Allowable Insulation Distance Of Dry Resin Type Transformer

Insulation stands as a cornerstone component in transformer design, directly impacting both the total manufacturing cost and long-term operational reliability. For high-voltage transformers rated at 110 kV and 220 kV—widely used in power transmission networks—insulation-related expenses account for 18% to 25% of the total unit cost. This significant cost share stems from the stringent material and structural requirements imposed by high-voltage environments, where insulation must withstand extreme electrical stress without degradation.

Suboptimal choices in insulation design—such as undersized insulation gaps, incompatible materials, or improper structural dimensions—can have severe consequences. When insulation gaps are set too narrow, for instance, it increases the risk of partial discharge, insulation aging acceleration, and even catastrophic breakdown. These issues not only lead to unplanned maintenance costs and downtime but may also compromise the transformer’s service life, resulting in substantial financial losses for end-users. To mitigate these risks, engineers must base insulation design decisions—including material selection, structural configuration, dimensional specifications, and manufacturing processes—on a comprehensive understanding of the operational stresses that insulation systems endure.

Power transformers operate in dynamic electrical environments, exposing their insulation systems to two primary types of electrical stress: rated working voltage and transient overvoltage.

During normal operation, transformers are continuously subjected to their rated working voltage. Insulation systems must maintain structural integrity and electrical performance indefinitely under this steady-state stress, as any degradation could lead to leakage current, overheating, or failure. This requirement demands high-quality insulation materials with excellent dielectric strength and thermal stability.

In addition to rated voltage, transformer insulation must also withstand transient overvoltages—sudden voltage spikes that occur due to normal switching operations (e.g., capacitor bank switching, load changes) or unexpected system faults (e.g., lightning strikes, short circuits). In rare cases, these transient overvoltages can reach magnitudes up to four times the phase voltage, though their duration is typically measured in hundredths of a second (generally less than 0.1 seconds). Despite their short duration, these spikes pose a significant threat to insulation, as they can exceed the material’s dielectric strength and cause immediate breakdown.

Notably, both rated working voltage and switching-related overvoltages primarily affect the main insulation of the transformer’s windings. This main insulation refers to the dielectric barriers between windings and grounded components, as well as between individual windings. Ensuring the robustness of this main insulation is critical to preventing inter-winding or winding-to-ground faults.

Dry-type resin transformers—valued for their fire safety, low maintenance, and environmental friendliness—share common main insulation components with oil-immersed transformers, including insulating paper tubes, angle rings, and component separators. However, their insulation design requires specialized considerations to address the unique thermal and electrical characteristics of dry-type operation.

First and foremost, insulation strength remains a non-negotiable requirement. Dry-type transformers rely on solid insulation materials (e.g., epoxy resin-impregnated paper) that must meet strict dielectric performance standards to withstand rated and transient voltages. Beyond electrical performance, thermal management is a key design priority. Unlike oil-immersed transformers, which use oil as a cooling medium, dry-type units depend on air cooling. As such, insulation design must incorporate sufficient air cooling ducts between windings to facilitate effective heat dissipation. These ducts ensure that air can circulate freely around the windings, reducing hotspots and preventing insulation degradation caused by overheating.

Equally important is the strategic placement of insulation components. Insulating parts must be positioned to minimize airflow resistance, allowing cool air to contact the winding surfaces uniformly. This requires precise alignment of insulation paper tubes, angle rings, and separators to create unobstructed airflow paths. Additionally, the design must account for mechanical stability, ensuring that insulation components remain securely in place during transportation, installation, and operation—even under vibration or thermal expansion.

By integrating these considerations into the insulation design process, manufacturers can produce dry-type resin transformers that deliver reliable electrical performance, long service life, and efficient thermal management, meeting the demanding requirements of modern power systems.