I. Project Overview and Technical Specifications for Kenya's 2 Units OSFSZ-150MVA-220/132KV Autotransformer Power Transformer

This solution is developed by Hengfengshuai Electric, providing a comprehensive end-to-end solution for two (2) units of OSFSZ-150MVA-220/132KV three-phase oil-immersed autotransformers for Kenya's grid upgrade and hub substation projects. With years of experience in R&D, manufacturing, and overseas project services for power transmission and distribution equipment, our products strictly comply with IEC, GB 1094, and Kenya's KEBS standards. The design is adapted to local conditions including an altitude of 2,200m, ambient temperature range of -1°C to +40°C, and annual average temperature of 30°C, addressing the plateau and high-temperature environment while coping with grid voltage fluctuations, outdoor dust, and intense UV radiation.

The transformer incorporates a tertiary winding, is equipped with an On-Load Tap Changer (OLTC), adopts YNa0d11 vector group, features dual cooling modes (ONAN/ONAF), and achieves IP65 protection rating. It enables stable voltage transformation between HV and LV grids, ensuring reliable power supply for industrial, residential, and renewable energy integration.

Main Technical Parameters of the Transformer

Parameter	Specification	Remarks
Equipment Type	Three-phase core-type oil-immersed autotransformer	Built-in tertiary winding, suitable for HV grid networking
Rated Capacity	150MVA	Continuous rated operating capacity
Voltage Combination	220kV/132kV	HV backbone grid transformation scenario
Voltage Regulation	MR On-Load Tap Changer (OLTC)	No-interruption voltage regulation, adaptable to grid voltage fluctuations
Vector Group	YNa0d11	Standard autotransformer connection, compatible with tertiary winding output
Short-Circuit Impedance	Uk=12.5%	Suppresses system short-circuit current, meeting HV grid design requirements
Cooling Method	ONAN/ONAF (OFAF forced oil circulation)	Dual cooling modes, adapted to high-temperature, high-altitude heat dissipation needs
Winding Material	Electrolytic copper	Excellent conductivity, resistance to thermal aging and short-circuit impact
Insulation Configuration	Basic Impulse Insulation Level (BIL)	Reinforced insulation performance under low pressure at high altitude, protects against lightning overvoltage
Transformer Oil	Shell Diala S4 ZX-I	Adapted to high-temperature environments, oxidation-resistant, low volatility, stable insulation
Noise Level	82dB(A)	Complies with outdoor substation noise control standards
Protection Rating	IP65	Fully sealed structure, dustproof, waterproof, sand-resistant, suitable for outdoor installation
Operating Environment	Altitude 2,200m, ambient temp -10°C~+40°C, annual average 30°C	Specially optimized for Kenya's plateau high-temperature environment

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II. Why Choose the OSFSZ-150MVA-220/132KV Autotransformer Solution

Hengfengshuai's autotransformers stand out in high-voltage power systems. The core advantage can be summarized in four words: Economical and Efficient. Highly suitable for Kenya, with low initial investment and low maintenance costs.

This is reflected in the following five aspects:

1. Material Savings and Significantly Reduced Manufacturing Costs (Core Advantage)
Due to the electrical direct connection between HV and LV windings in addition to magnetic coupling, a portion of the transmitted power is conducted directly without full electromagnetic induction. You only need to manufacture winding materials equivalent to 60MVA to exchange 150MVA of power. Compared with conventional two-winding transformers of the same capacity, copper savings reach approximately 40%, silicon steel savings approximately 30%, significantly reducing manufacturing costs.

2. Low Losses and High Operating Efficiency
With less winding conductor material and lower DC resistance, load losses (copper losses) are far lower than those of conventional transformers of the same capacity.
For a 150MVA hub transformer operating at full load year-round, every 1kW reduction in loss saves nearly 10,000 kWh annually. Over the full lifecycle, the electricity cost savings are substantial.

3. Compact Size, Light Weight, Easy Transport and Installation
With reduced core and winding materials, tank dimensions and total weight are approximately 30%~40% lighter than conventional transformers.
For 220kV substations, this means lower civil foundation requirements, easier indoor installation, or convenient deployment in mountainous areas with transport constraints.

4. Simpler and More Reliable Voltage Regulation
Since the on-load tap-changer is only installed at the end of the series winding or common winding, the switch's current capacity and insulation level are much lower than those of conventional transformers.
This results in lower failure rates, smoother switching transitions, and longer service life.

