Calculate i the voltage distribution across various units as a percentage of total voltage across the string and ii string efficiency. Nov 05, 2014 problem 3 each line of a 3phase system is suspended by a string of 3 similar insulators. An ideal insulator should not allow leakage of current from the line conductor to the earthed crossarm besides providing adequate clearance between the line conductors and metal work. The disc near the line conductor is extremely stressed and takes the maximum voltage in the absence of stress. Suspension insulators or string insulators are very widely used in an electrical overhead transmission system. Aug 01, 2015 methods of improving string efficiency the maximum voltage appears across the insulator nearest to the line conductor and decreases progressively as the crossarm is approached. Field distributions are calculated for three types of strings under dry, uniform pollution, nonuniform pollution distribution. String efficiency of a suspension insulator youtube. Solved calculation of string efficiency for suspension. If a protective corona ring inserts capacitances from the line, with the link of the middle. Thus 100% string efficiency of suspension insulators is an ideal case for which the voltage across each disc will be exactly the same. For high voltage a string of suspension insulator is used on the basis of voltage of the line number of insulator are decided. But actually, in addition to self capacitance of porcelain disc there also exists capacitance in between the metallic link of suspension insulator and grounded tower body.
In the previous article, we have discussed different types of insulators used in an overhead transmission line. The string efficiency of suspension insulators can be derived using the following diagram. It shall be noted that the number of discs in suspension insulator can be increased or decreased by adding extra discs or removing a disc. For suspension type of insulators, the ratio of voltage across the whole string to the product of number of discs and the voltage across the disc nearest to the conductor is known as string efficiency.
How can we achieve the maximum string efficiency across an. It consists of 3disc string suspension insulators with a metallic link between them to provide a capacitive effect between them. Figurea below shows a typical suspension insulator. The overhead line insulators provide insulation between the overhead line conductors and the earthed crossarm to which they are connected and also provide support to the conductors. The greater the string efficiency, the more uniform is the voltage distribution. How can we know the rating of a transmission line by the. Thus, nominal load and voltage overload at the separate insulator will depend on the string design and the number of insulators in it. The cost of pin type insulator increases rapidly as the working voltage is increased. A string of suspension insulators consists of a number of porcelain discs connected in series through metallic links. Jul 23, 2017 in the previous article, we have discussed different types of insulators used in an overhead transmission line.
The suspension type insulator has the following advantages. How to learn any language in six months chris lonsdale. The voltage applied across the string of suspension insulators is not uniformly distributed across various units or discs. String efficiency of suspension insulator eduright. String insulator definition of string insulator by merriam. Therefore, in this types of insulators in transmission lines insulator is not economical beyond 33 kv. Apr 25, 2018 string efficiency of suspension insulator string. Structural advantage of using vstrings when comparing the relative advantages and disadvantages of using suspension insulators vs. The greater the composite suspension insulator string efficiency, the more uniform is the voltage distribution. Hubbell dead end insulator is one main of suspension insulators in hubbell for high voltage transmission and distribution lines.
It consists of the amount of ceramic ware insulator units connected with one another by metal links to create a versatile string. Pdf investigation on optimal nanoparticles for enhancing. Dec 07, 2017 suspension insulators or string insulators are very widely used in an electrical overhead transmission system. Give reasons for unequal potential distribution over a string of suspension insulators. The number of insulator units depends on the operation voltage and other factors such as contamination, mechanical strength, lightning, and altitude. An overhead 3phase transmission line, which has phase voltage 30 kv, is hanging from a three insulators suspension strain. String efficiency of suspension insulator when the voltage is applied across the suspension insulator string, it is unequally distributed across the individual unit. The string efficiency which the insulator consists of 5, 6, 7 insulators string with guard ring equals 90. A suspension insulator strain consists of a series of alternately insulators and metal parts, which bind each insulator to the next. The porcelain portion of each disc is between two metal links. If the average spacing of disk type insulator is 146 mm and the number of insulators vary from 3 to 4 pieces, than string clearance for the same applied voltage may vary up to half of the meter 438 584 mm.
Pin type insulator pin type insulator are secured to the cross arm on the pole. Then improve the efficiency of the string by using a longer cross arm and we get efficiency 68. Jul 23, 2017 in this article, we will be talking about voltage distribution and string efficiency of suspension insulator. The conductor is suspended at the bottom end of this string while the top end is secured to the crossarm of the tower. Composite suspension insulator can be used one by one to form strings. Sep 25, 2011 string efficiency is an important consideration since it decides the potential distribution along the string. String efficiency shows the utilization of suspension insulator. The greater string efficiency of suspension insulators, the more uniform is the voltage distribution. Potential distribution over a suspension insulator string the figure below shows a 3disc string of suspension insulator. To evaluate these voltages, string efficiency term is.
