Jiangsu Suqian Rongxin Metal Products Power Quality Improvement Project-A success story in medium-frequency furnace harmonic mitigation and power quality improvement
Since commissioning, the dominant 5th, 7th and 11th characteristic harmonics have been effectively filtered, equipment heating and control-system interference have been markedly reduced, resonance risk has been eliminated, and the grid runs more stably while equipment lasts longer and energy losses drop. The project delivers benefits across four dimensions: equipment safety, production efficiency, system stability and energy cost.
Project Facts
| Item | Details |
|---|---|
| Project name | Jiangsu Suqian Rongxin Metal Products power quality improvement project |
| Project type | Industrial enterprise power quality retrofit |
| Application scenario | Metal products plant 35 kV busbar (high-harmonic loads such as medium-frequency furnaces) |
| Key problems | Severe characteristic harmonic pollution; equipment damage, production restrictions, electrical safety and energy cost |
| Core solution | H5+H7+H11 filter compensation bank, 17550 kvar total capacity |
| Design concept | Tiered mitigation, precision filtering, safe compensation (three in one) |
| Applicable standards | GB/T 14549-1993 "Power Quality – Harmonics in Public Supply Networks" |
| Key results | Harmonics brought into compliance; higher power factor; lower equipment failure rate; reduced electricity costs |
1. Project Background
1.1 Project Overview
Located at the Jiangsu Suqian Rongxin Metal Products Co., Ltd. facility, the site is a typical metal products manufacturing plant equipped with multiple high-power medium-frequency induction furnaces, whose rectifier/inverter stage is a classic nonlinear harmonic source. As capacity expanded, power quality problems became increasingly prominent, directly affecting production efficiency and product quality, and making mitigation an urgent need.
1.2 Industry Background
In the metal products industry, medium-frequency induction heating equipment is widely used, and the power quality problems it introduces are typical:
- Complex harmonic sources: the rectification and inversion process of medium-frequency furnaces produces rich characteristic harmonics that fluctuate widely with load;
- Chain of hazards: harmonics not only overheat and damage capacitors, but also disturb precision temperature control systems, driving up reject rates;
- Need for mitigation: specific harmonics must be filtered in a targeted way to safeguard continuous, stable production.
2. Customer Challenges
2.1 Harmonic Environment at a Glance
When the on-site medium-frequency furnaces operate, they produce harmonic current dominated by the 5th, 7th and 11th orders. With no effective filtering in place, system harmonic distortion far exceeded the limits set by GB/T 14549-1993 "Power Quality – Harmonics in Public Supply Networks". When conventional reactive power compensation capacitors were switched in, they tended to resonate in parallel with the system inductance, amplifying harmonic current several-fold — causing capacitor swelling, oil seepage and even explosion — while also disturbing voltage and affecting the normal operation of other precision equipment.
2.2 Main Problems Faced
| Problem category | Typical symptoms | Impact dimension |
|---|---|---|
| Equipment damage | Frequent capacitor failure; noisy transformers with high temperature rise | Equipment safety |
| Production restrictions | Unstable medium-frequency furnace heating efficiency; high product QC rejection rate | Production efficiency |
| Electrical safety | False tripping of switches; protection systems disturbed into mal-operation | System stability |
| Escalating energy cost | Higher line losses; low power factor leading to power-factor adjustment penalties | Economic cost |
2.3 Summary of Problem Impact
Harmonics have become the core bottleneck constraining Rongxin Metal Products' capacity release and cost control. The customer urgently needed a large-capacity, highly targeted mitigation solution adapted to medium-frequency furnace duty that systematically addresses both "harmonic amplification" and "frequent equipment failures".
3. Solution
3.1 Design Approach
Tailored to the medium-frequency furnace load characteristics, the design followed a "tiered mitigation, precision filtering, safe compensation" approach:
- Focused H5 filtering: the dominant 5th harmonic, the main source of pollution, is filtered with priority;
- Complementary H7 treatment: further suppresses the 7th harmonic to prevent the superposition of characteristic harmonics from exceeding the distortion limit and to ensure full power quality compliance;
- H11 high-frequency treatment: targets the 11th harmonic, suppressing high-frequency resonance risk and protecting temperature control and monitoring equipment;
- Detuned protection: a detuned design (tuning point set slightly below the target frequency) effectively avoids parallel resonance points and protects the capacitors.
