How Does Electric Tractions Works? Question and Answer

Electric Traction Theory
Steam Locomotive, Diesel Engines, Electric traction, Advantages, Electrical transmission, which is usually applied to high power units, has following advantages, The Direct and Alternating Current.

what is electric traction?
electric Traction means to use electic motors for railway service, Act of drawing or being drawn is known as traction.If electric supply is used for driving a locomotive, the system is known as electric traction.Electric traction may be A.C. or D.C. powered.e.g.600V dc is given to tramways and trolley buses.

ELECTRIC TRACTION
The electric locomotive and electric motor coach may be regarded as natural developments that have followed steam traction. New conditions have set new standards in railway travel. This is exemplified in the rapid development of electric suburban train services for the new built-up areas spreading in all directions round large cities.

Electric Traction Drives
This page describes the way electric motors on locomotives and multiple units drive the axles and wheels. See also the Electronic Power, Multiple Unit Operation, DC Traction Motor Systems and Electric Traction Glossary pages.

Answer tips/answer samples of What is electric traction?
Electric traction systems use DC motors, but nowadays, some people tend to use magnetic traction instead of electric ones.

ELECTRIC TRACTION FOR AUTOMOBILES - Free PDF download
a comparison concerning electric traction drives for passenger cars is given. Electric traction drives presently available on the market are analyzed and future developments are described.

Power Supply Installation in Electric Traction - Free PDF download
The book on "Power Supply Installation in Electrical Traction" was brought out by Institution of Railway Electrical Engineers (IREE) long back. Since, lot of changes have taken place in the field of Power Supply Installation, it has become necessary to incorporate the changes in this volume. Few additions and modifications in the field of Power Supply Installations are included in this book.

Question and Answer of Electric Traction

1. Overall efficiency of steam locomotive system is close to answer 5 to 10 percent
2. Maximum horse power of steam locomotive is answer 1500
3. The efficiency of diesel locomotives is nearly answer20 to 25 percent
4. The range of horsepower for diesel locomotives is 1500 to 2500
5. What motor is used in tramways? answer DC series motor
6. The advantages of electric braking is It prevents wear of track
7. What is the braking system on the locomotives answer Regenerative breaking on electric locomotives
8. What is the coefficient of adhesion highest? when answer the rails are dry
9. The estimated speed of the train, including the time of stop at a station, in addition to the actual running time between stops, is called its answer Schedule speed
10. Which of the following types of services consume the least specific energy? Main line service
11. Locomotives have two bogies with two driving axles with individual drive motors.
12. A composite system is made up of answer single phase power received is converted into DC or three phase power AC system
13. For 600 volts DC line for tram cars what is the correct voltages Track are connected to negative of the supply
14. Free running and coasting periods are generally long in case of which of the following services? answer Main line service
15. A train runs at an average speed of 50 kmph between stations situated 2.5 km apart. The train accelerates at 2 kmph and retards at 3 kmph. Speed time curve may be assumed to be trapezoidal. The maximum speed with these parameters will be answer 57.75kmph
16. Suri transmission is answer Hydro mechanical
17. When a locomotive for Indian Railways is designed as WAMI, what does the letter W indicate? answer The locomotive is to run on broad gauge track
18. The main differece between speed time curve of main line service as compared to suburban services lies in answer longer free running periods, longer coasting periods and shorter acceleration and braking periods

Transformer Built In Protection and Cooling Tutorials

Protection Devices Built In For Safe Operation of A Transformer

Conservator

It is a sort of a drum, mounted on the top of transformer. A level indicatoris fixed to it. Conservator is connected through a pipe to the transformer containing oil. This oil expanse and contracts depending upon the heat produced so the oil level in the conservator rises and falls. Pipe connected to the conservator is left open to the atmosphere through a breather so that extra air any go out or come in.

Breather

Is is a box containing calcium chloride to absorb moisture of air entering the conservator as it sis well known fact that the insulating property of the transformer oil is lost even if a small amount of moisture enters in it, so the dry air is allowed to pass in through this breather.

Temperature Gauge

It is fitted to a transformer which indicates the temperature of transformer oil.Explosion Vent

It protects the transformer tank from the gases induced by any type  of short circuit in the transformer.

