Parts of a Power transmission line and Transmission tower

February 19, 2016


Transmission line parts


1. Insulator.
2. Bundle of two conductors (some lines have 4).
3.Spacer to hold the two conductors apart.
4. Earth wire at top of tower or pylon.
5. The three bundles on one side of the tower make up one electrical circuit. Most lines have two circuits, one each side.
6.Identity plate saying which line it is and who owns it.  Also usually has a safety warning notice about the dangers of electrocution.

7.Anti-climbing device - barbed wire to stop unauthorised climbing

Transmission tower -

A power transmission tower consists of the following parts, 1) Peak of transmission tower 2) Cross arm of transmission tower 3) Boom of transmission tower 4) Cage of transmission tower 5) Transmission Tower Body 6) Leg of transmission tower 7) Stub/Anchor Bolt and Base plate assembly of transmission tower. The main parts among these are shown in the pictures.

Types of Transmission Tower

According to different considerations, there are different types of transmission towers. The transmission line goes as per available corridors. Due to unavailability of shortest distance straight corridor transmission line has to deviate from its straight way when obstruction comes. In total length of a long transmission line there may be several deviation points. According to the angle of deviation there are four types of transmission tower- 1. A – type tower – angle of deviation 0o to 2o. 2. B – type tower – angle of deviation 2o to 15o. 3. C – type tower – angle of deviation 15o to 30o. 4. D – type tower – angle of deviation 30o to 60o.

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Difference between earthing and grounding

February 19, 2016



Grounding is the commonly word used for earthing in the North American standards like IEEE, NEC, ANSI and UL etc while, Earthing is used in European, Common wealth countries and Britain standards like IS and IEC etc.
Ground is a source for unwanted currents and also as a return path for main current. While earthing is done not for return path but only for protection of delicate equipments. It is an alternate low resistance path for current. Earth is used for the safety of the human body in fault conditions while Grounding (As neutral earth) is used for the protection of equipments.

Earthing:
·         Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth for example electrical equipment’s frames, enclosures, supports etc.
·             The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present. Generally green wire is used for this as a nomenclature.
·            Under fault conditions the non-current carrying metal parts of an electrical installation such as frames, enclosures, supports, fencing etc. may attain high potential with respect to ground so that any person or stray animal touching these or approaching these will be subjected to potential difference which may result in the flow of a current through the body of the person or the animal of such a value as may prove fatal.
·            To avoid this non-current carrying metal parts of the electrical system are connected to the general mass of earth by means of an earthing system comprising of earth conductors to conduct the fault currents safely to the ground.
·             Earthing has been accomplished through bonding of a metallic system to earth. It is normally achieved by inserting ground rods or other electrodes deep inside earth.
·          Earthing is to ensure safety or Protection of electrical equipment and Human by discharging the electrical energy to the earth.

Grounding:

·         Grounding means connecting the live part (it means the part which carries current under normal condition) to the earth for example neutral of power transformer.
·         Grounding is done for the protections of power system equipment and to provide an effective return path from the machine to the power source. For example grounding of neutral point of a star connected transformer.
·         Grounding refers the current carrying part of the system such as neutral (of the transformer or generator).
·              Because of lightening, line surges or unintentional contact with other high voltage lines, dangerously high voltages can develop in the electrical distribution system wires. Grounding provides a safe, alternate path around the electrical system of your house thus minimizing damage from such occurrences.
·           Generally Black wire is used for this as a nomenclature.

All electrical/electronic circuits (AC & DC) need a reference potential (zero volts) which is called ground in order to make possible the current flow from generator to load. Ground is May or May not be earthed. In Electrical Power distribution it is either earthed at distribution Point or at Consumer end but it is not earthed in Automobile( for instance all vehicles’ electrical circuits have ground connected to the chassis and metallic body that are insulated from earth through tires). There may exist a neutral to ground voltage due to voltage drop in the wiring, thus neutral does not necessarily have to be at ground potential.

