1. High speed biased differential relay The DMH type relay provides high speed biased differential protection for two or three winding transformers. The relay is immune to high inrush current and has a high degree of stability against through faults. It requires a max of two cycles operating time for current above twice relay rated …
Protection Of Generators And Transformers
As Generators and transformers are major components of a power system, so it is quite necessary to take all the preventive measures for the protection of transformers and generators. These are the following ways (ANSI codes) we use to protect transformers and generators from faults: 87/G1 Generator differential protection (87/G1): the protection is provided with …
Ceramic (Porcelain and Glass) Insulators
Materials Porcelain is the most frequently used material for insulators. Insulators are made of wet, processed porcelain. The fundamental materials used are a mixture of feldspar (35%), china clay (28%), flint (25%), ball clay (10%), and talc (2%). The ingredients are mixed with water. The resulting mixture has the consistency of putty or paste and …
EHV/HV Underground Cable Sheath Earthing (part 2/2)
Continued from previous part: EHV/HV Cable Sheath Earthing (part 1/2) Accessories for HT Cable Sheath Bonding 1. Function of Link Box? Link Box is electrically and mechanically one of the integral accessories of HV underground above ground cable bonding system, associated with HV XLPE power cable systems. Link boxes are used with cable joints and …
EHV/HV Underground Cable Sheath Earthing (part 1/2)
In urban areas, high voltage underground cables are commonly used for the transmission and distribution of electricity. Such high voltage cables have metallic sheaths or screens surrounding the conductors, and/or armour and metallic wires surrounding the cables. During earth faults applied to directly earthed systems, these metallic paths are expected to carry a substantial proportion …
Segregated phase bus system
In this construction all the phases are housed in one metallic enclosure as earlier, but with a metallic barrier between each phase, as illustrated in Figure 1. The metallic barriers provide the required magnetic shielding and isolate the busbars magnetically from each other, like an isolated phase bus system (IPB). The metallic barriers transform the enclosure into somewhat like Faraday Cages. The …
Direct high voltage testing of cable insulation systems
DC testing has been accepted for many years as the standard field method for performing high-voltage tests on cable insulation systems. Whenever DC testing is performed, full consideration should be given to the fact that steady-state direct voltage creates within the insulation systems an electrical field determined by the geometry and conductance of the insulation, …
High-voltage transmission lines and Electromagnetic Interference (EMI)
The corona discharge produces radio noise and in lesser extent television ( TV ) disturbances around high-voltage transmission lines. This can be easily observed by all of us when we drive under a high-voltage line. The radio produces hissing, crackling noise close to the line or under the line, but disturbance diapering fast as we …
Be extremelly carefull when racking in and racking out of circuit breaker
Arc flash incident, bad racking? There are many reasons causes arc flash incidents. Some of arc flash explosions occur when substation personnel insert or remove (rack in or out) circuit breakers from low or high voltage switchgear cubicles. Manual racking in and racking out circuit breakers poses potentially lethal arc flash exposure. Assumptions and complacency …
Typical constructions of overhead lines
Along streets, alleys, through woods, and in backyards, many of the distribution lines that feed customers are overhead structures. Because overhead lines are exposed to trees and animals, to wind and lightning, and to cars and kites, they are a critical component in the reliability of distribution circuits. Overhead constructions come in a variety of …
