ELECTRIC LAMPS – PART – 02 - OPERATION OF FLUORESCENT TUBE LIGHT WITH GLOW STARTER

FLUORESCENCE

A few materials have the property of reflecting light incident on them; reflected light has a longer wave length than that of the incident light. This property is called fluorescence and the materials are known as fluorescent or phosphors.

FLUORESCENT MATERIALS

1. Zinc Silicate                   Green  5200

2. Calcium Tungstate          Blue  4600

3. Magnesium Tungstate      Blue weight  4800

4. Zinc Beryllium Silicate    Yellow white 6000

5. Cadmium Silicate            Yellow pink  6100

6. Cadmium Borate             Pink 6200

FLUORESCENT LAMPS

Lamps which are coated with fluorescent, discharge ultra-violet radiations. They emit radiation of longer wavelength, in the visible spectrum.

Fluorescent lamps are more energy efficient than incandescent light bulbs of an equivalent brightness because more of the energy input is converted to usable light and less is converted to heat.

Fluorescent lamps require a ballast, which is a device used to provide and control the voltage in the lamp, and stabilize the current in the circuit.

OPERATION 

1. They produce light when an electric current passes between two electrodes (also called cathodes) in a tube filled with low-pressure mercury vapor and inert gases, such as argon and krypton.

2. Mercury is useful in lighting because it contributes to the bulbs' efficient operation and life expectancy.

3. The mercury within fluorescent lamps poses no health risk.

4. The electric current excites the mercury vapor in the tube, generating radiant energy, primarily in the ultraviolet (UV) range.

5. The energy causes a phosphor coating on the inside of the tube to "fluoresce," converting the UV light into visible light.

CONSTRUCTION DETAILS

1. It consists a glass of tube of 25 mm diameter.

2. Length varies from 0.6 m to 1.5m

3. Inert gas used are Argon and krypton at low pressure (2.8

    mm of Hg column) plus a few drops of mercury.

4. A tungsten filament which is coated with electron emitting

    materials are connected across the ends of the tube.

    Normally opened bimetallic strips start glow as a result

    the strips are heated and are closed.

5. Voltage operated glow starter is used to start the operation

    of the tube light.

6. A glow starter contains a glass bulb filled with a mixture of

    hydrogen and helium used to produce a glow in the starter

    and a bimetallic strip which is normally open.

7. A capacitor of 0.05 micro farad is connected across the

    bimetallic strip

8. The capacitor gets charged due to the arc and radio

    interference is controlled. The starter does not consume any

    power.

9. A choke is provided as a ballast (an electrical device for

    starting and regulating fluorescent and discharge lamps)

    which gives high impulse about 1200 V for starting and later

    on, maintain 230 V which is sufficient to maintain the

    discharge.

10. When supply is switched on, full voltage appears across the

     starter.

12. Due to small gap between the strips an arc is produced, the

      strips are heated and are closed.

13. The circuit is closed and current flows through it.

14. After some time, the strips are cooled down and opened.

15. This interruption of current causes a very high voltage

      induced in the choke which is sufficient to start the

      discharge.

16. Once the discharge happens the starter is removed of

      circuit as the discharge gets a low resistance path through

      the tube.

17. Fluorescent tube lamp gives light like day light in which

      colour distinction is possible.

ADVANTAGES

1. Its lamp efficacy is 40 lumens per watt.

2. The life of lamp is about 4000 hours.

3. Its light is uniform.

4. It gives pleasant light.

5. It consumes 50% less energy than incandescent lamp for the

    same voltage.

6. It can be used in any direction.

7. It can be used in both ac and dc supply.

DISADVANTAGES

1. Stroboscopic effect.

2. Magnetic hum associated with choke causing disturbance.

APPLICATIONS 

1. Linear fluorescent, U-tube, and Circline lamps are used for

    general illumination purposes.

2. They are widely used in commercial buildings, schools,

    industrial facilities, and hospitals.

3. Bug zappers contain a fluorescent lamp that emits ultraviolet

    light, attracting unwanted insects.

[Bug zappers: An electrical device that can injure or kill by means of electric currents]

STROBOSCOPE

Scientific instrument that provides a flashing light synchronized with the periodic movement of an object; can make moving object appear stationary.

APPLICATIONS OF STROBOSCOPE

1. In medicine, stroboscopes are used to view the vocal cords for 

    diagnosis of conditions that have produced dysphonia.      

   [Dysphonia is the medical term for disorders of the voice]

2. Flashing lamp strobes are used in night clubs and for lighting 

    effect where they give the impression of dancing in slow motion.

