Basic Electrical Theory

This ppt covers basic fundamentals of Electrical engineering including several laws applicable on it.

1. Basic Electrical Theory

2. Contents:- Basic Electrical Terms. Introduction. Types of Generating stations. Single Phase & 3-Phase Supply. Star & Delta Connection. Basic Laws abbreviated for Electrical Engineering. Description of Electrical Components. Concept of Earthing System. Difference between Neutral & Earth or Ground. Difference between Switchyard & Substation.

3. 1 . Basic Electrical terms Electric Charge (Q) - Characteristic of subatomic particles that determines their electromagnetic interactions. Unit of Charge is Coulomb . Current ( I ) - The rate of flow of charged particles is called current. Current is the number of electrons that pass in one second(charge/electron). Unit of Current is Ampere . Voltage(V) - Voltage is a measure of the potential energy that causes a current to flow through a transducer in a circuit. Voltage is always measured as a difference with respect to an arbitrary common point called ground. Voltage is also known as electromotive force or EMF. Unit of Voltage is Volts . Energy - The energy is the area under the power curve. The movement of charged particles through a wire or other medium is called current or electricity. Power - The rate at which energy is transferred from an active source. P ower is the rate, per unit time, at which electrical energy is transferred by an electric circuit. Unit of Power is in Watt/Kilowatt . Switchgear - In an electric power system, switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream.

4. 2. Introduction How Electricity is generated ? Electricity is the energy generated by the movements of electrons (negative charge) and positrons (positive charge) within conductive materials. Opposites attract. Positive and negative charges come together, creating two types of energy: Static electricity (generated by friction) and dynamic electricity (known as a current). Generation:  electricity is produced in plants capable of drawing electrical energy from primary energy sources. These primary energies may be renewable (wind, solar power, tidal power, etc.) or non-renewable (coal, natural gas, oil, etc.). The companies which (fully or partly) own the various power plants sell the energy generated to companies which supply it commercially. Transmission:  once the energy has been processed and turned into electricity, it is sent through overhead or underground wires from the plants to substations. There, transformers ensure sufficient electrical voltage .  Substations tend to be above ground near to power plants, or on the outskirts of cities, though if they are not too large, they may also be within the actual city, inside a building. Distribution:  from the substations, electricity is distributed to the homes in the surrounding area. As a consumer, you cannot choose your electricity distributor; it is determined by where you live. That company is responsible for ensuring electricity reaches your home properly, and takes care of repairs when needed. It is also the company which owns your electricity meter and sends readings from it to your commercial energy supplier.

5. 3. Types of Generating Stations Hydroelectric Power stations A generating station which utilises the potential energy of water at a high level for the generation of electrical energy is known as hydroelectric power station. In a hydroelectric power station , water head is created by constructing dam across a river or lake. From dam water is led to water turbine thus captures the energy in the falling water changes the hydraulic energy into mechanical energy in the turbine shaft and the turbine drives the alternator which converts mechanical energy into electrical energy.

6. Nuclear Power Stations The generating station in which nuclear energy is converted into electrical energy is known as nuclear power station. In nuclear power station, heavy elements such as Uranium or Thorium are subjected to nuclear fission in a special apparatus known as reactor. The heat energy thus released is utilised in raising steam at high temperature and pressure. The steam runs the steam turbine which converts steam energy into mechanical energy and thus turbine drives the alternator which converts mechanical form into electrical energy.

7. Thermal Power Station A  thermal power station  is a power station  in which heat energy is converted to electric power. In most, a steam-driven turbine converts heat to mechanical power as an intermediate to electrical power. Water is heated, turns into steam and drives a steam turbine which drives an electrical generator. After it passes through the turbine the steam is condensed in a condenser and recycled to where it was heated. This is known as a Rankine cycle. thermal power stations are so designed to produce heat for industrial purposes, for district heating, or desalination of water, in addition to generating electrical power.

8. Gas Turbine Power Station A generating station which employs gas turbine as the prime mover for the generation of electrical energy is known as gas turbine power plant. In this air is used as the working fluid, the air is compressed by compressor and is led to combustion chamber where heat is added to air, thus raising the temperature. The hot and high pressure air from combustion chamber them passed to gas turbine where it expands and does the mechanical wok. The gas turbine drives the alternator which converts mechanical energy into electrical energy.

