In the power construction field, 10kV distribution stations serve as crucial hubs in the power supply and distribution system, acting as transfer stations for transmitting grid power to end-users. Among them, the 10kV dry-type transformer is the "heart" of this transfer station. Since dry-type transformers were introduced to China from abroad in the late 1980s, their annual growth rate has exceeded 25%, becoming the mainstream in distribution rooms due to advantages in energy conservation, environmental protection, and performance. The 150 kva dry type transformer, as a commonly used model, is widely applied in various scenarios such as industrial parks and commercial complexes. After installing a new dry-type transformer, electrical handover tests are essential to ensure its safe commissioning. JINSHANMEN TECHNOLOGY CO., LTD, a professional manufacturer, mainly produces oil immersed power transformers, dry-type power transformers (including the 150 kva dry type transformer), 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. Meanwhile, the company also provides technical support for related equipment such as the pad mounted distribution transformer.
1. Application Analysis of 10kV Dry-Type Transformers
10kV dry-type transformers are widely used in power systems, characterized by air as the cooling medium. Their simple structure, convenient maintenance, long service life, high reliability, and strong flame retardancy significantly reduce maintenance workload. They can be installed in load centers, making them increasingly valued and promoted. Compared with oil-immersed transformers, the 150 kva dry type transformer has obvious advantages: low loss and high efficiency - the SC(B)9 series reduces losses by 10% compared to the current new national standard (GB/T10228); good moisture resistance, capable of normal operation at 100% humidity without drying after shutdown; no need for a separate transformer room, core lifting maintenance, or load-bearing beams, saving civil engineering space; no oil, avoiding toxic gas emissions and environmental pollution, and eliminating the need for oil collection pits, reducing civil engineering costs. Additionally, it features low noise, fire resistance, small size, light weight, easy installation, low partial discharge (usually below 10PC), strong short-circuit resistance, low operation and maintenance costs, and a 30-year service life. It is also equipped with differential, overcurrent, 10kV zero-sequence current, overload, and temperature protection. Among them, differential and overcurrent protection trigger tripping for 35kV and 10kV side switches; 10kV zero-sequence current protection trips the 10kV side switch; overload and temperature protection send alarms. Similar to the 150 kva dry type transformer, the pad mounted distribution transformer also has high operational reliability, and JINSHANMEN TECHNOLOGY CO., LTD provides comprehensive technical solutions for both.
2. Test Objectives and Requirements
2.1 Test Objectives
The core objective of electrical handover tests for 10kV dry-type transformers is to verify the mechanical properties between windings and leads, winding resistance balance, protection reliability and sensitivity, and other performance indicators against technical specifications. This ensures the 150 kva dry type transformer and other models operate safely after commissioning. For equipment like the pad mounted distribution transformer, similar performance verification is also required before operation.
2.2 Safety Requirements for Test Equipment
Test power must adopt the "one switch per machine" system, connected to a leakage protector with a rated leakage current ≤30mA and action time <0.1ms. The test instrument shell must be well grounded with a grounding wire cross-section ≥5mm², and power cords must be undamaged and non-aging. Knobs should rotate smoothly without interruptions or sudden jumps. Multimeters, megohmmeters, current-voltage meters, mobile power strips, insulating gloves, and boots must be qualified and within the validity period. Tools should have good insulation. A safety warning area must be set up to prohibit unauthorized access, and operators must hold relevant qualifications. These requirements also apply to tests for the pad mounted distribution transformer.
3. Test Procedures, Methods and Requirements
3.1 Measuring DC Resistance of Windings with Bushings
For transformers with capacity ≤1600kVA (such as the 150 kva dry type transformer), the mutual difference between phase measurements should be <4% of the average value, and between line measurements <2% of the average value. Unbalance rate = [(Maximum three-phase measured value - Minimum three-phase measured value) / Three-phase arithmetic average value] × 100%. Measurement methods: Use an inductive load quick-measuring ohmmeter in accordance with its technical requirements; for a double-arm bridge, wire as shown in Figure 1; for a single-arm bridge measuring high-resistance windings, subtract the lead resistance. Compare with the factory test value at the same temperature: the change should not exceed 2%. Convert resistances at different temperatures using the formula: Rx = Ra × (T + tx) / (T + ta), where Rx = resistance at tx, Ra = measured resistance at ta, T = conversion coefficient (235 for copper, 225 for aluminum), tx = target temperature, ta = measurement temperature.
3.2 Checking Transformation Ratio of All Taps
Check the transformation ratio at all tap positions. The ratio should be consistent with the manufacturer's nameplate data and follow transformation ratio rules. The allowable deviation for the rated tap is ±0.5%, and for other taps, within 1/10 of the transformer impedance value (but not exceeding 1%). This check is equally important for the 150 kva dry type transformer and pad mounted distribution transformer to ensure voltage regulation accuracy.
3.3 Checking Winding Connection Group and Polarity
This check ensures parallel operation and protection polarity, usually using the DC method: connect a dry battery to AB, BC, AC (A positive, B negative), and observe the direction and maximum value of the low-voltage voltmeter (a positive, b negative). Correct connection group and polarity are essential for the coordinated operation of the 150 kva dry type transformer with other equipment.
3.4 Measuring Insulation Resistance of Windings with Bushings
For 10kV dry-type transformers, use a 2500V, 5000V, or 10,000MΩ+ megohmmeter for primary side to ground and primary side phase-to-phase measurements. For 10,000/400V transformers, use a 500V megohmmeter for the secondary side. The insulation resistance should not be less than 70% of the factory test value. This index directly reflects the insulation reliability of the 150 kva dry type transformer.
3.5 AC Withstand Voltage Test
Transformers with a rated winding voltage <10kV require an AC withstand voltage test with a 50Hz power supply and a nearly sinusoidal waveform (wiring as shown in Figure 2). The current-limiting resistor is selected at 0.2-1.0Ω/V. To measure capacitive current, connect a milliammeter and a parallel short-circuit protection switch to the high-voltage coil tail of the test transformer. This test simulates the actual operating conditions of the 150 kva dry type transformer and verifies insulation durability.
4. Conclusion
Electrical handover tests for 10kV dry-type transformers (including the 150 kva dry type transformer) are critical to ensuring safe and reliable operation. Through strict implementation of the above test methods and data analysis, the performance status of the transformer before commissioning can be fully mastered, avoiding potential faults. JINSHANMEN TECHNOLOGY CO., LTD, with its professional R&D and production capabilities, not only provides high-quality dry-type transformers and pad mounted distribution transformer but also offers technical guidance for test and commissioning, contributing to the stable operation of the power supply and distribution system.