Heavy Industry and Metallurgy
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40MVA industrial transformer for heavy industry and metallurgy, built for RKEF smelting with dust-proof, surge-resistant, low-THD design.
Industrial Transformer Solutions for Heavy Industry and Metallurgy
Heavy industry and metallurgy place extreme demands on power equipment, especially in electric arc furnaces, submerged arc furnaces, and RKEF smelting systems. Engineers must design transformers that withstand continuous ultra-high currents, frequent impact loads, severe harmonic distortion, and high-temperature dust-laden environments. Manufacturers adopt high-impedance configurations, reinforced electromechanical structures, and advanced sealing protection to ensure long-term operational stability under nonlinear and shock-intensive conditions. Ongoing technological innovation drives rectifier transformers toward greater mechanical strength, lower total harmonic distortion, intelligent monitoring, and extended service life to support large-scale nickel-iron and stainless steel production.
Case Study: 40MVA Rectifier Transformer for Nickel-Iron Smelting in an Indonesian Industrial Park
Application scenarios: RKEF rectifier transformer for electric arc furnaces/submerged arc furnaces
Core challenges: Highly conductive dust, 10,000-ampere current surges, and ultra-high harmonic pollution .
Project Background and Pain Points
This project is a key project of the “Belt and Road” initiative, serving a stainless steel smelting base with an annual output of 3 million tons.
- Conductive dust: The smelting workshop is filled with high concentrations of graphite powder and metal dust. If this dust falls into the transformer bushing or control box, it can easily cause a short circuit and explode the machine.
- Current surge: During the moment when the electrodes rise or fall or the material collapses in an electric arc furnace, a surge of up to 5 times the rated current can be generated . Under such enormous electromagnetic force, the coils of a conventional transformer can loosen and deform like an accordion, eventually leading to an inter-turn short circuit.
- Harmonic pollution: The rectification process generates a large number of 5th, 7th, and 11th harmonics, which cause the transformer core to overheat, generate loud noise, and cause the insulating oil to age five times faster than in the normal environment .
Design Concept – A Steel Beast Tamed by Electric Current
The dual extreme conditions of ‘nonlinear impact load’ and ‘high conductivity environment’ in the RKEF nickel-iron smelting process , Kerun Intelligent Control has abandoned the steady-state design logic of conventional power transformers and instead built a high-impedance impact-resistant rectifier system customized for the metallurgical industry based on the ‘strong electromechanical-thermal coupling model’ .”
By introducing ‘fully coaxial low-voltage copper tube windings’ and ‘mechanical pre-pressurization and fastening technology ,’ we have physically constructed a rigid framework capable of withstanding a 100kA short-circuit current surge. Simultaneously, to address the potential hazard of conductive dust, we have adopted IP54-rated fully enclosed stainless steel protection and a doubled creepage distance strategy, ensuring that this ‘smelting heart’ can maintain full-load output with zero failures for 25 years , even in a workshop filled with metal particles and high-temperature radiation .
Kerun Solutions
Dust Resistance: Giving the equipment an “insulating protective suit”
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- Pain point: Metal dust adheres to the surface of the porcelain bottle, causing surface flashover.
- Kron’s countermeasures :
- Composite insulating bushing: Abandoning traditional porcelain bushings, the entire high-voltage side uses silicone rubber composite bushings . Its hydrophobic surface prevents conductive dust from forming a continuous conductive path.
- IP54 Stainless Steel Terminal Box: All control lines and instrument junction boxes are made of 304 stainless steel and equipped with a positive pressure ventilation system to prevent dust intrusion.
Shock Resistance: The coil is virtually indestructible.
- Pain point: Frequent current surges can loosen the coil.
- Kerun’s countermeasures :
- Copper tube winding: The low-voltage side current is as high as tens of thousands of amperes. We abandoned the traditional copper busbar and used oil-cooled hollow copper tubes or integral copper plates for winding, which improved the mechanical strength by 50%.
Harmonic Absorption: Special Phase-Shifting Technology
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- Pain point: Harmonics cause voltage distortion in the power grid, interfering with the control system.
- Kerun’s countermeasures :
- 24 -pulse rectification phase shift: Using Extended Delta connection, through special phase angle design, the 5th, 7th, 11th and 13th harmonics are canceled out inside the transformer, reducing THD (Total Harmonic Distortion) to below 4% , without the need for additional filtering devices.
Core Technical Parameters
The parameters of metallurgical transformers are completely different from those of ordinary transformers. The following are their specific parameters.