3. It is also used for frequency measurement.

STROBOSCOPIC EFFECT IN A TUBE LIGHT

In any type of discharge lamp this discharge is actually extinguishes twice per cycle of the supply, so there is a slight stroboscopic effect. [After every half-cycle, the current in an AC circuit is zero. At that instant the tube remains off.]

Due to this the periodic fluctuations in the light output of a lamp caused by the cyclic variations of the current on AC circuits.

This effect causes multiple image appearance of moving objects and makes the movement appear jerky.

This effect is more at lower frequencies.

METHODS OF MINIMIZING THE EFFECT

1. By using 3 lamps on the separate phases of a 3-phase supply.

2. By using twin tube lights with one of the chokes having a

    capacitor in series with it and the lamp.

3. By operating the lamp from a high frequency supply.

INTERVIEW QUESTIONS IN ELECTRICAL ENGINEERING – PART - 50 – What is the difference between feeder and distributor?

In India we have the following supply systems:

DOMESTIC CONSUMPTION [single phase]

Voltage (V) – 240 (+/- 6%)

Frequency (f) – 50 (+/- 3%)

INDUSTRIAL CONSUMPTION [3-phase]

Voltage (V) – 415 (+/- 6%) [Phase – Phase]

Frequency (f) – 50 (+/- 3%)

MULTISTORY BUILDINGS

Voltage (V) – 415 (+/- 6%)

Voltage (V) – 240 (+/- 6%) [Phase – Neutral]

Frequency (f) – 50 (+/- 3%)

DISTRIBUTION SYSTEM

The part of power system which distributes electric power for local use is known as distribution system.

IMPORTANT TERMS IN DISTRIBUTION SYSTEM

BUSES

The network nodes being referred as buses.

FEEDER

1. The feeder may be defined as the line carrying power from the secondary sub-station to the distribution sub-station.

[OR]

'Feeder' is a line which supplies a point of distribution network, without being tapped at any intermediate point.

In the definition the expression 'without being tapped at any intermediate point' means that feeders are not tapped at any intermediate point to give supply for direct use to consumers.

DISTRIBUTOR

'Distributor' is a line from which tappings are taken along its length to provide supply to various consumers.

The distributor is supplied from a distribution sub-station where a high voltage (11 KV) is stepped down to a much lower distribution voltage (415V and 240V) for domestic, commercial and industrial use.

SERVICE MAINS

Service mains is generally a small cable which connects the distributor to the consumer’s terminals.

TYPES OF FEEDERS

(a) OVERHEAD (OH) FEEDER

1. High voltage transmission is carried out by the OH system.

2. This system initial cost is low.

3. This is system is common used in rural areas and identification of fault location is easy.

(b) UNDERGROUND (UG) FEEDER

1. This system is more safe, free from interruption of service on account of thunderstorms and lightning.

2. This system initial cost is high.

3. This system is mostly used in cities and identification of fault location is very difficult.

INTERVIEW QUESTIONS IN ELECTRICAL ENGINEERING – PART – 49 - What are the types of Sub-stations (SS)? & Major equipment in SS and its function.

SUBSTATION

Substation may be defined as the equipment or an assembly of equipment, which changes one or more characteristics of the supply example power factor, frequency etc.

GENRAL CLASSIFICATION OF SUBSTATION

Step – Up or primary substations

Step-down or secondary sub-stations

Distribution substations

Primary Grid substations

SUBSTATIONS BASED ON DESIGN

1. Indoor substations: Apparatus are installed within the substations.

2. Outdoor substations: These substations are erected for distribution of power in localities and are further classified as pole mounted substations and foundation mounted substations.

BASED ON OPERATING VOLTAGES

High Voltage substations – 11 kV and 66 kV

Extra High Voltage substations – 132 kV and 400 kV

Ultra-High Voltage substations – above 400kV

TYPES OF SUBSTATIONS

01. SWITCHING SUBSTATIONS

Switching substation means for switching operation of power lines without transforming voltage level to another level as per needs.

02. GRID SUBSTATIONS

These are the substations from where bulk power is transmitted from one point to another point in the grid. These are important because any disturbance in these substations may cause the failure of grid.

03. CONVERTING SUBSTATIONS

These substations converting AC to DC or vice-versa and converting frequency form higher to lower or vice-versa.

03. FREQUENCY CHANGING SUB-STATION

There are many industrial applications for which frequencies lower or higher than the frequencies of normal supply are needed. High frequency heating and dielectric heating are examples. The substations which are installed for this particular purpose are called frequency changing substations.

