INTRODUCTION

Lightning arresters are often referred to as “soldiers of the power system” because they play a crucial role in protecting electrical systems and equipment from the destructive effects of lightning strikes. Just like soldiers defend and protect their territory, lightning arresters safeguard power systems.

Lightning is a natural phenomenon that generates extremely high voltages and currents. When lightning strikes occur, they can induce surges or transient overvoltages in power lines, which can potentially damage or destroy electrical equipment connected to the system. These overvoltages can disrupt power transmission and distribution, cause equipment failure, and even pose a safety hazard.

What is a surge arrester in the substation?

Lightning/Surge arresters are devices specifically designed to protect power systems from such overvoltages. They are connected in parallel with the electrical equipment or conductors and provide a low-impedance path for the lightning surge to follow, diverting the excess energy safely to the ground. By doing so, they limit the voltage levels to a safe range, preventing damage to the equipment.

In this sense, lightning arresters act as the first line of defense against lightning strikes. They absorb and dissipate the enormous energy associated with lightning surges, acting as “soldiers” that shield the power system from harm. Without lightning arresters, the electrical infrastructure would be highly vulnerable to lightning-induced damage, leading to frequent disruptions, costly repairs, and extended power outages.

The metaphorical term “soldiers of the power system” emphasizes the vital role played by lightning arresters in maintaining the reliability and resilience of electrical grids, protecting equipment, and ensuring an uninterrupted power supply.

Today, lightning arresters are an integral part of modern power systems. They have evolved to incorporate advanced technologies and features to ensure optimal protection against lightning strikes. The design and installation of lightning arresters are based on extensive research, testing, and standards developed by organizations such as the Institute of Electrical and Electronics Engineers (IEEE) and the International Electrotechnical Commission (IEC).

Where is the surge arrester placed in the substation?

To protect a unit of equipment from transients occurring on an attached conductor, a surge arrester is connected to the conductor just before it enters the equipment.

What is an arrester used for?

The purpose of using a surge arrester is to always limit the voltage across the terminals of the equipment to be protected below its insulation to withstand voltage. This is achieved by connecting elements with an extremely nonlinear voltage-current characteristic (varistor) in parallel to the terminals of the equipment.

How Does a Lightning Arrester Work?

• Metal oxide (MO) surge arresters containing ceramic MO elements mainly made from zinc oxide and bismuth oxide are used.
• The resistor elements offer non-linear resistance such that for normal frequency the power system voltage resistance is high and the lightning arrester does not conduct.
• When a surge voltage travels along the line and comes to the arrester the gap breaks down and the resistance is low the surge is diverted to the earth.
• After a few microseconds, the surge vanishes and the power frequency voltage is set up across the arrester and the arc current reduces.

• All electrical equipment in an electrical system needs to be protected from voltage surges.
• The rating of the arrester, the class of the arrester, and the location of the arrester all play a part in surge protection.
• Surge arresters protect the equipment of transmission and distribution systems, worth several magnitudes more than the arresters themselves, from the effects of lightning and switching overvoltages.

What are the tests conducted on surge arresters?

1. Insulation Withstand Test- is an electrical test carried out on a component or product to determine its insulation strength.
2. Residual Voltage test This test confirms that no dangerous voltages are present after the supply has been removed as a result of circuits retaining a charge.
3. Power Frequency Voltage versus Time Curve
4. Internal Partial Discharge Test
5. Moisture ingress Test (For Station type Surge Arrester)

Causes for Failure of Metal Oxide Surge Arresters

• Incorrect arrester specification corresponding to actual system voltage and overvoltage stress
• Overloading due to:

o Temporary overvoltages (cracking, puncturing)

o Switching overvoltages (cracking, puncturing, and flashover)

o Lightning overvoltage (change of characteristic/aging, flashover, puncturing).

• External pollution or moisture penetration
• The consequence of aging: Increase in the continuous resistive leakage current. This is a good indicator of the arrester’s condition.

Methods for Monitoring of Degradation of MOSA

• Visual inspection

               Locating external abnormalities on the arrester gives practically no information about the internal of the arrester.

• Surge counters

               Frequently installed on MOSA, but has no practical use for diagnosis of the condition of the arresters.

• Temperature measurements–Thermo Vision

               Frequently used method. Detects the increased block temperature on the housing surface of the arrester.

• Leakage current measurements

               For in-service testing, the method with the indirect determination of the resistive leakage current with compensation for harmonics in the voltage provides the best available information quality with respect to diagnostic efficiency.