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A surge arrester is a line of defense that prevents damage to electric systems. But just as in the case of protective devices, it has to be tested regularly. It should be tested frequently to make sure that it is functioning within safe parameters and offering protection.
In this guide, we'll discover how to test a surge arrester, explaining steps such as measuring its leakage current and using a multimeter. This ensures your equipment remains safe and compliant with international standards.
Here are situations that call for a test:
Lightning or switching surges: Each time lightning strikes or there is a high-energy surge, the internal metal oxide varistor (MOV) of a surge arrester can degrade slightly. After such a major mishap, a performance check is recommended to ensure that the arrester is still performing excellently.
Planned Maintenance: Surge arresters are normally planned to have their testing done at least once every 12 to 24 months, even in situations where there is no lightning strike or high-energy surge event. Conducting frequent tests enables you to notice early signs of failure.
After long-term installation: Arresters that have been installed for a long time need to be tested to confirm they can still operate within safe limits.
Visible damage: In case of any visible injury, such as cracks, dirt or burn marks on the arrester, it should be tested. These defects can affect the performance of the arrester and increase more chances of failure.
Here are the right tools needed for accurate and reliable results:
Insulation resistance tester (megger): This is a measuring device that is used to read the insulation resistance of the line and earth terminals.
Leakage current meter: This is a device that is used to test the amount of current flowing on the arrester during normal voltage conditions.
Multimeter: A multimeter is used to check the voltage and continuity before and after testing.
Infrared Thermometer: This tool is used to detect abnormal heating on the arrester surface.
Personal Protective Equipment: PPE is used to protect linemen who want to test arresters in high-voltage environments.
Before testing a surge arrester, it is important to prepare properly. This ensures that you get accurate readings and maintain personnel safety. Here's how to do so:
Verify system isolation: Ensure the circuit is de-energized or isolated. Use proper procedures, like the lockout/tagout (LOTO), to prevent accidental re-energization, which could cause fatalities. Confirm that the arrester is fully disconnected from the line and earth terminals.
Discharge the arrester: Even when the circuit is de-energized, arresters can retain residual voltage, which could cause injury. Use an insulated discharge rod to safely discharge the arrester completely before handling.
Check the environment: Is the test area dry, clean, and free from debris? Is there any unauthorized personnel present in the test area? Keep unauthorized persons away from the test zone for safety reasons.
Gather your tools: Prepare your test tools - multimeter, infrared thermometer, leakage current meter, and insulation resistance tester. Ensure they are in good condition so that you can get accurate results.
An arrester's physical appearance can reveal its internal condition. Visually inspect the arrester for physical damage. Therefore, conduct a visual inspection for the following:
Cracks or chips: Check for cracks or chips on the porcelain or polymer housing.
Discoloration: Check for discoloration or burn marks, as this could be an indication of a partial discharge or flashover.
Loose terminals: Check if the terminals are loose or corroded. Inspect for damaged connectors.
Debris buildup: Check for the buildup of debris, such as dust, salt, or oil film.
Moisture ingress: Check for signs of moisture ingress, like rust or stains on the surface and around joints.
If you find any sign of contamination, clean the surface with a dry cloth and a recommended cleaning solution. If physical damage is severe, don't proceed with testing; otherwise, you'll get inaccurate results. Replace the arrester immediately.
Use an insulation resistance tester to determine whether the arrester's insulation is still intact. To do this, first, disconnect both line and ground connections. Connect one terminal of the insulation resistance tester to the arrester's top terminal. Connect the other terminal of the tester to the base terminal.
Select a suitable DC test voltage, which is usually 1000V for low-voltage arresters and up to 5000V for high-voltage arresters. Press the test button and observe the reading. Note down the outcome and redo the test in case of any error or discrepancy.
If the outcome exceeds 100 MΩ, it indicates that the arrester is well insulated. If the outcome is 20-100 MΩ, then this indicates that the insulation is moderate; however, you should keep track of its operation after some interval. If the outcome is below 20 MΩ, the insulation of the arrestser is of poor quality, possibly due to moisture or internal damage.
When there is an abrupt decrease in insulation resistance relative to the past test results, it indicates the development of an insulation failure. Another precaution is as follows: after each test, wait a few seconds so that the internal charge can be dissolved before handling the terminals.
Using a leakage current measurement helps to measure the flow of current through the arrester under normal operating voltage. With this, you'll be able to know the health of the metal oxide varistor elements inside.
Reconnect the arrester to the system or energize the line under nominal voltage conditions. Clamp the leakage current meter around the arrester's grounding conductor. Note the amount of leakage current in microamperes (µA) or milliamperes (mA).
In case the current is stable or low, the arrester is in good condition. In case it develops gradually over time, it means that the arrester is old or has been impure. In the case of a sharp rise in the current levels, it is an indicator that there is an internal breakdown, and it is advisable to replace it immediately.
