking a little care.So, at the time of work follow the precaution that saves our life from electricity shock.

AIR CONDITIONER

 WHAT IS AIR CONDITIONING? CONCEPT OF AIR CONDITIONER (A.C.)?

Air conditioning: Air conditioning means make the atmosphere appropriate.It means in summer it becomes the air cool and in winter it becomes the air hot.

OR

By the controlling of condition of air,make the air suitable and comfortable for human and industry is known as air conditioning.

Factor affecting the comfort of air conditioning:

1.Temperature of air: The temperature of comfort air conditioning room should be 21°C.

2.Humidity of air: The humidity of air of comfort air conditioning room should be below 60% in summer and not more than 40% in winter.

3.Purity of air: The air of comfort conditioning room should be free from dust,smoke,bed smell etc.

4.Motion of air: The motion of air in comfort conditioning should be uniform in desired place.

Function of air conditioning:

1.To control the temperature: It keeps the air cold in summer and hot in winter.

2.To control the humidity: It controls the humidity of air.It keeps the humidity of desired place 50%t to 60%.Thus it prevents from many skin diseases.

3.To clean the air: It cleans (free from dust,smoke,bed smell etc) the air.Thus it prevents from lungs,breath diseases.

4.To control the air flow: It spread the air uniformly at desired place.

PRINCIPAL,CONSTRUCTION AND WORKING OF AIR CONDITIONER:

 Principal: Air conditioning is a process to remove the heat from one area and replaced with cold,pure (free of dust,smoke etc) and uniform air.

Air conditioner

Construction: The main parts of air conditioner is given below:

1. Compressor
2. Condenser coils
3. Expansion valve.
4. Evaporator coils.
5. Fans
6. Connecting pipes.
7. Refrigerant/coolant

Refrigerant/coolant: It is a working substance that transfer the heat from cold body to hot body.The coolant used in air conditioner is mainly FREON gas.In air conditioner it flow through connecting pipes and changes state from liquid to vapour and vapour to liquid.

Working: According to above given diagram.When compressor start working,it compress the coolant gas and increases the temperature of gas.Thus compressor convert the coolant gas in high pressure and high temperature gas.This gas goes to condenser through connecting pipe.

 Condenser Unit

This condenser unit is placed in outdoor means outside of our home.

The heat absorbed by condenser coil to the coolant gas is expelled in atmosphere by the fan that is available in condenser unit.Thus the coolant turns back into liquid at same temperature.

The high temperature and high pressure liquid coolant will leave the condenser and enter the expansion valve through connecting pipe.In expansion valve the pressure and temperature of liquid coolant coming from condenser is decreases.

This low pressure and low temperature liquid enters in evaporator coils.

Evaporator Unit

The evaporator coils are very important to an air conditioner.This evaporator coils is always placed in indoor conditioning unit where the air conditioner picks up the heat from inside our home.The inside hot air blows over the evaporator coils,the cold and de-pressurized liquid coolant absorb the heat from inside home air.Thus by the absorbing inside heat the liquid coolant start vapourize.

Thus the main function of evaporator coil is absorb the heat from inside of our home and it vapourize the liquid coolant that flow inside the evaporator coils.The result of this our home losses heat and starting cools down.

The fan available in evaporator unit circulates the cold air from this coil surface for the cooling effect.

This hot gas/coolant after absorbing heat again goes through the compressor.Thus this process is repeated continuously in a cycle and air conditioner cools our home continuously.

Conclusion: The final conclusion is that air conditioner is a device that remove the heat from an area and replace it with cold air by expelled the hot air in outside the atmosphere.

Important links:

Electrical circuit and parts of air conditioner?

INDIAN ELECTRICITY RULES (PART-1)

 WHAT IS INDIAN ELECTRICITY RULES?

Indian Electricity Rule

Indian electricity rule is a rule that is follow by generation,transmission and distribution company as well as consumer.This rule is very helpful for smooth operation of electric generation,transmission and distribution in our country.