Pipes

These are fitted for cooling the transformer oil. The hot oil circulates through these pipes where it becomes cool due to the air touching.

Important Facts About Transmission and Distribution Transformer

1. Eddy current losses in a transformer are minimised by laminating the core, the lamination being insulated from each other by a light coat of core plate varnish.

2. The basic property of the transformer is that it changes the voltage level of an alternating current signal without changing power, frequency or shape.

3. The primary and secondary voltages are 180 degree out of phase in transformer.

4. Eddy current lossesin transformer core are reduced by decreasing the thickness of laminations.

5. The resistance of low voltage side of a transformer is less than the resistance of its high voltage side.

6. The efficiency of a transformer is normally in the range of ninety ot ninety eight percent.

7. The reactance of transformer is determined by its leakage flux.

8. The principle of working of a transformer is mutual induction.

9. Transformer is used to change the valuesof voltage.

10. The path of the magnetic flux in a transformer has low reactance.

11. Electric power is transformed from one coil to the other coil in a transformer magnetically.

12. Ideal transformer assumptions do not include zero reactance of windings.

13. Preferably, the resistance between the primary and the secondary of a transformer should be as low as possible.

14. The main function of the iron core in a transformer is to decrease the reluctance of the magnetic path.

15. Magnetic circuit is common in the two windings of a transformer.

16. A transformer operates at power factor depending on the power factor of the load.

17. The lamination are made from nickel alloy steel stampings.

18. The steel for construction of transformer core is made so as to have high permeability and low hysteresis.

19. The special silicon stell in used for laminations because hysteresis losses are reduced.

20. Power transformer are designed to have maximum efficiency at near full load.

Cooling Of Transformer

Natural Cooling

The cooling is provided through natural circulation of air. The surface area of the core and the transformer winding are sufficient to dissipate the heat generated. It is used for small transformer from ten kva to fifteen kva.

Natural Oil Cooling

The transformer is placed in tank filled with oil known as transformer oil. The oil used in the tank not only helps cooling the transformer but also provides insulating for the winding. The oil takes the heat produced by the transformer, the oil circulate through the pipes and tank. The hot oil becomes lighter in weight and goes up from where comes down through pipes to the bottom of the tank after cooling. The oil level should never fall below the upper ends of pipes.

Oil Blast Cooling

In this method radiator tanks are provided to the side walls of the main tank. The oil circulators through these radiators from the main tank. The radiator tanks are cooled by air blast. The system of cooling is known as oil blast type. It is used for transformer rated above five hundred kva.

Force Water Cooling

The winding of transformer is placed inside the tank containing oil and cold water is passed through the copper pipe spiral kept in the transformer oil. The cold water absorbs and carrier away the heat of the oil. The pressure of the water is not kept greater than the pressure of the oil in the tank because in case of leakage in the pipe, the water will enter into the oil. It is used for transformer having output greater than five hundred KVA.

Force Air Cooling

In this method the air is first filtered to eliminate moisture and dust particless and this filetered air under pressure is forced to passed through the winding care of the transformer and the dusts provided in them. This method is used where there 

is a scarcity of water.

Power Transformer Tutorials Links

Tutorials on Electrical Power Factor Correction

All About Power Factor Links

Power Factor Meter
A direct reading instrument for measuring power factor. It is provided with a scale graduated in power factor.

Power Factor Relay
Power system device function numbers. A relay that operates when the power factor in an alternating current circuit rises above or falls below a predetermined value.

Power Feeder
A feeder supplying principally a power or heating load.

Power Frequency
The value of frequency used in the Electrical power system, such as 50 hz or 60 Hz.

Power Inverter
A converter unit in which the direction of average power flow in from the DC circuit to the alternating circuit.

Power Monitor
A functional module that monitors the status of the primary power source to the system, and signals when that power has strayed outside the limits required for reliable system operation. Since most systems are powered by an alternating current source, the power monitor is typically designed to detect dropout or
brown out conditions on alternating current lines.

