BATTERY ELIMINATOR

 BATTERY ELIMINATOR

WORK EDUCATION

A battery eliminator is a device that convert A.C. voltage in suitable D.C. voltage It is most common item in these days. They are mostly used in transistors, radios, tape recorders, record players etc. They are manufactured in different ranges like 3 V, 6 V, 9 V, and 12 volts. A most common battery eliminator consists of

1. a centre tapped or different tappings step down transformer,

2. a on/off switch, a band/rotary switch,

3. two diodes/four diodes (Bridge type) rectifier,

4. capacitors,

5. a choke

6. an indicating lamp fitted in box with main supply lead and plug on one side and a connector to connect the device is fitted on the other side and

7. two leads with battery clips are taken out to connect any device.

The transformer is used for reducing the voltage of 250/230 V to 0 to 12 volt. The band/rotary switch is used to select the voltage according to the range of voltage of the device to be used. The diode rectifier converts A. C. into D.C. The filter circuit consisting of capacitors and choke/ resistor is used to smoothen the pulsating D.C. into pure D.C. The other components like toggle switch is used to switch ON the main A.C.supply , the indicating lamp is used to indicate the working of the battery eliminator. In the battery eliminator, when the diodes are connected in Bridge form, the four diodes are needed.

DIODE- A diode is a two terminal electronic component that coducts current primarily in one direction because it has low resistance in one direction and high resistance in other

CAPACITOR –The capacitor is a component which has the ability or capacity to store energy in the form of an electrical charge producing a potencial different across its plate much like a small rechargeable battery

BATTERY ELIMINATOR

 BATTERY ELIMINATOR

WORK EDUCATION

A battery eliminator is a device that convert A.C. voltage in suitable D.C. voltage It is most common item in these days. They are mostly used in transistors, radios, tape recorders, record players etc. They are manufactured in different ranges like 3 V, 6 V, 9 V, and 12 volts. A most common battery eliminator consists of

1. a centre tapped or different tappings step down transformer,

2. a on/off switch, a band/rotary switch,

3. two diodes/four diodes (Bridge type) rectifier,

4. capacitors,

5. a choke

6. an indicating lamp fitted in box with main supply lead and plug on one side and a connector to connect the device is fitted on the other side and

7. two leads with battery clips are taken out to connect any device.

The transformer is used for reducing the voltage of 250/230 V to 0 to 12 volt. The band/rotary switch is used to select the voltage according to the range of voltage of the device to be used. The diode rectifier converts A. C. into D.C. The filter circuit consisting of capacitors and choke/ resistor is used to smoothen the pulsating D.C. into pure D.C. The other components like toggle switch is used to switch ON the main A.C.supply , the indicating lamp is used to indicate the working of the battery eliminator. In the battery eliminator, when the diodes are connected in Bridge form, the four diodes are needed.

DIODE- A diode is a two terminal electronic component that coducts current primarily in one direction because it has low resistance in one direction and high resistance in other

CAPACITOR –The capacitor is a component which has the ability or capacity to store energy in the form of an electrical charge producing a potencial different across its plate much like a small 

rechargeable battery

ELECTRIC MOTOR

 ELECTRIC MOTOR

WORK EDUCTION

ELECTRIC MOTOR (DC MOTOR) An electric motor is a device for converting electric energy into mechanical energy. Thus, an electric motor is the revenue of an electric generator.There are two types of electric motors: AC motor and () DC motor. We shall here be described DC Motor

Principle. When a coil carrying current is placed in a magnetic field, it experiences a torque. As result of this torque, the coll begins to rotate.

Construction. It consists of the following five parts:

1. Armature. The armature consists of a large number of turns of insulated copper wire wound over a soft iron core

2 Field Magnet. The magnetic field (B) is supplied by a permanent magnet NS

3. Split-ring or Commutator. These are two halves of the same metallic ring. The ends of the armature coil are connected to these halves which also rotate with the armature.