The company or consumer who does not follow this rule can be penalized. So,the knowledge of electricity rule is necessary for company as well as consumer.Now we will discuss all the electricity rule one by one.

The Indian electricity rule is define below:

Rule 28: Related to voltage

Voltage: The work done to bringing a unit positive charge from infinity to that point in electric field.

OR

It is an electric pressure that is responsible for flow of current in electric circuit.

Its unit is volt and measure with voltmeter that is connected parallel to the circuit.

According to rule 28 the voltage is categories as given below:

1. Low Voltage: Does not exceed 250V.
2. Medium Voltage: 250V to 650V
3. High Voltage: 650V to 33 kV
4. Extra high Voltage: above 33 kV

Note- (a)The voltage variation between low and medium voltage is up to +/-6%.(But in practical in distribution system the variation is +/-10%).

(b)The variation in case of high and extra high voltage is up to +/-12.5%.

Rule 31

According to this rule electrical supplier is responsible for provide fuse unit or MCB to the consumer.

Rule 32

The electric supplier should be mark on earthed or neutral conductor and this is the property of supplier.Thus it is very useful for connection of consumers.

Rule 33

If the consumer uses medium,high or extra high voltage,than he should be install his own earthing system.The responsibility of maintenance of earthing system should be the consumer.

Rule 34  

The bare conductor should be install at proper height.Its height such that it is not come in contact with person without the help of stair,table etc.A switch is also install with the bare conductor.This switch is helpful at the time of emergency or at the time of work for deading the conductor.

Rule 35

The consumer must install danger plate at medium,high and extra high voltage site where transformer,generator and other electric equipment install.

Rule 36 

Before doing work on electric equipment,the metal body of equipment should be earthed thus it discharge the charges on metal body of electric equipment.

Rule 38 

The insulation of cable that is connected to electric equipment (motor,generator,welding set etc) should be better quality and it should be work properly in every type of environment.

If the sheath of cable is metal than it is connected to frame of equipment and it should be earthed.

Rule 42 

If the AC and DC circuit is available on same pole than there should be proper distancing between them that prevent the short circuiting between them.

All the electric equipment connected such that it works on rated voltage means at the time of high voltage the electric accident should not be occur.

Rule 43 

At generating stations and substations for fire extinguishing bucket of clean and dry sand and fire extinguisher is necessary.The first aid box is also very necessary.

→All the staff should be trained for using fire extinguisher and first aid box.

Rule 44 

On all electric site (generating stations,substations,factory etc) the shock treatment charts must be install.

Rule 45

The electric installation (electrical fitting,electrical repairing etc) work should be completed be licences contractor or lineman.If electric work done is completed by unlicensed contractor or lineman the supplier should be deny for electric connection

→The general maintenance could be done by unlicensed person.

Rule 46

The periodic inspection and testing of electric installation should be done by after every 5 years.The inspection fees should be pay by the consumer.

Rule 47

Before giving connection to consumer the supplier survey (inspection and testing) the electric installation.If supplier found such things that effect the supply system than supplier can deny for connection and advice consumer for improvement in electric installation.

→If every thing is satisfactory at electric installation than supplier is agree for electric connection to consumer.

Rule 48

If the value of leakage current in any electric installation is more than 1/5000 to the total electric current than supplier can be deny for electric connection.

Rule 49

If the value of leakage current in any electric installation is more than 1/5000 to the total electric current than supplier can cut the supply of consumer by giving the notice of 48 hours and supplier restore the supply of consumer when supplier is satisfy that the reason of leakage current is rectify.

Rule 50

The consumer should be fulfill given below condition for electric connection:

1. There should be a main switch (circuit breaker,linked switch) that is mainly situated near the incoming of supply and it is capable of break the main supply of electric installation.
2. Every circuit has a fuse and main switch.
3. The live conductor should not be placed in open.
4. Insulating material such that it is not affected by weather and environment.
5. All the electric equipment has a switch that is helpful at the time of ON/OFF of electric equipment.