9. 4. Single Phase  Supply & 3Phase  Supply Single Phase  Supply A single-phase electric power is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Because the voltage of a single phase system reaches a peak value twice in each cycle, the instantaneous power is not constant.   Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase traction power networks may operate at 16.67 Hz A single phase system consists of just two conductors (wires): one is called the phase, through which the current flows and the other is called neutral, which acts as a return path to complete the circuit.

10. 3Phase  Supply In a symmetric three-phase power supply system, three conductors each carry an alternating current of the same frequency and voltage amplitude relative to a common reference but with a phase difference of one third of a cycle between each. The common reference is usually connected to ground and often to a current-carrying conductor called the neutral. Due to the phase difference, the voltage on any conductor reaches its peak at one third of a cycle after one of the other conductors and one third of a cycle before the remaining conductor.  This phase delay gives constant power transfer to a balanced linear load. The amplitude of the voltage difference between two phases is 3 (1.732...) times the amplitude of the voltage of the individual phases.

11. 5. Star & Delta Connection In a Star Connection, there are 4 wires: 3 phase wires and 1 neutral wire whereas in a Delta Connection, there are only 3 wires for distribution and all the 3 wires are phases (no neutral in a Delta connection). The following image shows a typical Star and Delta Connection.

12. Calculations for Star & Delta Conversion Three branches in an electrical network can be connected in numbers of forms but most common among them is either star or delta form. In delta connection, three branches are so connected, that they form a closed loop. As these three branches are connected nose to tail, they form a triangular closed loop, this configuration is referred as delta connection. On the other hand, when either terminal of three branches is connected to a common point to form a Y like pattern is known as star connection. But these star and delta connections can be transformed from one form to another. For simplifying complex network, delta to star or star to delta transformation is often required.

13. 6. Basic Laws abbreviated for Electrical Engineering Ohm's law – It states that the  current  through a  conductor  between two points is directly  proportional  to the  voltage  across the two points. Mathematically abbreviated as I=V/R , where I is Current , V is Voltage and R is Resistance . Lenz's law – Lenz’s law of electromagnetic induction states that the direction of the current induced in a conductor by a changing magnetic field (as per Faraday’s law of electromagnetic induction) is such that the magnetic field created by the induced current opposes the initial changing magnetic field which produced it. The direction of this current flow is given by Fleming’s right hand rule . Faraday Laws of Electromagnetic Induction - There are two laws according Michael Faraday :- First law - Whenever a conductor is placed in a varying magnetic field, EMF  induces  and this emf is called an  induced  emf and if the conductor is a closed circuit than the  induced  current flows through it. Second law - Faraday  discovered that when the same amount of current is passed through different electrolytes/elements connected in series, the mass of substance liberated/deposited at the electrodes is directly proportional to their equivalent weight.

14. Kirchoff’s Current Law & Kirchoff’s Voltage Lw Gustav Kirchhoff’s Current Law  is one of the fundamental laws used for circuit analysis. His current law states that for a parallel path  the total current entering a circuits junction is exactly equal to the total current leaving the same junction . This is because it has no other place to go as no charge is lost. In other words the algebraic sum of ALL the currents entering and leaving a junction must be equal to zero as:  Σ I IN  = Σ I OUT . Kirchhoff’s voltage law states that for a closed loop series path  the algebraic sum of all the voltages around any closed loop in a circuit is equal to zero . This is because a circuit loop is a closed conducting path so no energy is lost. In other words the algebraic sum of ALL the potential differences around the loop must be equal to zero as:  ΣV = 0 . 

15. Fleming’s Left Hand Rule and Fleming’s Right Hand Rule Whenever a current carrying conductor comes under a magnetic field , there will be a force acting on the conductor . The direction of this force can be found using Fleming’s Left Hand Rule (also known as ‘Flemings left-hand rule for motors’). Similarly if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor. The direction of this force can be found using Fleming’s Right Hand Rule . In both Fleming’s left and right hand rules, there is a relation between the magnetic field, the current and force. This relation is directionally determined by Fleming’s Left Hand rule and Fleming’s Right Hand rule respectively. These rules do not determine the magnitude but instead show the direction of any of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known. Fleming’s Left-Hand rule is mainly applicable to electric motors and Fleming’s Right-Hand rule is mainly applicable to electric generators. It is found that whenever a current carrying conductor is placed inside a magnetic field , a force acts on the conductor , in a direction perpendicular to both the directions of the current and the magnetic field.