05. POWER FACTOR CORRECTION SUBSTATION

Substations which are used to correct or improve the power factor are known as power factor correction substation. Generally synchronous motors are used for this purpose. Therefore, they are also called synchronous sub-stations.

06. MOBILE SUBSTATIONS

Mobile substations needed for temporary requirements such as for construction purposes. It requires special purpose and designs.

07. CINEMATOGRAPHY SUBSTATIONS

The cinematography substations are special purpose substations and are required to meet the special requirements.

08. MINING SUBSTATIONS

Mining substations as the name indicates are substations required for special purposes they need special design considerations, because of the extra for safety needed in the operation of the electric supply.

09. TOWN SUBSTATIONS

These substations step – down the voltage at 33 / 11 KV for further distribution in the towns and any failure in such substations results in the failure of supply for whole of the town.

MAJOR EQUIPMENTS IN SS

1. TRANSFORMER

Step up and step down the voltage.

2. BUS BAR

A bus bar (sometimes pronounced "buzz bars") in electrical power distribution refers to thick strips of copper or aluminium that conduct electricity within a switchboard, distribution board, substation, or other electrical apparatus.  The size of the bus bar is important in determining the maximum amount of current that can be safely carried.

3. ISOLATORS

Isolators or disconnect switches operate under no load condition. They are not equipped with arc-quenching devices.

4. SWITCHES

1. OIL SWITCH - The oil switch has both the blade and the contact mounted in a oil-filled tank. The switch is usually operated from a handle outside of the case. As the switch is opens, the arc formed between the blade and contact is quenched by the oil.

2. AIR-BREAK SWITCH – The air-break switch has both the blade and the contact equipped with arcing horns. [Arcing horns are piece of metal between which the arc resulting from opening a circuit carrying current is allowed to form]

5. CIRCUIT BREAKER

The circuit breaker (CB) which normally gets signal from protective relays to operate, is an automatic switch which can interrupt the fault current.

6. FUSES & RELAYS

FUSE - A fuse is a short piece of metal, inserted in the circuit, which melts when excessive current flows through it and thus breaks the circuit.

RELAY - Relay is device which senses abnormal conditions on a power system by constantly monitoring electrical quantities of the system, which differ under normal and abnormal conditions.

7. CONTROL BOARDS and 8. CONTROL ROOM

ELECTRIC TRACTION - PART - 11 - TYPES OF TRACTION SYSTEMS

ADVANTAGES OF ELECTRIC TRACTION SYSTEM

1. It is a clean traction system.

2. Well suited for underground railways.

3. No need for separate generator is required for lights and

    fans, power can be drawn directly from the lines.

4. Speed control is possible.

5. It has the advantages of rapid acceleration and retardation.

6. Less maintenance is required.

7. It can be started instantly.

8. It can take large overloads.

9. Pollution free.

10. Very economical system.

DISADVANTAGES OF ELECTRIC TRACTION

1. Its initial cost is very high.

2. Failure of supply paralyses the whole system.

3. It produces electro-magnetic interference with the

    neighboring telecommunication lines.

Electric traction is suitable for suburban and urban raiway where frequent starting and stopping and high schedule speeds are required.

It is capable of handling greater volume of traffic.

The system can be subdivide into and run in sections during the periods of light traffic.

Frequent service of trains can be maintained leading to increased traffic during these periods.

SYSTEMS OF TRACTION

1. DIRECT STEAM ENGINE SYSTEM

Steam engine drive is the most widely used traction system in almost all the UNDERDEVELOPED countries.

ADVANTAGES

1. Simplicity in design.

2. No telecommunication interferences

3. Low capital cost, because track electrification is not

    required.

4. Seep control is simple

DISADVANTAGES

1. Poor thermal efficiency.

2. Noisy in operation.

3. Due to unbalanced reciprocating part there is considerable wear on the track.

4. Corrosion of steel structure due to smoke emitted by the engine.

5. It pollutes the atmosphere.

6. Low efficiency.

7. It takes own time for starting.

8. No suitable for underground system.

9. High maintenance cost.

10. Speed of locomotive is very low.

2. DIRECT INTERNAL COMBUSTION SYSTEM  

It is suitable for road and light railway work, it is unsatisfactory work on railways. [buses, cars and trucks]

ADVANTAGES

1. It has low initial cost.

2. Very compact and self-contained unit.

3. Speed control with gear and arrangement is quite simple.

4. It has a efficiency of 25%.

5. Its braking arrangements are simple.

DISADVANTAGES

1. The life of the equipment (vehicle) is short.

2. Overload capacity is low.

3. Manintenace and running costs are fairly high.

4. It produces air pollution.

5. It requires gear arrangement for speed control.

3. DIESEL ELECTRIC DRIVE

This system is used in Indian Railways.

