Resistance is one of the most basic elements encountered in electrical and electronics engineering. The value of resistance in engineering varies from very small value like, resistance of a transformer winding, to very high values like, insulation resistance of that same transformer winding. Although a multimeter works quite well if we need a rough value of resistance, but for accurate values and that too at very low and very high values we need specific methods. In this article we will discuss

History of MeggerThe device is being used since 1889, popularity raised during 1920s since the long back device is same in its uses and purpose of testing, few real improvements appeared in recent years with its design and quality of tester. Now high-quality options are available which are easy to use and quite safe.What is Megger?Insulation resistance IR quality of an electrical system degrades with time, environment condition, i.e., temperature, humidity, moisture and dust particles. It also g

Rectifier type instrument measures the alternating voltage and current with the help of rectifying elements and permanent magnet moving coil type of instruments. However the primary function of rectifier type of instruments work as voltmeter. Now one question must arises in our mind why we use rectifier type of instruments widely in the industrial world though we have various other AC voltmeter like electrodynamometer type instruments, thermocouple type instruments etc? The answer to this questi

Working Principle of Electrostatic Type InstrumentsAs the name suggests the electrostatic type instrument use static electrical field to produce the deflecting torque. These types of instrument are generally used for the measurement of high voltages but in some cases they can be used in measuring the lower voltages and powers of a given circuit. Now there are two possible ways in which the electrostatic force can act. The two possible conditions are written below,Construction of Electrostatic Ty

What is a Permanent Magnet Moving Coil (PMMC)?A Permanent Magnet Moving Coil (PMMC) meter – also known as a D’Arsonval meter or galvanometer – is an instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field.A PMMC meter places a coil of wire (i.e. a conductor) inbetween two permanent magnets in order to create stationary magnetic field. According to Faraday’s Laws of electromagnetic induction, a current carrying conduc

In order to understand the concept of errors in measurement, we should know the two terms that defines the error and these two terms are written below:True ValueIt is not possible to determine the true value of a quantity by experiment means. True value may be defined as the average value of an infinite number of measured values when average deviation due to various contributing factor will approach to zero.Measured ValueIt may be defined as the approximated value of true value. It can be found

Basically there are three types of measuring instruments and they are Electrical measuring instruments Mechanical measuring instruments. Electronic measuring instruments.Here we are interested in electrical measuring instruments so we will discuss about them in detail. Electrical instruments measure the various electrical quantities like electrical power factor, power, voltage and current etc. All analog electrical instruments use mechanical system for the measurement of various electrical quant

The principle of working and construction of induction type meter is very simple and easy to understand that’s why these are widely used in measuring energy in domestic as well as industrial world. In all induction meters we have two fluxes which are produced by two different alternating currents on a metallic disc. Due to alternating fluxes there is an induced emf, the emf produced at one point (as shown in the figure given below) interacts with the alternating current of the other side resulti

Electromagnetic RelayElectromagnetic relays are those relays which are operated by electromagnetic action. Modern electrical protection relays are mainly micro processor based, but still electromagnetic relay holds its place. It will take much longer time to replace all electromagnetic relays by micro processor based static relays. So before going through detail of protection relay system we should review the various types of electromagnetic relays.Electromagnetic Relay WorkingPractically all th

Definition of Protective RelayA relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit.Now let’s have a discussion on some terms related to protective relay.Pickup Level of Actuating Signal:The value of actuating quantity (voltage