In a properly balanced system, the phase currents balance each other, so that the total neutral current is also zero. For individual systems, this is not completely possible, but we strive to come close in aggregate. This balancing allows maximum efficiency of the distribution transformer’s secondary winding


The small difference between earthing and grounding concept is:-


§  There is no major difference between earthing and Grounding, both means “Connecting an electrical circuit or device to the Earth”. This serves various purposes like to drain away unwanted currents, to provide a reference voltage for circuits needing one, to lead lightning away from delicate equipment. Even though there is a micro difference between grounding & earthing.


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Ho to make earth pit and do earthing in home

February 19, 2016

How to make earth pit.





1. Excavation on earth for a normal earth Pit size is 1.5M X 1.5M X 3.0 M 

2. Use 500 mm X 500 mm X 10 mm GI Plate (Plate may be use as big as possible to contact more and more area of Earth for low resistance & best result) 

3. Make a mixture of Wood Coal Powder Salt & Sand all in equal part 
(a) Wood Coal Powder use as good conductor of electricity, anti corrosive, rust prove for GI Plate for long life. 
(b) Salt use as electrolyte to form conductivity between GI Plate Coal and Earth with humidity 
(c) Sand has used to form porosity to cycle water & humidity around the mixture 

4. Put GI Plate (EARTH PLATE) of size 500 mm X 500 mm X 10 mm in the mid of mixture 

5. Use Double GI Strip size 30 mm X 10 mm to connect GI Plate to System Earthling 

6. It will be better to use GI Pipe of size 2.5" diameter with a Flange on the top of GI Pipe to cover GI Strip from EARTH PLATE to Top Flange 

7. Cover Top of GI pipe with a T joint to avoid jamming of pipe with dust & mud and also use water time to time through this pipe to bottom of earth plate 

8. Maintain less than one Ohm Resistance from EARTH PIT conductor to a distance of 15 Meters around the EARTH PIT with an other conductor dip on the Earth at least 500 mm deep. 

9. Check Voltage between EARTH PIT conductor to Neutral of Mains Supply 220V AC 50 Hz it should be less than 2.0 Volts 
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How to make an extension box

February 19, 2016
Here, I am going to discuss about how to make an extension box , containing 3 switchess and three plug sockets. The circuit lay out is as shown below.
Wiring diagram of extension box
Main requirements
  1. Switch Board
Switch board is a board made up of either wood or plastic (PVC) and is meant for mounting
switches and sockets.

      2. Mounting of Switches and Sockets
The procedure of cutting of holes of appropriate size and fixing of switches and sockets on switch
board is known as mounting of switches

3. Wiring of Switch Board
The procedure of making electrical connections to switches and sockets according to the wiring
diagram is known as wiring of switch board.


Apparatus:
  • Switch board of appropriate size, 
  • Three single pole (SP) switches (250 V, 5 A),
  •  3 three pin socket ( 250 V, 5 A),
  • 1/ 18 SWG wire, 
  • Screw driver set, 
  • Pliers,
  •  Insulation stripper, 
  • Test lamp, etc.

 Stepwise Procedure:

1. Mark the positions of switches and socket on the switch board.
2. Cut the holes on the switch board for housing switches and socket, as per marking.
3. Fix the switches and socket on the switch board.
4. Make the wiring of switch board as per wiring diagram.
5. Also, connect proper earthing connection as per wiring diagram.
6. Make sure that all the connections are as per wiring diagram and are tight.
7. Test the switch board




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Signals and Systems Notes-1

January 18, 2016
What is Signal?
Signal is a time varying physical phenomenon which is intended to convey information.
OR
Signal is a function of time.
OR
Signal is a function of one or more independent variables, which contain some information.
Example: voice signal, video signal, signals on telephone wires etc.
Note: Noise is also a signal, but the information conveyed by noise is unwanted hence it is considered as undesirable
What is System?
System is a device or combination of devices, which can operate on signals and produces corresponding response. Input to a system is called as excitation and output from it is called as response.
For one or more inputs, the system can have one or more outputs.
Example: Communication System
white'>Signal is a function of one or more independent variables, which contain some information.

Example: voice signal, video signal, signals on telephone wires etc.
Note: Noise is also a signal, but the information conveyed by noise is unwanted hence it is considered as undesirable

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SHORT CIRCUIT CHARACTERISTICS OF AN ALTERNATOR

January 18, 2016
The three terminals of the armature are short circuited .


