Basic Electrical Theory

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

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. Power 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.

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.

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.

• 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.

• 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.

• 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.

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.

• 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.

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.

• 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.

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.

• 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 IIN = Σ IOUT.
 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.

• 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.

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

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.

• 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.

• 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.

• 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 IF. 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.

• 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
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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• Sulphur Hexafluoride Circuit Breaker
A circuit breaker in which SF6 under pressure gas is used to extinguish the arc is called
SF6 circuit breaker. SF6 (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.

• 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.

• 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.

• Isolator Switch
Isolator 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.

• Colour Code of Wires generally used in India

• 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.

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.

• 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.

• 4 BASIC TYPES OF TEMPERATURE MEASURING SENSORS
1. 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.
2. Resistive Temperature Measuring Devices(RTD) - Resistive 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.
3. 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.
4. 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.

• 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.

• 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 star 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.

• 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.

• 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.

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.

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

• 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.

• 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) .

• 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.

• 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 3.0mm2 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
6.0mm2 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.

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

• 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.

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.

Basic Electrical Theory

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