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

Transformers are among the most critical system equipment that ensures safe and efficient conversion of electrical energy. For this reason, the tests and maintenance that need to be done on transformers are not only procedures that come to the fore when a malfunction occurs. The main purpose is to constantly monitor the electrical, thermal and mechanical health of the transformer; It is about noticing small deteriorations before they turn into major malfunctions. Because a neglected connection problem, insulation weakness or oil degradation in a transformer may, over time, affect not only the equipment itself but also the continuity of the entire facility to which it is connected.

The first step in maintenance is always safety. Before working on the transformer, the relevant section must be disabled in the correct maneuvering order, all connections must be made secure and voltage free must be confirmed. Especially in oil-based power transformers, simply cutting off electrical energy is not enough; In-tank pressure, hot surface, oil level and auxiliary systems should also be taken into account. Therefore, transformer maintenance should be planned in accordance with the working discipline on primary equipment.

Visual inspection is the basis of maintenance in transformers. At this stage, oil leakage, radiator condition, tank body, paint damage, rust, bushing surfaces, connection terminals, conservator, silica gel breather, Buchholz connections and cooling equipment in oil-filled transformers should be visually inspected. In dry type transformers, resin surfaces, body, ventilation ducts, dust accumulation, cracks, connection tightness and traces of overheating should be carefully checked. Although visual inspection may seem simple, this is the first sign of most serious malfunctions.

In oil-filled transformers, the condition of the oil is one of the most critical topics of the maintenance program. Dissolved Gas Analysis, or DGA, is one of the most powerful methods to understand the thermal and electrical stresses inside the transformer at an early stage. Thanks to the analysis of gases dissolved in oil, developing faults such as overheating, partial discharge, arcing or insulation deterioration can be detected before they become larger. In addition, the moisture, dielectric strength, acidity and general quality of the oil are also important for the service health of the transformer.

One of the most basic topics in electrical tests is transformer turns ratio. This test checks whether the winding ratio of the transformer complies with the label value and steps. Rate deviation; It may indicate issues such as winding problem, wrong tap position or internal connection defect. Particularly after maintenance, after OLTC intervention or in questionable operating situations, ratio testing provides invaluable information.

Winding resistance measurement is one of the basic tests that must be performed on transformers. Winding resistance test; It provides important data on winding continuity, internal connections, solder or connection areas and especially tap changer contact health. Abnormal increases are more easily noticed when values ​​are compared between phases or with previous measurements of the same transformer. That's why taking measurements alone is not enough; Trend following is very important here.

Insulation and dielectric health considerations are critical to long-life operation of the transformer. Tests such as insulation resistance, power factor or tan delta, capacitance; Helps understand signs of moisture, contamination, aging and deterioration in the main insulation system. Especially in power transformers, the dielectric state between winding-ground and windings tells much more than simple visual control. Therefore, the appropriate dielectric test package should be included in the maintenance plan according to the type and criticality of the transformer.

Bushings are among the most sensitive external equipment of the transformer and should be evaluated separately during maintenance. Surface contamination, cracks, oil leaks, porcelain or composite body damage, terminal looseness and thermal anomaly are the first points to look for. In addition, bushing capacitance and power factor measurements are important diagnostic tools to monitor bushing health, especially in high voltage transformers. Because a bushing failure can often have critical consequences that can disable the entire transformer.

The maintenance program becomes even more important in transformers with on-load tap changer, i.e. OLTC. Because in many power transformers, one of the parts that are exposed to the most mechanical and electrical stress is the OLTC system. Step change behavior, motor driver group, auxiliary contacts, mechanical synchronization, diverter compartment status in oiled types and necessary electrical controls should be carefully monitored. When OLTC is neglected, the voltage regulation of the transformer may be disrupted and the risk of serious internal faults may increase.

Cooling system control is directly decisive for the life of the transformer. In oil-filled transformers, fans, pumps, radiators, thermometers, alarm and trip contacts, automatic control logic and auxiliary feeds must operate correctly. Failure to activate the fan or pump group in the transformer under load on hot days can seriously reduce the insulation life. In dry type transformers, the cleanliness of the cooling channels, the health of the fans if there is a fan system, and not obstructing the air flow are of great importance.

Protection and auxiliary accessories are also a natural part of care. The Buchholz relay, pressure relief elements, oil level indicators, temperature indicators, dehumidification system, alarm contacts and auxiliary wiring should be checked regularly. Although these elements do not seem as large as the main transformer, they are often the first parts that indicate an impending malfunction. Therefore, not only the main tank of the transformer, but also all its auxiliary systems should be evaluated as a whole.

Thermal camera inspection is a very efficient maintenance tool in transformers. When bushing terminals, cable connections, busbar contact points, radiator connections, OLTC connections and auxiliary panel interiors are thermally examined, hot spots due to looseness or increased resistance can be detected early. What is important here is not the only temperature value, but the evaluation of the differences between similar phases and similar connections. Thermal anomaly is often the first visible sign of a growing problem in the field.

The maintenance approach in dry type transformers focuses more on cleaning and air circulation, unlike oil-filled transformers. Cooling channels and surface accumulations clogged with dust reduce cooling efficiency, which can increase the winding temperature and shorten life. Therefore, regular cleaning of dry-type transformers, connection tightness control, monitoring of surface cracks and verification of temperature monitoring systems should be at the center of the maintenance plan.

One of the most important aspects of maintenance is record keeping. DGA results, oil test reports, ratio and winding resistance measurements, bushing evaluations, thermal images, OLTC maintenance records and accessory checks should be archived regularly. Because many transformer problems are understood not with a single measurement, but with changes over time. When trend monitoring is done, slow-moving deteriorations are noticed before a malfunction occurs. In summary, the tests and maintenance that must be done on transformers are; It consists of visual inspection, oil and insulation health monitoring, ratio and winding resistance tests, dielectric evaluations, bushing and OLTC checks, cooling system verification, thermal inspection and record management. If transformer tests, maintenance plan, MV/HV connections and operational safety will be evaluated together in your facility transformer maintenance and testing, HV/MV testing, maintenance and repair, LV/MV/HV project design and consultancy and SA operation responsibility It is possible to progress in integration with services.