electrialstandards

Percentage Impedance of a Transformer:- Percentage impedance of a Transformer is donated by Z%. The impedance of a transformer is marked on most nameplates. Definition:- The percentage impedance of a transformer is the volt drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage. It is also the percentage of the normal terminal voltage required to circulate full-load current under short circuit conditions Measuring Impedance Transformer impedance can be measured by means of a short circuit test.  With one winding shorted, a voltage at the rated frequency is applied to the other winding sufficient to circulate full load current - see below: The percentage impedance can then be calculated as follows: Z%  =  Impedance Voltage   x  100 Rated Voltage Changing the Impedance Value The most economical arrangement of core and windings leads to a 'natural' value of impedance determined by the leakage flux.  The leakage flux is

Strain Insulator Strain insulators working principle is same as that of suspension insulators and they have only difference is that when insulator used in vertical position then it is known as suspension insulator and when used in horizontal position then it is known as strain insulator.  When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a great tensile load of conductor or strain. A   strain insulator   must have considerable mechanical strength as well as the necessary electrical insulating properties. Rated System Voltage Number of disc insulator used in strain type tension insulator string Number of disc insulator used in suspension insulator string 33KV 3 3 66KV 5 4 132KV 9 8 220KV 15 14 Stay Insulator   For low   voltage   lines, the stays are to be insulated from ground at a height. The insulator used in the stay wire is called as the   stay insulator   and is us

Air circuit breakers as clear from the name that these circuit breakers operate at atmospheric pressure. ACBs are still preferable choice up to   voltage   15 KV. Even ACB’s can be used for LT also . MCCB’s can be used upto 630/ 800A above that limit air circuit breakers are used. Working Principle of Air Circuit Breaker Main aim for every circuit breaker is to prevent rebuilt of arcing after electric current goes zero by creating a situation where in the contact gap will withstand the system recovery voltage. For interrupting arc it creates an arc   voltage   in excess of the supply voltage. Arc   voltage is defined as the minimum   voltage   required maintaining the arc. This   circuit breaker   increases the arc   voltage by mainly three different ways, Air circuit breaker increases the arc   voltage   by cooling the arc plasma. As the temperature of arc plasma is decreased, the mobility of the particle in arc plasma is reduced; hence more voltage   gradient i

Suspension Insulator As discussed earlier Pin type insulators are useful for using at 33KV and above 33 KV it becomes uneconomical to use Pin type insulators. This is mainly due to increased size, Weight of pin type insulator. Thus it become very difficult for handling and replacement of Such insulators. Due to above stated problem Suspension type insulators are developed. It is quite interesting to know about suspension insulators, Suspension type insulators consists of   numbers of insulators are connected in series to form a string and the line conductor is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because of their disc like shape. Suspension type insulators are very economical to use and advantages and disadvantages for the suspension type insulators are as below:- Suspension Insulator Advantages:- 1. In suspension type insulators each disc is designed for normal   voltage   rating 11KV and 15KV on the higher voltage side

SF6 Circuit Breaker As clear from the name circuit breaker which operates in Sulphur Hexfluoride gas is known as SF6 circuit breaker. It is most widely used in HT Breakers. SF6 has excellent insulating property. SF6 Gas has high electro-negativity. Which means that they have ver high affinity to absorb electrons. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion.  SF6 gas can absorb electron in two different ways  SF6  + e ----->     SF6- SF6  + e ----->     SF5-  + F You can see from above that SF6 when comes in contact with free electrons then they absorb the electrons and these –ve ions are much heavier then free electrons which will leads to lower mobility of charged particle in SF6 gas as compared to other gases. As everyone knows that this charged particle mobility is majorly responsible for conducting electric current through a gas. Hence, for heavier and less mobile charged particles in SF6 gas, it

SF6 Circuit Breaker Vacuum Circuit Breaker Criteria Puffer Circuit Breaker Self-pressuring circuit-breaker Contact material-Chrome-Copper Energy requirements for Opeartion Energy requirement for the operation is high as  the mechanism needed to supply the energy for compressing the gas. Operating Energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over short distances. The mechanism does not have to provide the energy to create the gas flow Operating energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over very short distances. Arc Energy Because of the high conductivity of the arc in the SF6 gas, the arc energy is low. (arc voltage is between 150 and 200V.) Because of the very low voltage across the metal vapour arc, energy is very low. (Arc voltage is between 50 and 100V.) Contact Erosi