Conclusion: Thus final conclusion is that the knowledge of Indian electricity rule is good for both supplier as well as consumer and it prevent from any type of electrical accident.

ELECTRIC QUANTITIES ASSOCIATED WITH HUMAN INJURY

WHAT IS THE SEVERITY OF DIFFERENT ELECTRICAL QUANTITIES ON HUMAN BODY?

WHICH CURRENT IS MORE DANGEROUS AC OR DC?

The electrical quantities effect (loss) the human body more severely.The current is more severe than voltage.Because electric shock that effect (loss) human body is mainly due to electric current pass through the body.

The different electrical quantities severity that effect (loss) human body is given below:

1.Current: The intensity of shock is depend upon magnitude of current.So,high magnitude current is more dangerous than low magnitude current.

→Severity: AC is more dangerous than DC.Because value of maximum current at AC is more than DC at same voltage.

In case of AC;

Imax = √2.Irms 

In case of DC;

Imax = Irms

2.Voltage: According to ohm's law the current pass through the body is directly proportional to applied voltage.

I ∝ V 

Means higher the voltage higher the current.Thus high magnitude voltage is more dangerous than low voltage magnitude.

3.Frequency: Low frequency voltage is more dangerous than high frequency voltage.

Time period (T) = 1/f (frequency)

By above formula we see that low frequency has more time period than high frequency.Thus the current wave pass through the body take more time and thus it effect (loss) the body more.

4.Resistance: Low magnitude of  resistance is more dangerous than high magnitude resistance.According to ohm's law current is inversely proportional to resistance.

I ∝ 1/R

Means lower the resistance of body higher the current flow through it and it is more effect (loss) the body.

Electrical Danger Plate Yard

SEVERITY OF AC AND DC:

We know that AC and DC,both is dangerous for human body.But AC is more dangerous as compare to DC.The root mean square value of AC and DC both are same for same magnitude of voltage.But at the time of electric shock the max value of AC also works and it is √2 times than DC at same voltage.

Imax = √2.Irms = √2.Idc

 Thus AC is more dangerous than DC for human body.

Conclusion: All the electrical quantities like current voltage etc are very dangerous for human being.So,at the time of electric work,at the time of use of electric equipment should be take suitable precaution.

SUBSTATION

 WHAT IS SUBSTATION? TYPE OF SUBSTATIONS?

EQUIPMENT USED IN SUBSTATION?

Substation: It is a place where lot of electric equipment (like transformer, circuit breaker, Current transformer, voltage transformer etc) install and operate for control of transmission and distribution of electric power. 

OR

It is a place where mainly voltage transformation take place with the help of electric equipment (transformer).

Main functions of substation is given below:

1. To close and open the power lines. 
2. To raise or lower the voltage,this operation is known as voltage transformation operation.
3. To convert a.c. into d.c. or vice versa.
4. To change the frequency of supply,this operation is known as frequency operating operation.
5. To improve the power factor at the end of the line by the use of capacitor bank or synchronous condenser,this operation is known as power factor correction operation.

TYPES OF SUBSTATIONS:

According to design substation has two types.

1. Outdoor substation
2. Indoor substation

1.OUTDOOR SUBSTATION: In this type of substation the electric equipment are installed in open,so this type of substation is called outdoor substation.This type of substation is mainly used for voltage up to 66 kV and above.It is used for receive and transmit large electric energy,so high rating of equipment used.So, such type of electrical substations require a large site and generally installed outside the city.

Main parts of outdoor substation:

1.Control room: In this type of substation a small building is required (as compared to indoor substation) for control room.It is a place from all the electric equipment can be control and operate.

The given below image show the building of control room and equipment installed in control room:

Building of control room

Control Room

The given below equipment install in control room:

a) Power transformer control panel: By the operation of this panel we can switch on and off the power transformer.

b) Circuit Breaker: By the operation of CB we can switch on and off the power lines (outgoing feeders).

c) Tap changer panel: By the help of tap changer panel we can change the secondary voltage of transformer.

d) Miscellaneous equipment: Battery,DC distribution panel,AC distribution panel,Battery charging panel etc is also installed in substation building.

