Zhejiang Hongyan Electric Co., Ltd. 
Quick Answer
We delivered two customized 33 kV harmonic filter systems for a 12-pulse electric arc furnace project in India.
Our customer needed to reduce harmonic distortion and improve the power factor of an industrial network operating multiple 12-pulse rectifier loads. After reviewing the electrical data and harmonic spectrum, our engineering team developed an outdoor filtering solution based on 5th, 7th, and 11th harmonic branches.
The systems were designed and manufactured by CHYN for installation on two 33 kV bus sections. They also work with dynamic reactive power compensation equipment to support changing furnace operating conditions.
According to our engineering simulation, the proposed solution could reduce voltage THD from 8.96% to 4.37% and current THD from 8.38% to 3.52%. The power factor was designed to improve from approximately 0.91 to above 0.95.
Project Overview
| Project Item | Details |
| Project location | India |
| Main application | 12-pulse electric arc furnace power system |
| System voltage | 33 kV |
| Equipment supplied | Two outdoor harmonic filter systems |
| Filter branches | 5th, 7th, and 11th |
| Main objectives | Harmonic mitigation and power factor improvement |
| Original power factor | Approximately 0.91 |
| Target power factor | At least 0.95 |
| Installation | Outdoor |
| CHYN scope | Engineering, manufacturing, testing, and supply |
| Design reference | IEEE 519 requirements |
What Did Our Customer Need to Solve?
The customer was operating a large industrial power system with multiple 12-pulse rectifier loads connected to the 33 kV network.
Although 12-pulse rectifiers generally produce fewer low-order harmonics than 6-pulse rectifiers, they can still introduce significant harmonic currents into the power system. In this project, the main harmonic concerns included the 11th, 13th, 23rd, and 25th orders.
When several rectifier loads operate at the same time, their combined harmonic current can affect the upstream bus, transformers, cables, and other electrical equipment.
The customer also needed to improve power factor.
The original operating power factor was approximately 0.91, while the project target was at least 0.95. This meant that the solution needed to address both harmonic distortion and reactive power demand.
A standard capacitor bank alone would not have been suitable. Capacitors can improve power factor, but without proper reactor coordination, they may interact with the harmonic source and create resonance.
For this reason, the customer needed a harmonic filter supplier that could review the complete system rather than simply provide standard capacitor equipment.
What Did We Supply for the India Project?
We manufactured and supplied two complete outdoor harmonic filter systems for the customer’s 33 kV network.
Each system included three filter branches designed around the main harmonic requirements:
- 5th harmonic filter branch
- 7th harmonic filter branch
- 11th harmonic filter branch
The complete outdoor assemblies also included the main equipment required for high-voltage filtering and compensation, such as:
- High-voltage filter capacitors
- Dry-type air-core reactors
- Disconnecting equipment
- Surge arresters
- Protective fuses
- Supporting insulators
- Busbars and conductors
- Steel support structures
- Measurement and protection interfaces
- Control equipment
The systems were not selected as standard catalogue products.
Our engineering team configured the filters according to the customer’s network voltage, load characteristics, harmonic spectrum, power factor requirement, and outdoor installation conditions.
As both the manufacturer and supplier, we were able to coordinate the electrical design, component ratings, mechanical structure, and protection requirements within one project.
Why Were 5th, 7th, and 11th Filter Branches Used?
The filter configuration was selected according to the harmonic spectrum and the behavior of the 12-pulse rectifier system.
The 11th and 13th harmonics were among the most important components in the customer’s harmonic data. Higher-order components were also considered during the analysis.
A harmonic filter does not only absorb one exact harmonic order. Its final performance depends on the tuning point, system impedance, capacitor value, reactor value, and load condition.
The 5th, 7th, and 11th branches were therefore designed as a coordinated system rather than three independent capacitor banks.
The lower-order branches also help control the overall impedance characteristics of the network and reduce the risk of unwanted resonance.
At the same time, the capacitors in the filter branches provide reactive power to support power factor improvement.
This allows the system to perform two functions:
- Reduce harmonic current entering the 33 kV network.