3.2 Core Equipment Configuration
| Item | Configuration |
|---|---|
| System voltage | 35 kV |
| Total capacity | 17550 kvar |
| Branch configuration | H5 + H7 + H11 combined filter branches |
| Features | Combined reactive compensation and harmonic filtering, switched to match the medium-frequency furnace characteristic harmonic spectrum for simultaneous power quality improvement |
4. Project Implementation
4.1 Implementation Process
The project was executed in a strictly standardized process:
| Phase | Work content |
|---|---|
| 1. On-site survey | Long-duration power quality measurement of the furnaces' operating conditions to capture accurate harmonic data |
| 2. Solution design | Filter parameters calculated from measured data and a complete 17550 kvar packaged solution customized |
| 3. Manufacturing | High-quality filter reactors and HV filter capacitors selected, assembled and factory-tested |
| 4. Installation & commissioning | Removal of the old equipment and installation of the new bank during an outage window, followed by energization and commissioning |
| 5. Acceptance & commissioning | Branch currents and filtering performance verified before formal commissioning |
4.2 Quality and Safety Assurance
- All reactors use Class H insulation with excellent high-temperature performance, suited to harsh conditions;
- The packaged design reserves sufficient cooling passage and safe clearances;
- During commissioning, repeated switching tests were performed to suppress inrush impact and ensure smooth switching.
5. Project Results
5.1 Key Technical Indicator Comparison
With the 17550 kvar H5+H7+H11 filter compensation bank installed, system power quality has been fundamentally improved. The comparison is as follows:
| Indicator | Before (current status) | After | Improvement/result |
|---|---|---|---|
| Total harmonic voltage distortion (THDu) | 9% ~ 13% (substantially exceeded) | < 3% | Meets GB/T 14549-1993 (35 kV limit 3%) |
| 5th harmonic current content | 22% ~ 28% | < 5% | Substantially reduced |
| 7th harmonic current content | 12% ~ 18% | < 4% | Strong suppression |
| 11th harmonic current content | 8% ~ 12% | < 3% | Clear improvement |
| Power factor (PF) | 0.78 ~ 0.85 (highly variable) | ≥ 0.95 | Stably compliant |
| Capacitor failure rate | Avg. 2 ~ 3 groups damaged per month | Substantially reduced | Clear improvement |
| Transformer operating condition | High noise, high temperature rise | Smooth, quiet operation at normal temperature | Clear improvement |
Note: the "after" figures above are expected values derived from equipment performance and system evaluation. Final values are subject to commissioning acceptance measurements.
5.2 Technical Results
| Result | Improvement |
|---|---|
| Harmonic mitigation | 5th, 7th and 11th harmonic current substantially reduced; voltage distortion meets the GB/T 14549-1993 limits |
| Reactive compensation | Power factor stably raised above 0.95, avoiding power-factor adjustment penalties |
| Safety protection | Resonance hazards eliminated; capacitors run at normal temperature with extended life |
| Equipment condition | Smooth, quiet transformer operation; higher medium-frequency furnace heating efficiency |
5.3 Economic Benefits
- Penalties avoided: a compliant power factor saves power-factor adjustment charges;
- Losses reduced: lower harmonic current reduces copper losses in lines and transformers, saving electricity costs;
- Maintenance cost down: the failure rate of capacitors and associated equipment has dropped significantly, reducing maintenance and replacement costs.
5.4 Operating Performance
- Medium-frequency furnaces operate more stably and the product pass rate has improved significantly;
- Voltage fluctuation on the plant grid has decreased, so lighting and office equipment run more reliably;
- Energy savings have been realized, aligned with energy-saving and emission-reduction policies.
6. Customer Value
| Value dimension | Value delivered |
|---|---|
| Production assurance | Power quality-related shutdown risks resolved, safeguarding order delivery |
| Asset protection | Extended service life of core assets such as transformers and cables |
| Cost reduction & efficiency | Measurable economic returns through electricity savings and reduced penalties |
| Management improvement | Transparent, data-driven electrical system operation; better equipment management |
7. Summary and Outlook
7.1 Project Significance
This project is a typical benchmark for medium-frequency furnace harmonic mitigation in the metal products industry. By configuring an H5+H7+H11 combined filter bank, it successfully resolved the complex power quality problems caused by large-capacity nonlinear loads, validating the "tiered mitigation, precision filtering, safe compensation" strategy in an industrial setting.
7.2 Outlook
Going forward, we will continue to deepen our work in industrial power quality, launching smarter, more efficient mitigation products for special loads such as medium-frequency furnaces and electric arc furnaces, and helping more manufacturers achieve safe, efficient and sustainable development.
Conclusion
Centered on a 17550 kvar H5+H7+H11 filter compensation bank, the Jiangsu Suqian Rongxin Metal Products power quality project systematically resolved the harmonic pollution caused by nonlinear loads such as medium-frequency furnaces.
While simultaneously providing reactive compensation and equipment protection — making the grid more stable, the equipment more durable and the electricity bill more economical, and providing a replicable engineering benchmark for power quality improvement in the medium-frequency furnace industry.
Deployed Equipment
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High-Voltage Reactive Power Compensation Device – Outdoor Frame TypeThe RWTBBSeries High-Voltage Reactive Power Compensation Device &ndash; Outdoor Frame Typeis designed for6kV, 10kV, 24kV, and 35kV three-phase power systems.It provides effective reactive power compensation to: Stabilize and balance network voltage Improve overall power factor Reduce energy losses in the distribution network Enhance power supply reliability and qualityEngineered for outdoor applications, this frame-structured compensation device ensures durable operation and high efficiency
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