What causes surges?
Electrical surges occur primarily because of electric charge, i.e. lightning. Though it happens once a while, the power running through voltage lines are tremendous and can majorly effect an industrial plant. The operation of high voltage devices like refrigerators, elevators or any hefty machinery may require a sudden or heavy flow of electricity, thus causing fluctuation in the flow. The irregular flow can cause severe damage to devices in the network therefore it becomes important to install surge protection devices.
How does Surge Arrester work
Out of the surges that occur, not all occur due to lightning. There are some that arise due to rush or irregular flow of voltage. Arresters are devices that control and regulate the flow of electricity within the network. They protect insulation or components from or instantaneous voltage.
The arrester device is fitted into the system that captures the incoming state of current. When at time of switching voltages, the Metal Oxide Varistor (MOV), a component of arrester comes into play. It is a semiconductor device that is highly sensitive to voltage. It acts as an insulator at standard voltage, i.e. does not let electricity to pass through it. But at high voltages, the MOV serves as a conductor. It works as a switch that is open when there are a standard AC voltage and a switch that is closed when lightning or high voltage is present.
Types of Surge Arrester
According to the sensitivity of the equipment, different machinery components may require an elaborate setup of arresters.
Following are the type of arresters at various levels of the network – depending on the class.
Station Class – These are stationed at electric power plants and other high voltage areas. They act as a barrier when the current is irregular for the machine to handle because of lightning or overvoltage.
Intermediate Class – Serving the same purpose as the station class arresters, the intermediate ones are designed to be used in medium voltage equipment areas, such as electrical utility stations, substations, transformers, etc.
Distribution Class – Distribution class are found on exposed lines that have direct connections to rotating machines, especially in transformers.
Likely applications may be small distribution networks and equipment such as distribution transformers, feeding residential or small industrial loads, not directly exposed to the atmosphere and hence to direct lightning strokes. Surge protection instruments can be fitted for the following reasons:
· Protection of AC and DC traction systems
· Protection of series capacitor banks
· Protection of cables
· Protection of transmission lines
· Installation in polluted areas and areas with high seismic activities