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ELECTRICAL MEASURING INSTRUMENTS
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Voltmeter-A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit
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Wattmeter-The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit
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Meggar-The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms
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A typical multimeter would include basic features such as the ability to measure voltage, current,
and resistance
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AC Bridges-AC bridges are often used to measure the value of unknown impedance (self/mutual inductance of inductors or capacitance of
capacitors accurately)
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Power factor meter- Power factor meter is a direct reading instrument which gives the direct indication of power factor of a circuit
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Frequency meter-A frequency meter is an instrument that displays the frequency of a periodic electrical signal
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Phase sequence
indicator is the indicator that determines the phase sequence of the three phase supply system
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Wheatstone bridge- A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance
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A clamp
meter measures the vector sum of the currents flowing in all the conductors passing through the probe, which depends on the phase relationship of
the currents
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Oscilloscope-An oscilloscope is a laboratory instrument commonly used to display and analyze the waveform of electronic signals
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Varmeter-The instrument which measures the reactive power of the circuit are called varmeter
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KVARh meter22
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These instruments can measure
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Trivector meters are normally used in substations and to measure the power flowing through the feeders
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ELECTRICAL LAWS
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The magnitude of the electrostatic force of interaction between two point charges is directly
proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them
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If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs,
the force between them is attractive
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Gauss’s law- Gauss's Law
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The electric
flux through an area is defined as the electric field multiplied by the area of the surface projected in a plane perpendicular to the field
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Ohm’s law- Ohm's Law deals with the relationship between voltage and current in an ideal conductor
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The constant of proportionality is called the "resistance", R

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The amount of heat released is proportional to the square of the current such that

This relationship is known as Joule's first law or Joule–Lenz law
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The value of e is the open circuit voltage at the terminals, and the value of r is e divided by the current with the terminals short circuited
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Norton’s theorem- Norton's Theorem
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The value of r is the same as that in the Thevenin equivalent and the current i can be found by dividing the
open circuit voltage by r
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Maximum power transfer theorem- In electrical engineering, the maximum power transfer theorem states that, to obtain maximum external power from
a source with a finite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals
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Laws of resistance- The laws of resistance states that the Resistance “R” offered by a conductor depends upon following factors:
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The Resistance “R” is Inversely proportional with it’s Cross Sectional Area: “A”
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Fleming's left hand rule helps
you to predict the movement
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Fleming’s right hand rule- Fleming's right-hand rule (for generators) shows the direction of induced current when a conductor moves in a magnetic field
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When a conductor such as a wire attached to a circuit moves through a magnetic field, an electric current is induced in the wire due to Faraday's law of induction
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Fleming's right-hand rule gives which direction the current flows
The right hand is held with the thumb, first finger and second finger mutually perpendicular to each other (at right angles), as shown in the diagram
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The first finger is pointed in the direction of the magnetic field
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The direction of rotation of the thumb gives the direction of the magnetic lines of force
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Right hand thumb rule- Imagine the conductor to be held in your right hand with the fingers curled around it
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Faraday's First Law
Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil
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Faraday's Second Law
It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages
with the coil
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This imaginary voltage source is directed opposite to the voltage source of that replaced resistance
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Millman’s theorem- In electrical engineering, Millman's theorem(or the parallel generator theorem) is a method to simplify the solution of a circuit
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This theorem is nothing but a combination of Thevenin's Theorem and Norton's Theorem
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This theorem is also called as PARALLEL GENERATOR THEOREM
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Star-Delta transformation/Delta-Star transformation- Star Delta Transformations allow us to convert impedances connected together from one type of
connection to another
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Delta to Star Transformations Equations

Star Delta Transformation Equations

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The total resistance of a series circuit is equal to the sum of the individual resistances
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The voltage drop across a resistor in a series circuit is proportional to the ohmic value of the resistor
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The current through a branch of a parallel network is inversely proportional to the amount of resistance of the branch
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The total resistance of a parallel circuit is found by the general formula:

or one of the formulas derived from this general formula
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" These transformations are useful for solving circuits
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In
general, source transformations can be summarized by keeping two things in mind:
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Impedances remain the same