- Supply part of the reactive power required by the industrial load.
Because the furnace operating condition can change, the passive filtering system was also coordinated with dynamic reactive power support. This helps the complete power quality system respond more effectively to load variation.
How Did We Design the Harmonic Filter System?
We began with the customer’s actual electrical data.
The information reviewed by our engineering team included:
- System voltage and frequency
- Number and type of rectifier loads
- Harmonic current spectrum
- Existing power factor
- Required power factor
- Network short-circuit conditions
- Outdoor installation environment
- Equipment operating sequence
The filter design was based on the combined operation of the rectifier loads rather than the performance of only one unit.
This was important because harmonic currents do not always increase through simple arithmetic addition. The phase relationship between different loads can affect the final combined harmonic current.
Our engineers therefore used the supplied operating data to establish a project-specific simulation model.
The model was used to check:
- Voltage THD
- Current THD
- Harmonic current distribution
- Filter branch performance
- Reactive power output
- Capacitor loading
- Reactor loading
- Resonance risk
- Power factor improvement
This process helped us confirm the filter configuration before manufacturing the equipment.
For high-voltage harmonic projects, this engineering stage is essential. Two plants with similar rectifiers may still require different filter systems because the transformers, network strength, load combination, and operating conditions may be different.
What Did the Simulation Show?
Our simulation compared the 33 kV network before and after the proposed harmonic filter system was connected.
| Simulation Parameter | Filter Off | Filter On |
| Voltage THD | 8.96% | 4.37% |
| Current THD | 8.38% | 3.52% |
| Power factor | Approximately 0.91 | Approximately 0.952 |
The results indicated that the proposed filters could significantly reduce both voltage and current distortion.
The simulated power factor also increased to approximately 0.952, which was above the project target of 0.95.
These figures are engineering simulation results, not post-commissioning field measurements. They were used to verify the expected performance of the solution before production.
Actual operating values may vary according to the number of rectifiers in service, load level, upstream grid conditions, background harmonics, and final site configuration.
Why Was an Outdoor Design Required?
The customer required both filter systems to be installed outdoors.
Outdoor high-voltage equipment must be designed for more than electrical capacity. It also needs to withstand the installation environment over long-term operation.
For this project, we used a frame-type outdoor structure incorporating the capacitors, reactors, isolating equipment, surge protection, conductors, and supporting components.
The design considered:
- Outdoor insulation requirements
- Electrical clearances
- Corrosion resistance
- Moisture protection
- UV exposure
- Mechanical strength
- Equipment temperature rise
- Maintenance access
The supporting structures and fastening components were prepared with suitable corrosion-protection treatment.
The dry-type air-core reactors were selected for outdoor industrial service and coordinated with the filter capacitor ratings.
The capacitor units were designed to withstand the combined effects of fundamental-frequency voltage, harmonic current, and normal parameter variation.
We also checked the filter branches for overvoltage, overcurrent, and overload conditions.
These checks are important because a harmonic filter capacitor carries more than normal reactive current. It may also absorb harmonic current from the network, increasing its electrical and thermal loading.
How Did Our Factory Support the Project?
CHYN is not only a company that prepares power quality calculations. We are the actual manufacturer and supplier of the equipment used in our projects.
For this India project, our work covered the main stages from engineering review to equipment preparation.
Our scope included:
- Reviewing the customer’s electrical information
- Analyzing the harmonic spectrum
- Calculating the compensation requirement
- Selecting the filter branch configuration
- Coordinating capacitors and reactors
- Checking harmonic and reactive power performance
- Designing the outdoor support structure
- Preparing protection and measurement interfaces
- Manufacturing the equipment
- Completing factory inspection
- Preparing technical drawings and documentation
Having engineering and manufacturing capabilities within the same company helps us manage the relationships between different parts of the system.
For example, changing the capacitor capacity affects reactive power output. Changing the reactor value affects filter tuning. The network impedance also affects the final filtering performance.
These factors cannot be treated separately.
By manufacturing the complete system, we can review the overall design before the equipment is delivered to the customer.
