Active Harmonic Filter Retrofit and Capacity Upgrade for a Hong Kong Commercial Building
Project Overview
- Project type: Existing AHF system retrofit
- Retrofit scope: Replacement of existing failed AHF modules while retaining the original CT measurement and distribution arrangement
- Location: Hong Kong
- Application: Commercial building power distribution system
- Equipment: Wall-mounted Active Harmonic Filter
- Configuration: 6 units × 150A AHF
- Total compensation capacity: 900A
This case study covers a retrofit of an existing active harmonic filter installation in a commercial building power distribution system in Hong Kong. Six wall-mounted AHF units had been installed in 2016. By 2025 the original units experienced operational failures and required replacement to restore the building’s harmonic mitigation capability. Winzele assessed the existing installation and delivered a parallel AHF retrofit that re-used the original electrical infrastructure.
Project Background
The original system consisted of six wall-mounted AHF units installed in 2016. The original design drawings and the on-site arrangement are shown below. The installation included a dedicated AHF incoming cabinet and an existing CT measurement arrangement for current sampling.
Original AHF system design diagram reviewed at the start of the retrofit project.
Existing wall-mounted AHF installation before the retrofit.
The retrofit had to meet several requirements at the same time:
- Replace the failing AHF units with new equipment
- Improve harmonic performance compared with the original configuration
- Maintain compatibility with the existing electrical infrastructure, including the incoming switchgear and the existing CT arrangement
- Complete the changeover with minimum disruption to building operation
Retrofit Engineering Assessment
Before proposing a solution, Winzele engineers evaluated the existing installation on site:
- Installation position and available space for the wall-mounted units
- Incoming switch arrangement
- Existing CT interface and secondary wiring
- Condition of the existing wiring and connections
CT interface verification before the retrofit — the existing measurement arrangement had to be confirmed before the new units could be connected.
Incoming switch and installation position verification during the site assessment.
The assessment confirmed that the existing infrastructure could be retained and reused, and that the retrofit could be carried out with the new AHF units connected to the existing distribution system.
Retrofit System Design
Based on the site assessment and the original system documents, Winzele designed a retrofit scheme that followed the original system architecture:
- CT sampling arrangement was kept consistent with the original design
- The new AHF units were arranged in a parallel configuration
- The retrofit design minimized changes to the building’s electrical infrastructure
Retrofit system diagram with the CT wiring detail, drawn from the original system design.
Dual-unit parallel CT wiring diagram used for the wall-mounted AHF configuration.
The diagrams are based on the original system design and the on-site verification. The retrofit re-used the existing CT secondary terminals, with the new units connected in parallel.
Factory Testing and Delivery
The replacement AHF units were prepared and tested before delivery:
- Parallel operation was verified during factory testing
- Commissioning checks and burn-in were carried out before shipment
- The equipment was then shipped to the Hong Kong forwarder
AHF equipment prepared for shipment to the Hong Kong forwarder after factory testing.
Factory Parallel Testing and Commissioning Preparation
Before delivery, the AHF units were tested and configured according to the retrofit requirements.
Because the project required multiple wall-mounted AHF units operating in parallel, Winzele performed parallel operation tests and commissioning verification before shipment to ensure proper communication, current sharing and system compatibility.
The retrofit configuration included:
- Each installation area: 2 × 150A wall-mounted AHF units
- Total units supplied: 6
- Total compensation capacity: 900A
Factory verification included:
- Parallel operation testing of multiple AHF units
- Communication and current sharing verification
- Operating parameter adjustment before site installation
Factory parallel operation test of two 150A wall-mounted AHF units before delivery.
Factory commissioning and parameter verification before shipment for the Hong Kong retrofit project.
Harmonic Performance Verification
Harmonic performance was verified in stages rather than as a single before/after comparison.
Voltage Harmonic (THDu)
The AHF units were commissioned in stages. Voltage harmonic levels were recorded with 0, 2 and 6 units in operation.
| AHF Operating Condition | Phase A | Phase B | Phase C |
|---|---|---|---|
| Before AHF operation (0 units) | 14.2% | 15.6% | 11.0% |
| During staged commissioning (2 units) | 9.1% | 9.2% | 7.8% |
| After commissioning (6 units) | 2.2% | 2.6% | 2.0% |
Because the AHF units were commissioned progressively, the THDu values reflect the improvement trend as additional compensation capacity was connected.
Voltage harmonic (THDu) measurements during staged AHF commissioning with 0, 2 and 6 units in operation.
Current Harmonic (THDi)
The AHF compensates the harmonic current generated by the building’s nonlinear loads. Current harmonic was measured before the retrofit units were switched in and after all six units were in operation.
| Operating Condition | Phase A | Phase B | Phase C |
|---|---|---|---|
| Before AHF operation | 22.6% | 23.0% | 22.2% |
| After six AHF units operation | 2.6% | 2.6% | 2.4% |
Current harmonic (THDi) comparison before and after all six AHF units were commissioned.
Operating Verification
After commissioning, the retrofit system was checked under normal operating conditions:
- Busbar voltage
- Operating current
The AHF touchscreen interface is displayed in Chinese. The two parameters shown during the operating check are labelled in the comparison header below:
Busbar voltage and operating current measurement during normal operation of the retrofitted system.
Project Value
This project demonstrates Winzele’s retrofit capability on an existing AHF installation:
- Retrofit of an existing harmonic filter system without replacing the surrounding infrastructure
- Multi-unit parallel AHF application (6 × 150A, 900A total)
- Engineering adaptation to an existing CT and wiring arrangement
- Multi-unit parallel operation verification before delivery
- Measured power quality improvement verified through staged commissioning
The project upgraded an existing harmonic compensation system without major modification to the building’s distribution infrastructure. The result is an upgraded commercial building harmonic mitigation solution, with the original infrastructure retained and the compensation capacity increased to 900A.
Related Solution
- Harmonic Mitigation Solutions — active harmonic filter solutions for industrial power quality improvement
- Active Harmonic Filter (AHF) — active harmonic filter for dynamic harmonic compensation of nonlinear loads
Related Case Study
- Active Harmonic Filter Solution for Ningxia Monocrystalline Silicon Manufacturing Plant — AHF harmonic mitigation for a semiconductor manufacturing plant, with current THD reduced from 30.41% to 2.98% after compensation