16. The below reference images shows both Fleming’s Right and Left Hand Thumb Rule :

17. 7. Description of Electrical Components Resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.

18. Inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil around a core.

19. Capacitors A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals. The effect of a capacitor is known as capacitance.

20. Power Diode A power diode  is a two terminal device, where one terminal is an anode, and the second terminal is a cathode. If the anode voltage is higher than the cathode voltage, then the diode is forward biased and the forward current flows through the diode  I F . In this position the current through the power diode increases steadily and the voltage also increases. When the diode is reverse biased, only a small current flows through the diode – this is called leakage current. It can be ignored in many cases. In this position, the current is relatively negligible until some reverse voltage level occurs – this is called breakdown voltage.

21. Power Transistors The transistor which is used for controlling large voltage and current is a power BJT (bipolar transistor) also known as a power transistor . It is a current control device that operates in 4 regions cut-off, active, quasi saturation, and hard saturation based on the supplies given to the transistor. The main advantage of a power transistor is it acts as a current control device.

22. Rectifier A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known as rectification, since it "straightens" the direction of current. In half-wave rectification of a single-phase supply, either the positive or negative half of the AC wave is passed, while the other half is blocked. Mathematically, it is a  step function  (for positive pass, negative block): passing positive corresponds to the ramp function being the identity on positive inputs, blocking negative corresponds to being zero on negative inputs. Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single  diode  in a  single-phase supply , or three in a  three-phase supply . Rectifiers yield a unidirectional but pulsating direct current; half-wave rectifiers produce far more  ripple  than full-wave rectifiers, and much more filtering is needed to eliminate  harmonics  of the AC frequency from the output.

23. Power Inverter A  power inverter , or  inverter , is a  power electronic  device or circuitry that changes  direct current  (DC) to  alternating current  (AC). Output Power - A power inverter will often have an overall power rating expressed in  watts  or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Output Frequency - The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60  Hertz .  Output Voltage - The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 120 or 240 VAC at the distribution level, even when there are changes in the load that the inverter is driving.

24. Insulated Gate Bipolar Transistor(IGBT) An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating layers (P-N-P-N) that are controlled by a metal–oxide–semiconductor (MOS) gate structure. Since it is designed to turn on and off rapidly, the IGBT can synthesize complex waveforms with pulse-width modulation and low-pass filters, so it is also used in switching amplifiers in sound systems and industrial control systems. It is used in switching power supplies in high-power applications: variable-frequency drives (VFDs), electric cars, trains, variable speed refrigerators, lamp ballasts, arc-welding machines, and air conditioners.

25. Silicon Controlled Rectifier(SCR) It is a multi-layer semiconductor device, hence the “silicon” part of its name. It requires a gate signal to turn it “ON”, the “controlled” part of the name and once “ON” it behaves like a rectifying diode, the “rectifier” part of the name. In fact the circuit symbol for the  thyristor  suggests that this device acts like a controlled rectifying diode. An SCR conducts when a gate pulse is applied to it, just like a diode. It has four layers of semiconductors that form two structures namely; NPNP or PNPN. In addition, it has three junctions labelled as J1, J2 and J3 and three terminals anode, cathode and a gate. Modes of operation Forward blocking mode (off state) Forward conduction mode (on state) Reverse blocking mode (off state) Forward blocking mode In this mode of operation, the anode (+) is given a positive voltage while the cathode (−) is given a negative voltage, keeping the gate at zero (0) potential i.e. disconnected. In this case junction J1 and J3 are forward-biased, while J2 is reverse-biased, allowing only a small leakage current from the anode to the cathode. When the applied voltage reaches the break over value for J2, then J2 undergoes avalanche breakdown. At this breakover voltage J2 starts conducting, but below breakover voltage J2 offers very high resistance to the current and the SCR is said to be in the off state.