5. Lower Short-Circuit Impedance and Better Voltage Regulation
Autotransformers have less leakage flux, and the percentage short-circuit impedance is typically lower than that of conventional transformers of the same capacity.
This means that under drastic load changes, the voltage fluctuation on the secondary side (132kV) is smaller, delivering higher power quality and less impact on downstream user equipment.

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III. Design and Development Phase for Kenya OSFSZ-150MVA-220/132KV Power Transformer

Electromagnetic Scheme Design

Hengfengshuai Electric's design team, combining local operating conditions with international standards, completes the electromagnetic scheme design using professional simulation software. Addressing the challenges of insulation and heat dissipation performance degradation due to thin air at high altitude, insulation clearances and temperature rise parameters are recalculated. High-permeability silicon steel is selected to reduce operating losses, high-purity electrolytic copper windings optimize current distribution, and BIL insulation design reinforces the equipment's resistance to high temperatures and lightning impulse, meeting long-term full-load operation requirements.

Structural Drawings Design

After the electromagnetic scheme is finalized, the team completes the full set of structural drawings with targeted optimizations: optimized core lamination and clamping structures to control noise and prevent loosening during operation; primary and tertiary winding processes designed in conjunction with the vector group to enhance short-circuit withstand capability; upgraded insulation materials and layout to suppress partial discharge at high altitude; tank structure optimized through finite element analysis, paired with double sealing to achieve IP65 protection. Core accessories are selected from specialized models resistant to extreme temperatures and adapted to plateau conditions, uniformly using Shell special transformer oil to ensure overall operational stability.

Design Review

Upon completion of drawings and schemes, the company organizes a joint review involving technical, process, quality control, and overseas project teams. Items are checked point by point including grid compatibility, insulation and heat dissipation, protective structures, production processes, and cross-border transport conditions. A comprehensive review is conducted against international standards and local certification requirements, and only upon passing can the project proceed to the production phase.

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IV. Manufacturing Phase for Kenya OSFSZ-150MVA-220/132KV Power Transformer

1. Material Procurement and Incoming Inspection

Hengfengshuai Electric strictly implements the ISO9001 Quality Management System and SQA special inspection standards. All raw materials and supporting components are procured strictly according to customized design drawings. Incoming materials undergo 100% full-item re-inspection. Non-conforming materials are strictly prohibited from entering production, ensuring quality control from the source. Key material control standards for this project are as follows:

• Silicon Steel Sheets: High-permeability grain-oriented silicon steel is selected. Magnetic properties and loss parameters are re-inspected upon incoming receipt to ensure low-loss and low-noise performance.

• Electrolytic Copper Conductors: Resistivity, tensile strength, and bending performance are tested batch by batch to guarantee winding conductivity and mechanical strength, adapted for long-term full-load operation.

• Insulation Materials: Insulation paperboard, cable paper, end rings, angle rings, and other insulation components are strictly inspected for moisture content, electrical strength, and temperature resistance to prevent insulation failures caused by plateau humidity and UV aging.

• Transformer Oil: Shell Diala S4 ZX-I transformer oil is inspected for breakdown voltage, micro-water content, and oxidation resistance upon receipt, ensuring suitability across the full -10°C~+40°C temperature range.

• Seals and Tank Materials: Aging-resistant, UV-resistant, and temperature-differential-resistant sealing gaskets and special steel materials are selected to meet the long-term outdoor sealing requirements of IP65 protection.

All inspected and qualified materials are recorded in ledgers and stored in dedicated temperature- and humidity-controlled warehouses with dustproof and moisture-proof protection.

2. Core Manufacturing

Silicon steel sheets are precision-processed into standard shapes using Hengfengshuai Electric's fully automatic slitting and shearing equipment. Burrs are removed, and a special insulating coating is uniformly applied. The core adopts a multi-step stepped lap joint lamination process, effectively reducing joint reluctance, no-load losses, and operating noise. After stacking, clamping force is precisely controlled, with high-strength clamps and vibration-damping components added to prevent loosening or vibration during transport and operation. The completed core undergoes special performance tests; no-load loss and no-load current are measured and compared with design values for calibration. The core proceeds to the next process only after all indicators pass acceptance.