In this system gear system is eliminated. The diesel engine is coupled to a dc generator which supplies d.c traction motors.

ADVANTAGES

1. For conversion from steam engine to diesel traction, no modification of existing track is required.

2. No overhead transmission system is required hence capital is low.

3. The efficiency of the system is comparatively higher, about 25%.

4. The haulage capacity is larger as compared with steam locomotive.

5. Simple starting method.

Speed control with gear and arrangement is quite simple.

6. It has a efficiency of 25%.

7. Its braking arrangements are simple.

DISADVANTAGES

1. The diesel engine has a shorter life span.

2. Overload capacity is very much limited.

3. Maintenance and maintenance costs are fairly high.

4. Cooling systems are needed for diesel engine as well as for the motor generator set.

4. BATTERY – ELECTRIC SYSTEM

In this system vehicle carries batteries which run d.c. motors used for driving the vehicle. This system is not suitable for railways.

It is mainly used in mines, ports and large factories.

The batteries are connected in parallel for starting and running half of the maximum speed.

The batteries are connected in series for running at maximum speed.

ADVANTAGES

1. Low maintenance cost.

2. convenient to use.

3. Pollution free.

DISADVANTAGES

1. The major disadvantage is limited capacities of the batteries and the problem of charging them frequently.

ELECTRIC TRACTION - PART – 10 - COEFFICIENT OF ADHESION & THREE PROBLEMS

COEFFICIENT OF ADHESION

This is the ratio of the tractive effort force just necessary slip the wheels on the track to the adhesive weight.

It reduces with increase in the speed.

It is represented as μ.

μ = tractive effort to slip wheels/adhesive weight

It is usually less than one.

The normal value of μ with dry rails is 0.25 and maximum value is 0.3 when the track has been cleaned well.

If the rails are wet or greasy the value lies between 0.5 to 0.2

IMPORTANCE OF COEFFICIENT OF ADHESION

There is a minimum value of tractive effort at which driving wheels will not slip and the maximum value depends upon the dead weight over the driving axles. [Axle means a shaft on which a wheel rotates]

F is directly proportional to W

F = μ W [if ‘F’ is Newton and ‘W’ in ton]

F = μ 98.1 W in Newton

This means to haul (draw slowly or heavily) a train, there is a certain minimum weight of locomotive. Again, the maximum allowable weight on each driving axle is limited by the strength of track bridges etc., to between 15 and 30 ton.

TRAILING WEIGHT

That part of the weight of the locomotive engine which rests upon the rear pair of driving-wheels.

PROBLEM – 01

A locomotive accelerates a 400 ton train up a gradient of 1m in 100 at 0.8 kmphps. Assuming the coefficient of adhesion to be 0.25, determine the minimum adhesive weight of the locomotive. Assume train resistance 40 N per ton and allow 10 percent for the effect of rational inertia.

PROBLEM – 02

A train weighing 250 ton is accelerated up a one percent gradient with an acceleration of 1 kmphps. Determine the minimum adhesive weight of a locomotive for this purpose if the coefficient of adhesion is 0.2. Assume train resistance as 50 N/t and allowance for rotational inertia 10 percent.

PROBLEM – 03

A goods train weighing 300 ton is to be hauled by a locomotive up a gradient of 1% with an acceleration of 1 kmphps coefficient of adhesion 20% track resistance 45 N/t and effective masses 10% of dead weight. If axle load is not to exceed 20 ton determine the weight of locomotive and number of axles. 

ELECTRIC TRACTION – PART – 09 - SPECIFIC ENERGY OUTPUT AND ENERGY CONSUMPTION & TWO PROBLEMS

PROBLEM -01

An electric train has an average speed of 42 km per hour on a level track between stops 1500 m apart. It is accelerated at 1.7 kmphps and braked at 3.3 kmphps. Draw the speed-time curve and estimate the specific energy consumption.

Assume tractive resistance as 50 N/ton and allow 10% for rotational inertia.

PROBLEM -02

A 400 ton electric train runs up an ascending gradient of 1% with the following curve.