26. Silicon Controlled Rectifier(SCR) Forward conduction mode An SCR can be brought from blocking mode to conduction mode in two ways: Either by increasing the voltage between anode and cathode beyond the break over voltage, or by applying a positive pulse at the gate. Once the SCR starts conducting, no more gate voltage is required to maintain it in the ON state. There are two ways to turn it off: Reduce the current through it below a minimum value called the holding current, or With the gate turned off, short-circuit the anode and cathode momentarily with a push-button switch or transistor across the junction. Reverse blocking mode When a negative voltage is applied to the anode and a positive voltage to the cathode, the SCR is in reverse blocking mode, making J1 and J3 reverse biased and J2 forward biased. The device behaves as two reverse-biased diodes connected in series. A small leakage current flows. This is the reverse blocking mode. If the reverse voltage is increased, then at critical breakdown level, called the reverse breakdown voltage (VBR), an avalanche occurs at J1 and J3 and the reverse current increases rapidly. SCRs are available with reverse blocking capability, which adds to the forward voltage drop because of the need to have a long, low-doped P1 region. Usually, the reverse blocking voltage rating and forward blocking voltage rating are the same. The typical application for a reverse blocking SCR is in current-source inverters.

27. Circuit Breaker A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. Operating Principle and Types A circuit breaker essentially consist of fixed and moving parts called electrodes. Under normal operating conditions these contacts remain closed and will not open automatically until and unless the system becomes faulty. When a fault occurs on any part of system, the trip coils of the circuit get energised and the moving contacts are pulled apart by some mechanism thus opening the circuit. There are 4 types of Circuit Breakers:- 1. Oil Circuit Breakers which employs insulating oil for arc extinction. 2. Air-blast Circuit Breakers in which high pressure air-blast is used for extinguishing the arc. 3. Sulphur hexafluoride Circuit Breakers in which sulphur hexafluoride gas is used for arc extinction. 4. Vacuum Circuit Breaker in which Vacuum is used for arc extinction.

28. Oil Circuit Breaker Oil circuit breaker is such type of  circuit breaker   which used oil as a dielectric or insulating medium for arc extinction. In oil circuit breaker the contacts of the breaker are made to separate within an insulating oil. When the fault occurs in the system the contacts of the circuit breaker are open under the insulating oil, and an arc is developed between them and the heat of the arc is evaporated in the surrounding oil.

29. Air Blast Circuit Breaker Air blast circuit breaker used compressed air or gas as the arc interrupting medium. In the air blast, circuit breaker compressed air is stored in a tank and released through a nozzle to produce a high-velocity jet; this is used to extinguish the arc. Air blast circuit breakers are used for indoor services in the medium high voltage field and medium rupturing capacity. Generally up to voltages of 15 KV and rupturing capacities of 2500 MVA. The air blast circuit breaker is now employed in high voltage circuits in the outdoors switch yard for 220 KV lines.

30. Sulphur Hexafluoride Circuit Breaker A  circuit breaker   in which SF 6  under pressure gas is used to extinguish the arc is called SF 6  circuit breaker. SF 6  (sulphur hexafluoride) gas has excellent dielectric, arc quenching, chemical and other physical properties which have proved its superiority over other arc quenching mediums such as oil or air.

31. Vacuum Circuit Breaker   A vacuum circuit breaker is a kind of circuit breaker where the arc quenching takes place in vacuum medium. The operation of switching on and closing of current carrying contacts and interrelated arc interruption takes place in a vacuum chamber in the breaker which is called vacuum interrupter.

32. Protective Relays A   protective relay  is a  relay  device designed to trip a  circuit breaker   when a fault is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, reverse  power  flow, over-frequency, and under-frequency.

33. Isolator Switch I solator switch  is used to ensure that an electrical circuit is completely de-energized for service or maintenance. Such switches are often found in  electrical distribution  and  industrial  applications, where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as  circuit breakers ,  transformers , and transmission lines, for maintenance. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Isolator can be manual or motor operated.

34. Colour Code of Wires generally used in India

35. Protective Layers of Underground Cables Core(Conductor): The Core is a conducting parts of a cable. This core may be one or more than one depending upon the type of service. The conductors are made of tinned copper or aluminum. The thickness of the core depends upon the rating of current and voltage rating.

36. Insulation : Insulation of cable is a layer of insulating materials which is provided over the core (conductor ). The thickness of insulation depends upon the voltage to be withstood by the cable, Commonly Impregnated paper is used for insulation. And also varnish cambric or rubber mineral are used for insulation. Metallic sheath : A metallic sheath of lead or aluminum is provided over the insulation of cable for protecting the cable from moisture, gases or other liquids (like) acids or alkalies in the soil and atmosphere. Bedding : Bedding is a layer in between metallic sheath and armoring. It consists of fibrous materials like jute or hessian tape. It protects the metallic sheath against corrosion and from mechanical injury due to armoring.   Armouring : Armoring is provided over the bedding which consists of one or two layers of galvanized steel wire or steel tape. It protects the core from mechanical injury which laying and also used as earthing purpose of the cable. Some cable has not provided armouring. Serving : A layer of fibrous materials is provided over the armouring to protect the armouring. This layer is known as serving of the cable.