3. Winding and Tertiary Winding Manufacturing

As the core component of the transformer, winding manufacturing is carried out entirely in Hengfengshuai Electric's Class 10,000 clean room with controlled temperature and humidity. Production personnel strictly follow drawing process requirements to complete the winding of the auto-primary winding, low-voltage winding, and tertiary winding, precisely controlling turns, conductor transposition, and coil tightness in accordance with the YNa0d11 vector group characteristics. During winding of electrolytic copper conductors, oil duct dimensions are strictly controlled to ensure smooth heat dissipation under high-temperature conditions. After each coil set is completed, quality inspectors immediately conduct full inspections of DC resistance, turns count, and appearance, eliminating issues such as turn deviation or conductor damage. All inspected and qualified coils are centrally managed.

4. Insulation Component Processing and Treatment

Insulation components are cut and formed using CNC processing equipment, with dimensional accuracy strictly controlled within high industry standard tolerances. Critical insulation components such as HV angle rings, electrostatic shields, and end insulation are refined using precision manual wrapping processes to optimize creepage paths and effectively suppress partial discharge under high-altitude conditions. After processing, all insulation components are sent to vacuum drying equipment for deep drying to thoroughly remove internal moisture, significantly enhancing insulation stability and service life under extreme environments.

5. Tank Manufacturing and Protection

Steel plates are processed by CNC cutting and fully automatic welding. Each tank undergoes kerosene leak testing and air tightness testing to comprehensively identify weld defects. After welding, the tank undergoes sandblasting, rust removal, and passivation treatment, followed by layered spraying of UV-resistant and corrosion-resistant specialized paint, with anti-corrosion grade adapted to Kenya's outdoor environment with heavy dust and strong sunlight. In line with IP65 protection design requirements, flange, interface, and cover sealing structures are optimized with double sealing design. Finished tanks undergo positive and negative pressure mechanical strength tests to check deformation and sealing reliability, ensuring no deformation or leakage during long-distance transport or under plateau temperature differential conditions.

6. Core and Coil Assembly

Production personnel precisely fit the inspected core and multiple coil sets, sequentially installing various custom insulation components, leads, the On-Load Tap Changer (OLTC), and tertiary winding connection assemblies. Cleanliness in the assembly area is strictly controlled to prevent metal dust and debris from entering, avoiding short-circuit failures during operation. Leads are joined using high-strength welding processes, balancing conductivity and mechanical stability. The OLTC undergoes pre-installation debugging, with repeated testing of tap change flexibility and accuracy to ensure stable on-load voltage regulation. After overall assembly, full appearance, structural, and wiring inspections are conducted.

7. Multi-Stage Drying Treatment

In response to Kenya's high-altitude, high-temperature, and moisture-prone environment, Hengfengshuai Electric applies a three-stage vacuum drying process to the transformer core and coil assembly, with total drying time meeting stringent HV equipment standards to thoroughly remove residual moisture from the insulation system and windings:

1. Primary Drying: Pre-drying of individual coils after winding to remove moisture absorbed during the winding process.

2. Intermediate Drying: Overall drying after coil assembly and insulation installation to eliminate moisture introduced during assembly.

3. Final Drying: After full assembly of the core and coil assembly, it is placed in a dedicated drying tank for high-temperature vacuum deep drying, ensuring insulation performance meets standards and is adapted to high-altitude low-pressure conditions.

8. Final Assembly and Vacuum Oil Filling

The dried core and coil assembly is precisely lowered into the tank. Workers sequentially install the tank cover, HV bushings, LV bushings, conservator, radiators, temperature control system, cooling fans, Buchholz relay, monitoring instruments, and all other accessories. Wiring and piping are strictly completed according to design drawings, with careful verification of OLTC and tertiary winding external interfaces. After final assembly, high-grade vacuum evacuation is performed, with vacuum level maintained and held for an extended period. Subsequently, Shell Diala S4 ZX-I transformer oil is slowly injected at a controlled flow rate. The entire oil filling process is regulated to ensure complete impregnation of the core and coil assembly without trapped air bubbles, guaranteeing stable insulation performance.

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V. Testing and Validation Phase for Kenya OSFSZ-150MVA-220/132KV Power Transformer (FAT)

Before shipment, the two transformers undergo a full suite of routine tests, special type tests, and high-altitude simulation tests at Hengfengshuai Electric's test center in strict accordance with IEC 60076, GB 1094, and Kenya's local power standards. Only after all test data meets requirements and official factory test reports are issued can the equipment be dispatched.