4. Brushes or Sliding Contacts. These are two flexible metal plates or carbon rods B1, and B2, which are So fixed that they constantly touch the revolving rings.

S. Battery. The battery consists of a few cells and is connected across the brushes. The brushes pass the current to the ring from where it is carried to the armature

Working. Let us suppose that the battery sends current to the armature in the direction shown in Fig). Applying Fleming's Left Hand Rule (Motor Rule), we find that arm AD experiences a force which is acting outwards and perpendicular to it and arm BC experiences a force which is acting inwards and perpendicular to it. These two forces for a couple whose moment (ie, torque) makes the armature rotate in the anticlockwise direction.

(b) After the armature has completed half a revolution (ie, has turned through 180), the direction of current in the arms AD and BC is reversed. Now arm BC experiences an outward force and arm AD experiences an inward force,. The armature thus continues to rotate about its axis in the same, Le., anticlockwise The speed of rotation of the motor can be increased by

(i) increasing the strength of the current through the armature, (i) increasing the number of turns in the coil of the armature, (ii) increasing the area of the coil, and (iv) increasing the strength of the magnetic field.

Uses of DC Motors

1. These are used in electric fans (exhaust, ceiling or table)

2. These are used for pumping water.

3. Big DC motors are used for running tram-cars. 4. Small DC motors are used in various toys.

ELECTRICAL ACCESSORIES

 KENDRIYA VIDYALAYA NO 2 DARBHANGA

ELECTRICAL ACCESSORIES

 Switches. These are used to switch 'on' and switch off the current in any circuit with the phase wire.

 Double Pole Main Switch. It is used in the circuits to control the supply mains at the main board and the whole circuit.

 Wall Sockets. These are used in the circuits to connect any appliance, machine, equipment, table fan, etc., or to test any appliance or equipment by taking the supply wires in series with test lamp through these.

WORK EDUCATION

 Batten or Angle Holders. These are used in the circuits in which the bulbs are attached for lighting fixed on the wooden blocks or junction boxes with walls.

 Pendent Holders. These are used where hanging lighting is required. These are mostly connected with ceiling roses fixed on the wooden boards or junction boxes with roofs.

 Ceiling Roses. These are used in the circuits fixed on the wood blocks or junction boxes with roofs with which connection for ceiling fans, exhaust fans, tube lights and pendant lights

 Fuse Carriers. These are used to control different circuits to divide loads on the circuit and save the circuits in the case of short circuits or overload.

 Multiple Holders. These are used with the batten holders, angle holders or pendent holders to take the additional connections for the appliance, light or equipment, etc.

 Multiple Plugs. These are attached with 2-pin or 3-pin wall sockets to take the additional connections for the appliances and equipment or machines, etc.

 Plugs. These are attached with wall-sockets or multiple-plugs or holders to take the supply for any appliance, equipment, machine or light.

 Connectors. These are attached with the terminals of any appliance or equipment to give the supply

 Bed Switches. It is one of the switch which controls the connection of any light or fan, etc., and is mostly connected for the easy control near the bed

ELECTRICAL ACCESSORIES

 

 

Faraday's Laws of Electromagnetic Induction

 WORK EDUCATION

Faraday's Laws of Electromagnetic Induction :

First Law. Whenever any conductor is made to rotate in a magnetic field, and hence cuts the magnetic lines of force or the flux, e.m.f. will be induced in that conductor.

Second Law. The second law states that the magnitude of the induced e.m.f. is directly proportional to the rate of change of flux linked with the conductor.

