Mongolia South Gobi Coal Washing Plant 35 kV Power Quality Success Story
Since commissioning, the dominant 5th harmonic has been effectively filtered, harmonic distortion has dropped markedly, the power factor has been raised and stabilized, and equipment overheating and control-system interference have been significantly reduced — delivering dual gains in production capacity and energy efficiency.
Project Facts
| Item | Details |
|---|---|
| Project name | Mongolia South Gobi coal washing plant 35 kV power quality improvement project |
| Project type | Industrial enterprise power quality retrofit |
| Application scenario | Coal washing plant 35 kV busbar (high-harmonic loads such as VFDs) |
| Key problems | Severe characteristic harmonic pollution; equipment damage, production restrictions, electrical safety and energy cost |
| Core solution | H5 filter compensation bank, 5000 kvar total capacity |
| Design concept | Tiered mitigation, precision filtering, safe compensation (three in one) |
| Applicable standards | IEEE 519-2022 (limits), IEC 61000-3-6 (assessment), GB/T 14549-1993 (reference) |
| Key results | Harmonics brought into compliance; higher power factor; lower equipment failure rate; reduced electricity costs |
1. Project Background
1.1 Project Overview
The project is located at a large modern coal washing plant in South Gobi Province, Mongolia. As a key coal washing base for the region, the site is equipped with multiple high-power VFD-driven heavy-medium cyclones, centrifugal dewatering machines and long-distance belt conveyor systems.
As production capacity has continued to expand, harmonic pollution from the VFDs has grown increasingly severe — threatening grid security and directly constraining both washing precision and equipment lifetime — making mitigation a pressing priority.
1.2 Industry Pain Points
In the coal washing industry, VFD-driven equipment has raised the level of automation but at the same time brings typical power quality challenges:
- Complex, dynamically changing harmonic sources: the VFD rectifier stage produces rich 5th, 7th and 11th characteristic harmonics that fluctuate sharply with coal feed rate and coal quality;
- Precision control disturbance: harmonics cause false trips of the PLC and DCS systems, distort heavy-medium density control and reduce clean coal recovery;
- Shortened equipment life: harmonic current overheats capacitors and raises transformer noise, sending failure rates up and keeping maintenance costs high.
2. Customer Challenges
2.1 Harmonic Environment at a Glance
When the on-site VFDs operate, they produce harmonic current dominated by the 5th, 7th and 11th orders. With no effective filtering in place, the system harmonic distortion far exceeded the limits. 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 VFD output, fluctuating washing 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 reactive power penalty billing | Economic cost |
3. Solution
3.1 Design Approach
Tailored to the VFD 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;
- Reserved H7/H11 expansion: expansion interfaces for H7/H11 branches are reserved so additional branches can be added cost-effectively as measured harmonic composition dictates, avoiding over-investment;
- 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 | 5000 kvar |
| Branch configuration | H5 filter branch |
| Features | Combined reactive compensation and harmonic filtering, switched to match the VFD characteristic harmonic spectrum |
4. Project Implementation
4.1 Implementation Process
The project was executed in a strictly standardized process:
- On-site survey: long-duration power quality measurement of the coal washing plant's operating conditions to capture accurate harmonic data;
- Solution design: filter parameters calculated from measured data and a complete 5000 kvar packaged solution customized;
- Manufacturing: high-quality filter reactors and HV filter capacitors selected, assembled and factory-tested;
- Installation & commissioning: removal of the old equipment and installation of the new bank during an outage window, followed by energization and commissioning;
- 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 (Before/After)
5.1 Key Technical Indicator Comparison
With the 5000 kvar H5 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) | 8.5% ~ 12% (substantially exceeded) | < 3% | Meets IEEE 519-2022 and GB/T 14549-1993 (35 kV limit 3%) requirements |
| 5th harmonic current content | 25% ~ 30% | < 4% | Substantially reduced |
| 7th harmonic current content | 15% ~ 20% | < 3% | Strong suppression |
| Power factor (PF) | 0.75 ~ 0.82 (highly variable) | 0.96 ~ 0.98 | Stably compliant |
| Capacitor failure rate | Avg. 2 ~ 3 groups damaged per month | Substantially reduced | Clear improvement |
| Transformer operating temperature | 85 ℃ ~ 95 ℃ (high-temperature alarm) | 65 ℃ ~ 70 ℃ | Approx. 20 ℃ reduction |
5.2 Economic Benefits
- Penalties avoided: with the power factor stabilized above 0.96, monthly savings of approx. RMB XX in reactive power penalty charges are achieved (to be completed based on actual electricity bills);
- Losses reduced: lower harmonic current reduces copper losses in transformers and lines, with expected annual electricity cost savings of approx. RMB XX;
- Maintenance cost down: the failure rate of capacitors and associated equipment has dropped significantly, reducing maintenance, replacement and downtime losses.
5.3 Operating Performance
- Heavy-medium cyclones operate more stably and clean coal recovery has improved;
- 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 VFD harmonic mitigation in Mongolia's coal washing industry. By configuring a 5000 kvar H5 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 coal washing plants and mines, and helping more manufacturers achieve safe, efficient and sustainable development.
Conclusion
Centered on a 5000 kvar H5 filter compensation bank, the Mongolia South Gobi coal washing plant 35 kV power quality project systematically resolved the harmonic pollution caused by nonlinear loads such as VFDs, 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 coal washing 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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