Rated values and system parameters
| Parameter Item | Specifications | Remarks |
|---|---|---|
| Rated Power | 40,000 kVA (OFAF) | Continuous operating capacity under strong oil-cooled / water-cooled conditions |
| Phases | 3 Phase | |
| Frequency | 50 Hz | |
| Grid-side rated voltage (Line Voltage) | 150,000 V | High-voltage side (Primary) |
| Rated voltage | 600 V – 1200 V (Multi-tap) | Secondary side, wide-range voltage regulation |
| Rated current on valve side | 35,000 A – 60,000 A | Ultra-high current design, copper tube water-cooled winding |
| Voltage Regulation | On-Load Tap Changer (OLTC) | On-load tap changer, 17/27 gears, shifting without stopping. |
| Vector Group | Yd11 / Dd0 (Dual winding) | Composition of a 12-pulse rectifier system |
| Short-circuit impedance | 8.5% – 12.0% (adjustable) | High impedance design limits short-circuit current surge. |
| Thermal Class of Insulation | Class A (105° C) | Oil-immersed standard, with a 20% overload margin. |
| Design ambient temperature | +40° C (Max) / +30° C (Avg) | Adapted to equatorial tropical climate |
Rectification and Harmonic Isolation Characteristics
| Parameter Item | Specifications | Remarks |
|---|---|---|
| Rectifier Pulse Number | 12/24 Pulse (System) | Eliminating the 5th, 7th, 11th, and 13th harmonics through phase shifting. |
| Phase Shift Angle | 0° , 15° , 30° , —15° (Optional) | Designed according to the requirements of multiple transformers in parallel |
| Current unbalance | < 1.0% | Ensure uniform current in each phase to prevent localized overheating. |
| Total Harmonic Distortion ( THDi ) | < 5.0% (Grid Side) | Compliant with IEEE 519 power quality standards |
| Overload Capability curve | 150% for 2 hours | Meets the requirements of the periodic overload process of the electric arc furnace |
| K—Factor (Harmonic Resistance Level) | K—13 / K—20 | Designed specifically for nonlinear rectified loads |
Energy Loss and Energy Efficiency
| Parameter Item | Specifications | Remarks |
|---|---|---|
| No-load loss | ≤ 24.5 kW | High-permeability laser-etched silicon steel sheets |
| Load Loss | ≤ 285 kW (at 75° C) | High current copper loss is addressed through optimization of copper tube windings. |
| Total Efficiency | ≥ 99.25% | Measured at 75% load |
| Noise Level | ≤ 68 dB(A) | Maintains low noise even under heavy load |
Insulation level
| Parameter Item | Specifications | Remarks |
|---|---|---|
| High-voltage lightning impulse withstand (HV BIL) | 650 kV (Peak) | Full wave impact |
| High-voltage power frequency withstand capability (HV Power Freq.) | 275 kV (rms, 1 min) | |
| Low-voltage power frequency withstand (LV Power Freq.) | 10 kV (rms, 1 min) | |
| Partial discharge quantity | ≤ 100 pC | Measured at 1.5 times the rated voltage |
Power distribution systems often use isolation transformers, which provide electrical isolation between different circuits or systems, which helps prevent electrical noise or interference in one system from affecting the operation of another system. Isolation transformers are important to improve the reliability of power distribution systems by acting as a barrier and minimizing the effects of electrical noise and interference. At the same time, they serve as an important component in the power distribution system of commercial and industrial buildings. They is a necessary function for the operation of building systems and equipment. Selecting the proper transformer for a specific application is important to ensure optimum electrical performance and efficiency. In conclusion, the reliability of the power distribution system can be maximized through the use of isolation transformers, which are achieved by minimizing electrical noise and interference.
Part Two: List of Key Components
| Serial Number | Accessory Name | Specifications/Model (Spec/Type) | Quantity | Functional Description and Advantages |
|---|---|---|---|---|
| 1 | On-load tap changer (OLTC) | Vacuum Type | 1 Set | Vacuum arc extinguishing tech increases contact life, maintenance-free for 300,000 cycles. |
| 2 | Gas relay (Buchholz Relay) | Double Float | 1 Set | Dual protection with gas alarm and trip, vibration-resistant for steelmaking furnaces. |
| 3 | Pressure relief valve (PRD) | LMPRD / Qualitrol | 2 Sets | Instant pressure relief during short circuits to prevent explosion, dual configuration for safety. |
| 4 | Oil surface temperature controller (OTI) | AKM345 | 1 Set | Shockproof, oil-filled, suitable for high-vibration environments, with 4 contact sets. |
| 5 | Winding Temperature Controller (WTI) | AKM345 + CT | 1 Set | Monitors coil temperature in real time with 4-20mA output for remote monitoring. |
| 6 | Maintenance-free dehumidifier (Breather) | Smart Breather | 1 Set | Self-regenerating, no silica gel replacement needed, ideal for unattended areas. |
| 7 | Forced oil-fired air-cooled system (OFAF Cooler) | Integrally Mounted | 1 Group | Low-noise fan, galvanized radiator for corrosion protection. |
| 8 | Magnetic level gauge (MOG) | Magnetic Type | 1 Set | Dual-color display, high/low alarm contacts for easy reading in dusty environments. |
| 9 | High-voltage bushing (HV Bushing) | RIP / RIS (dry) | 3 Pcs | Oil-free, explosion-proof, and maintenance-free, reducing leakage risk. |
| 10 | Low-voltage outgoing terminal (LV terminal) | Water-Cooled Busbar | 6-12 Pcs | Water-cooled copper busbar, designed for 40kA current to prevent overheating. |
| 11 | Online monitoring device (DGA Monitor) | Hydran M2 (Optional) | 1 Set | Monitors dissolved gases for predictive maintenance of transformers. |
| 12 | Stainless steel control box | IP55 / SS316L | 1 Set | Dustproof, corrosion-proof, and rainproof, made from durable 316L stainless steel. |
Split-unit transportation
- Challenges: The transformer weighs 90 tons, and the roads on the Indonesian islands have limited load-bearing capacity.
- Solution: Use nitrogen-filled transportation. The radiator, oil tank, and bushings are disassembled and packaged separately. The transformer body is evacuated and then filled with 03MPa high-purity nitrogen . This not only reduces the transportation weight by 20%, but also prevents moisture from entering the transformer body during sea transport.
Economic Value and ROI Analysis
Core value: ” The biggest profit comes from keeping production running next to the steel furnace .”
- Improve smelting efficiency
- Data: On-load tap changers (OLTCs) allow voltage regulation without power interruption .
- Value: Compared to non-excitation voltage regulation (which requires power outage to change gears), it reduces furnace downtime by about 1 hour per day.
- Extend equipment lifespan
- Data: Harmonic-resistant design and reinforced mechanical structure.
- Value: Ordinary transformers typically have a lifespan of only 8-10 years in harsh smelting environments, while the Kerun solution is designed for a lifespan of 20 years . This postpones the costly equipment replacement cycle .
