Kenya S11 OLTC 33/11kV Main Transformer Substation Solution

I. Project Overview & Technical Specifications for Mombasa 33/11kV Main Transformer

This customized solution is developed by Hengfengyou Electric, serving the new construction, expansion and retrofitting of municipal hub and port main substations in Mombasa. It is also compatible with supporting projects including coastal industrial parks, centralized coastal photovoltaic power stations, port-adjacent mining facilities and coastal county distribution networks. The complete package consists of integrated oil-immersed on-load tap changing main transformers: 3 sets of S11-2.5MVA 33/11kV units and 2 sets of S11-7.5MVA 33/11kV units.

Hengfengyou Electric has deep expertise in the export market of power transmission and transformation equipment across East Africa. All products comply with IEC 60076, GB 1094, Kenya KS national standards and KEBS grid access codes, precisely adapting to the unique climatic conditions of Mombasa: high humidity and heavy salt spray corrosion all year round in coastal areas, frequent heavy rains in rainy seasons, sharp day-night temperature differences, high temperatures and sandstorms in inland stretches during dry seasons. The local 50Hz power grid features long 33kV transmission lines and concentrated high-power loads at ports, resulting in wide voltage fluctuations.

The equipment undertakes core power conversion and voltage regulation functions between 33kV high-voltage transmission lines and 11kV medium-voltage distribution networks, delivering stable power supply for port loading/unloading operations, urban industrial and commercial facilities, and residential zones.

All main transformers adopt high-purity electrolytic copper windings with Ynd11 vector group and low-loss energy-saving S11 structure, equipped with ONAF oil natural air forced cooling. They are applicable to both indoor municipal hub substations and open-air port switchyards. Each unit is internally fitted with a vacuum-type OLTC (On-Load Tap Changer) offering 17 tap positions for wide-range voltage regulation to counteract voltage fluctuations induced by impact loads at ports. Strict temperature rise limits are implemented, with enhanced anti-salt-spray, moisture-proof and anti-corrosion treatments as priority design features. The transformers can operate continuously round the clock with resistance to high temperatures, torrential rains and mild sandstorms, balancing dynamic voltage regulation, low energy loss and easy maintenance.

Master Technical Parameter Table for 33/11kV Main Transformers

II. Six Core Advantages of Hengfengyou Mombasa 33/11kV Main Transformer Solution

Targeted at new construction and expansion projects of municipal hub and port substations in Mombasa, this solution addresses local pain points including defects of coastal 33kV backbone grids, severe salt-spray corrosion at ports, drastic voltage fluctuations from high-power port loads, harmonic interference from photovoltaic systems and limited local maintenance resources. The combined package of 3×2.5MVA and 2×7.5MVA transformers perfectly fits both urban and port core scenarios while covering extended supporting projects. Its core strengths are detailed below:

1. Batch supply with dual capacity models to precisely match new construction & expansion demands of Mombasa municipal and port substations Traditional urban and port retrofitting projects adopt phased transformer procurement, extending design, production and logistics cycles while raising civil engineering and switchgear matching costs. This project unifies design, synchronous production and full-container sea freight direct delivery to Mombasa Port for all 5 transformers. The two capacity tiers serve differentiated scenarios: 2.5MVA units suit secondary urban hubs, small supporting PV facilities and processing sites near ports with moderate loads and compact footprint, ideal for capacity expansion of existing urban facilities; 7.5MVA units act as flagship models for new-build projects of core municipal hubs, port logistics parks, heavy industrial terminals in free trade zones and port-adjacent mining zones with concentrated high-power loads. Uniform foundation dimensions, interchangeable cooling and voltage regulation spare parts across both models enable shared spare stock, drastically cutting civil engineering matching costs, equipment inventory and overall investment for clients at urban and port sites.
2. Built-in vacuum OLTC with 17 wide-range tap positions to resolve voltage fluctuation issues in Mombasa ports and urban hubs Mombasa ports and municipal hubs face distinct voltage disturbance characteristics: frequent startup/shutdown of large port lifting and container handling equipment generates impact loads; long-distance urban transmission lines create significant voltage drop; fluctuating daytime output of coastal photovoltaic systems easily causes severe deviation of 11kV bus voltage. Conventional off-circuit tap changers require power outage for tap adjustment, directly triggering port shutdowns and large-scale urban blackouts. Each unit is equipped with a built-in vacuum tap changer with ±8×1.67% regulation range across 17 positions, enabling automatic voltage stabilization under load to maintain bus voltage within ±3% tolerance. The fully sealed vacuum arc-extinguishing structure inside the transformer tank isolates salt spray and moisture from ports, reducing corrosion and oil leakage of tap changers, and suiting unattended urban hub substations and open-air port switchyards with low maintenance frequency.
3. S11 full-coil low-loss design + strict temperature rise control for stable full-load operation round the clock under 40℃ high temperature High magnetic permeability silicon steel sheets paired with full electrolytic copper windings deliver S11 energy efficiency superior to conventional transformers used in East Africa, adapting to 24-hour continuous heavy loads at Mombasa municipal hubs, alternating peak/off-peak port loads and wide day-night load gaps of supporting PV stations. Continuous reduction of transmission line losses aligns with Kenya Ministry of Energy’s policy of loss reduction and efficiency improvement for urban and port power grids. The transformer limits top oil temperature rise to ≤55℃ and winding temperature rise to ≤60℃, paired with ONAF forced air cooling. No overheating occurs under full load under direct exposure to extreme 40℃ sunlight, allowing long-term stable operation in both enclosed indoor urban substations and open-air port switchyards.
4. Coastal enhanced weather-proof anti-corrosion structure customized for heavy salt-spray environments of Mombasa ports and coastal urban districts The most severe environmental challenge for Mombasa ports and coastal urban zones is heavy Atlantic salt spray, persistent torrential rains and high air humidity. Conventional transformers suffer tank corrosion, seal leakage and insulation failure after short-term operation. This equipment adopts exclusive coastal weather-proof configurations: high-temperature resistant coastal transformer oil and thickened EPDM moisture-proof sealing gaskets block internal condensation and salt spray penetration. The tank features a multi-layer composite anti-corrosion coating system consisting of epoxy zinc-rich primer and thickened UV-resistant salt-spray topcoat. Integrated waterproof and dustproof sealing is applied to bushings and fan bases. The air cooling system is fitted with detachable thickened anti-corrosion filter screens for convenient regular cleaning during rainy seasons at port and urban sites. The complete anti-corrosion process is tailor-made for Mombasa ports and coastal urban areas.
5. Ynd11 winding harmonic suppression to stabilize power quality at Mombasa ports and municipal hubs Variable-frequency port lifting equipment, inverters in free trade zone factories and inverters of urban supporting PV systems generate massive harmonics, which easily trigger voltage distortion, transformer overheating and metering instrument malfunctions. The Ynd11 winding configuration effectively eliminates triple harmonics and mitigates voltage distortion on both 33kV and 11kV sides, ensuring continuous operation of port equipment and safe power consumption for urban residents and industrial/commercial users. The high-voltage star and low-voltage delta grounding architecture adapts to the two mainstream grounding protection schemes of Mombasa municipal main grids and independent port power supply networks, with stronger withstand capability against short-circuit faults.
6. Full-copper windings with superior short-circuit resistance for lightweight unattended maintenance at Mombasa urban and port sites Frequent startup/shutdown of high-power port equipment and elevated short-circuit risks of aging urban lines require robust transformer performance. Winding ends are rigidly reinforced and pass short-circuit dynamic and thermal stability tests per KS standards, resisting deformation and damage under sudden short-circuits to drastically cut maintenance frequency for suburban hub stations and open-air unattended port substations. Low no-load loss characteristics accommodate continuous full loads in urban areas, fluctuating port loads and long-term light-load operation of supporting sites without overheating risks.

Verified Benchmark Project Cases

Hengfengyou Electric has established a track record in power transformation markets for Mombasa cities and ports. Same-series OLTC transformers have been deployed in benchmark projects covering port logistics, urban industrial hubs, coastal photovoltaic stations, port-adjacent mining zones and coastal urban distribution networks, providing long-term field operation validation for this complete new-build and expansion solution for municipal and port hubs:

• Case 1: Heavy Industrial Port Park Substation, Mombasa Free Trade Zone (Port Substation Expansion Scenario) Four same-series on-load tap changing transformers were previously deployed to serve heavy industry and container logistics production lines in the park. Original off-circuit tap changing equipment suffered continuous coastal salt-spray erosion, and voltage fluctuations induced by impact loads of lifting equipment caused over four maintenance shutdowns monthly. After replacement with Hengfengyou enhanced anti-corrosion copper-core OLTC transformers, bus voltage remains stable long-term. Units passed 720-hour accelerated salt-spray aging tests without tank corrosion or tap changer oil leakage, operating continuously for 28 months with consistent temperature rise compliance. Transmission losses of the park dropped by 18%, earning the company the title of Annual Premium Equipment Supplier from the Mombasa port general contractor.
• Case 2: Core Municipal Hub Substation, West Mombasa (Urban Hub Expansion Scenario) Located adjacent to coastal high-humidity salt-spray zones, the substation supplies power to downtown industrial, commercial and residential loads of hundreds of thousands of residents, with severe non-linear harmonic loads from chemical and food processing plants. The Ynd11 winding suppresses harmonic distortion efficiently, and standardized short-circuit impedance simplifies relay protection commissioning on the 33kV side. Units have run at full load for 3 consecutive years without winding overheating, insulation aging or tank corrosion issues, cutting annual maintenance costs by 38% compared with imported equipment.
• Case 3: 15MW Coastal Supporting PV Substation, Northern Mombasa (New Energy Supporting Scenario for Ports) This station delivers green power supply to ports, exposed to sea wind and salt spray. Outdated transformers without on-load tap changers frequently caused bus voltage out-of-limit conditions due to fluctuating photovoltaic output. Customized 17-position vacuum OLTC transformers accommodate intermittent PV loads, while thickened anti-corrosion and dust-proof air cooling suits coastal environments for unattended outdoor operation. Only two annual maintenance tasks are required: filter screen anti-corrosion cleaning and oil sample testing, making this project a demonstration model for new energy retrofits supporting Mombasa ports.

III. Design & Development Phase of Mombasa 33/11kV On-Load Tap Changing Transformers

Centered on core demands of new construction and expansion for Mombasa municipal and port substations, the technical team conducted multiple rounds of electromagnetic simulation combining local parameters of coastal 33kV power grids, extreme 40℃ high temperature, coastal high salt-spray and high humidity climate, and KS/KEBS standards, addressing differentiated load characteristics of core municipal hubs and port logistics parks. Key optimizations include: adjusted ratio of high magnetic permeability silicon steel sheets to reduce S11 losses; precisely matched voltage regulation curves for 17-position OLTC; extended insulation creepage distance on high and low voltage sides to suppress partial discharge in coastal high-humidity environments. Three-dimensional drawings optimize core vibration damping, double-layer thickened anti-corrosion tank design, air cooling layout and sealed structure of built-in tap changers. Port-specified units receive extra thick anti-corrosion coatings, while PV supporting urban units feature reinforced harmonic suppression design.

A joint review was organized by cross-functional teams covering electromagnetic design, process engineering, quality inspection and East Africa overseas project management. Key verification items include tap changing performance under port impact loads, temperature rise under urban extreme operating conditions, coastal dedicated weather-proof anti-corrosion structures, container dimensions for direct sea freight to Mombasa Port, KEBS grid access qualifications and on-site installation conditions of municipal and port substations. Production commences only after full pass of all review items.

IV. Manufacturing Phase (Full-Process Quality Control per ISO9001)

1. Full incoming inspection of raw materials: Electrolytic copper, low-loss silicon steel sheets, damp-resistant insulation, coastal dedicated high-temperature transformer oil and OLTC sealing gaskets all undergo salt-spray and high-low temperature accelerated aging tests. Units exclusively supplied for Mombasa ports and core urban areas receive additional 720-hour accelerated salt-spray testing, with raw materials stored in constant-temperature dust-proof partitioned warehouses.
2. Fully automatic numerical cutting of iron cores, multi-stage stepped lamination to reduce noise and losses; production proceeds only after measured loss compliance.
3. Ynd11 copper winding fabrication in Class 10,000 dust-free workshops with multi-layer heat dissipation oil channels reserved. Windings for port and urban industrial supporting units feature enhanced anti-harmonic reinforcement; DC resistance and turn balance of each unit are tested individually.
4. Multi-layer composite insulation wrapping followed by high-temperature vacuum deep dehydration and degassing to eliminate hidden risks of insulation dampening in high-humidity Mombasa port and urban environments.
5. Integral sealed welding of tanks with sectional air tightness leakage testing; three-gradient salt-spray resistant anti-corrosion spray coating applied. Port-specified units receive thicker anti-corrosion layers, with dual dustproof and waterproof sealing for flanges and fan bases.
6. Dust-free assembly of core and coil assemblies, silver brazing high-temperature welding of leads. 33kV/11kV bushing terminals comply with high-voltage cable installation standards for Mombasa ports and urban areas.
7. Three-stage high-temperature vacuum drying of complete units to fully remove internal moisture from insulation, adapting to coastal high-humidity operating environments.
8. Vacuum filling with coastal dedicated transformer oil for Mombasa; full sealing reinforcement of OLTC pipelines; pre-installation of thickened anti-corrosion dustproof filter screens for air cooling systems, with double-layer dust screens upgraded for heavy-load port units.