1. Routine Tests (Performed on Each Unit)

• Winding DC Resistance Measurement: Covers all tap positions of the OLTC, with three-phase unbalance ratio controlled within standard limits.

• Voltage Ratio and Vector Group Verification: Full-tap verification of ratio and phase angle, confirming accuracy of YNa0d11 vector group, with errors meeting HV equipment standards.

• Insulation Resistance, Absorption Ratio, and Polarization Index Testing: Evaluates overall insulation condition, ensuring the equipment is dry and moisture-free, suitable for high-altitude insulation requirements.

• Dielectric Dissipation Factor Testing: Assesses overall insulation system performance, with indicators better than national and IEC standards.

• Winding and Bushing AC Withstand Voltage Test: Short-duration power-frequency withstand test on main insulation, with no breakdown or flashover.

• Insulation Oil Testing: Shell Diala S4 ZX-I transformer oil tested for breakdown voltage, micro-water content, and dissolved gas analysis (DGA), all indicators qualified.

• No-Load Loss and No-Load Current Testing: Measured values controlled within allowable deviation from design values.

• Load Loss and Short-Circuit Impedance Testing: Uk=12.5% measured at rated tap, fully meeting Kenya grid short-circuit protection design requirements.

• Cooling System Test: Both ONAN and ONAF cooling modes tested separately; fan start/stop and temperature control interlocking functions verified.

• Protection Rating Sampling Inspection: Simulated rain and dust environments to verify IP65 dustproof and waterproof performance on site.

2. Type Tests (Full Suite on First Prototype)

For the first 150MVA large-capacity HV transformer, Hengfengshuai Electric conducts comprehensive type tests to fully verify the equipment's capability under extreme conditions:

• Lightning Impulse Test (BIL): Full-wave and chopped-wave lightning impulse tests completed, verifying the equipment's ability to withstand lightning overvoltage, suitable for Kenya's plateau outdoor areas prone to lightning strikes.

• Partial Discharge Test: Partial discharge level measured under high voltage, effectively mitigating discharge risks caused by low pressure at high altitude.

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VI. Packaging and Transport Phase for Kenya OSFSZ-150MVA-220/132KV Power Transformer

Component Protection and Packaging

After successful testing, bushings, radiators, instruments, and other precision accessories are disassembled and individually sealed for packaging. Equipment interfaces are fitted with sealed covers. The tank is filled with dry nitrogen for protection, and insulating oil is retained inside the tank to protect the core and coil assembly. The equipment is secured on heavy-duty steel skids and wrapped with waterproof and dustproof tarpaulins. Accessories are packed in shockproof and moisture-proof wooden crates, with international transport warning labels clearly marked on all packages. A full set of documentation including certificates of conformity, test reports, bilingual instruction manuals, and certification documents is included with the shipment.

Intermodal Cross-Border Transport

The project adopts a combined transport model of "domestic road + ocean shipping + local delivery". Customs clearance and heavy cargo transport permits are arranged in advance for both countries. Throughout the transport process, 3-axis shock recorders and temperature-humidity recorders are installed for real-time monitoring of equipment condition. Transport routes are pre-surveyed overseas to identify height and weight restrictions. Anti-corrosion measures against salt spray are reinforced during the ocean shipping phase to ensure the equipment arrives safely at the site.

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VII. On-Site Delivery and Installation for Kenya OSFSZ-150MVA-220/132KV Power Transformer

1. On-Site Unpacking and Handover Inspection

Upon arrival at the project substation in Kenya, Hengfengshuai Electric's overseas technical service team, together with the owner, local supervision, and power operation & maintenance departments, jointly conduct the unpacking and handover inspection. Inspection items include: checking the main body and all accessories for dents, rust, oil leaks, or deformation; verifying accessory specifications and quantities against the packing list; checking the nitrogen pressure inside the tank to confirm sealing integrity; and retrieving shock and temperature-humidity recorder data from the transport process to verify that all parameters remained normal and the equipment is intact. After all inspection items are passed, all parties sign the official handover documents.

2. Standardized On-Site Installation

Hengfengshuai Electric dispatches a senior overseas technical team for on-site supervision throughout the installation process. Considering the local 2,200m altitude and outdoor installation environment, the installation strictly follows international HV transformer installation standards. Core procedures are as follows:

• Equipment Positioning: Large professional lifting equipment is used for unloading and precise positioning of the main body. Levelness is carefully adjusted within standard tolerances.