37. Contactors A contactor is an electrically-controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch.

38. 4 BASIC TYPES OF TEMPERATURE MEASURING SENSORS Thermocouples - Thermocouples  are voltage devices that indicate temperature measurement with a change in voltage. As temperature goes up, the output voltage of the thermocouple rises - not necessarily linearly. Often the thermocouple is located inside a metal or ceramic shield that protects it from exposure to a variety of environments. Metal-sheathed thermocouples also are available with many types of outer coatings, such as Teflon, for trouble-free use in acids and strong caustic solutions. Res istive Temperature Measuring Devices(RTD) - R esistive temperature  measuring devices  also are electrical. Rather than using a voltage as the thermocouple does, they take advantage of another characteristic of matter which changes with temperature - its resistance. In general, RTDs are more linear than are thermocouples. They increase in a positive direction, with resistance going up as temperature rises. Thermometers - A  thermometer  is a device that  measures temperature or a  temperature gradient (the degree of hotness or coldness of an object). A temperature sensor (e.g. the bulb of a  mercury-in-glass thermometer  or the pyrometric sensor in an  infrared thermometer ) in which some change occurs with a change in temperature; Thermometers are widely used in technology and industry to monitor processes, in  meteorology , in medicine, and in scientific research. Silicon Diode – The Silicon Diode Sensors is a device that has been developed specifically for the cryogenic temperature range. Essentially they are linear devices where the conductivity of the diode increases linearly in the low cryogenic regions.

39. Induction Motor An  induction motor  or  asynchronous motor  is an  AC electric motor  in which the  electric current  in the  rotor  needed to produce torque is obtained by  electromagnetic induction  from the  magnetic field  of the  stator  winding.  When the 3-phase stator windings are fed by 3-phase supply, a magnetic flux of constant magnitude but rotating at synchronous speed is set up. The flux passes through the air gap and sweeps past the rotor conductors which yet are stationary. Due ton relative speed between the rotating flux and stationary conductors, an emf is induced in the latter according to Faraday’s law of electromagnetic induction. Its magnitude is proportional to relative velocity between the flux and conductors and its direction is given by Fleming’s Left Hand Thumb Rule. In AC motors , the rotor does not receive electric power by conduction but by induction same way as the secondary of a 2-winding transformer receives its power from primary. So an induction motor is also known as rotating transformer.

40. Concept of Star & Delta Starters for Motor A star delta starter will start a motor with a star connected stator winding. When motor reaches about 80% of its full load speed, it will begin to run in a delta connected stator winding. A s tar delta starter is a type of reduced voltage starter. We use it to reduce the starting current of the motor without using any external device or apparatus. This is a big advantage of a star delta starter, as it typically has around 1/3 of the inrush current compared to a DOL starter. The starter mainly consists of a TPDP switch which stands for Tripple Pole Double Throw switch. This switch changes stator winding from star to delta. During starting condition stator winding is connected in the form of a star. Now we shall see how a star delta starter reduces the starting current of a three-phase induction motor.

41. Alternators An  alternator  is an  electrical generator  that converts  mechanical energy  to  electrical energy in the form of  alternating current. A conductor moving relative to a magnetic field develops an  electromotive force  (EMF) in it ( Faraday's Law ). This EMF reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a rotating magnet, called the  rotor  turns within a stationary set of conductors wound in coils on an iron core, called the  stator . The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn. The  rotating magnetic field induces an  AC voltage  in the stator windings. Since the currents in the stator windings vary in step with the position of the rotor, an alternator is a synchronous generator. The speed of the alternator depends upon its pole and mathematically calculated by Synchronous Speed= 120f/P , where F is Frequency and P is No. of Poles .

42. Transformer A  transformer  is defined as a  passive electrical device  that transfers electrical energy from one circuit to another through the process of  electromagnetic induction . It is most commonly used to increase (‘step up’) or decrease (‘step down’)  voltage  levels between circuits. The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance. In the applications of Transformer the voltage can be step up or step down as per consideration or requirement by Changing number of turns. If number of turns is more on primary side and less on secondary then it is said Step Down Transformer and Vice-versa keeping frequency same at any conditions.

