What should be paid attention to when inspecting dry transformers？

Regular inspection of dry-type transformers is critical to ensuring long-term operational safety, reliability, and efficiency. Below is a detailed, actionable inspection framework designed to identify potential issues early and maintain optimal performance.

During normal operation, dry-type transformers should emit a steady, low-volume electromagnetic hum—consistent with the natural vibration of core laminations and windings. Any deviation from this baseline requires immediate attention. Listen closely for irregular sounds such as sharp whistling, rattling, knocking, or buzzing, which may indicate loose core clamping bolts, deformed windings, faulty cooling system components, or internal insulation damage. Additionally, check for excessive vibration by placing a hand lightly on the transformer frame (ensuring safe distance from live parts) or using a vibration meter; abnormal vibration often correlates with mechanical loosening or misalignment, which can worsen over time and lead to component failure.

The insulation surface of windings and structural components is a key indicator of transformer health. Inspect thoroughly for signs of degradation, including discoloration, creepage marks, or carbonization—these issues are often caused by local overheating, exposure to corrosive gases (e.g., sulfur dioxide, ammonia in industrial environments), or moisture ingress. Pay special attention to high-voltage winding ends, terminal connections, and areas near cooling vents, as these are prone to dust accumulation and subsequent creepage. Corrosive gases can erode insulation materials over time, reducing their dielectric strength and increasing the risk of short circuits. If any discoloration or carbonization is detected, clean the affected area (using dry compressed air or a lint-free cloth) and investigate the root cause (e.g., poor ventilation, proximity to corrosive processes) to prevent recurrence.

For dry-type transformers equipped with forced air-cooling systems (fans), consistent performance of these components is essential to managing temperature rise. Verify that all cooling fans start and stop automatically as designed (triggered by the temperature controller) and operate without unusual noise or stalling. Check fan blades for dust buildup, damage, or misalignment—accumulated debris can reduce airflow efficiency and cause overheating. Inspect fan motors for signs of overheating (e.g., hot-to-touch casings, burnt odors) and ensure electrical connections to the cooling system are tight and free of corrosion. For transformers in high-dust environments, schedule regular cleaning of fan filters and air intakes to maintain unobstructed airflow.

Loose or corroded electrical connections are a common cause of local overheating and transformer failures. Examine all high-voltage and low-voltage terminals, busbars, and cable joints for signs of overheating—indicated by discoloration, melted insulation, or a burnt smell. Ensure connections are tightened to the manufacturer’s specified torque to minimize contact resistance, which can generate excessive heat under load. Additionally, check cable heads for leakage (in applicable designs) or creepage traces; poor cable termination can lead to electrical discharge and insulation breakdown. For outdoor or harsh-environment installations, inspect connections for corrosion and apply anti-corrosion compounds if necessary to protect against moisture and chemical damage.

Winding temperature rise is directly tied to the insulation class of the transformer (e.g., Class F, Class H) and must not exceed the manufacturer’s specified limits. Use the built-in temperature controller or a calibrated infrared thermometer to monitor winding temperatures during normal load conditions. For Class F insulation (common in many dry-type transformers), the maximum allowable temperature rise is typically 100K (above ambient temperature). Sustained temperatures exceeding this limit accelerate insulation aging, shortening the transformer’s service life and increasing the risk of insulation failure. If temperature rise consistently approaches or exceeds the specified value, investigate potential causes such as overloading, inadequate ventilation, or malfunctioning cooling systems.

Supporting porcelain insulators (or composite insulators) play a critical role in isolating live components from the transformer frame and ground. Inspect each insulator for cracks, chips, or discharge traces—even minor damage can compromise insulation integrity and lead to electrical arcing. Discharge marks (often appearing as faint black lines) indicate voltage stress and may precede insulator failure. Ensure insulators are clean and free of dust, oil, or other contaminants, which can reduce their surface resistance and cause creepage. If any cracks or discharge signs are found, replace the insulator immediately to prevent short circuits or ground faults.

Winding pressure plates are designed to secure windings tightly to the core, preventing mechanical movement and vibration during operation. Over time, thermal cycling and vibration can loosen these pressure plates or their fastening bolts. Inspect all pressure plates for signs of loosening, displacement, or deformation—loose plates can cause windings to shift, leading to increased noise, vibration, and potential insulation damage. Use a torque wrench to re-tighten bolts to the manufacturer’s recommended specifications, ensuring uniform pressure across the windings. Pay special attention to corner bolts and plates near the core yoke, as these areas are subject to higher mechanical stress.

Proper indoor ventilation is essential to dissipate heat generated by the transformer and maintain a stable operating environment. Ensure the transformer room or enclosure has adequate airflow, with no obstructions (e.g., storage items, equipment) blocking air intakes or exhaust vents. The recommended minimum clearance around the transformer (typically 800mm from walls and 300mm between adjacent units) should be maintained to facilitate air circulation. Additionally, inspect the core air ducts for dust, debris, or foreign objects—blocked ducts restrict heat dissipation and can cause localized overheating of the core. Check the core itself for signs of rust or corrosion, which can occur if moisture enters the transformer or ventilation is poor. If rust is detected, clean the affected area and address the moisture source (e.g., leaky roofing, high humidity) to prevent further deterioration.