Operating Principle of Single-phase Induction MotorA single-phase induction motor consists of a squirrel cage rotor and a stator carrying a single-phase winding. When a single-phase AC supply is fed to the stator winding, a pulsating magnetic field (not the rotating) is produced. Under these conditions, the rotor does not rotate due to inertia. Hence, a single-phase induction motor is inherently not self-starting, but requires some auxiliary starting means.If the stator winding of a single-phase induction motor is excited and the rotor is rotated by an auxiliary means and the starting device is then removed, the motor continues to rotate in ... Read More

The differences between a single-phase and a three-phase induction motor are given below −A 1-phase induction motor requires single-phase AC supply, whereas a 3-phase induction motor need a source of 3-phase AC supply for its operation.1-phase induction motors produce low starting torque, whereas 3phase induction motors produce high starting torque.The efficiency of a 1-phase induction motor is less as compared to a 3phase induction motor.The power factor of a 1-phase induction motor is low, while the power factor of a 3-phase induction motor is high.1-phase induction motors are simple in construction, reliable and economical as compared to 3phase induction motors.1-phase ... Read More

The util.promisify() method basically takes a function as an input that follows the common Node.js callback style, i.e., with a (err, value) and returns a version of the same that returns a promise instead of a callback.Syntaxutil.promisify(original)ParametersIt takes only one parameter −original −This parameter takes an input for the function and returns them as a promise.Example 1Create a file with the name "promisify.js" and copy the following code snippet. After creating the file, use the command "node promisify.js" to run this code.// util.promisify() Demo example // Importing the fs and util modules const fs = require('fs'); const util = ... Read More

An electrical transformer is tested at the transformer manufacturer premises and at the consumer’s site and also periodically in regular and emergency basis during its service life to confirm its specifications and performance.Types of Transformer TestsTests of transformer done at the manufacturer’s premises −Type testsRoutine testsSpecial testsTests of transformer done at the consumer’s site −Pre-commissioning testsPeriodic testsEmergency testsType Tests of TransformerThe type tests of a transformer are performed at the manufacturer’s premises to prove the design expectations and consumer’s specifications. The type tests are performed in a prototype unit, not in all manufactured units and these tests confirm the basic ... Read More

When the transformer is in operation, heat is generated due to copper losses in the windings and iron losses in the core. The removal of heat from the transformer is known as cooling of the transformer.Transformer Cooling MethodsFor the dry type transformersAir Natural (AN) CoolingAir Forced (AF) or Air Blast (AB) CoolingFor oil immersed type transformersOil Natural Air Natural (ONAN) CoolingOil Natural Air Forced (ONAF) CoolingOil Forced Air Forced (OFAF) CoolingOil Forced Water Forced (OFWF) CoolingAir Natural (AN) CoolingThe air natural (AN) cooling is used in dry type, self-cooled transformers. In this method, the natural circulation of surrounding air is ... Read More

Magnetic Leakage or Leakage FluxThe part of magnetic flux that does not follow the desired path in a magnetic circuit is known as leakage flux.In most of practical magnetic circuits, the path of a large part of the magnetic flux is through iron part of the magnetic circuit and the rest part of magnetic flux flows through air. The magnetic flux in the air gap is known as useful flux $(\varphi_{g})$ since it can be used for various useful purposes.Consider a magnetic circuit having an iron core with a coil wound on it and having a narrow air gap. The ... Read More

What is a Smart Grid?A smart grid is a digitally enabled electrical grid that collects, distributes and works on the information about the behaviour of all suppliers and consumers in order to improve the efficiency, reliability and sustainability of electricity service.Smart Grid = Information Technology + Electrical GridThe smart grid uses a two-way digital communication of technologies and computer processing which enables electricity industry to better manage energy delivery and transmission. It is capable of providing real time information and enable the nearby quick balancing of supply and demand.How does a Smart Grid Work?In addition to the traditional grid’s generating ... Read More

A singly-excited system is type of excitation system used in electromechanical energy conversion which requires only one coil to produce the magnetic field. In the singly-excited system, there is only one set of electrical input terminals and one set of mechanical output terminals. The examples of singly-excited system are electromagnetic relay, hysteresis motor, solenoid valve etc.In a singly excited system, a coil is wound around a magnetic core and is connected to a voltage source so that it produces a magnetic field. Due to this magnetic field, the rotor which is made up of ferromagnetic material, experiences a torque urging ... Read More

When the EMF is induced by self and mutual inductance occur simultaneously, the relative polarities of these two induced EMFs must be determined before making any circuit calculations. The induced EMF in a coil due to mutual inductance may either aid or oppose the induced EMF due to self-inductance depending upon the sense of the windings and the directions of the currents in the coils.Dot Notation or Dot RuleThe dot rule or dot convention may be stated as follows −If both currents enter the dotted ends of the coupled coils or if both currents enter undotted ends, then the sign ... Read More

B-H Curve or Magnetisation CurveThe B-H curve or magnetisation curve is the graph plotted between magnetic flux density (B) and magnetising force (H). The B-H curve indicates the manner in which the magnetic flux density varies with the change in magnetising force.The following figure shows the general shape of B-H curve of a magnetic material. The nonlinearity of the curve shows that the relative permeability μr of a magnetic material is not constant but varies depending upon the magnetic flux density.Magnetic HysteresisThe phenomenon of lagging of magnetic flux density (B) behind the magnetising force (H) in a magnetic material subjected ... Read More