Dry Type Step Down Transformer Test Guide | Complete Test Items for 500 KVA Dry Type Transformer

          As core power distribution equipment in industrial and commercial power systems, dry type step down transformer features fire resistance, low noise, and high safety, widely used in indoor power supply, building power distribution, new energy stations and other scenarios. To ensure long-term stable and safe operation of equipment, standardized testing and inspection are essential before commissioning and during operation. Whether it is a conventional small-capacity dry-type transformer or a mainstream 500 kva dry type transformer, complete testing procedures must be implemented in accordance with national and industry standards to eliminate potential equipment faults.     

          JINSHANMEN TECHNOLOGY CO., LTD is a professional manufacturer of transmission and distribution equipment. The company mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment. All dry-type transformer products including dry type step down transformer and 500 kva dry type transformer undergo strict factory tests, and we provide professional on-site commissioning and testing guidance for global customers.

 

          The test work of dry type step down transformer is divided into two key stages: handover acceptance test (before commissioning) and preventive test (during operation). The handover test focuses on verifying installation quality, insulation performance and operational accuracy, which is the key link to ensure the qualified grid connection of new equipment. The preventive test is used to detect aging, dampness and hidden faults of equipment during long-term operation, suitable for operating transformers such as 500 kva dry type transformer.

          In accordance with the GB50150 standard, for 35kV and below, 1600kVA and below conventional dry-type transformers (including 300kVA, 500kVA and other common models), on-site commissioning must complete 6 core tests. These items cover all key performance indicators of dry type step down transformer, fully verifying equipment safety and stability.

          Test Purpose: Detect winding wire welding quality, tap changer contact performance and inter-turn short circuit faults.

          Judgment Standard: Phase resistance difference ≤2%, line resistance difference ≤1%; the deviation from factory value ≤2%.

          Operation Points: Use a DC resistance tester (10A and above is recommended), adopt four-terminal wiring method, measure the resistance of high voltage side (AB, BC, CA) and low voltage side (ao, bo, co) respectively, and record the ambient temperature for data correction.

          Test Purpose: Evaluate the overall insulation state of the transformer, judge whether the insulation layer is damp, dirty or damaged.

          Judgment Standard: The insulation resistance at 20℃ is generally ≥1000MΩ, not less than 70% of the factory value; absorption ratio R60/R15 ≥1.3.

          Operation Points: Use 2500V megohmmeter for high-voltage winding, 1000V/2500V megohmmeter for low-voltage winding. Test high voltage to low voltage & ground, and low voltage to ground respectively. Insufficient absorption ratio indicates damp insulation.

          Test Purpose: Verify whether the transformer turns ratio is accurate and the wiring group (such as Dyn11) conforms to the nameplate standard.

          Judgment Standard: Transformation ratio error ≤±0.5%, wiring group is consistent with the nameplate.

          Operation Points: Adopt automatic transformation ratio tester to measure the corresponding ratio of AB-ab, BC-bc, CA-ca. Excessive error is usually caused by wrong tap gear or inter-turn winding faults.

          Test Purpose: Destructive test to assess the main insulation strength of the transformer, eliminate hidden insulation faults.

          Judgment Standard: Apply specified power frequency voltage for 1 minute, no breakdown, flashover or abnormal noise.

          Operation Points: Insulation resistance test must be qualified before the test. Non-tested windings are short-circuited and grounded. Boost slowly and keep voltage for 60s, and test insulation resistance again after the test with no obvious decline.

          Test Purpose: Detect multi-point grounding faults of the transformer iron core to avoid local overheating and equipment burnout.

          Judgment Standard: Insulation resistance tested by 2500V megohmmeter ≥10MΩ.

          Test Purpose: Ensure correct grid-connected phase sequence and avoid phase sequence errors leading to power failure or equipment damage.

          Judgment Standard: The ABC phase sequence of high and low voltage sides is consistent, and the phase is accurate.

          For small and medium capacity equipment such as 500 kva dry type transformer, no additional dielectric loss (tanδ) and winding deformation tests are required under normal conditions, which can simplify the test process on the premise of meeting national standards. It is only necessary to equip with 2500V megohmmeter, DC resistance tester and transformation ratio tester to complete all standard tests.

In the test of small-capacity dry type step down transformer, attention should be paid to test line contact accuracy to avoid data deviation caused by poor contact. The most effective diagnosis method is to compare the field test data with the factory original data to judge the equipment health status.

 

          Appearance inspection (dust cleaning, crack check) → Winding DC resistance test → Insulation resistance test → Transformation ratio & group test → Iron core insulation test → AC withstand voltage test (final high-risk test) → Phase check (before power transmission)

          a. Before all insulation and withstand voltage tests, completely disconnect the transformer from the power grid, and reliably ground the equipment shell to prevent residual charge injury.

          b. The withstand voltage test shall be carried out after all low-risk tests are qualified to avoid irreversible damage to defective equipment.

          c. For small-capacity dry-type transformers, match the capacity of the test equipment to avoid overload operation of the test instrument.

 

          Standardized testing is the core guarantee for the long-term safe operation of dry type step down transformer and 500 kva dry type transformer. Strict implementation of handover and preventive tests in accordance with GB50150 standards can effectively eliminate equipment hidden dangers and extend the service life of transformers.

          As a professional global transformer manufacturer,JINSHANMEN TECHNOLOGY CO., LTD adheres to strict quality inspection standards for all dry-type transformer products, provides one-stop solutions including product production, factory testing, on-site commissioning and technical guidance, and guarantees reliable and stable power distribution equipment for global customers.