Magnetic field The Magnetic field is a force which is generated due to energy change in a volume of space. A magnetic field is produced by an electrical charge in motion e.g. current flowing in a conductor, orbital movement and spin of electrons. The magnetic field can be described by imaginary lines as shown in … Read more
Each of the following questions consists of two statements, one labelled ‘Assertion (A)’ and the other labelled the ‘Reason (R)’. Examine the two statements carefully and decide if the Assertion (A) and Reason (R) are individually true and if so whether the Reason (R) is the correct explanation of the Assertion (A). Select your answers … Read more
Insulating Materials for Cables The insulating materials (dielectrics) used for cables must have low discharge current, low dissipation factor (low loss tangent), and should be chemically stable. The materials generally used are impregnated paper, bituminous compounds, rubber, compressed air, mineral oil etc. In the present days, cross-linked polyethylene cables (XLPE) are manufactured for 11 kV, … Read more
In electrical machines, the insulation system must withstand the high electrical stresses and severe mechanical stresses induced by the magnetic field of the moving rotor. In machines, multi-turn windings are put in narrow armature slots, which are usually grounded. Rotating machine stator insulation construction is divided into principal types: Random wound conductor machines with small … Read more
The insulating materials used in power and distribution transformers must possess the following properties: Good electrical properties to withstand the power frequency (50 Hz) voltages and impulse overvoltages. Good mechanical properties to withstand fabrication and handling during manufacture and electromagnetic forces during overload, short circuit, and normal operating conditions. Good thermal stability and low ageing … Read more
Solid insulating materials may be natural organic substances like paper, cloth, rubber, etc. or inorganic materials like Mica, Glass, or synthetic materials like plastics. The different solid insulating materials are: Paper and Pressboards Fibrous materials (unimpregnated and impregnated) Impregnated coating, filling, and bonding materials Resins (Polymers) Natural and synthetic rubbers Inorganic Insulating Materials: a) Glass b) … Read more
In this article, we will know about different liquid insulating materials. An ideal insulating liquid must have the following properties: High electric strength, impulse strength, and volume resistivity. Low dielectric dissipation factor. High or low dielectric constant (depending on application). High specific heat and thermal conductivity. Excellent chemical stability and gas-absorbing properties. Low viscosity, low-density, … Read more
Meissner’s Effect The repulsion of magnetic flux from the interior of a piece of superconducting material as the material undergoes to the transition to the superconducting phase is known as Meissner’s Effect. In superconductor B = 0 µo( H + M ) = 0 M = − H ……………………. (1) Also, M = χmH ……………. (2) from … Read more
There are two types of superconductor materials Type-1 superconductor Type-2 superconductor Type-1 superconductor They are also called as Soft Superconductor. Their critical field and transition temperature are low. They exhibit complete Meissner’s and Silsbee rule. The change of state from normal to superconductivity and vice-versa is abrupt. Examples: Zn, Pb, Hg, Al, In, etc. Type-2 superconductor They are also called as Hard Superconductor … Read more
Before selecting an insulation system for a particular application, the following properties need to be considered. Mechanical Thermal Environmental including chemical Electric Economic 1. Mechanical properties The mechanical properties considered are the tensile strength, elongation, tensile modulus, compressive modulus, impact strength etc. 2. Thermal properties Include temperature and time of exposure. In this, the important … Read more