Surge arresters
Surge arresters are also sometimes called as lightning arresters (but technically they are different), they are used to protect electrical systems from voltage surges or transient over-voltages. Transient means anything which happens for a very short period of time. These surges can occur due to various factors such as lightning strikes, switching operations, or equipment faults.
Fig1-Surge arrestor of different voltage levels (PC-Megger.com)
Lightning arresters
They are not really an equipment ,they are towers which are also called lightning mast (LM) tower, it is of significant height with spike installed on its top to attract the lightning during thundering ,this spike is grounded so that the lightning voltage can be earthed . Height of lightning mast tower is higher than all the equipment placed in the switchyard, so that lightning will first fall on this tower and get grounded and will protect all other equipment in a factory/substation.
Surge arrestors typically consist of a metal oxide varistor (MOV) or a gas discharge tube that has the ability to conduct high voltages. MOVs can change its resistance based on the applied voltage. If the voltage across it increases the resistance decreases and vice versa. When a surge occurs, the surge arrestor detects the overvoltage and rapidly activates, shunting the excess energy away from the protected equipment or circuit.
A MOV consist of approximately 90% of Zinc oxide and a small amount of other metal oxides. The ceramic powders of the metal oxides are kept intact between two metal plates called the electrodes. Thus MOV becomes as a large number of diodes connected in series.The MOV varistor starts conducting when a specific voltage is applied across the connecting leads and stops conducting when the voltage falls below the threshold voltage.
The surge arrestor is usually installed at the entry point of a electrical system, such as the main electrical panel or distribution board and also placed as first equipment in the Substations to stop high voltage from entering the internal circuit and equipment and thus protecting the remaining equipment and circuits.
(PC-pintrest)
Testing and commissioning of Surge Arresters :
- Insulation Resistance Test: An insulation resistance test is conducted to verify the insulation integrity of the surge arrestors. This test measures the resistance between the terminals of the surge arrestor and its housing or ground. It ensures that there are no electrical leaks or faults in the insulation. 2.5 Kv or higher voltage is injected using a IR tester between both ends of S.A and its value is measured. In substations only visual inspection and IR test is conducted usually. However we can also conduct some other tests as explained below.
- Voltage-Withstand Test: This test assesses the ability of the surge arrestor to withstand high voltages. The surge arrestor is subjected to a higher voltage than its rated voltage for a specific duration to ensure it can handle transient over-voltages without failure.
- Surge Current Rating Test: Surge arrestors are designed to handle specific surge currents. This test verifies whether the surge arrestor can handle the anticipated surge currents without damage. Surge currents are simulated using appropriate equipment to replicate real-world conditions.
- Grounding Verification: Surge arrestors rely on a proper grounding system to effectively divert surges. During the commissioning process, the grounding system is checked to ensure it meets the required standards and provides a low-impedance path for surge currents.
Surge Arrester Counter
This counter is installed with Surge arresters which displays leakage current values and as per the current value, health of Surge arrester is determined. If the leakage current value is in green zone then it means that arrester is in healthy condition ,and if value of leakage current is high and it goes in red zone then it means that arrester needs to be replaced.
Surge arresters test kit: There are kits available nowadays which can live test Surge arresters on load by measuring leakage current values. If these values are found to be in permissible range then a S.A is considered to be healthy. It is also to be noted that metal oxide varistor (MOV) deteriorate over time due to various reasons . As MOVs deteriorate, their clamping voltage may increase, meaning they may not provide the same level of protection as when they were new. This can leave the connected equipment more vulnerable to voltage surges. To ensure the continued effectiveness of surge protection, it is recommended to periodically inspect and test MOV-based surge arresters.
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FAQs
- What is the primary purpose of a surge arrester?
The primary purpose of a surge arrester is to protect electrical and electronic equipment from damage caused by voltage surges, including those resulting from lightning strikes, switching operations, and other transient events. - How does a surge arrester work?
Surge arresters work by providing a low-impedance path for transient surges to follow. They are designed to limit the voltage across the protected equipment by conducting the surge current safely to the ground. - Where are surge arresters typically installed?
Surge arresters are commonly installed at critical points in electrical systems, such as distribution substations, overhead power lines, and near sensitive electronic equipment, including computers and communication systems. - What types of surges do surge arresters protect against?
Surge arresters protect against various types of surges, including lightning-induced surges, switching surges, and other transient voltage disturbances that can occur in power systems. - Are surge arresters only used for lightning protection?
While surge arresters are commonly associated with lightning protection, they also protect against voltage surges originating from other sources, such as load switching, equipment faults, and line faults. - Are there different types of surge arresters?
Yes, there are different types of surge arresters, including metal-oxide surge arresters (MOA), gapped surge arresters, and silicone-carbide (SIC) surge arresters. Metal-oxide surge arresters are the most widely used type. - What is the lifespan of a surge arrester?
The lifespan of a surge arrester depends on factors such as the type of arrester, its operating conditions, and the specific manufacturer. - How often should surge arresters be inspected and maintained?
Surge arresters should be visually inspected regularly, and their condition should be assessed based on manufacturer recommendations and industry standards. Routine maintenance may include cleaning, inspection, and testing. - Can surge arresters be used in residential applications?
Yes, surge protectors designed for residential use are a common form of surge arresters. They are used to protect household electronics and appliances from voltage surges. - Are surge arresters a substitute for proper grounding?
Surge arresters are not a substitute for proper grounding. Grounding is a fundamental part of electrical safety and helps discharge electrical surges effectively. Surge arresters complement grounding by providing an additional layer of protection. - Can surge arresters wear out over time?
Surge arresters can deteriorate over time due to environmental factors, exposure to surges, and aging. It’s important to monitor their condition and replace them when necessary to maintain their protective capabilities. - Are there standards and regulations governing the use of surge arresters?
Yes, there are international standards and regulations, such as IEEE and IEC standards, that provide guidelines for the selection, installation, and maintenance of surge arresters to ensure their effectiveness and safety. Compliance with these standards is essential. - What should I consider when selecting a surge arrester for a specific application?
When selecting a surge arrester, factors to consider include the system voltage, surge energy capacity, voltage protection level, location of installation, and manufacturer’s recommendations. Consulting with a qualified engineer is advisable for proper selection.
Read fundamentals of surge arrestor here.