2.YARD: It is the place where all the equipment is installed and operate in open.

The given below image show the yard of substation and the equipment installed in yard:

Substation yard

The given below equipment is installed in substation yard:

a) Isolator cum earth switch: It is a switch that can connect and break the main circuit (power line) from substation.It is always operate at no load.A earth switch also connect to it.With the help of this earth switch be can earth the main circuit.

b) Potential transformer: It is used for metering purpose.

c) Supporting isolator: This isolator is used for the support of  main circuit.

d) Breaker panel (Primary side): This is used for switch on and off main circuit.This is mainly operate by control panel that is situated in control room.

e) Current transformer: This is used for metering and protection purpose.

f) Lighting Arrestor: This is used to protect the other equipment from lighting.

g) Power transformer: It is a device that transfer power by the transformation of voltage (primary side to secondary side).

(For more information see the transformer topic in this site).

h) Neutral current transformer (NCT): It is a device used for earthing of neutral of power transformer ( transformer which have star winding).

The advantages and disadvantages of outdoor substation is given below:

1.Advantages:

a) Small building is required.

b) The fault location is easier.

c) In future the extension of installation is easier.

d) The construction work required is less.

e) Maintenance is easy.The work of maintenance can be carried out without making more of substation dead.

2.Disadvantages:

a) More space is required for the substation.

b) The dirt and dust deposits upon the outdoor substation equipment.

c) More maintenance is required.

d) The effect of temperature on equipment due to change in weather reduces the life of equipment.

2.INDOOR SUBSTATION: In these type of substation all the electrical equipment is installed in the building of substation.It is generally used up to 66 KV.It is mainly used where the surrounding atmosphere is contaminated with impurities and metal corroding gases,conductive dust etc.

In this type of substation all the electric equipment used same as outdoor substation but it is install in a panel.The panel is divided in different chamber and all the electrical equipment install in different chamber and it is insulated by sulfur hexa-fluoride (SF6) gas.

The advantages and disadvantages of outdoor substation is given below:

1.Advantages:

a) If a fault occurs on any section of the bus bar,that section can be isolated without affecting the supply from other section.

b) Easy operation.

c) Less space required.

2.Disadvantages:

a) Fault location is difficult.

b) Risk of fire is more.

c) Future extension is not easy.

d) Capital cost is high.

e) Time required for completion is more.

→Thus final conclusion is that outdoor substation is suitable for transmit and receive large electric power above 66 KV and indoor substation is used for transmit and receive small power up to 66 KV in urban area.

SPECIAL TYPE TRANSFORMER CONNECTION

WHAT IS OPEN DELTA,INTER CONNECTED,SCOTT CONNECTION AND TERTIARY WINDING OF TRANSFORMER?   

1.OPEN DELTA CONNECTION: In this type of connection one phase remove from three phase delta connection,thus remains two phase form an open delta circuit.

By removing one phase from delta,remains two phase from V-shape.Thus it is also known as three phase V-V transformer.

The given below images show open delta connection type transformer.

Open delta connection

Uses: The use of open delta connection type transformer is given below:

1.When three phase load on transformer is much less than rated capacity of transformer and no small capacity transformer is available.

2.When one phase of delta connection type transformer is damage and thus we can use this type of connection.But load on the transformer should be 58% of the rated capacity of transformer.

3.When at starting the load on transformer is less.But in future it will be increase.So we use this type of connection.

Drawbacks:The drawbacks of this type of connection is given below:

1.The capacity of this type of transformer is 58% of delta-delta connection transformer.

2.The power factor of this type of transformer is less (86.6%).

3.On increasing load the voltage will become unbalanced.

2.INTER CONNECTED STAR CONNECTION: The connection of this type of transformer is like zig-zag.So this connection is also known as zig-zag connection.

