Due to the limitations for higher voltage in pin type insulators, suspension Insulator types are employed in towers. Suspension type insulator includes one or more insulator parts connected together in series to form a string, and they are hanged to the cross arm of the tower or supporting structure and carry a power conductor at its lowest extremity. Also, we call this type of composite unit a string-type insulator.
The conductors are suspended at the bottom end of the strings while the other head of the insulator string is attached to the cross arm of the tower or supporting structure.
In suspension insulators, each porcelain disc is designed to work at 11 kV, and as the operating voltage increases, the number of discs in the string and in series increases as well. For example, the number of insulator discs required is 12 in 132 KV transmission lines.
Advantages of Suspension Insulator
We use suspension insulator in many different applications as they have some benefits over other ones. Here are some advantages of the suspension insulator listed below:
- The types of suspension insulators are economical compared to the pin type insulators when we have a high voltage overhead transmission line.
- Each insulator disc in a suspension insulator is designed to work for 11KV. However, for any operating voltage, we can use a string of insulators. For instance, six discs are necessary for a 66 kV transmission line.
- If one of the units in a string fails, we need to replace only that unit/disc rather than the whole series of disks in the string.
- Mechanical tensions on the suspension insulator are less as a flexible suspension string keeps the line and can move easily.
- As the conductors carrying current and are suspended from a tower or supporting structure by suspension series of suspension insulators, the position and height of the conductor are always lower than the total height of the tower or supporting structure. As a result, the conductors are safe from lightning and protected by the tower.
Disadvantaged of Suspension Insulator
As every device has its own disadvantages, it is better to mention some of the suspension type insulator’s weaknesses:
- The suspension insulator string is expensive compared to the pin and post type insulator. However, in higher voltage lines is more economical.
- Suspension insulator needs higher supporting structure rather than for pin or post insulators. This higher structure is used to keep the ground clearance of current conductors.
- We have a larger amplitude of free swing of conductors in suspension insulator systems. So, more distance between conductors should be considered.
Types of Insulator
The robust operation of overhead lines depends to a considerable extent upon the good selection of insulation. There are various types of insulators but the most frequently used are pin type, suspension type, shackle insulator, and strain insulator.
Pin Type Insulator
As the name implies, the pin insulator attaches the conductor to the cross-arm on the pole. There is a groove on the top of the pin insulator to keep the conductor. The conductor passes by the groove and is fixed by the same material as the conductor. We use pin type insulator for the distribution and transmission of electrical power for voltages up to 33 kV. For a larger operating voltage of 33 kV, the pin type insulator is too bulky and not economical any more.
If the voltage capacity increased for the line, the cost of pin type insulator will increase so much and are not affordable and economical anymore for usage. As a result, this insulator is not economical beyond 33 kV. For higher voltages (>33kv), using suspension insulator types is a usual act.
Several number of porcelain discs connect to each other in series to form a string of insulators name suspension insulator. Each one of the discs is designed for a low voltage of 11 kV. The disc number in strings is variable and depends on the operation voltage. For example, three discs are required in the string while the line’s voltage is 33 kV.
For higher voltage lines, we use a strain insulator. For lower voltage transmission lines, a strain insulator is a series of suspension insulators. We use a disc consisting of many strain insulator in the vertical direction.
In recent days, a strain insulator is used instead of the shackle insulator. However, we use shackle types in lower voltage lines either in a vertical position or in a horizontal position. They can be fixed to the cross arm or the pole with a bolt directly.
Differences between Conductors and Insulators
The way of bonding atoms together affects the electrical properties of the substances they form. For example, if the metallic bond holds materials together, electrons float easily between the metal ions. By applying an electrical force, these electrons will be free to flow in the system. For instance, if a copper wire is attached to the poles of a battery, the electrons will move inside the wire. As an electric current flows in the cables, the copper is called to be a conductor.
The movement of electrons inside a conductor is not actually so simple. A free-electron will be accelerated at first but then will collide with an ion. In their collision, some of the electron’s energy will be absorbed by the ion. As a result, an observer will notice the temperature of the wire rise, and that is why ions have faster movements.
This electrical energy conversion from the motions and movements of the electrons to heat energy is known as electrical resistance. The wire warms and heated up quickly because the electric current flows in a high resistance material. In a low resistance material same like copper wire, most of the energy maintained in the moving electrons, so the element is good for moving electrical power from one point to another. Copper is generally used in electrical wiring because of its excellent conducting property and relatively low cost.
On the other hand, we have the exact opposite situation in some other materials, same as ceramics and plastics. In such materials, the electrons are all locked into covalent or ionic bonds. If we put these kinds of materials between the poles of a battery, there is no current of electrons in the system and simply no electrons free to move. These materials are known as insulators.