Show that in a string of suspension insulators, the disc nearest to the conductor has the highest voltage across it. Ssen 603831 insulators for overhead lines with a nominal voltage above 1 000 v part 1. Suspension insulators or string insulators are very widely used in electrical overhead transmission system. For obtaining uniform voltage distribution, the string efficiency should be as good as possible. If we consider glass suspension string units with the specific number of insulators maintaining for a certain voltage class of transmission line, we can estimate the value of voltage drop on each insulator. Voltage distribution over suspension insulator string.
Evaluation of string efficiency and voltage distribution. Suspension insulator for voltages greater than 33 kv, it is a usual practice to use suspension type insulators, consisting of a number of glass or porcelain discs connected in series by metal links in the form of a string. Porcelain suspension insulators suspension and tension towers for high voltage transmission lines. Potential distribution over a string of suspension insulators p. Types of insulators in transmission lines properties of. Find the voltage across each insulator unit and string efficiency. These capacitances could be made negligibly small by increasing the distance between the.
Compared with existing cleaning robots using jets of water or waterair, this robot mechanism is superior in insulation as it uses a porcelainclamping method, and is more useful in mountainous or salt damage areas by. This unequal potential distribution is undesirable and is usually expressed in terms of string efficiency. Both a and r are true and r is not the explanation of a c. The capacitances between each cappin junction and the tower and between the cap and pin of each unit determine the voltage distribution. In this distribution of voltage, disc nearest to the conductor will be at higher potential than the other discs. In the ideal case, the value of string efficiency will be 100%, but, in a normal case, it is impossible to achieve 100% string efficiency, yet effort should be made to improve it as close to this value as possible. The string efficiency can be improved by using long cross arms. Composite suspension insulator string efficiency is an important consideration since it decides the potential distribution along the string. Thus 100% string efficiency is an ideal case for which the volatge across each disc will be exactly the same. Other end of string is secured to the cross arm of tower. Of course, the number of disks varies as it has different creepage distance in each particular case. They consist of number of porcelain discs connected in series by metal link in the form of string. Methods of increasing string efficiency in insulator.
Although it is impossible to achieve 100% string efficiency, yet efforts should be made to improve it as close to this value as possible. If the voltage across the line unit is 175 kv, calculate the line to neutral voltage. The analysis and simulation of voltage distribution over. For higher voltages, a string of suspension insulators is used. The capacitance to ground is 10% of the capacitance of each insulator unit. Suspension insulator consists of porcelain disc units mounted one above each other. Voltage distribution in a suspension insulator strain. For high voltages 33 kv, it is a usual practice to use suspension type insulators shown in fig. To evaluate these voltages, string efficiency term is used. The capacitance between the links and the earth is 0,2 c, where c is the capacitance of an insulator determine the potential distribution along the insulators strain. More the utilization of discs of insulator more will be the string efficiency. When ac voltage is applied to the string, the voltage distribution is nonuniform across a string insulator. Types of insulators in transmission lines electrical4u.
In this article, we will be talking about voltage distribution and string efficiency of suspension insulator. Each unit operates the voltage of about 11kv and hence depending upon the voltage the appropriate number of discs are connected in series with the string. String efficiency of suspension insulators and methods of. Voltage distribution over a suspension insulator string. In the ideal case, the value of string efficiency will be 100%, but, in a normal case, it is impossible to achieve 100% string efficiency, yet effort should be made to. The disc nearest to the conductor has much higher potential than the other discs. Evaluation of string efficiency and voltage distribution of. The suspension insulator separates the line conductors and supports them electrically. A 3 phase over head transmission line is supported by three discs of suspension insulators. Suspension type insulators are used whose cost is less at high voltages. Investigation on optimal nanoparticles for enhancing performance of suspension insulators string conference paper pdf available in aip conference proceedings 21661 september 2019 with 25 reads. String efficiency and methods to improve string efficiency. The maximum voltage appears across the insulator nearest. This is because of the capacitances formed between the metal parts of the insulators and tower structure.