43. 8. Concepts of Earthing System An earth or, grounding system is the point of reference in an electrical circuit from which the voltages are estimated. The earthing system or to our friends over the pond; grounding system also has the function of providing a common return path for electric current through a physical connection to the geology. In an electrical installation, an earthing system or grounding system electrode connects specific parts of that installation with the Earth’s conductive surface for safety and functional purposes. An Earthing, Grounding system provides: Personal protection – living beings in the vicinity of substations by not exposing to unsafe potentials under steady-state or fault conditions. Electrical system operational protection. Potential (voltage) grading earthing. Electromagnetic pulses protection. Lightning protection. Voltage protection, within reasonable limits under fault conditions (such as lightning, switching surges or inadvertent contact with higher voltage systems), and ensure that insulation breakdown voltages are not exceeded, i.e. insulation co-ordination. Graded insulation in power transformers. Voltage limiting to earth on conductive materials which enclose electrical conductors or equipment. 

44. There are 4 Methods of Earthing commonly known i.e Plate Earthing Pipe Earthing Rod Earthing Strip or Wire Earthing

45. Plate Earthing In plate earthing system, a plate made up of either copper with dimensions 60cm X 60cm X 3.18mm(i.e 2ft X 2 ft X 1/8”) or galvanised iron(GI) of dimensions 60cm X 60cm X 6.35mm(i.e 2ft X 2ft X ¼”) is buried vertical in the earth(earth pit) which should not be less than 3m(10ft) from the ground level. For proper earthing system, follow the above mentioned steps in the earth Plate Introduction to maintain the moisture condition around the earth electrode or earth plate.

46. Pipe Earthing A galvanized steel and a preforated pipe of approved length and diameter is placed vertically in wet soil in this kind of system of Earthing. It is the most common system of earthing. The size of the pipe to use depends on the magnitude of current and type of soil. The dimension of the pipe is usually 40mm(1.5”) in diameter and 2.75mt(9ft) in length for ordinary soil or greater for dry and rocky soil. The moisture of the soil will determine the length of pipe to be buried but usually it should be 4.75m(15.5ft) .

47. Rod Earthing It is the same method as Pipe Earthing. A copper rod of 12.5mm(1/2”) diameter or 16mm(0.6”) diameter of galvanized steel or hollow section 25mm(8.2ft) are buried upright in the earth manually or with the help of a pneumatic hammer. The length of embedded electrodes in the soil reduces earth resistance to desired value.

48. Strip or Wire Earthing In this method of earthing, strip electrodes of cross section not less than 25mm X 1.6mm(1” X 0.06”) is buried in a horizontal trenches of a minimum depth of 0.5m. If copper with a cross section of 25mm X 4mm(1” X 0.15”) is used and a dimension of 3.0mm 2 if it’s a galvanized iron or steel. If at all round conductors are used, there cross-section area should not be too small, say less than 6.0mm 2 if it’s galvanized iron or steel. The length of the conductor buried in the ground would give a sufficient earth resistance and this length should not be less than 15m.

49. 9. Differences Between Neutral, Earth or Ground Earth or Ground Neutral It is the least resistance path and is used as a safety purpose against residual currents In an AC circuit which carries current in normal condition, it is the return path, it balances the load In normal condition, it doesn’t carry any current but in case of insulation failure, it might carry minor current A neutral wire is always charged It cannot be turned into neutral It can be turned into earth It can come from a neutral line or can be separately executed It comes from a neutral line Earth is the surging point of appliances Neutral is the return path of the electrical current supply, it is also called a reference point

50. Difference between Switchyard & Substation Substation - A substation is an electrical system with high-voltage capacity and can be used to control the apparatus, generators,  electrical circuits , etc. The Substations are mainly used to convert AC (alternating current) to DC (direct current). Some types of substations are tiny in size with an inbuilt transformer as well as related switches. Other types of substations are very huge with different  types of transformers ,  equipment , circuit breakers, and switches.

51. Switchyard – The switchyard is the mediator among the transmission as well as generation, and equal voltage can be maintained in the switchyard. The main purpose of this is to supply the generated energy from the power plant at the particular level of voltage to the nearby transmission line or  power grid.   switchyard ,  is  a  substation  without transformers that operates only at a single voltage level. Switchyards  are generally classified by voltage level, circuit breaker and bus arrangements.   Switchyards  are often located directly adjacent to or near a power station.