Dry type transformers undergo rigorous testing to verify performance, insulation integrity, and safety. These tests are categorized into routine inspections (for mass-produced units) and type certifications (for new designs or modified models).
Routine tests are non-negotiable quality checks performed on every dry type transformer before it leaves the factory. These tests validate that each unit meets basic design specifications and operational safety requirements:
This test measures the direct current resistance of the transformer’s high-voltage and low-voltage windings. The goal is to verify the uniformity of winding resistance across phases, detect poor solder joints or loose connections, and ensure consistent current distribution. Deviations in resistance values can indicate manufacturing defects that may lead to local overheating during operation.
Conducted to assess the insulation strength of the transformer’s windings, core, and external components. The test applies a specified power frequency voltage (higher than the rated voltage) for a set duration (typically 1 minute) to simulate overvoltage conditions. A passing result confirms that the insulation can withstand transient voltage spikes without breakdown, preventing short circuits or electrical hazards.
This test verifies the accuracy of the transformer’s voltage conversion ratio. By measuring the voltage ratio between the primary and secondary windings (both under no-load conditions), technicians ensure the transformer delivers the exact output voltage specified in its design. This is critical for compatibility with downstream equipment and grid systems.
Unlike the power frequency test, this test applies an alternating voltage at twice the rated frequency to the secondary winding (with the primary winding open). The higher frequency simulates the magnetic flux density experienced during normal operation, allowing technicians to detect insulation weaknesses in the windings, such as inter-turn or inter-layer defects. This test is particularly effective for identifying hidden insulation issues that may not be uncovered by other methods.
Performed with the secondary winding open-circuited and the primary winding energized at the rated voltage and frequency. The test measures no-load current and no-load loss (primarily core losses, including hysteresis and eddy current losses). These data reflect the efficiency of the transformer’s magnetic circuit and core design, helping to validate energy-saving performance.
Conducted with the transformer operating under rated load conditions. The test measures load loss (copper losses) and short-circuit impedance, evaluating the transformer’s efficiency and ability to withstand rated current. Load tests also verify the transformer’s thermal performance, ensuring it does not exceed temperature rise limits during prolonged operation.
Uses a megohmmeter to measure the resistance between windings, between windings and the core, and between windings and the ground. This test assesses the overall insulation condition, detecting moisture absorption, contamination, or insulation degradation. A high insulation resistance value indicates reliable insulation performance, while a low value may signal the need for maintenance or replacement.
Type tests are comprehensive evaluations conducted for new transformer models, modified designs, or products with significant material/process changes. These tests go beyond routine inspections to validate the transformer’s long-term reliability, mechanical strength, and performance under extreme conditions:
Simulates the impact of a lightning strike or switching overvoltage on the transformer. A high-voltage impulse (with a specific wave shape and amplitude) is applied to the windings to test their ability to withstand sudden voltage surges. This is critical for transformers installed in outdoor or exposed environments, where lightning strikes are a potential risk.
Detects and measures partial discharges (small electrical arcs) within the insulation system. Partial discharges, if left unchecked, can gradually erode insulation and lead to premature failure. The test uses sensitive sensors to monitor discharge activity under normal and overload conditions, ensuring the transformer’s insulation remains intact throughout its service life.
One of the most rigorous type tests, this test simulates a three-phase short circuit at the transformer’s secondary terminals. The test evaluates the mechanical strength of the windings, core, and structural components, as short-circuit currents can generate extreme electromagnetic forces. It also measures short-circuit impedance and dynamic thermal performance, ensuring the transformer can withstand fault currents without permanent damage.
Dry type transformers are defined by their unique design—unlike oil-immersed transformers, their cores and windings are not immersed in insulating oil. Instead, they rely on air for insulation and cooling, making them ideal for indoor, environmentally sensitive, or fire-prone areas.
Dry type transformers use two primary cooling methods, which directly impact their output capacity and application scope:
Relies on natural convection of air to dissipate heat generated by the windings and core. Under AN mode, the transformer can operate continuously at its rated capacity, with temperature rise controlled by the surrounding air flow. This cooling method is energy-efficient, low-maintenance, and suitable for low-to-medium load scenarios.
Incorporates fans or blowers to direct forced air over the windings and core, enhancing heat dissipation. When switched to AF mode, the transformer’s output capacity can be increased by up to 50% compared to natural cooling. This makes it ideal for intermittent overload operation (e.g., peak power demand periods) or emergency situations. However, continuous overload operation is not recommended—overloading significantly increases load loss and impedance voltage, leading to reduced efficiency and accelerated insulation aging.
Dry type transformers are widely used in scenarios where safety, low maintenance, and environmental compatibility are priorities:
- Urban Infrastructure: High-rise buildings, residential complexes, commercial centers, and public facilities (e.g., airports, railway stations, and subway systems) benefit from their fireproof and explosion-proof design.
- Industrial Settings: CNC machinery, production lines, petrochemical plants, and food processing facilities rely on dry type transformers for stable power supply to sensitive equipment.
- Renewable Energy Systems: Solar power plants, wind farms, and energy storage systems use dry type transformers to convert voltage for grid integration.
- Special Environments: Indoor locations, clean rooms, and areas with strict fire safety regulations (e.g., hospitals, data centers, and nuclear facilities) prefer dry type transformers over oil-immersed units.
Dry type transformers combine robust testing protocols with flexible cooling and versatile applications, making them a reliable choice for modern power systems. Whether for routine power distribution or specialized industrial use, their design prioritizes safety, efficiency, and long-term performance—backed by rigorous testing to meet global industry standards.