Assuming that the coil has N number of turns and the flux linked with the coil changes from the initial value o/wb(weber) to the final valueo/ wb in time t second, then the flux linked is the product of the number of turns and the flux linked with the coil. There have,

Initial flux linked=No/1

Final flux linkage-No/2

Induced e.m.f.= e= N(o/1-o2)/t

Fleming's Right Hand Rule. This rule is applied for generators to find out the direction of the induced current. In this case, the direction of the induced emf in a conductor depends upon the direction of motion conductor and also upon the direction of magnetic lines of force which can be expressed by Fleming's right hand rule Stretch out the fore finger, the middle finger and the thumb of right hand mutually perpendicular to each other. If the fore finger denotes the direction of magnetic lines of force and the thumb, the direction of motion of the conductor, then the middle finger indicates the direction

of induced current

Fleming's Left Hand Rule. This rule is applied for motors to find out the motion of a conductor carrying current when placed in a magnetic field. In this case there is a definite relation between the magnetic lines of force, direction of the current and direction of the motion of the conductor which can be expressed by Fleming's left hand rule. Stretch out the thumb, the fore-finger and the middle finger of the left hand perpendicular to each other. If the fore-finger points in the direction of the lines of magnetic field and the middle finger indicates the direction of the current, then the thumb indicates the direction of the motion of the conductor.

work experience

 

 HOUSE WIRING

WORK EDUCATION

There are various system of house wiring

1.CLEAT WIRING

2.C.T.S (T.R.S WIRING) OR P.V.C WIRING

3.WOODEN CASING AND CAPPING WIRING

4.LEAD-SHEATHED WIRING

5.CONDUIT WIRING

Cleat wiring- Material required for wiring –wooden round block, wood screw, wire ,Wooden Boards switches-single way and two way; batten holders and pendant holder : Ceiling Roses; D.P. main switch; fuse carrier; neutral link etc.

Uses. This method of wiring is well adopted to temporary work and has been used in huts built for military and naval purposes. Faults are easily located in this method of wiring.

P V C Wiring - - Material required for wiring- Wooden pegs, Wooden round blocks, Wooden board, Tin clips, Screws, Nails, Wire C.T.S. or T.R.S. or P.V.C . (Single core or two core). Copper wire for earthing-16 S.W.G. Switches-single way, two way: D.P. main switch-iron clad or bakelite according to the requirement ; fuse carrier ; neutral link ; batten holders-brass or bakelite ; ceiling roses; pendant holders-brass or bakelite etc.

Uses. This type of wiring is suitable for every place as it is water proof, steam proof within limits and appearance is good one. An advantage of this type of wiring is that it can be erected very easily and quickly and the saving in labour for ordinary house and workshop wiring. Faults can be easily located. Wiring can easily be replaced.

Casing-Caping Wiring-- Material required for wiring- Wooden pegs ; round porcelain cleats; casing-capping. Wooden Boards, Round blocks. Copper wire for earthing-16 S.W.G. or 14 S.W.G. Wooden screws, Wire V.I.R. Switches—Single way and two way; D.P. main switch-iron clad or bakelite ; fuse carrier and neutral link ; ceiling roses ; batten holders-brass or bakelite ; pendant holders-brass or bakelite:

.Uses. The appearance is good one. This type of wiring generally seen in buildings and houses etc.

Conduit and Concealed Wiring- - Material required for wiring-- Flat and round wooden pegs, saddles ; hooks or crampet, beavy or light gauge conduit, le 16 or 14 gauge metal- Wooden board or iron boards, Wooden Screws , Ebonite sheet: bends, elbows ,t tee , Junction boxes-one way,

Two wayThree way , socket ; porcelain connector-one way, two way o three way; earthing clamp ; copper wire for earthing-14 or 16 S.W.G bushes ; porcelain tubes switches-single w and two way; D.P. main switch-iron clad or bakelite ; neutral link : ceiling rose ; batten holder ; pendant holder; water tides : brackets etc.

Uses. 1. Efficient mechanical protection, 2. Ready inspection for alterations and repairs. 3. Can be made mechanically and electrically perfect. 4. Absolute freedom from fire,

Lead Covered Wiring

All materials which are required for CTS. wiring except C.T.S. wire and batten etc. are used with this type of wiring,

Uses. Appearance is good and maintenance is easy. This type of wiring is generally used in high buildings or for consumers mains by supply undertakings.

