What Tests and Maintenance Are Required for Surge Arresters?

Surge arresters are critical elements that protect transformers, cables, circuit breakers and other switchgear equipment by limiting transient overvoltages caused by lightning and switching. However, because this equipment often operates passively, it may appear problem-free in the field for a long time, and this can cause the maintenance need to be overlooked. Yet the surge arrester looking healthy from the outside does not mean that its internal structure is equally healthy. Therefore, the tests and maintenance required for surge arresters are necessary not only for routine inspection but also to understand whether protection actually continues. For related context, see What Is a Surge Arrester? What Does It Do, How Does It Work and What Types Are There?.

The first step of maintenance is always safety. Before working on a surge arrester, the related section should be taken out of service with the correct operating sequence, absence of voltage should be verified and safe working conditions should be established according to the field procedure. If the surge arrester is located near a transformer, MV cubicle, busbar or cable termination, not only the surge arrester itself but also its connection points and grounding path should be evaluated together. Because the protection success of the surge arrester depends not only on its own structure but also on installation quality and grounding arrangement. For related context, see What Is a Transformer? What Does It Do and What Types Are There?.

Visual inspection is the basis of surge arrester maintenance. At this stage, cracks, breaks, deformation, swelling, puncture marks, surface contamination, carbon traces, signs of water ingress, corrosion, terminal looseness and wear on connecting conductors should be searched for on the body. Regardless of whether it has a silicone or porcelain body, deterioration visible on the outer surface is often the first sign of deeper problems. Especially in surge arresters operating outdoors, UV effect, pollution, salt, industrial atmosphere and moisture can affect performance in the long term. For related context, see What Is High Voltage (HV)? Which Values Are Considered High Voltage?.

Surface cleaning is also an important part of maintenance. The dirt layer accumulating on the body can increase surface leakage currents in humid weather and mislead measurement results. Therefore, the surge arrester surface should be cleaned with a suitable method, but harsh interventions that may damage the insulating surface should be avoided. While cleaning, connection caps, terminal bolts and the area around the grounding line should also be checked. Because even a mechanically small looseness can reduce protection performance during an impulse. For related context, see What Is a Current Transformer? What Does It Do, How Does It Work and How Is It Selected?.

Connection and grounding path check is one of the most critical subjects in surge arrester maintenance. The phase connection and grounding connection of the surge arrester should be short, solid and low impedance. A loose bolt, oxidized contact surface, broken conductor strand or unnecessarily long connecting conductor can increase the residual voltage level during an impulse and cause the equipment to be protected to see a higher voltage. Therefore, the connection path at both ends of the surge arrester should be looked at with the same seriousness as its body.

In many applications, surge arresters are used together with a surge counter or disconnector. If these auxiliary elements exist, they must definitely be checked during maintenance. The surge counter value alone does not definitively show the health of the device, but it provides important operating information about how many impulse events have occurred in the field. In structures with a disconnector, it must be verified that the disconnecting element has not accidentally operated, has not mechanically deteriorated and that the surge arrester has not remained silently disconnected from the system. Otherwise, the surge arrester may appear to be in service while protection has actually been lost.

Thermal inspection is one of the most valuable diagnostic methods in the field. With thermal camera or suitable infrared measurement performed while energized, it is observed whether there is a temperature difference between similar surge arresters. A surge arrester behaving significantly hotter than others in the same phase group or same equipment set may indicate increased internal losses and the start of deterioration. Here, comparison with similar devices and change over time are more meaningful than a single temperature reading. Comparisons made under conditions where solar effect is low provide healthier results.

One of the strongest methods for understanding surge arrester health is monitoring leakage current behavior. However, there is an important distinction here: in MOV surge arresters, simple total AC current readings often do not provide a healthy interpretation. What is truly meaningful is the resistive component or third-harmonic-based evaluation. Because as aging, moisture ingress or internal deterioration increases, the resistive current component that causes heating also changes. Therefore, resistive leakage current or watts-loss tracking stands out in advanced condition monitoring applications.

Watts-loss assessment is an important diagnostic tool especially in more critical and high-voltage applications. The power loss caused by the small currents passing through the surge arrester can show internal deterioration starting at an early stage. However, in these types of tests, the measurement approach must be established correctly so that external leakage currents caused by surface contamination do not affect the results. Since a dirty body, damp surface or incorrect connection methods may lead to incorrect interpretations, these tests should be performed by experienced teams and with a suitable test setup.

In some applications on the low- and medium-voltage side, insulation resistance testing can also be used as a practical verification method. Especially when faulty surge arresters show short-circuit or low-resistance behavior, this test provides fast screening. However, here too the test method should be selected carefully because surface leakage current may distort the result. Insulation resistance measurement is not a single test that tells everything; it gains value more with a pass-fail logic when interpreted together with other findings.

In some fields, reference voltage, V-I characteristic or manufacturer-specific diagnostic methods can also be used. Such tests help evaluate the behavior of the internal MOV blocks of the surge arrester more sensitively; however, they may not be routine and practical methods for every facility. Therefore, when creating a maintenance program, the same approach should not be applied to all surge arresters; distribution type, station type, duty criticality, environmental conditions and operating history should be considered together.

Comparison is very important in surge arrester maintenance. Temperatures, leakage current values, surge counter history and visual conditions of similar surge arresters in the same facility should be evaluated together. Because the absolute value of a single device can sometimes be misleading; in contrast, differences compared with partner devices reveal the problem earlier. Especially in three-phase structures, clear deviations between phases are strong signs requiring detailed inspection.

At the final stage, all findings must be recorded. Visual inspection results, cleaned areas, tightened connections, thermal images, counter records, leakage current measurements, watts-loss results and replacement recommendations should be archived regularly. When trend tracking is not performed, surge arrester deterioration is often noticed only after a fault occurs. In summary, the tests and maintenance required for surge arresters consist of visual inspection, cleaning, connection and grounding verification, surge counter-disconnector check, thermal inspection, leakage current and watts-loss assessment under suitable conditions and insulation tests when required. If surge arresters in your facility will be evaluated together with transformer and switchgear equipment, it is possible to proceed in an integrated way with HV/MV testing, maintenance and repair, LV/MV/HV project design and consultancy for system design and HV operation responsibility services in operation processes.