The machine is driven at approximately synchronous rated speed and measurements of armature short circuit currents are made for various values of field currents usually up to and above rated armature current.
The machine is driven at approximately synchronous rated speed and measurements of armature short circuit currents are made for various values of field currents usually up to and above rated armature current.


In conventional synchronous machines the short circuit characteristics is practically linear because the iron is unsaturated up to rated armature current
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Open Circuit Characteristics (OCC) of an Alternator

January 18, 2016
To obtain the open circuit characteristics the machine is driven at rated speed without the load. Readings of the line-to-line voltage are taken for various values of field current. The voltage, except in very low voltage machines, is stepped down by the means of a potential transformer.

Experimental set up-

OCC




If not for the magnetic saturation of the iron, the open circuit characteristics would be linear as represented by the air gap line.


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Three phase alternator

January 18, 2016

The three-phase alternator has three single-phase windings spaced so that the voltage induced in any one is phase-displaced by 120 degrees from the other two.
The voltage waveforms generated across each phase are drawn on a graph phase-displaced 120 degrees from each other.
•The three phases are independent of each other.
•One point from each winding can be connected to form a  neutral and thus make a wye connection.
•The voltage from this point to any one of the line leads will be the phase voltage. The line voltage across any two line leads is the vector sum of the individual phase voltages. The line voltage is 1.73, (Ö3 ), times the phase voltage.
Since the windings form only one path for current flow between phases, the line and phase currents are equal.
A three-phase stator can also be connected so that the phases form a “delta” connection.
•In the delta connection the line voltages are equal to the phase voltages, but the line currents will be equal to the vector sum of the phase currents.
•
•Since the phases are 120 degrees out of phase, the line current will be 1.73, (Ö3 ), times the phase current. Both "wye" and the "delta" connections are used in alternators.
•The frequency of the AC generated by an alternator depends upon the number of poles and the speed of the rotor.
•When a rotor has rotated through an angle so that two adjacent rotor poles (a north and a south) have passed one winding, the voltage induced in that one winding will have varied through a complete cycle of 360 electrical degrees.
•A two pole machine must rotate at twice the speed of a four-pole machine to generate the same frequency.
The magnitude of the voltage generated by an alternator can be varied by adjusting the current on the rotor which changes the strength of the magnetic field.
•A two pole alternator produces one electrical cycle for each complete mechanical rotation.
A four pole alternator will produce two electrical cycles for each mechanical rotation because two north and two south poles move by each winding on the stator for one complete revolution of the rotor.
f = (nRotor)(p/2)/60 = (nRotorp)/120
where   nRotor is the speed of the rotor in revolutions per minute,
  p is the number of poles
  f is the electrical line frequency produced by the alternator.
In an alternator the output voltage varies with the load.
•There are two voltage drops.{ IR & IXL }
•The IXL drop is due to the inductive reactance of the armature windings.
Both the IR drop and the IXL drop decrease the output voltage as the load increases.
•The change in voltage from no-load to full-load is called the “voltage regulation” of an alternator.
•A constant voltage output from an alternator is maintained by varying the field strength as required by changes in load.

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Single phase alternator

January 18, 2016




The two poles of the stator winding are connected to each other so that the AC voltages are in phase, so they add.As the rotor (field) turns, its poles will induce AC voltages in the stator (armature) windings. Since one rotor pole is in the same position relative to a stator pole as any other rotor pole, both the stator poles are cut by equal amounts of magnetic lines of force at any time. As a result, the voltages induced in the two poles of the stator winding have the same amplitude or value at any given instant. 