General Specifications of House Wiring -Following are the general specifications of wiring

1. Power wiring should be carried out separately from the lighting wiring

2. Copper conductor should be used.

3. Wooden pegs used in walls or ceiling should be of hard seasoned wood.

4. The main board should be at a height of 150 cm. from the level of the ground

5. The iron clad main switch, conduit fittings and 3-pin wall sockets should be earthed.

6. The switch board of the room should be fixed on the left side of the door and at a height of 150 cm.

7. The fan should be controlled both with the switch and regulator.

8. In kitchen, the wiring should be in conduit system to protect the wires from smoke.

Common Faults found in the Domestic Installation

1.Accidental damage caused by other workman who fails to understand the system of wiring.

2. Cases of leakage and accidents due to lower quality accessories.

3. Short circuit occurs when rats cut the insulation or wires in the P.v.c. wiring

4.Earth fault due to touching of live wires to the metal parts

EARTHING

 

                                        KENDRIYA VIDYALAYA NO -2 DARBHANGA                                                                                                                                                                                   

 

                                                                  WORK EDUCATION

TOPIC- EARTHING

. Earthing. A wire coming from the ground to 2.5 to 3  metres deep from an electrode (plate or so) is called earthing

The earth's potential is always taken as zero for all practical purposes. The electrical appliances or machines when connected  with earth attain zero potential and are said to be earthed

Object of earthing  -  To save human life  from danger or shock or death  on  blowing fuse of any apparatus which become leaky.                                                                                                                                                          2. To protect large buildings from atmospheric lighting

3. To protect all machines fed from O.H. lines from  atmospheric  lighting by taking all voltage of lighting through lightning arresters.

4. To maintain the line voltage constant ( neutr al of every alternator, transformer is earthed).

Good earthing --     It  is that earthing Which gives very low resistance to the flow of heavy Current of a circuit.

 Double earthing -  Double earth is used to give minimum resistance to the flow of whole current of that apparatus in case short circuit or leakage or any other such fault happens.                                                                             Second reason –If one earth is out of order, second will do the work

For double earthing.- Two earthing is done at a distance of about 5 metres, and the two earth wires should be fixed with the f thimble (lugs) of proper sizes with the apparatus at two different places. Precaution should be taken that the two wireshoud not each others.                                                         

What should be the resistance of a good earth ?                                                                                                                              The earth resistance for copper wire is 1 ohm  and for GI wire it should not be more than 3 ohm

                    Earth resistance is measured by earth tester. As the total current is to pass through the earth wire the earth resistance should be kept as low as possible. The resistance increases in hot days (summer days),

To Reduce Earth Resistance

1. By pouring water. The dampness of the soil and coal salt paste depends upon the atmospheric conditions. In summer season fresh salt water should be poured through the pipe over the coal bed.  The soil resistance can be lowered only to a certain limit by the above method, and in order to lower it further, following are the additional steps to be taken:

2 Increase in plate area, In case of increase in plate area, the decrease of resistance value is not in direct proportion to the area. It is found that to reduce the resistance value by one-sixth, the increase in area by 36 times more for the same soil condition and depth of Electrode. So this method is not used.                        3. Increase in depth. The increase of depth below the ground level  of the same plate reduces the resistivity of the  earthing system.It  is found that plate area reduces to fifty percent when the depth is doubled  for the soil resistance With this method also the soil resistance  value cannot be lowered as much as desired, on account of excavation  work; however, it helps to a great extent.                                                                                                                  4. Electrodes in parallel. In this system of lowering earth resistance the soil resistance fall considerably as the number of electrodes inter connected in parallel are increased for the same depth. This method  is suitable only where great area of a free soil is available for earthing The plates should be-so place d in parallel as not to overlap the earthing region covered by the individual electrode, If R and R, etc., are the earth resistance of each electrode and R The total earth resistance of the system,then

        1|R= 1\R1+1\ R2+……….