Here's a tip: compare the present values on all arresters in the same circuit to show elements that may be wearing out.
This step helps to verify that the arrester still limits surge voltage effectively during a simulated surge. It requires specialized lab equipment and should be performed by qualified technicians to get accurate results.
To conduct this test, disconnect the arrester from the power system. Connect the arrester to a high-voltage test set or impulse generator capable of supplying short-duration surge pulses. Apply a known test voltage as outlined in specifications. Measure the corresponding residual voltage across the arrester terminals using a voltage divider.
Compare the measured variables to the manufacturer's data. If the result is within ±10% of the rated value, the arrestser is in good condition. If the result is significantly higher, it means the varistor elements have degraded and the protective performance has reduced.
Every test and result should be documented to identify performance trends and schedule maintenance. Have a test log to record the following information:
Date and time of test
Arrester identification (location, rating, serial number)
Environmental conditions (dry or wet, hot or cold)
Measured values (insulation resistance, leakage current, residual voltage, temperature)
The model and calibration date of the test tool used
Remarks or observations
Compare current readings with previous readings. If there are gradual degradation trends, that means the arrester is aging. If there are abrupt changes, that means there is an insulation failure due to moisture ingress.
After completing the tests, safely discharge any residual charge using an insulated rod. Reconnect the arrester properly to the line and ground terminals. Tighten the bolts and inspect the installation once more for cleanliness.
Remove the lockout/tagout device and restore power once personnel are clear. Once the power has been restored, watch the arrester work for a few minutes. Make sure that there are no sparking, overheating, or discharge.
High leakage current: Leakage current may increase due to moisture ingress, surface contamination, or degradation of the zinc oxide elements. The arrester is commonly advised to be cleaned, dried, or replaced.
Low insulation resistance: If there is low insulation resistance, this could be a result of water or dust accumulation, a cracked surface, or prolonged exposure to pollution. It is recommended that you replace the arrester to avoid flashover failures.
Surface cracks: Surface cracks should not be overlooked, as they may be one of the outcomes of mechanical stress, physical impact, or UV degradation. The best course of action is to change the arrester.
Abrnomal heating: The arrester may be subjected to abnormal heating, which may be due to poor electrical contact of the terminals. It may also be caused by discharge partially within the arrester or a large leakage current caused by internal breakdown.
Abnormal residual voltage: When the value of the test on the residual voltage is greater than the rated value, the arrester can become ineffective. Immediately replace it in order to protect the system.
When initiating any test, make sure that the system is totally de-energized and isolated. Safety is guaranteed by following the lockout/tagout (LOTO) procedure.
Always discharge the arrester safely to ground before connecting test leads. This is because arresters can retain a residual charge.
Always wear personal protective equipment, such as insulated gloves, safety goggles, and appropriate footwear, to minimize the risk of injury.
Verify tools and equipment before you use them to get accurate results and prevent short-circuits.
Keep a safe distance between the test area and nearby conductive materials to avoid contact during measurement.
Follow the manufacturer's guidelines to ensure the arrester adheres to the safety and testing recommendations.
Routine maintenance intervals: For indoor or clean environments, surge arresters should be tested every 24 months. For outdoor or high-pollution areas, surge arresters should be tested every 12 months. For heavy-duty or coastal installations, surge arresters should be tested every 6-12 months.
After abnormal operating events: Test surge arresters after a major lightning strike, a high fault occurrence, or the appearance of physical damage.
According to International Standards: Industry standards such as IEC 60099-5 recommend periodic testing of surge arresters to maintain protection and reliability.
Regular testing of surge arresters helps to maintain their effectiveness. By following proper procedures and using the right tools, you can prolong the life of your surge arresters.
If you need surge arresters for indoor or outdoor installations, feel free to contact us at Haivol Electrical.
No, a surge arrester is not the same as a surge protector. A surge arrester is a device installed at the service entrance of a building to protect the electrical system from high-energy surges. A surge protector is usually smaller, installed on secondary circuits, to protect sensitive equipment from smaller surges that pass the main arrester.
When a surge arrester fails, it can cause short circuits, service interruptions, safety risks, and damage other equipment. Simply put, it can become unprotective against high-energy surges.
The lifespan of a surge arrester is 3 to 5 years. However, the lifespan of a surge arrester can be greatly affected by a lot of factors, such as frequency and intensity of power surges, harsh environmental conditions, and the quality of the device.
A surge arrester contains metal oxide varistors (MOVs) - ceramic discs made of zinc oxide, that divert excess voltage to the ground. They act as insulators during normal voltage levels but become conductors when there is a voltage spike.
Yes, lightning can strike an arrester. This is why there are specialized arresters, such as a lightning arrester, to divert high voltage to the ground when this occurs.
