In mining power systems, main power transformers play a critical role in ensuring continuous production and operational safety. Mining enterprises are characterized by heavy loads, frequent load fluctuations, and harsh operating environments, which place stringent demands on transformer reliability, overload capability, cooling performance, and long-term stability.
This project involves the construction of a 35kV main substation and associated power supply system for an iron mining operation (Liusi Iron Mine), designed to provide reliable electricity for mining production processes such as ore extraction, crushing, conveying, and auxiliary facilities.
Mining operations are characterized by highly concentrated loads, frequent load fluctuations, and long continuous operating cycles. The substation is required to operate continuously under demanding conditions while maintaining strong overload capability and stable voltage regulation.
Specification | Details |
Model | SZ20-25000/35 |
Capacity | 25,000 kVA × 2 (Dual Units) |
Voltage Ratio | 35 ± 3 × 2.5% / 10.5 kV |
Tap Changer | On-Load Tap Changer |
Cooling Method | ONAN / ONAF |
Vector Group | YNd11 |
Short-Circuit Impedance | 10% |
Figure 1. Outline of 35kV SZ20-25MVA/35-NX2 Oil Transformer
Complex Load Profile: Handles high inrush currents from combination of large motors, crushers, and conveyor systems.
High Continuity: Mining production is highly sensitive to interruptions; dual-transformer parallel configuration enhances redundancy.
Harsh Environments: Engineered for dusty conditions, extreme temperature variations, and long-term heavy-load operation.
The substation was successfully energized and commissioned in April 2025 (with on-site positioning in December 2024), and the transformers have met all design and operational requirements.
Figure 2. Main Transformer Positioning on Site
International Compliance:
Huawan transformers comply with IEC 60076 standards (Power Transformers) and can be customized to meet ANSI / IEEE C57 standards for export-oriented projects.
Prior to delivery, the SZ20-25000/35 oil-immersed power transformers underwent comprehensive Factory Acceptance Testing (FAT) in accordance with IEC 60076 and relevant international standards, ensuring reliable performance under demanding mining operating conditions.
The FAT scope included, but was not limited to:
Winding DC resistance measurement
Voltage ratio and phase displacement verification
No-load loss and no-load current test
Load loss and short-circuit impedance test
Applied AC withstand voltage test
Induced voltage withstand test
Insulating oil dielectric strength and oil quality tests
On-load tap changer (OLTC) operational and switching tests
These tests verified the transformer’s electrical performance, insulation integrity, thermal behavior, and voltage regulation reliability, ensuring readiness for safe and long-term operation in the mining substation.
High Thermal Capacity: Better suited for heavy and fluctuating loads like crushing and hoisting. Superior Cooling: The combination of natural and forced air cooling (ONAN/ONAF) maintains safe temperatures.
Real-time Voltage Control: High-voltage OLTC adjusts voltage without power interruption, protecting downstream equipment.
Huawan Expertise in Mining Power Transformers
In-depth understanding of mining power demand characteristics
Customized 35kV / 110kV / 220kV oil-immersed transformer solutions
Compliance with IEC, GB, and utility standards
Focus on lifecycle efficiency and long-term reliability
Extensive experience in mining, metallurgy, cement, and heavy industry projects
Q: Why use oil-immersed transformers in mining?
A: They provide higher thermal capacity, stronger overload capability, and better cooling for continuous mining operations.
Q: What is the advantage of an OLTC?
A: It allows voltage regulation without interrupting power, ensuring stable voltage to sensitive mining equipment.
Q: Can Huawan customize for international projects?
A: Yes, we provide flexible designs compliant with IEC, GB, and ANSI/IEEE standards worldwide.
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Empowering the Grid, Serving Customers, Advancing Society