Use of long cross arms reduces the ratio of capacity to earth to capacity per insulator thereby increasing the string efficiency. Ssen 60372 locking devices for ball and socket couplings of string insulator units dimensions and tests. The results obtained shows that antifog and or combination of antifog and standard disc insulator strings perform better under polluted. Composite suspension insulator,composite suspension insulator. Find the string efficiency of a 37 kv string containing 20 insulators. Both a and r are true and r is the correct explanation of a b. Orient power insulator has excellent suspension insulator specifications model and suspension insulator properties,meanwhile can supply customers lots of suspension insulator image.
String insulator definition is a series of two or more suspension insulators flexibly connected. However, there is a significant thing to be considered in case of these string. String efficiency is defined as the ration of conductor voltage and the voltage across the disc nearest to conductor multiplied by number of discs. The conductors are placed below the suspension insulators and hence it partly protects the conductor from lightning. We talked about advantages and disadvantages of each type of insulators. Apr 25, 2018 string efficiency of suspension insulator. A string of 4 insulators has selfcapacitance equal to 4 times the pintoearth capacitance. The string is free to swing in any direction and, therefore, great flexibility is provided to the transmission line.
Assume that the shunt capacitance between each insulator and earth is 18th of the capacitance of the insulator itself. A suspension type insulator has three units with selfcapacitance c and ground capacitance of 0. Calculate the string efficiency of 50 kv string containing insulators. String effeciency and methods to improve string effeciency. Evaluation of string efficiency and voltage distribution of 400 kv over a string of glass suspension type insulator in different atmospheric condition ijsrdvol. String efficiency of a string of suspension insulators. Suspension insulators,iec u70c suspension insulators. String efficiency of suspension insulators are affected the environments, the numbers of disc insulators. String efficiency of a string of suspension insulators home category electrical engineering mcq questions and answers power system transmission and distribution previous.
String efficiency is an important factor as it suggests the overall potential distribution along the string of insulators. Each disc is provided with a metal cap at the top and a metal pin under. Therefore, each disc forms a capacitor c as shown in figureii. Problem 3 each line of a 3phase system is suspended by a string of 3 similar insulators. The suspension insulator is mainly classified into two types. The potentials across the first and second insulator are 8 and 11 kv respectively. The conductor bound into a groove on the top o f the insulator. Jul 09, 2015 string efficiency is an important factor is transmission line designing. The comparison of the string suspension porcelain 567.
In this project, calculate the voltage distribution along a string of 5 suspension insulators, and determine the efficiency of string and we get efficiency equal to 53. Company profile and product overview lapp insulators. But actually, in addition to self capacitance of porcelain disc there also exists capacitance in between the metallic link of suspension insulator and grounded tower. As for the wetted water contamination string insulator condition which the insulator consists of 5, 6, 7 insulators string without guard. Mar 16, 2017 evaluation of string efficiency and voltage distribution of 400 kv over a string of glass suspension type insulator in different atmospheric condition ijsrdvol. An adequate length of leakage of path is obtained by providing insulator with 2. The greater the string efficiency, the more uniform is the voltage distribution in the each disc insulator. Calculation of voltage distribution along porcelain. A suspension insulator is basically a string of number of porcelain disc connected in series though metallic link. A new cleaning robot system for suspension insulator strings was developed to prevent a power failure, which can have severe effects on the national industry and economy. When our customers think of trouble free transmission insulators with the longevity to outpace life time expectations of the transmission lines supported, they think of porcelain suspension insulators from lapp insulators.
String efficiency of suspension insulators is an important. Ppt overhead line insulators powerpoint presentation. String efficiency of suspension insulators performance tests of insulators. The effect can be either selfcapacitive or mutual capacitive. As for the wetted water contamination string insulator condition which the insulator consists of 5, 6, 7 insulators string without guard ring equals 98. Purpose of guard ring in suspension insulator electrical. String efficiency of suspension insulator electrical concepts. String efficiency is important for the overhead transmission line.
Figure i shows 3disc string of suspension insulators. String efficiency of a suspension insulator duration. This constitutes a series of connected capacitors, with each ones capacitance being created by two successive metal connectors clips with the porcelain as a dielectric. Voltage distribution over a suspension insulator string fig. Potential distribution over a string of suspension insulators. The efficient string, efficient string upgrade, and solved problems on string efficiency and voltage distribution should be introduced in a complex way, and use many formulas, if you need the details about voltage distribution in suspension insulators please contact orient. In this study, the voltage distribution over an insulator string of suspension insulators and the string efficiency have been investigated with respect to the atmospheric conditions such as wind.
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