In this type of connection primary winding may be star or delta connected,but secondary is in the form of zig-zag.Thus be obtain different phase by this connection.

The given below image shows the inter connected star connection:

Inter connected star connection

3.SCOTT CONNECTION: This connection is introduced by Charles F.Scott.So this connection is known as Scott connection.

This type of connection is mainly used to convert three phase supply into double phase and double phase supply into three phase.So this is also known as phase changing supply transformer.

The given below images show the scott connection transformer:

Scott connection

This type of transformer made by the combination of two single phase transformer.In above image horizontal transformer is known as main transformer and the vertical transformer whose one end of primary winding is tapped with mid point of primary winding of  main transformer is known as teaser transformer.Thus we get the supply from secondary of these transformer.

At the time of scott connection the main point should be remembered in mind:

1.The number of turns in primary winding of teaser transformer is 86.6% of the number of turns in primary winding of main transformer.

2.The number of turns in secondary of both the transformer is always same.So we gets the same voltage.

3.On three phase side the tapping is done at 50% on primary winding in main transformer and in teaser transformer the tapping is done at 86.6% on primary winding.

4.If number of turns in primary winding N1 and secondary winding N2.

Than transformer ratio of main transformer is,

K = N2/N1

and the transformation ratio of teaser transformer is,

K = N2/0.866N1

= 1.15 K

Uses: This type of transformer is used for those machines which works on double phase supply or single phase machines run separately (like: ac arc welding,ac traction,ac arc furnace etc).

Drawbacks: 

1.The main and teaser transformer works on different power factor,which is undesirable.

2.It works on only 86.6 capacity.

3.TERTIARY WINDING: In star-star connection type transformer.The third harmonic waves are more effective.So we cannot get pure sinusoidal wave with this transformer and also in unbalanced load the neutral point shift towards one of the phase.Due to this an extra delta winding is used in Y-Y transformer it is third winding of this transformer,So it is called tertiary winding.

The given below image shows the tertiary winding of a transformer.

Tertiary winding

Uses: The uses of tertiary winding in transformer is given below.

1.For the supply of phase compensating devices.

2.For the interconnection.

3.For the use of voltage winding in testing transformer.

→ In delta-delta,delta-star and star-delta transformer neutral is fixed.So we get pure sinusoidal wave with this transformer,because delta winding is a close circuit and it reduce the effect of third harmonic waves.

TYPES OF TRANSFORMER

DIFFERENT TYPES OF TRANSFORMER:

The different type of transformer is given below:

1.According to the construction of magnetic circuit:

a) Core type transformer: In this type transformer the winding is wound on the both side of limbs.The given below image shows the core type transformer.

Core Type

Main features of core type transformer is given below:

a) It provides a single magnetic path.

b) The primary and secondary winding are mostly of cylindrical form and concentric.

c) Most of the portion of the core gets covered by two winding.

d) The two winding are uniformly distributed over two limbs of transformer.

e) The repairing of winding is easy.

f) Due to uniform distribution of winding natural cooling is quite effective.

b) Shell type transformer: In this type of transformer the winding (both primary and secondary) is wound on the central limb.So entire flux passes through the central part of iron core.But outside the central core it divides into two half going in each direction.The given below image shows the shell type transformer.

Shell Type

Main features of Shell type transformer is given below:

a) The core provides double magnetic path.

b) It provide good mechanical protection to winding,because it wound on central limb.

c) Low leakage flux.

d) Natural cooling is poor.

→ If shell type and core type transformer compare,then we see that core type transformer has more space for insulation so it is preferred for high voltage.

2.According to  the connections:

1.Star-Delta connection: In this type of connection the voltage phase displacement in both side voltage is 30 degree.The total bush in this type of transformer is 7 (4 in HV side and 3 in LV side).The advantages and disadvantages of this type of transformer is given below:

Advantages:

a)The primary is connected to star and secondary is connected in delta.So,the primary side phase voltage is less (57.73%) to the line voltage so the less number of turns as well as insulation required in this type of transformer.

b) In the primary side due to presence of neutral point protective relay can be used for protection purpose.

c) There is no possibility of displacement of neutral point.

d) Due to delta connection in secondary side the third harmonic waves does not effective.