1. Uniform acceleration of 1.6 km/hr./sec. for 25 sec.

2. Constant speed for 50 sec.

3. Coasting for 30 sec.

4. Braking at 2.56 km/hr./sec.

Calculate the specific energy consumption if train resistance is 50 N/ton, effect of rotational inertia 10%, overall efficiency of transmission gear and motor 75%. 

ELECTRIC TRACTION – PART – 08 – QUADRILATERAL SPEED TIME CURVE & TWO PROBLEMS

PROBLEM -01

The following data relate to a 200 ton electric train running according to the following quadrilateral speed-time curve.

(1) Uniform acceleration from rest to the at 2kmphps for 30 sec.

(2) Coasting retardation for 50 sec.

(3) Duration of braking 15 sec.

(4) Up gradient – 1%

(5) Train resistance – 40 T/ton

(6) Overall efficiency of gear and motor – 75%

Find the schedule speed.

PROBLEM -02

An electric train accelerates uniformly from rest to a speed of 50 km/hr. It the coasts for 70 seconds against a constant resistance of 60 N/t and is then braked to rest with uniform retardation of 3 kmphps in 15 sec. Calculate 
(1) Uniform acceleration

(2) Coasting retardation

(3) Schedule speed if station stops are of 25 sec. duration. 
Allow 10% for rotational inertia. 

How will the schedule speed the affected if duration of stops is reduced to 20 seconds, other factors remaining the same?

ELECTRIC TRACTION - PART - 07 - TRAPEZOIDAL SPEED TIME CURVE & FOUR PROBLEMS

PROBLEM - 01

An electric train has an average speed of 50 km per hour on  a level track between stops 1500 m apart. It is accelerated at 1.7 kmphps and is braked at 3.3 kmphps. Draw the speed-time for the run.

PROBLEM - 02

An electric train is to have acceleration and braking, retardation of 0.8 kmphps and 3.2 kmphps respectively. if the ratio of maximum to average speed is 1.3 for stops of 30 sec.Find schedule speed for a run of 1.5 km. Assume simplified trapezoidal speed-time curve.

PROBLEM - 03

An electric train has a schedule speed of 25 km per hour between station 800 m apart. The duration of stop is 25 seconds, the maximum is speed is 20 percent higher than the average running speed and braking retardation is 3 kmphps. calculate the rate of acceleration required to operate this service.

PROBLEM - 04

A suburban electric train has a maximum speed 70 km per hour. The schedule speed including a station stop of 20 seconds is 45 kmph. If the acceleration is 3.5 kmphps, find the value of retardation when the average distance between stops is 4 km.

ELECTRIC TRACTION – PART – 06 - IMPORTANT TERMS IN TRACTION AND TWO PROBLEMS

DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT

DISTANCE is a scalar quantity that refers to "how much ground an object has covered" during its motion.

DISPLACEMENT is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.

DIFFERENCE BETWEEN SPEED AND VELOCITY

SPEED – The rate of change in distance with respect to time.   Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity.  This means it carries no direction information with it.

VELOCITY – The rate of change in displacement with respect to time.  Since displacement is a vector quantity, then velocity is also a vector quantity.  It has both magnitude and direction.

Both speed and velocity are typically measured in units of miles per hour, kilometers per hour (Km/hr), or meters per second (m/s).

INSTANTANEOUS SPEED

The speed at any given instant in time.

CREST SPEED OR PEAK SPEED

This is the maximum speed of the train during a run.

AVERAGE SPEED

This is the average speed of a train during a run. It is equal to the total distance divided by the total time.

Average speed = total distance covered / total time taken

SCHEDULE SPEED

This is the ratio of the distance between two destinations and the total time to cover the distance, including time wasted in stoppages.

Schedule speed = Distance / [time for run + time for stop]

FACTORS AFFECTING SCHEDULES SPEED

(a) Peak speed                 (c) Braking retardation

(b) Acceleration               (d) Duration of stoppages.

PROBLME - 01

A train has a speed of 60 km/hr. between two stops, 5 km apart. The duration of stop is one minute. The acceleration and retardation are 2 km/hr./sec. and 3 km/hr./sec. respectively. Calculate the maximum speed of the train.

PROBLME - 02

A train is required to run between two stations 1.5 km apart at the average speed of 40 km/hr. The run is to be made to a simplified quadrilateral speed-time curve. If the maximum speed is to be limited to 60 km/hr. acceleration to 2 km/hr. /sec. and coasting and braking retardation of 0.16 km/hr./sec. and 3.2 km/hr./sec. respectively. Calculate the duration of acceleration, coasting and braking periods.