Power Factor Question and Answer

1. If a current of 10 amperes at a power factor of 0.8 lagging is taken from 250 Volt alternating current supply, the reactive power of the system will work out to be 1500 VAR.
2. Many industrial tariffs penalise consumers whose power factor falls below 0.8.
3. Power factor improvement may be achieved the use of synchronous motor.
4. One of the reasons for improving the power factor is to decrease the reactive power.
5. The power factor of incadescent bulb is unit.
6. The power facotor of an inductive circuit can be improved by connecting a capacitor to it in series.
7. The capacitor of power factor correction are rated in terms of KVAR.
8. In an alternating current circuit, a low value of with reactive volt ampere compared with watts indicates high power factor.
9. It is not easy to find the value of impedance for a parallel circuit but power factor can easily be obtained as a ratio of active current to line current.
10. In a series circuit consisting of resistance and reactance, power factor is a defined as the ratio of resistance to impedance.
11. In pure reactive circuit, the power factor is zero.
12. Power factor is defined as the ratio of watts to volt ampere.
13. For a parallel circuit consisting of resistance and reactance the value of power factor is the ratio of impedance to resistance.
14. The power factor of an alternating current circuit containing both a resistor and a conductor is between 0 - 1 leading.
15. In a given circuit when power factor is unity the reactive power is zero.
16. A poor power factor results in overloading of transformer as well as alternators.
17. For the same load, if the power factor of load is reduced, it will draw more current.
18. The power factor of the magnetizing component of a transformer is always leading.
19. Another reason for improving the power factor is to avoid poor voltage regulation.
20. The advantage of using static capacitors to improve the power factor is that they are almost loss free.

Causes of Low Power Factor
1. Arc lamps and industrial heating furnaces are typical of low power factor operating equipments.
2. During the night time when load is less the supply voltage increase which in turn, causes the magnetising current of transformers and motors to increase. Therefore, the power factor at which the system operates becomes low.
3. Mostly alternating current motors are of induction type. These operate on low lagging power factor.

The Adverse of Low Power Factor
1. With low p.f. cost of generation and transmission increases due to increase in current and use of thicker wires and bigger switches.
2. Low pf. makes the voltage regulation of generators, transformer and transmission line greater.
3. For a given p.f. to be supplied, the current is increased due to low p.f. in causes increase in copper losses, and decreases the efficiency of both apparatus and supply system.
4. With low pf generators, transformer, swithes transmission lines become over loaded.

Electrical Transformer tutorials Current Potential and Auto tutorials

Current Transformers The primary of this transformer consists of a few turns or even a single turn to carry the current to be measured and is connected in series with the main circuit. The secondary winding with large number of turns supplies a reduced current to the ammeter. The meter scale is calibrated directly in terms of the primary circuit current.The core is worked at low flux density so that, at all loads, secondary current is a constant ratio of the main circuit current. When the cuurent is flowing in the primary circuit, the secondary circuit should not be opened. In that case high voltage may be induced in the secondary and the core may become over saturated, heated up and thereby damage the magnetic properties permanently.

Potential Transformer
This is used to reduce the primary voltage to a safe value for operation of voltmeter and other instrument. Primary is connected to the H.T. to be measured and the secondary to a voltmeter. It is so designed that the ratio of primary to secondary is constant throughout. To limit the short circuit in case of failure of the transformer, limiting resistances are placed in series with the H.T. winding.

Auto-transformer works on the priciple of self Induction
It has only one winding which performs the function of both primary and secondary winding. As in ordinary transformer, the transformation ratio in autotransformer, is also equal to the turns ratio.
In case of step down transformer, the complete winding acts as primary winding while the tapped section of this winding works as secondary winding. In the step up transformer, the whole winding works as secondary winding and its there is much saving of copper. These transformers are used as regulating transformers where only a small variation of voltage is required. It is mainly used for starting and speed control of induction motors. It suffers from a disadvantage that the two windings are not electrically separate and in case of failure of insulation between the two, either a sever shock may be felt on the low voltage side.

Various parts of a Transformer
Primary winding
Secondary winding
Oil level
Conservator
Breather
Drain cock
Tube for cooling
Transformer Oil
Earth Point
Explosion vent
Buchhol's Relay
H.T. Terminals
L.T Terminals


Free Pdf file about the kinds of Transformer

Current Transformers
Current transformers are used in electrical grids for measurement and protective applications to provide signals to equipment such as meters and protective relays by stepping down the current of that system to measurable values.