This also makes communication easier for overseas customers and EPC contractors. They can work with one supplier for the filter capacitors, reactors, structures, protection interfaces, and system design.
Why Should Buyers Avoid Selecting Harmonic Filters Only by Capacity?
A common mistake is to select a harmonic filter only according to system voltage and reactive power capacity.
This approach may work for a basic capacitor bank, but it is not sufficient for a network with large nonlinear loads.
The correct filter configuration also depends on:
- Main harmonic orders
- Harmonic current magnitude
- Transformer impedance
- Short-circuit capacity
- Existing capacitor banks
- Load variation
- Number of operating rectifiers
- Local harmonic limits
If the filter is tuned incorrectly, it may not absorb the intended harmonic current.
It may also interact with the power system and create resonance at another frequency. This could increase harmonic voltage or place additional stress on capacitors and reactors.
An experienced harmonic filter manufacturer should therefore review the complete network before confirming the equipment.
For this project, our filter design was based on the customer’s actual operating data and the combined rectifier load.
What Information Do We Need for a Similar Project?
For a new industrial harmonic filtering project, customers can send us the following information:
- Single-line diagram
- System voltage and frequency
- Transformer capacity
- Transformer impedance
- Load type and quantity
- Rectifier pulse number
- Existing power factor
- Required power factor
- Harmonic measurement report
- Harmonic current spectrum
- Active and reactive power data
- Existing capacitor equipment
- Load operating sequence
- Installation environment
- Ambient temperature and altitude
- Available installation area
- Local utility requirements
Where a harmonic report is not yet available, we can first review the main electrical and load information.
However, measured harmonic data normally allows us to prepare a more accurate solution and reduce uncertainty during the filter design.
Can We Supply Similar Systems for Other Industrial Loads?
Yes. The engineering method used for this project can also be applied to other high-power nonlinear loads.
Typical applications include:
- Electric arc furnaces
- Ladle furnaces
- Steel rolling mills
- Large rectifier systems
- Electrolysis plants
- Mining equipment
- Medium-frequency furnaces
- Cement production lines
- Chemical processing facilities
- Industrial substations
Depending on the project, the final solution may include:
- Passive harmonic filters
- High-voltage capacitor banks
- SVG
- SVC
- APF
- Combined filtering and dynamic compensation systems
The final configuration depends on whether the main issue is harmonic distortion, low power factor, voltage fluctuation, rapidly changing reactive power, or several problems occurring together.
As a power quality equipment manufacturer and harmonic filter supplier, we can customize the voltage level, filter branches, structure, control method, and protection configuration according to the actual network.
What Did This India Project Demonstrate?
This project demonstrated our ability to manufacture and supply large outdoor harmonic filtering systems for complex industrial networks.
Our customer received:
- Two project-specific 33 kV harmonic filter systems
- 5th, 7th, and 11th filter branches
- Outdoor high-voltage equipment
- Harmonic and reactive power simulation
- Coordinated capacitor and reactor design
- Protection and measurement interfaces
- Technical drawings and documentation
The project also showed why harmonic mitigation and power factor improvement should be considered together.
Instead of installing separate products without coordination, the customer selected a complete solution developed around the actual rectifier load and 33 kV network.
Conclusion
For this 12-pulse electric arc furnace project in India, we delivered two outdoor 33 kV harmonic filter systems.
Each system included 5th, 7th, and 11th harmonic filter branches designed to reduce harmonic distortion and provide reactive power support.
Our engineering simulation indicated that the solution could reduce voltage THD from 8.96% to 4.37% and current THD from 8.38% to 3.52%. The power factor was also designed to increase from approximately 0.91 to above 0.95.
At CHYN, we combine power quality engineering with in-house manufacturing. As a harmonic filter manufacturer, reactive power compensation equipment supplier, and power quality system factory, we provide complete project support from data review and simulation to equipment production and technical documentation.
For overseas industrial customers and EPC contractors, we can develop customized harmonic filtering and reactive power compensation systems based on the actual network, load characteristics, installation environment, and project requirements.