What are the Tests and Maintenances That Should Be Done on Surge Arresters?

Surge arresters are critical elements that protect transformers, cables, breakers and other switchgear equipment by limiting temporary overvoltages caused by lightning and switching. However, since these equipment often operate in a passive state, they may appear trouble-free in the field for a long time, which may lead to the need for maintenance being overlooked. However, just because the surge arrester looks solid from the outside does not mean that its internal structure is equally healthy. For this reason, the tests and maintenance that must be done on surge arresters are not only for routine control; It is necessary to understand whether the protection really continues.

The first step in maintenance is always safety. Before working on the surge arrester, the relevant section must be disabled in the correct operating order, voltage relief must be verified and safe working conditions must be created according to the field procedure. If the surge arrester is located near a transformer, MV cubicle, busbar or cable head, not only the surge arrester itself, but also the connection points to which it is connected and the grounding path should be evaluated together. Because the protection success of the surge arrester depends not only on its own structure, but also on its installation quality and grounding scheme.

Visual inspection is the basis of surge arrester maintenance. At this stage, cracks, fractures, deformation, swelling, puncture marks, surface contamination, carbon traces, signs of water ingress, corrosion, terminal looseness and wear on the connection conductors should be looked for on the body. Regardless of whether it has a silicone or porcelain body, deteriorations on the outer surface are often the first sign of deeper problems. Especially in surge arresters operating outdoors, UV effects, contamination, salt, industrial atmosphere and humidity can affect performance in the long term.

Surface cleaning is also an important part of maintenance. The layer of dirt accumulated on the body can increase surface leakage currents in humid weather and mislead the measurement results. For this reason, the surge arrester surface should be cleaned with the appropriate method, but harsh interventions that would damage the insulating surface should be avoided. While cleaning, the connection heads, terminal bolts and the grounding line should also be checked. Because even a seemingly small mechanical looseness can reduce the protection performance at the time of impact.

Connection and grounding path control is one of the most critical topics in surge arrester maintenance. The phase connection and grounding connection of the surge arrester must be short, solid and low impedance. Loose bolt, oxidized contact surface, broken conductor wire or unnecessarily long connection conductor; It may increase the residual voltage level during impact and cause the equipment to be protected to see higher voltage. Therefore, not only the body of the surge arrester, but also the connection path at both ends should be looked at with the same seriousness.

In many applications, surge arresters are used with surge counters or disconnectors. If these auxiliary elements are present, they must be checked during maintenance. The surge counter value alone does not accurately indicate the health of the device, but it provides important operational information about how many shock events occur in the field. In structures with disconnectors, it must be verified that the disconnecting element is not activated accidentally, is not mechanically damaged, and the surge arrester does not remain silently disconnected from the system. Otherwise, even though the surge arrester appears to be active, the protection may actually be lost.

Thermal examination is one of the most valuable diagnostic methods in the field. With a thermal camera or appropriate infrared measurement when energized, it is observed whether there is a temperature difference between similar surge arresters. If a surge arrester behaves significantly hotter in the same phase group or in the same type of equipment array, it may indicate that internal losses have increased and deterioration has begun. Here, comparison with similar devices and change over time are more meaningful than a one-time temperature reading. Comparisons made under conditions where the sun effect is low give better results.

One of the most powerful methods for understanding surge arrester health is monitoring leakage current behavior. However, there is an important distinction here: Simple total AC current readings in MOV surge arresters often do not give a reliable interpretation. What is really meaningful is the evaluation based on the resistive component or the 3rd harmonic. Because as aging, dehumidification or internal deterioration increases, the resistive current component that causes heating also changes. For this reason, resistive leakage current or watts-loss monitoring comes to the fore in advanced condition monitoring applications.

Watts-loss evaluation is an important diagnostic tool, especially in more critical and high voltage applications. Power loss caused by small currents passing through the surge arrester may indicate early deterioration in the internal structure. However, in this type of tests, the measurement approach must be established correctly so that external leakage currents caused by surface pollution do not affect the results. Since dirty body, damp surface or incorrect connection methods may lead to erroneous interpretations, these tests should be performed by experienced teams and with appropriate test equipment.

In some applications on the low and medium voltage side, insulation resistance testing can also be used as a practical verification method. This test provides a quick elimination, especially in cases where faulty surge arresters exhibit short circuit or low resistance behavior. However, here too, the test method must be chosen carefully, as the surface leakage current may distort the result. Insulation resistance measurement is not the only tell-tale test; It gains value when interpreted together with other findings, in a pass-fail logic.

In some areas, reference voltage, V-I characteristic or manufacturer-specific diagnostic methods may also be used. Such tests serve to evaluate more precisely the behavior of the internal MOV blocks of the surge arrester; However, it may not be a routine and practical method for every facility. Therefore, the same approach should not be applied to all surge arresters when creating a maintenance program; distribution type, station type, mission critical, environmental conditions and operating history should be considered together.

Comparison is very important in surge arrester maintenance. The 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; On the other hand, differences compared to partner devices reveal the problem earlier. Especially in three-phase structures, significant deviations between phases are strong signs that require detailed examination.

In the final stage, all findings should be recorded. Visual inspection results, cleaned areas, tightened connections, thermal images, meter records, leakage current measurements, watts-loss results and replacement recommendations should be archived regularly. If trend monitoring is not done, surge arrester failure is often noticed only after the failure occurs. In summary, the tests and maintenance that must be done on surge arresters are; It consists of visual control, cleaning, connection and grounding verification, surge counter-disconnector control, thermal inspection, leakage current and watts-loss evaluation under appropriate conditions and insulation tests when necessary. If surge arresters will be used together with transformers and switchgear equipment in your facility HV/MV testing, maintenance and repairfor system design LV/MV/HV project design and consultancy and business processes SA operation responsibility It is possible to progress in integration with services.