• Accessory Installation: Radiators, cooling fans, bushings, conservator, piping, temperature control devices, Buchholz relay, tertiary winding external connection assemblies, and other accessories are installed in proper sequence according to standard procedures. All flange and interface seals are reinforced to meet IP65 protection requirements without any leakage hazards.

• Vacuum Oil Refilling and Circulation: A secondary vacuum evacuation is performed on the equipment, followed by refilling with Shell Diala S4 ZX-I transformer oil of the same type. Oil filling rate is strictly controlled, and oil circulation/filtration is completed.

• Static Settling and Degassing: After oil filling, the equipment is left to settle for an extended period. Residual gas in piping, relays, and the tank is vented multiple times to avoid insulation faults caused by air gaps.

3. On-Site Commissioning Tests (SAT)

After installation and settling, the on-site team conducts a full set of on-site commissioning tests in accordance with IEC standards, Kenya power operation & maintenance specifications, and domestic DL/T series standards. Test data is compared point-by-point with the factory FAT report to ensure no performance degradation after installation. Test items include: full insulation oil testing, winding DC resistance measurement, voltage ratio and vector group re-verification, insulation resistance and absorption ratio testing, winding deformation testing, full-tap OLTC operation testing, dual cooling system start/stop and interlock testing, Buchholz and protection circuit verification, partial discharge re-measurement, and insulation withstand re-testing. All test data pass, and protection devices operate with correct sensitivity and signal accuracy.

4. No-Load Energization and Formal Commissioning

After all on-site commissioning tests are passed, the work area is cleaned, and all electrical connections and safety protection devices are restored. In accordance with HV equipment commissioning procedures, multiple no-load energization switching tests are conducted, with real-time monitoring of inrush current, equipment sound, and instrument readings to verify protection system response performance. The equipment operates continuously and stably under no-load conditions for 24 hours, with continuous monitoring of oil temperature, temperature rise, noise, vibration, and leakage. After all parameters remain normal, load is gradually applied, and the transformer is finally connected into Kenya's 220kV/132kV HV grid for commercial operation.

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VIII. Comprehensive Quality Control and Documentation Delivery

1. Full-Process Key Quality Control Points

Hengfengshuai Electric has established a full-chain quality control system from design and R&D to on-site operation and maintenance. For overseas HV projects and plateau special conditions, control requirements are set above industry standards. The six core control points are as follows:

• Design Control: Electromagnetic scheme and structural drawings undergo multiple reviews; high-altitude adaptation, IP65 protection, on-load voltage regulation, and other special designs are verified point by point.

• Material Control: All raw materials and components undergo 100% re-inspection, preventing substandard materials from entering production from the source.

• Process Control: Semi-finished products including cores, coils, insulation, and assemblies are inspected at each process step. Critical processes are documented with video records for full traceability.

• Testing Control: Factory FAT and on-site SAT tests cover all required items with bidirectional data comparison. Non-conforming equipment is prohibited from proceeding to the next stage.

• Transport Control: Real-time monitoring with smart recorders throughout the journey. Transport routes are pre-surveyed, and modular protection measures address various risks during cross-border transport.

• On-Site Control: Installation processes are standardized with on-site supervision by resident technical personnel. Multiple verification tests are conducted after completion.

2. Technical Documentation and Operation & Maintenance Training

After project commissioning, the owner receives a full set of bilingual (Chinese-English) technical documentation, including test reports, drawings, operation and maintenance manuals, spare parts catalogs, and certification documents. At the same time, hands-on training is provided to local operation and maintenance personnel, covering key points of equipment inspection, maintenance, and fault diagnosis under plateau conditions.

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IX. Solution Summary

This project for 2 units of OSFSZ-150MVA-220/132KV power transformers is a typical case of Hengfengshuai Electric's HV equipment adapted to East African plateau conditions. The company has completed customized design and manufacturing specifically for Kenya's high altitude, high temperature, dusty environment, and voltage fluctuations, leveraging mature processes, stringent quality control, and a comprehensive overseas service system to deliver highly reliable power transformation equipment.

Hengfengshuai Electric hfs@hengfengshuai.com has deep experience in the African power market, with extensive cross-border project implementation expertise. We can customize power transformer solutions at various voltage levels according to different countries' climates, grid standards, and certification requirements, supporting Africa's grid upgrades and industrial development. We welcome inquiries and cooperation opportunities from clients worldwide.