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Electrical Degree and Mechanical degree in Synchronous machines

January 18, 2016
Angle in Electrical and Mechanical Units

Consider a synchronous machine with two magnetic poles. The idealized radial distribution of the air gap flux density is sinusoidal along the air gap. When the rotor rotates for one revolution, the induced emf, which is also sinusoidal, varies for one cycle as illustrated by the waveforms in the diagram below. If we measure the rotor position by physical or mechanical degrees or radians and the phase angles of the flux density and emf
by electrical degrees or radians, in this case, it is ready to see that the angle measured in mechanical degrees or radians is equal to that measured in electrical degrees or radians, 
i.e.
                                           Î¸=θm
where Î¸   is the angle in electrical degrees or radians and θm   the mechanical angle.
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Construction of Synchronous Machines

January 18, 2016

Stator and Rotor

The armature winding of a conventional synchronous machine is almost invariably on the stator and is usually a three phase winding. The field winding is usually on the rotor and excited by dc current, or permanent magnets. The dc power supply required for excitation usually is supplied through a dc generator known as exciter, which is often mounted on the same shaft as the synchronous machine. Various excitation systems using ac exciter and solid state rectifiers are used with large turbine generators.
    There are two types of rotor structures: round or cylindrical rotor and salient pole rotor as illustrated schematically in the diagram below. 
1- Non salient pole , 2- Salient pole 


Generally, round rotor structure is used for high-speed synchronous machines, such as steam turbine generators, while salient pole structure is used for low-speed applications, such as hydroelectric generators. The pictures below show the stator and rotor of a hydroelectric generator and the rotor of a turbine generator.


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Synchronous Machines

January 18, 2016

1 Introduction
With the development of the technology and the way in which human labour is get-ting minimized and the comforts increasing tremendously the use of electrical energy is ever increasing. Basically electric power is the main source of energy for carrying out many func-tions, as it is a clean and efficient energy source, which can be easily transmitted over long distances. With the availability of Transformer for changing the voltage levels to a very high value (of say 132kV to 400kV) the use of AC power has increased rapidly and the DC power is used only at remote places where AC power cannot be supplied through power lines or cables or for a few social purposes. A synchronous generator is an electrical machine producing alternating emf (Elec- tromotive force or voltage) of constant frequency. In our country the standard commercial frequency of AC supply is 50 Hz. In U.S.A. and a few other countries the frequency is 60 Hz. The AC voltages generated may be single phase or 3-phase depending on the power supplied. For low power applications single phase generators are preferable. The basic prin- ciples involved in the production of emf and the constructional details of the generators are discussed below.

1.1 Generation of emf

In 1831 Faraday discovered that an emf can be induced (or generated) due to relative motion between a magnetic field and a conductor of electricity. This voltage was termed as the induced emf since the emf is produced only due to motion between the conductor and the magnetic field without actual physical contact between them. The principle of electromagnetic induction is best understood by referring to Fig. 1. The magnetic field is produced by the two fixed poles one being the north pole from which the magnetic flux lines emerge and enter into the other pole known as the south pole. It was found that the magnitude of the voltage induced in the conductor is proportional to the rate of change of flux lines linking the conductor.
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Electrical Machines solved Questions-Gate 2016

January 18, 2016
MCQ 4.1 The slip of an induction motor normally does not depend on
(A) rotor speed (B) synchronous speed
(C) shaft torque (D) core-loss component

MCQ 4.2 A 220 V, 15 kW, 100 rpm shunt motor with armature resistance of 0.25 Ω,
has a rated line current of 68 A and a rated field current of 2.2 A. The
change in field flux required to obtain a speed of 1600 rpm while drawing a
line current of 52.8 A and a field current of 1.8 A is
(A) 18.18% increase (B) 18.18% decrease
(C) 36.36% increase (D) 36.36% decrease

MCQ 4.3 The locked rotor current in a 3-phase, star connected 15 kW, 4 pole, 230 V, 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 V, 57 Hz supply is
(A) 58.5 A (B) 45.0 A
(C) 42.7 A (D) 55.6 A

MCQ 4.4 A single phase 10 kVA, 50 Hz transformer with 1 kV primary winding draws 0.5 A and 55W, at rated voltage and frequency, on no load. A second transformer has a core with all its linear dimensions 2 times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformer. The primary winding of both the transformers have the save number of turns. If a rate voltage of 2 kV at 50 Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are
(A) 0.7 A, 77.8 A (B) 0.7 A, 155.6W
(C) 1A, 110W (D) 1A, 220W

MCQ 4.5 A 4 point starter is used to start and control the speed of a
(A) dc shunt motor with armature resistance control
(B) dc shunt motor with field weakening control
(C) dc series motor
(D) dc compound motor


                                                                      ANSWERS


Answers will be updated soon....
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