What are the Tests and Maintenances That Should Be Done on MV Heads?

MV headers are one of the most sensitive points of the medium voltage cable. Because while the cable is produced in a controlled manner in the factory, the header is often prepared and assembled in the field. For this reason, the tests and maintenance that need to be done on MV headsets are not only to check whether the accessory looks solid; It is done to detect early electrical stresses, workmanship-related weaknesses and environmental effects that may develop in the head area. The fact that many faults in medium voltage cable systems are concentrated in the header and splice areas clearly shows why this maintenance is so important.

The first step in maintenance is always safety. Before working on the MV header, the relevant line or cell must be disabled in the appropriate maneuver order, voltage-free status must be confirmed and the work area must be made safe. The cell to which the header is connected, RMU, transformer bushing or open air connection should also be evaluated together. Because the header is a termination system that works not alone, but together with the cable, equipment and display-grounding chain.

Visual inspection is the basis of maintenance. The headboard body should be carefully examined for cracks, cuts, punctures, swelling, dirt layers on the surface, carbon traces, scar formation, local erosion, UV aging, water marks or oily contamination. While looking for surface darkening, dust accumulation and tracking signs on indoor headsets; In addition to this, rain, UV, salt, industrial contamination and surface sealing become more important in outdoor environments. Even small deteriorations in the external appearance of the head can indicate the risk of major failure in the future.

Cleaning is an important part of MV head maintenance. Dirt accumulated on the surface, especially in outdoor hoods and dirty interior volumes, can increase surface leakage currents when combined with moisture. This increases the risk of tracking, erosion and flashover over time. For this reason, the head surface must be cleaned with the appropriate method, but the material used must not damage the silicone or polymer surface. Improper cleaning practice can shorten head life instead of providing maintenance.

The stress control zone in MV heads requires special attention. Because the electric field intensity naturally tends to increase in this region where the cable screen ends. The most critical design function of the headset is to make this transition safe. During maintenance, it should be evaluated whether the stress control element has slipped out of place, whether there is any deterioration on its surface, whether there is any trace formation or signs of local discharge in the screen cut area. This area is the most challenging part of the title.

Screen and grounding scheme is one of the most critical issues in MV header maintenance. Metal ekranın doğru noktada sonlandırıldığı, ekran topraklama bağlantısının sağlam olduğu, bonding düzeninde gevşeklik bulunmadığı ve ekran iletkenlerinin mekanik olarak güvenli tutulduğu doğrulanmalıdır. Loose or broken display connection not only causes fault behavior; It may also negatively affect the electric field distribution and operating safety of the head. For this reason, header maintenance cannot be considered independent of the screen-grounding chain.

Mechanical connections and shoe areas should also be checked. The equipment terminal to which the header is connected, cable lugs, bolted clamps, connector surfaces and plug-in fasteners, if any, should be examined for tightness and surface health. Looseness occurring in these regions often does not cause electrical faults in the first stage; However, as the contact resistance increases, heating begins and over time it causes serious problems in the head area. Therefore, mechanical tightness is not just an auxiliary control but a fundamental requirement in MV head maintenance.

In indoor MV headers, it should also be observed whether there is mechanical strain in the transition area close to the cable cell or transformer. Improper bending of the cable, pulling it in a way that puts excessive load on the header, or incorrect clamping may strain the termination area over time. For outdoor hoods, the effects of wind, vibration and cable weight on the hood should be evaluated separately. The head must be protected not only electrically but also mechanically.

Thermal camera inspection is an invaluable tool in MV header maintenance. Looseness or increased contact resistance can be noticed at an early stage, especially when the lug connections, terminal surfaces, contact points of plug-in headers and screen grounding tips are thermally examined. A significant temperature difference between phases is a strong sign that requires detailed examination at that point. Abnormal temperature rise in the header body should also be considered for internal degradation or surface discharge behavior.:contentReference[oaicite:1]{index=1}

The partial discharge approach is especially important in MV heads. Because if there is a workmanship-related gap, stress control defect, contamination or local insulation weakness in the head area, this may produce partial discharge behavior. PD measurement is a powerful diagnostic method to detect such punctate defects early. Especially in outdoor titles and critical feeds, some weaknesses that cannot be understood by visual control can be revealed more clearly with PD-based evaluation.:contentReference[oaicite:2]{index=2}

Headers are often not tested separately from the rest of the cable system; It is evaluated together with the cable. For this reason, in the maintenance approach of MV heads, VLF withstand test, tan delta and PD measurement are often applied throughout the cable system. The purpose here is to indirectly or directly evaluate not only the general condition of the cable, but also accessory areas such as headers and splices. The importance of these tests increases especially after head replacement, major repair or commissioning.:contentReference[oaicite:3]{index=3}

Leakage control also has a critical place in MV header maintenance. There should be no gaps, openings or material deterioration that would allow moisture ingress in the area where the header meets the cable outer sheath, the stress control area and the outer protection layers. Moisture is one of the main causes of long-term failures in medium voltage headers. For this reason, the sealing situation should be carefully monitored, especially in the headers rising from the external environment and underground.

In plug-in and separable heads, contact surfaces and screened body structure should be evaluated separately. Improper seating, surface contamination, interface degradation or improper installation of plug-in connections can affect both electrical performance and partial discharge behavior. In these types of titles, it is not enough to just look at the appearance; Manufacturer mounting dimensions, torque values ​​and fit accuracy should also be part of the maintenance decision.

At the end of the care, all findings should be recorded. Visual defects, thermal images, PD findings, tan delta results, torque checks, cleaned areas and replaced parts should be archived regularly. Because MV header malfunctions often do not occur suddenly, but with symptoms that grow over time. When trend monitoring is done, progressive deterioration in a particular topic can be noticed before any malfunction occurs. In summary, the tests and maintenance that must be done on MV heads are; It consists of visual inspection, cleaning, stress control and screen-grounding zone control, mechanical connection verification, thermal inspection and, when necessary, VLF, tan delta and PD evaluations applied with the cable system. If MV headers, cable accessories, RMU-cell-transformer connections and maintenance plan will be evaluated together in your facility HV/MV testing, maintenance and repair with LV/MV/HV project design and consultancy services can support the technical decision process.