What are the Tests and Maintenances That Should Be Done in Substations?

Substations are not facilities consisting of only a power transformer; They are live energy nodes that contain switchgear equipment, measurement transformers, surge arresters, protection relays, auxiliary DC systems, grounding infrastructure and many secondary circuits. For this reason, the tests and maintenance that need to be done in substations should be considered more broadly than the maintenance approach that focuses on a single piece of equipment. Failure of any critical part within the center can affect not only its own performance but the energy continuity and security of the entire facility.

The first step in substation maintenance is always safety. The section where the work will be carried out must be de-energized in the correct maneuver order, the separator and earth separator positions must be verified, the tension must be confirmed with suitable devices and site access must be made safe. Especially in MV and HV centers, maintenance does not only mean testing the equipment, but also creating the correct isolation and correct work permit. That's why preparation before maintenance is as important as the maintenance itself.

The general site inspection is the starting point of the maintenance program. At this stage, cells, transformer surroundings, cable ducts, busbar rooms, grounding conductors, areas where oil leakage is possible, ventilation, fire safety equipment, door locks, warning signs and access roads should be reviewed. Findings such as dust, moisture, corrosion, signs of overheating, loose connections, animal or pest effects, risk of water intake and signs of mechanical damage determine the direction of detailed maintenance.

In power transformer maintenance, different topics stand out according to oily and dry type design. In oil-filled transformers, oil level, leakage status, radiators, fans, Buchholz-like protection elements, connection terminals and bushing surfaces are checked. In addition, oil samples are taken and DGA, general oil quality and, if necessary, moisture or aging indicators are evaluated. On the electrical side, tests such as winding resistance, turns ratio, insulation evaluation, capacitance and power factor, if necessary, provide valuable information about the internal state of the transformer.

In dry type transformers, the cleanliness of the resin surface, cracks or surface deterioration, connection tightness, contamination in the winding areas, fan and ventilation arrangements and thermal traces stand out. However, regardless of the type, the basic purpose for the transformer is the same: protecting the health of the winding, insulation and connection. Both the electrical and thermal behavior of the transformer should be monitored regularly, especially in industrial centers experiencing large load changes.

Breakers are one of the most critical protection elements of the substation. Therefore, timing test, on-off times, synchronism between poles, contact resistance measurement, coil currents, spring winding system, auxiliary contacts and mechanical interlocks should be checked regularly. Even if the breaker seems to be working in the field, late tripping, incompatibility between phases or increased contact resistance can turn into a big problem in case of failure. Therefore, cutter maintenance should not be seen only as mechanical lubrication work.

For disconnectors and earthing switches, visible separation and safe earthing function must be verified separately. Check whether the separator blades have fully reached the final position, contact pressure, mechanical movement, interlock system, position indicators and auxiliary contacts. In earth separators, in addition, whether an effective earth path is formed, earth busbar connections and safe maneuvering order must be evaluated. Because substation maintenance safety often depends on the correct operation of these equipment.

Current transformers and voltage transformers are the basic data sources of the protection and measurement systems within the center. Therefore, ratio accuracy, polarity, burden effect, secondary circuit continuity, single-point grounding rule and connection logic should be reviewed regularly. While excitation and knee point evaluation may be necessary in CTs for protection purposes, phase relationship and secondary voltage accuracy come to the fore in VT circuits. In order for relays to make correct decisions, these measurement transformers must first work properly.

Surge arresters are among the silent but critical protection elements in the substation. Body cracks, surface contamination, moisture effect, connection tightness, grounding path, surge counter and disconnector status, if any, should be checked regularly. Thermal comparisons made in the energized state and, in appropriate applications, monitoring leakage current behavior can help detect early arrester aging. Particularly, surge arresters at transformer entrances, cable terminations and open field connection points should not be neglected.

Protection relays and secondary systems are a separate main topic of substation maintenance. Test scenarios should be applied to verify the accuracy of relay settings, secondary injection tests, alarm and trip logics, trip chain, auxiliary contact feedback, SCADA signals and, when necessary, the entire protection system. It is not enough just for the relay to be energized; The current-voltage information seen by the relay, the decision it makes and the command chain it transmits to the breaker must be tested as a whole.

Auxiliary AC/DC systems in the center are structures that are often remembered only in case of failure, but are of critical importance. Battery groups, rectifiers, DC distribution circuits, fuses, charger alarm outputs, breaker on-off feeds and emergency lighting infrastructure should be included in the maintenance program. If the auxiliary supply is weak, even the most accurate relay setting and the most robust breaker may not perform as expected at the time of the actual fault.

The grounding system is the backbone of substation safety. The main ground bar, equipotential connections, equipment bodies, doors, cable screens, lightning rod-grounding relationship and field grounding points should be examined regularly. Earth resistance or continuity checks should be made where necessary, and loose or corroded connections should be corrected. Especially in centers with large areas, the grounding network may weaken over time due to mechanical damage, corrosion or additional installations.

Thermal camera inspections are one of the most efficient tools of the substation maintenance program. When busbar connections, cable headers, breaker terminals, separator contact areas, transformer bushings, surge arresters, LV panel connections and battery connections are thermally scanned, invisible looseness and resistance increases can be detected early. What is important here is not a single temperature value, but the evaluation of the differences between similar phases and similar equipment.

One of the most critical but often neglected aspects of maintenance is record keeping. Oil analysis reports, on-off times, contact resistance measurements, relay test reports, grounding measurements, thermal images, battery results and field observations should be collected in a single history. Because many equipment problems occur not with sudden failure, but with slow change. If trend monitoring is not done, small deteriorations will only be noticed when a malfunction occurs.

In summary, the tests and maintenance that need to be done in transformer centers are; It consists of general field inspection, power transformer checks, breaker and switchgear equipment tests, disconnector and ground separator verifications, current-voltage transformer checks, surge arrester inspections, protection relay and secondary circuit tests, auxiliary DC system maintenance, grounding checks and thermal inspections. The correct maintenance approach is based on seeing the health of the center before the failure occurs, not just repairing the fault. If the substation general maintenance plan, MV/HV equipment tests, protection system verification and operational safety will be handled together in your facility. HV/MV testing, maintenance and repair, LV/MV/HV project design and consultancy, transformer maintenance and testing and SA operation responsibility It is possible to progress in integration with services.