Disadvantages:

a) Due to 30 degree phase displacement in both side voltage,this cannot be used in parallel with star-star or delta-delta connected transformer.

Application:

This connection is used in step-down power transformer.Mostly in secondary transmission substation.

2. Delta-Star connection: In this type connection the primary of transformer is delta and secondary is star connected.The voltage phase displacement in botn side voltage is 30 degree.The given image shows the delta-star connection transformer.The given below image show the delta star connection type transformer.

Delta star connection

Advantages:

a) The secondary side is star connected.So secondary side phase voltage is less (57.7%) than line voltage.So less number of turns in secondary side and low insulation level is required.

b) In the secondary side due to presence of neutral point protective relay can be used for protection purpose.

c) Due to delta connection in primary side the third harmonic waves does not effective.

Disadvantages:

a) Due to 30 degree phase displacement in both side voltage,this cannot be used in parallel with star-star or delta-delta connected transformer.

Applications:

a) This connection is used for step-up transformer and this type of transformer is used at generating station for high voltage transmission.

b) This connection is also used for 3 phase 4 wire distribution transformer.

3.Delta-Delta connection: In this type connection the primary and secondary side of transformer is delta connected.The phase voltage displacement on both side is zero degree.These type of connections are suitable for large transformer working on low voltage and high current.

Advantages:

a) Current in winding is reduced to 57.7% of line current.So cross sectional area of conductor reduces.

b) Unbalanced load do not effect much.

c) Third harmonic waves does not effective.

Disadvantages:

a) In this system neutral point is not available.Therefore 3 phase 4 wire connection is not possible.

b) High insulation is required.

c) Large number of turns required.

d) We cant obtain low voltage as similar to star-star connection.

Applications:

This connection type of transformer is used to low voltage transmission sub-stations.

4.Star-Star connection: In this type of connection the primary and secondary side of transformer is star connected.The phase voltage displacement on both side is zero degree.These type of connection are suitable for high voltage transformer which have small size.

The given image shows the star-star connected transformer,two NCT is used for neutral point earthing and for protection purpose:

Add caption

Star star connection

Advantages:

a) The phase voltage is less (57.7%) to line voltage.So less number of turns required.

b) Less insulation required.

c) Neutral point is available.So this type of connection is used for 3 phase 4 wire connection.

d) By earthing the neutral point system stability increases.

e) Due to presence of neutral point protective relay can be used for protection purpose.

f) In this type of connection line current equals to phase current.So conductor size is thick and it can bear overload current and short circuit current at some extent.So safety factor of system increased.

Disadvantages:

a) If the neutral is not earthed.Than at the time of unbalanced load neutral is shifted towards one of phase.So earthing of neutral is necessary.

b) Due to open circuit,third harmonic waves most effect this type of connection.

Applications:

This type of connection is used for transformer which is used in high voltage distribution substation.

3.According to utility: 

1.Power transformer: The power transformers should be designed for maximum efficiency at or near full load.So,it is put in operation during load periods and disconnected during light loads periods.

Power transformer are designed to have greater leakage reactance than is permissible in distribution transformers because in the case of power transformers,voltage regulation is less important than the current limiting effect of higher leakage reactance.The given shows the power transformer.

These are used in generating stations and substations at each end of power transmission lines.This transformer rating above 200KVA.

The given below image shows the power transformer.

Power transformer

2.Distribution transformer: The transformer used to step-down voltage to a standard service voltage is known as distribution transformer.They are kept in operation all the 24 hours in a day whether they are carrying any load or not.Therefore energy loss in iron throughout the day while energy loss due to copper losses when transformer is loaded.Therefore power transformer should be designed to have maximum efficiency at a load much lower than full load (about 50%).

This transformers rating up to 200KVA.

The given image shows the distribution transformer.

Distribution transformer