DIFFERENT TYPES OF INSULATORS USED IN THE TRANSMISSION LINES

⚡TYPES OF INSULATORS⚡

💡The use of proper insulator is an important part of the mechanical design of the overload lines. The various types of the insulators are:

1) Pin type insulator 

2) Suspension type insulator

3) Strain insulators 

4) Shackle insulators

5) Stay insulators

⚡PIN TYPE INSULATORS ⚡

⚡Pin insulators are the earliest developed overhead insulator, but are still commonly used in power networks up to 33 kV system. Pin type insulator can be one part, two parts or three parts type, depending upon application voltage. 

⚡In a 11 kV system we generally use one part type insulator where whole pin insulator is one piece of properly shaped porcelain or glass.

⚡As the leakage path of insulator is through its surface, it is desirable to increase the vertical length of the insulator surface area for lengthening leakage path. We provide one, two or more rain sheds or petticoats on the insulator body to obtain long leakage path.In addition to that rain shed or petticoats on an insulator serve another purpose. We design these rain sheds or petticoats in such a way that while raining the outer surface of the rain shed becomes wet but the inner surface remains dry and non-conductive. So there will be discontinuations of conducting path through the damp pin insulator surface.In higher voltage systems – like 33KV and 66KV – manufacturing of one part porcelain pin insulator becomes more difficult. The higher the voltage, the thicker the insulator must be to provide sufficient insulation. A very thick single piece porcelain insulator is not practical to manufacture.

⚡In this case, we use multiple part pin insulator, where some properly designed porcelain shells are fixed together by Portland cement to form one complete insulator unit. We generally use two parts pin insulators for 33KV, and three parts pin insulator for 66KV systems.

⚡DESIGNING CONSIDERATION OF ELECTRICAL INSULATORS⚡

💡The live conductor attached to the top of the pin insulator which is at the live potential. We fix the bottom of the insulator to supporting structure of earth potential. The insulator has to withstand the potential stresses between conductor and earth. The shortest distance between conductor and earth, surrounding the insulator body, along which electrical discharge may take place through the air, is known as flashover distance.

1. When the insulator is wet, its outer surface becomes almost conducting. Hence the flashover distance of insulator is decreased. The design of an electrical insulator should be such that the decrease of flashover distance is minimum when the insulator is wet. That is why the uppermost petticoat of a pin insulator has umbrella type designed so that it can protect, the rest lower part of the insulator from the rain. The upper surface of the topmost petticoat is inclined as less as possible to maintain maximum flashover voltage during raining.
2. The rain sheds are made in such a way that they should not disturb the voltage distribution. They are so designed that their subsurface at a right angle to the electromagnetic lines of force.

⚡SUSPENSION TYPE INSULATORS⚡

💡The suspension insulator separates the line conductors and supports them electrically. It consists the number of porcelain insulator units connected with each other by metal links to form a flexible string. The conductor is connected at the bottom of the string.

⚡ADVANTAGES ⚡

💡The suspension type insulator has the following advantages.

1. 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.
2. If one of the units is damaged, then it is replaced by the new one and hence no need of replacing the whole string.
3. The string is free to swing in any direction and, therefore, great flexibility is provided to the transmission line.
4. The conductors are placed below the suspension insulators and hence it partly protects the conductor from lightning.

⚡Properties of Insulator Material

💡The following are the properties of any insulating material they are,

• They should be mechanically strong
• The dielectric strength of the material should withstand high voltage stress
• The electrical insulating resistance should be high
• The material should be free from impurities, no cracks and non-porous
• The physical properties and electrical properties of an insulator should not be affected due to change in environment
• The safety factor must be taken.

⚡Suspension Insulator Construction and Working⚡

💡It consists of two main parts they are the cross-arms and the insulators (also called disc insulator) with the number of metallic links. A suspension insulator or suspension string is developed by connecting a number of insulators in series with the help of metallic links, where the conductor is suspended by the bottom-most insulator and the top end of the insulator are secured by cross-arms. These kinds of insulators are mainly used in an over-headed line.

⚡Types of Suspension Insulator⚡

💡The suspension insulator is mainly classified into two types.

1. Cap and Pin Type
2. Hewlett or Interlink Type

💡The detail explanation of the cap and pin and Hewlett type insulator are explained below.

⚡Cap-and-pin type Insulator⚡

💡A galvanised cast iron or forged steel cap and a galvanised forged-steel pin are connected to porcelain in the cap-and-pin type construction.The unit is joined either by ball and socket or clevis-pin connections.

⚡Interlink Type Insulator⚡

💡The interlink type unit employs porcelain having two curved channels with planes at the right angle to each other. U-shaped levelled covered steel links passed through these channels and served to connect the unit.

💡The Interlink type insulators are mechanically stronger than the cad-and-pin type unit. The metallic link continues to support the line if the porcelain between the link breaks. Thus the supply is not interrupted.

💡The only disadvantage of Hewlett type insulator is that it suffers from the disadvantages that the porcelain between the links is highly stressed electrically and, therefore its puncture stress is less as compared to other types.

⚡STRAIN INSULATORS⚡

⚡Electrical insulator that works in mechanical strain to resist the balanced electrical cable is known as strain insulator. These insulators give support to the transmission lines as well as radio antennas in electrical wiring. This insulator can be placed between two wires to separate them electrically from each other. The strain type insulator diagram is shown below.