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[1] Lenz's
law is named after Heinrich Lenz, and it says:
If an induced current flows, its direction is always such that it will oppose the change which produced it
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Faraday’s laws of electrolysis- Faraday's laws of electrolysis are quantitative relationships based on the electrochemical researches published
by Michael Faradayin 1834
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Quantity of electricity refers to the quantity of electrical charge, typically measured in coulomb
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C electricity (electric charge), the mass of an elemental material altered at an electrode is directly
proportional to the element's equivalent weight"
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This will be explained further in the next paragraph
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Laws of magnetisma
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) The force of attraction or repulsion exerted between two poles is inversely proportional to the square of the distance between them and directly
proportional to the product of the strengths of the poles (Coulomb’s second law)
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Second Law : According to this law, the force exerted between two point charges
i) is directly proportional to the product of their strengths
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and
iii) is inversely proportional to the absolute permittivity of the surrounding medium
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Directly proportional to their pole strengths (m1, m2),
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Inversely proportional to the absolute permeability (µ)of the surrounding medium
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Ampere’s law-The magnetic field in space around an electric current is proportional to the electric current which serves as its source, just as
the electric field in space is proportional to the charge which serves as its source
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While if the current is in the clockwise direction, the face of the coil will behave like South Pole
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Primary power lines 2
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Overhead lines 4
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Disconnect switch 6
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Current transformer 8
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Main transformer 10
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Security fence 12
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Isolator or Disconnector switch- In electrical engineering, a disconnector, disconnect switch or isolator switch[1] is used to ensure that an electrical
circuit is completely de-energized for service or maintenance
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High-voltage isolation switches are used in electrical substations to allow
isolation of apparatus such as circuit breakers, transformers, and transmission lines, for maintenance
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Reactor- A line reactor is an inductor wired between a power source and a load
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Its basic function is to detect a fault condition and interrupt current flow
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A circuit breaker is a device used to complete, maintain, and interrupt currents
flowing in a circuit under normal or faulted conditions
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1 ACB- Air circuit breakers are used to interrupt circuits while current flows through them
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They are oil filled to provide cooling
and to prevent arcing when the switch is activated
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3 VCB- A vacuum circuit breaker utilizes a vacuum to extinguish arcing when the circuit breaker is opened and to act as a dielectric to insulate
the contacts after the arc is interrupted
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A vacuum recloser is designed to interrupt and
reclose an AC current circuit automatically, and can be designed to cycle a set number of times before it must be reset manually
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4 SF6 CB- SF6 circuit breakers operate to switch electric circuits and equipment in and out of the system
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The gas also interrupts the current flow when the
contacts are open
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Auto reclosing circuit breaker- n electric power distribution, a recloser, or autorecloser, is a circuit breaker equipped with a mechanism that can
automatically close thebreaker after it has been opened due to a fault
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Bus coupler is a breaker used to couple two busbars in order to perform maintenance on other circuit breakers associated with that
busbar
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Busbar- In electrical power distribution, a busbar is a metallic strip or bar (typically copper, brass or aluminium) that conducts electricity within
a switchboard, distribution board, substation, battery bank, or other electrical apparatus
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Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads
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Large electric motors can be protected from overcurrent damage through the use of overload heaters and overload contacts
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Current transformers, together with voltage
(or potential) transformers (VT or PT), are known as instrument transformers
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A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit
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Potential transformer- Voltage transformers (VT) (also called potential transformers (PT)) are a parallel connected type of instrument transformer, used for
metering and protection in high-voltage circuits or phasor phase shift isolation
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The main use of this transformer is to measure the voltage through the bus
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This high voltage is very dangerous to the instruments used in the substation
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The lightening arrestors do not let the lightening to fall on the station
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Lightning arresters are protective devices for limiting surge voltages due to lightning strikes or equipment faults or other events, to prevent damage to equipment
and disruption of service
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Lightning arresters are installed on many different pieces of equipment such as power poles and towers, power transformers, circuit breakers, bus structures, and
steel superstructures in substations
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Switchgear panels- In an electric power system, switchgear is the combination of electrical disconnect switches, fuses or circuit breakers used to control,
protect and isolate electrical equipment
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This type
of equipment is directly linked to the reliability of the electricity supply
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A relay is a low-powered device used to activate a high-powered device
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Relays are also used to detect abnormal or undesirable operating conditions other than those caused by defective equipment
and either operate an alarm or initiate operation of circuit interrupting devices
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There are different types of relays
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Over current relay
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Differential relay
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Surge diverter- A surge diverter is a piece of equipment that diverts excess voltages (caused by spikes in the electrical supply) to earth, thus
protecting sensitive electrical and electronic equipment
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Surge absorber- A surge absorber also known as surge modifier is a protective device which reduces the steepness of the wave front of a particular
surge and minimizes the danger due to over voltage by absorbing surge energy
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Spike diverters-The spike diverters are the non-linear voltage dependent resistors being connected in parallel with the element which is to be
protected
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Over voltage suppressor-The over voltage suppressor is nothing but a capacitor being connected in parallel with the inductive circuit so that the
transient voltage occurring on account of different reasons may be suppressed
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Insulators- An insulator type usually made of porcelain that can be stacked in a string and hangs from a cross arm on a tower or pole and supports the
line conductor The purpose of the insulator or insulation is to insulate the electrically charged part of any equipment or machine from another
charged part or uncharged metal part
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In case of the high voltage overhead transmission and distribution the
transmission towers or poles support the lines, and insulators are used to insulate the live conductor from the transmission towers
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There are mainly three types of insulator used as overhead insulator likewise
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Suspension Insulator 3
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They have an advantage
in that one or more of the insulators in a string can be changed out without replacing the entire string
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Wave trap- Wave trap is an instrument using for tripping of the wave
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Its function is of trapping wave
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It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments here in the
substation
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Voltage regulators- Voltage regulators can be found both at the substation and out on distribution lines to help maintain a constant voltage level
along the entire feeder
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Their operation is basically the same as that of substation
regulators
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When the load on the line is low, the voltage drop is not very large and the customers near the end of the line have adequate voltage
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Voltage regulators
automatically adjust to these low and high load situations to assure all customers have proper voltage to run their electrical equipment
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Synchronous condenser- A synchronous condenser is a synchronous machine running without mechanical load and supplying or absorbing reactive
power to or from a power system
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