SPECIFICATION REQUIRED FOR EARTHING

 Following are recommended specifications as per 1sL for providing good earthing.                                     1. The earthing electrode should be situated at a place at least I.5  metres away from the building (outside) whose installation systemis being earthed.

2. The earth wire should be of same material as that ct electrode used.                                                                         3. The minimum sectional area of earth lead wire should be less than O'02 sq. inch (No. 8 S.W.G.) and not more than 0.1 inch.

4. The size of earth conductor as a general rule should notLess than half of the section of live line conductor.

5. The earth wire should be taken through G.I. pipe of 12 mm (1") dia. for at least 3'25 cm (1.5”) dia for at least 3.25cm (1’) length above and below ground surface to the earth electrode to safeguard against mecheni cal wear and tear

6. Loose earth and coal salt mixture should be filled around  the earth electrode for effective earthing                                                                                     7. The earth wire connected to the earth electrode should not  be necessarily run along the whole wiring system. All the earth  wire runs along the sub-circuits should be terminated and hook firmly at the main board and from where the main earth wire  should be run to the earth electrode. The loop earth wire show be of 14 SWG copper wire.

8. All the joints in the earth wire should be firmly done with  nut bolts of the same material as of earth wire.

 

 

 

ELECTRIC SHOCKS

 

KENDRIYA VIDYALAYA NO 2 DARBHANGA

ELECTRIC SHOCKS

 

Electric Shocks are received by touching the metal parts of the equipments when the live wire touches them and current comes in contact due to damaged weak insulation or loose connections at the terminals. The immediate effect of these shocks may be the heart effect or the death depending on the strength of the current and on the path it takes in passing to earth through voltage which is too high. The electric shock may occur

(a) From the domestic apparatus or appliances or equipments using with voltages upto 440 V in houses and offices.

(b) From equipments using with the voltage from any mains.

(c) From overhead lines with high voltage upto 1100 or above (a.c.) volts.

(d) From lightening where the voltage may be many millions and the strength of the current is immeasurable e.g. standing under the trees or in contact with metal railing etc.

 

Treatment for Electric Shocks

 

1. Switching off the current.

 

2. Removing the casualty from the contact of current.

 

3. Giving the artificial respiration.

 

4. Treating the burn.

 

5. Removing the casualties from fire.

 

6. Sending the casualty to the hospital or seeking medical aid

 

ELECTRICAL SAFETY TIPS FOR KIDS

• Never put fingers or other objects in an outlet
• Keep metal objects out of toasters
• Never use anything with a cord or plug around water
• Never pull a plug out by its cord
• Stay away from substations and power lines
• Don't climb on power poles
• Never fly kites near power lines
• Stay away from broken or fallen power lines
• Never touch or climb trees that are near power lines
• Never touch big, metal transformer boxes with warning signs
• Obey warning signs

 

 

ELECTRICAL SAFETY RULES

 

WORK EDUCATION

ELECTRICAL SAFETY RULES

 

General safety tips

•        Switch off all plugs when not in use

•        Be careful while using a water heater

·         Electric geysers should be switched off when not in use

·         Oven and microwave should not be left running without supervision

·         Always handle electric appliances with dry hands

·         Do not use a hair dryer in the bathroom

•        Do not cut and make adjustments to electric cords

·         Switch off all electric supply when on a vacation

·         Switch off mains in case of a fire

 

Safety Tips for Kids

• Never put fingers or other objects in an outlet
• Keep metal objects out of toasters
• Never use anything with a cord or plug around water
• Never pull a plug out by its cord
• Stay away from substations and power lines
• Don't climb on power poles
• Never fly kites near power lines
• Stay away from broken or fallen power lines
• Never touch or climb trees that are near power lines
• Never touch big, metal transformer boxes with warning signs
• Obey warning signs