⚡Working of Strain Insulator⚡

💡In the transmission line, at a corner line is a great tensile load. To maintain this huge tension, strain insulators are utilized at sharp corners. In high voltage transmission lines, these insulators include a set of suspension insulators. So, the suspension insulator string can be placed horizontal plane whereas the discs of an insulator are arranged in a vertical plane. To maintain high tensions, more than two suspension strings are connected in parallel. For fewer voltage lines like < 11 kV, then shackle insulators are employed like strain insulators.This is designed with porcelain or glass or fiberglass and includes supporting hardware and two cables. This insulator shape will reduce the space between the two cables. Generally, these insulators are in physical tension with radio antennas, overhead power lines, and guy-wires.Once the line voltage needs more insulation to compare with a single insulator then these insulators are connected in series to provide highly effective insulation. By using hardware, insulators are connected.

💡If one string is inadequate for the strain, then a weighty steel plate bundles numerous insulator strings mechanically. The single plate is over the hot end & the other one is situated at the support arrangement.

💡This system is used for long distances like when a transmission line crosses a canal, valley, pond, etc.
This insulator should include significant mechanical strength & the required electrical insulating assets.

⚡Tests⚡

💡To ensure the quality of insulators, this must go through these tests like type tests, performance, and routine tests.

• The type tests are dry flashover, thirty-second rain, wet flashover & impulse frequency tests.
• The performance tests are temperature cycle, electromechanical, puncture, mechanical strength, and porosity.
• The routine tests are high voltage, proof load, and corrosion.
• For all the insulators, the above tests are appropriate. So these insulators are main electrical insulators used to support and insulate the conductors.

⚡Applications of Strain Insulator⚡

💡The applications of strain insulators include the following:

• These are used for electrical wiring in transmission lines to support transmission lines and radio antennas.
• These are normally used in overhead wiring at outdoors. In this situation, they will expose to rainfall, in urban areas they will expose to pollution. In practice, the shape of the insulator will become significant, because a wet lane from one cable to others can make a low-resistance electrical lane.
• These are designed for horizontal mounting so the shape of flanges that are used for shed water & strain insulators used for vertical mounting is bell-shaped.
• These are used as the line is subjected to larger strain like river crossings, dead ends, sharp curves.
• This insulator reduces extreme tension on the line

⚡Advantages of Strain Insulator⚡

💡The advantages of strain insulators include the following.

• These are used for low voltages upto 11kv
• These are insulated from the ground for low-voltage lines.
• These are designed with porcelain
• If the insulator is damaged, the stay or guy wires will not drop to the ground.

⚡SHACKLE INSULATORS⚡

 💡An insulator that is used in distribution networks that works with low voltage is known as a shackle insulator. This insulator is also known as a spool insulator. These insulators can be worked in two positions like horizontal otherwise vertical. At present, the usage of this insulator has decreased because of the underground cable used in distribution purposes.

💡The insulator’s tapered hole distributes the load more consistently & also reduces the possibility of fracture once loaded heavily. The shackle insulator includes a conductor within the groove and it is fixed by using a soft binding wire. The shackle type insulator diagram is shown below.

⚡Shackle Insulator Construction⚡

💡The shape of the shackle insulator is round and it has a hole in the middle for bolting. A 25mm wide galvanized plate is available at both sides of the insulator. The other side of the plates is arranged in the region of the pole. The conductor is fixed within the channel and that is secured by using soft binding wires. These insulators are effective compare with strain insulators when the distribution line alters its angle.There shackle insulators are available in three different sizes like (50 mm x 65 mm), (75 mm x 90 mm) & (100 mm x 115 mm). Generally, the 75 mm x 90 mm & 100 mm x 115 mm sizes of insulators are applicable in main lines, whereas the 50 mm x 65 mm size insulator is used in house to provide low voltage connection.

⚡Shackle Insulator Working⚡

💡The surface of this insulator must be covered so that water cannot flow through it. The raw material used in this insulator is porcelain and it is aluminum silicate (Al2SiO5). This material is combined with feldspar, plastic kaolin & quartz to get final porcelain insulator material.

⚡Applications of Shackle Type Insulators⚡

💡The applications of this insulator include the following:

• It is used in a distribution system by arranging in between tower & conductors to support & insulate.
• These insulators are used in overhead lines with low & medium voltage.
• This insulator is used with a bolt by placing on the pole otherwise telegraph to avoid outflow current from conductors
• It can be used in both positions like horizontal & vertical position.

⚡Advantages and Disadvantages of Shackle Insulator⚡

💡The advantages and disadvantages are

• These are extremely dependable for conductors
• These are designed to meet up the demands of electricity. 
• These are used in vertical as well as horizontal positions.
• Porcelain Insulators bears a high amount of current and temperature
• The finest solution for maintaining protection in different electrical appliances
• These are applicable for low voltage distribution networks only.

⚡STAY INSULATORS⚡

💡Stay Insulators are available for various stay designs, our range of insulators includes both porcelain and polymer strain types. Double plate links and sheaves are also available for polymer strain type insulators.

💡Guy Strain Insulators are manufactured from wet process porcelain to ensure a life time of problem free service Strain insulators are typically used outdoors in overhead electric wiring . it is an insulator generally of extended shape, It is mainly used on the guy wire structure to balance the tension strength.

💡Guy Strain Insulators are known for their high mechanical strength and outstanding electrical properties. These Low Tension Guy Strain Insulators are made by using very high quality raw material which ensures high durability as well as irritate free work performance.