Instrument Transformers
Technical Information and Application Guide

Selecting Current Transformers
As engineers, we are aware that electrical power systems have grown. How much have they grown?

Current Transformer Principles and Operation
Used with watt transducers enable the owner to control demand as well as monitor building and/or tenant power consumption. When CT's are used with Current Transducers, the result is an excellent method of diagnosing the performance of fans,pumps, chillers.

Potential Transformer
Voltage transformers connected line-to-ground cannot be considered to be grounding transformers and must not be operated with the secondaries in closed delta because excessive currents may flow in the delta.
VOLTAGE TRANSFORMERS
Potential transformer are so small that they may be neglected for protective-relaying purposes if the burden is within the "thermal" volt-ampere rating of the transformer. This thermal volt-ampere rating corresponds to the full-load rating of a power transformer.

Auto Transformer
The currents drawn by these two windings are out of phase by 180◦. This prompted the use of a part of the primary as secondary. This is equivalent to fusing the secondary turns into primary turns.

Transformers vs. Autotransformers
A transformer converts audio from one voltage and impedance to a different voltage and impedance. Transformers are passive which means they do not require a  power supply to operate.

All About Electrical Distribution and Power Transformer Tutorials

This is All About Transformer its principles, Definition, Testing Facts and Tutorials

Transformer Classification

Transformer Definition
It is a static device for transforming electrical energy from one alternating current circuit to another without any change in frequency. It changes voltage from high to low and low to high with a corresponding increase or in decrease current. If the voltage is increased it is said to be stepped up. If it is decreased, then it is said as stepped down.

Electrical Transformer Principle
When one coil like primary is connected to the alternating current supply current flows and an alternating flux is set up in the core. Most of this flux links with the second coil secondary. Law of electromagnetic induction.If the circuit is completed, current will flow. The secondary voltage depends upon the ratio of secondary turns to primary turns.

The Testing of the Transformer

Two test are performed on the transformer which are open circuit test and short circuit test. These tests are performed to determine the parameter or constants of transformer, efficiency and regulation.

1. Open Circuit Test
This is also called no load test. It determined the iron losses and the no load current. One winding of the transformer, usually the low voltage side is connected to its normal supply with an ammeter to measure the voltage applied to the winding and a wattmeter to measure taken by transformer at no load. the high voltage winding is kept open. Under these conditions normal flux will be set up in the core, therefore, normal iron losses will occur. The current taken will be wattmeter will indicate the iron losses.

2. Short Circuit Test
This test is used to determine the full load copper losses and the equivalent resitances and reactances referred to the metering side. In this test on the high voltage winding a reduced value of the voltage is increased until full load current is flowing in this winding. The applied voltage is a small fraction of the normal working voltage, the mutual flux produced is very small and hence the core losses at this voltage can be neglected. The wattmeter during this test gives the total coppery losses.

What is Distribution Transformer?
Transformer up to a size of 200 KVA, used to step down the distribution voltage to a standard service voltage, are known as distribution transformers. They are kept in operation all the 24 hours a day whether they are carrying load or not. Energy is lost in iron losses throughout the day while the copper losses account for loss in energy when the transformer is loaded. Therefore, the distribution transformer should have their iron losses small as compared to full load copper losses, in other words, they should be designed to have maximum efficiency at a load much lower than full load about 50 percent. Owing to low iron loss, the distribution transformer have good all day efficiency. These transformer have a good voltage regulation.

What is Power Transformer?
These transformers have rating about 20 KVA and are in generating stations and substations at each of a power transmission line for stepping up or stepping down the voltage. They may be either single or three phase units. They are put in operation during load periods and are disconnected during light load periods. Therefore the power transformer should be designed to have maximum efficiency at or near full load. Power transformer are designed to have considerable greater leakage reactance than that permissible in distribution transformers because in the case of power transformer, voltage regulation is less important than current limiting effect of higher leakage reactance.

Important Facts About Transformer
1. In and ideal transformer on no load, the primary applied voltage is balanced by the secondary.
2. The concentric windings are used in core type transformer with LT winding placed next to core.
3. Cross over windings are used for high voltage winding of small rating transformers.
4. The magnitude of mutual flux in a transformer is same at all levels.
5. The induced emf in the transformer secondary will depend upon frequency, flux and number of turns in the secondary.