An air break switch is a type of switch that makes use of air as a dielectric and arc quenching medium. The contacts of an air break switch open in the air. Here, the arcing problem produced while opening the switch is resolved with the help of compressed air. These types of switches are generally operated at low voltage levels, i.e., voltage ranging from 450V up to 35kV. The current range of air break switches lies between 800 A and 10KA. The air pressure used by the air break switches ranges from 4 to 60 atmospheres. It can also be said that an air break switch is a switchgear device that makes use of air as an interruption medium.
Working of an Air Break Switch
An air break switch is typically used to open the circuit under the load. The arc that gets produced during the process of opening the switch is quenched in many ways. It can be extinguished by moving the contacts away from each other or by supply interruption. Usually, the arc is put out with the help of lengthening of the arcing horns present in the structure of the switch. These arcing horns are nothing but the pieces of metals between which the arc is formed. As the switch gets opened, the arcs tend to move far from each other, eventually breaking out. The main components of an air break switch include an arc extinguisher, a reservoir provided with a supply of compressed air, and an electro-pneumatic actuator. The arc extinguisher is connected to the compressed air reservoir with the help of an insulated line. It is used to quench the arc produced between the movable and the fixed contacts. The de-energized electromagnet tends to open the air blast valve through a system of various pneumatic devices. This helps supply the compressed air from the reservoir to the arc blowout chamber through the airline. This compressed air tends to act on the piston of the movable contact and separates the movable contact from the fixed contact. The arc that gets formed due to the opening of the contacts of the switch is required to be extinguished. The compressed air from the chamber is used for the purpose of arc quenching. The compressed air is directed through the outlets of the contacts to the gas escape channels. After some time, the air enters the cylinder of a pneumatic actuator and quenches the arc. After the arc extinguishes, the compressed air actuates the piston and breaks the isolating switch contacts. The contacts are closed and the incoming of the compressed air is then cut off. When the electromagnet gets energized, the valve opens and the compressed air is allowed to pass through the insulated airline. The air enters the cylinder, acts on the piston, and closes isolating switch contacts. Some of the air break switches are manufactured with air-filled isolating switches. Such switches consist of contacts that are packed in an insulated casing. The switch gets filled up with compressed air after being disconnected.
Types of an Air Break Switch
The air break switches can be broadly classified into two categories, namely single-pole air-break switch and the gang operated air-break switch.
Single-Pole Air Break Switch
A single-pole air break switch provides an opening for only one conductor. The working of a single-pole air break switch is similar to that of a normal air break switch.
Gang Operated Air Break Switch
A gang operated air break switch is used when the opening of more than one conductor at a time is required. Here, all the switches tend to open and close together.
Uses of an Air Break Switch
An air break switch is used in a number of commercial and industrial applications as given below:
1. Air break switches are typically used for switching and isolation purposes.
2. Air break switches are generally installed in the distribution networks as a switching point to make or break connections between cables, transformers, and other high voltage electrical devices.
3. Air break switches are used in overhead power transmission lines. Here, these switches are mainly used to perform on/off switching by connecting the power system of a part of the overhead line to the main distribution line or by disconnecting it from the main distribution line. This allows the user to simply isolate a part of the overhead line without affecting the rest of the power transmission system.
4. These types of switches can also be used in power generation lines.
5. In certain power distribution systems, air break switches tend to provide crucial point isolation.
6. It is typically used to provide overcurrent and short circuit protection.
7. They are used in industrial plants for various control and safety operations.
Advantages of an Air Break Switch
An air break switch is advantageous in the following ways:
1. An air break switch is more effective than ordinary switches.
2. The reliability of air break switches is significantly high.
3. Air break switches can be operated manually as well as automatically depending on the requirement.
4. The maintenance of air break switches is relatively easy and cheap.
5. The air break switches are capable of fast breaker and switching operations.
6. These switches do not cause fire and explosion hazards.
7. An air break switch does not require a compressor.
8. These switches allow the user to maintain the stability of the operation.
Disadvantages of an Air Break Switch
Certain limitations or disadvantages of an air break switch are listed below:
1. They are quite heavy and bulky in nature.
2. The air break switches are less efficient for deionizing and lengthening action at high currents.
3. These types of switches are not suitable for modern power systems.
4. Air break switches require high capacity equipment for the storage and production of compressed air.
5. There exist chances of air leakage resulting in reduced pressure.
6. Air has comparatively lower arc extinguishing properties.
7. There are chances of a high rate rise of re-striking voltage and current chopping.