V. Factory Acceptance Test (FAT) Verification Before Delivery

All units undergo routine, scenario-specific and type tests in strict accordance with IEC 60076, GB 1094, KS and KEBS standards. Dual-language Chinese-English test reports are issued prior to export sea freight direct to Mombasa:

1. Routine Tests: Winding DC resistance, transformation ratio and vector group verification, insulation resistance, power frequency withstand voltage, insulating oil testing, no-load & load loss measurement, full-range operation test of 17-position OLTC, 40℃ simulated temperature rise test, short-circuit impedance measurement.
2. Scenario-Specific Simulation Tests: Simulation of impact loads from port lifting equipment, continuous full-load operation simulation for urban areas, 720-hour accelerated salt-spray aging test, long-term light-load operation simulation for suburban stations, durability test of air cooling against sea wind and sand blockage.
3. Prototype Type Tests: Lightning impulse test, 720-hour salt-spray aging test, wet-dry cycling test, sand blockage test, sudden short-circuit dynamic and thermal stability test, OLTC tap change endurance test for 10,000 operations. All indicators must meet compliance standards before shipment. Test thresholds are optimized based on historical operating data of Mombasa port and municipal hub projects to precisely match core operating conditions of cities and ports.

VI. Cross-Border Packaging & Ocean Freight (Direct Delivery to Mombasa Port)

All transformers adopt heavy-duty moisture-proof sealed export packaging. Independent anti-rust wooden crates protect 33kV bushings, OLTC control cabinets, air cooling fans and temperature control accessories. Sealing covers are fitted to tank flanges, oil level gauges and tap changer interfaces; transformer tanks are filled with dry nitrogen to isolate salt spray during ocean transit and coastal condensation in Mombasa. Custom steel transport cradles paired with thickened waterproof salt-spray resistant tarpaulins are used, with large cargo sea freight markings printed on tanks for direct delivery to Mombasa Port.

Accompanying documents shipped with each unit include English as-built drawings, FAT test reports, KEBS PVOC certification, spare parts lists and Swahili operation & maintenance manuals, with key guidance on salt-spray anti-corrosion maintenance for port and urban sites highlighted in manuals.

Logistics adopts a combined transport scheme: domestic highway delivery to port + ocean freight direct to Mombasa Port + oversize land transport within Kenya. Export PVOC customs clearance and oversize vehicle passage permits for Mombasa urban and port areas are processed in advance. Temperature, humidity and impact recorders monitor cargo conditions throughout transit, with extra anti-collision and anti-salt-spray reinforcement applied during ocean shipping. Leveraging mature long-term sea freight solutions for complete equipment delivered direct to Mombasa Port, the 5 transformers are guaranteed synchronous on-time delivery to construction sites of municipal hub and port substations.

VII. Solution Summary

This complete substation solution for Mombasa 33/11kV power grids includes 5 oil-immersed on-load tap changing main transformers (3×2.5MVA + 2×7.5MVA) with built-in vacuum OLTC. It is primarily designed for new construction, expansion and retrofitting of municipal hub and port main substations in Mombasa, while covering extended scenarios including port-adjacent industrial parks, coastal photovoltaic power stations and suburban supporting distribution networks. This project serves as a benchmark coastal grid upgrade project of Hengfengyou Electric in Mombasa, Kenya.

Equipped with a coastal enhanced salt-spray resistant insulation system, S11 full-coil low-loss windings, 17-position built-in vacuum OLTC for uninterrupted tap change and Ynd11 harmonic suppression structure, the solution resolves core pain points of Mombasa urban and port 33kV power grids in one stop: severe voltage fluctuations, equipment corrosion induced by coastal salt spray, excessive transmission losses, industrial harmonic pollution at ports and high maintenance difficulty for outdoor stations.

Hengfengyou Electric maintains full expertise in Kenya’s KS, KEBS and PVOC export access codes as well as international transformer standards IEC and GB. We can customize complete sets of 33kV and 11kV oil-immersed on-load tap changing main transformers for new construction and expansion projects of Mombasa municipal and port substations, and also undertake similar grid retrofitting projects for other coastal cities across East Africa. Our products support capacity expansion of Mombasa’s 33kV backbone power grids, upgrading of municipal hubs and quality improvement of port power supply infrastructure. General contractors, local Kenyan power enterprises and foreign trade partners are welcome to discuss cooperation.

Contact Email: sales@hfy-transformer.com