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The S-7500kVA 33kV/6.6kV Oil Immersed Power Transformer is a three-phase power transformer designed for medium voltage power distribution and industrial substation applications. With a rated capacity of 7500kVA, a 33kV high-voltage winding, and a 6.6kV low-voltage winding, it provides a practical voltage transformation solution for facilities using 6.6kV medium voltage systems.
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S-7500
YAWEI
The S-7500kVA 33kV/6.6kV Oil Immersed Power Transformer is a three-phase transformer designed to connect a 33kV medium-voltage supply with a 6.6kV electrical distribution system. With a rated capacity of 7500kVA (7.5MVA), it is intended for substations and industrial power networks where substantial electrical loads are supplied at medium voltage.
The transformer is particularly suited to applications involving large motors, industrial feeders, process equipment, and other 6.6kV loads. Typical project environments include manufacturing plants, mining and mineral processing facilities, heavy industry, infrastructure installations, and private or utility substations.
Its oil immersed construction provides both electrical insulation and a medium for transferring heat away from the active parts. The Dyn11 vector group defines the winding connection and phase displacement between the 33kV and 6.6kV sides and should be coordinated with the grounding, protection, and downstream distribution system.
The final transformer configuration can be developed according to project-specific requirements, including rated parameters, impedance, insulation coordination, tap arrangement, cooling method, protection equipment, accessories, installation conditions, and applicable IEC or IEEE requirements.
The 7500kVA rating provides a substantial power transformation stage for medium-voltage electrical systems serving large and continuously operating loads.
Rather than being limited to small localized distribution, this 7.5MVA power transformer can be incorporated into plant substations and larger electrical networks where 6.6kV feeders supply motors, production equipment, and other medium-voltage loads.
The transformer capacity can be coordinated with the project's present demand, expected load growth, operating schedule, and required system margin.
The 33kV/6.6kV voltage ratio provides a direct transformation path between the incoming medium-voltage network and a 6.6kV industrial distribution system.
This arrangement is useful where 6.6kV is retained for high-power motors and process equipment, reducing the need to distribute substantial industrial loads at lower voltage levels.
The transformer can therefore be integrated with 6.6kV switchgear, incoming and outgoing feeders, motor control equipment, and plant distribution systems according to the electrical design.
The oil immersed construction uses insulating liquid as both a dielectric medium and a heat-transfer medium.
Heat generated by the core and windings is transferred through the insulating oil toward the tank and cooling surfaces. This allows the transformer to be configured for the thermal requirements associated with a 7500kVA rating.
The main tank, radiators, bushings, conservator arrangement, valves, and other accessories can be selected according to the required installation and operating conditions.
The active part is engineered around the electrical characteristics of the 33kV to 6.6kV transformation system.
The magnetic core uses grain-oriented electrical steel appropriate to the transformer design, while the winding arrangement is developed to satisfy the specified voltage, current, insulation, and mechanical requirements.
The active assembly also requires adequate mechanical support to withstand transportation forces and electromagnetic stresses associated with abnormal or short-circuit conditions.
The Dyn11 vector group establishes the winding connection and phase displacement required between the high-voltage and low-voltage systems.
The high-voltage winding uses a delta connection, while the low-voltage winding uses a star connection with the neutral point brought out. The “11” designation identifies the corresponding clock-hour phase displacement.
For system integration, the vector group should be checked against the upstream network, downstream switchgear, grounding arrangement, relay protection scheme, and any future parallel-operation requirements.
Transformer impedance is not only a transformer nameplate parameter; it also forms part of the electrical system design.
The selected impedance influences the voltage drop under load and the fault current available on the 6.6kV side. It therefore needs to be considered together with switchgear interrupting capacity, protection settings, feeder design, and the calculated short-circuit level.
For this reason, the final impedance of the 33kV 6.6kV power transformer should be established from the project's electrical study and technical specification.
A 7500kVA transformer can be integrated with appropriate monitoring and protection equipment to support substation operation and maintenance.
Depending on the approved specification, available equipment may include:
Oil temperature indicator
Winding temperature indicator
Oil level gauge
Pressure relief device
Buchholz relay
Conservator system
Cooling system monitoring
Grounding terminals
Transformer protection interfaces
Alarm and trip contacts
Remote monitoring interfaces
Communication and control functions where specified
The final selection should correspond to the project's protection philosophy rather than using an identical accessory package for every transformer.
The S-7500kVA transformer can be configured around the actual requirements of the installation rather than relying solely on a standard catalogue arrangement.
Engineering considerations may include:
7500kVA rated capacity
33kV primary voltage
6.6kV secondary voltage
Dyn11 vector group
Frequency
Tap arrangement
Impedance voltage
Insulation level and BIL
Winding conductor material
Cooling arrangement
Temperature-rise requirements
Transformer protection
Monitoring equipment
Bushing and terminal configuration
Conservator and radiator arrangement
Outdoor installation conditions
IEC, IEEE, or utility-specific requirements
The final design should be confirmed against the customer's single-line diagram, load data, site conditions, technical specification, and applicable standards.
>> Technical Parameters
| Type | Step downpower transformer |
| Model | S-7500-33/6.6 |
| Cooling Method | ONAN |
| Primary Voltage | 33KV |
| Secondary Voltage | 6.6kV |
| Rated Frequency | 50HZ |
| Rated Power | 7.5MVA |
| Winding Material | Copper |
| Voltage Regulation | OCTC (Off-Circuit Tap Changer) |
| Tapping Range | ±9×1.67% |
| Connection Group | Ynyn0d5 |
| Transformer Dimension | |
| Weight |
The transformer can serve as the main voltage transformation equipment between a 33kV incoming supply and a 6.6kV plant distribution network.
It can feed downstream switchgear, medium-voltage feeders, large motors, and process equipment.
Mining facilities may contain crushers, conveyors, pumps, ventilation systems, mills, and other high-power equipment.
Where these loads operate at 6.6kV, a 33kV to 6.6kV transformer can provide the required supply interface within the site substation.
Large manufacturing facilities often require dedicated medium-voltage distribution for production machinery and high-power motors.
The 7500kVA capacity can be incorporated into the plant's electrical distribution architecture according to the actual load profile.
Steel production and other heavy industrial processes can require substantial electrical capacity for motors, production lines, auxiliary systems, and process equipment.
The 33kV/6.6kV configuration provides a medium-voltage transformation stage suitable for these types of electrical networks.
The transformer can also be considered for large process facilities, infrastructure projects, private substations, and other installations where a 33kV supply must be transformed to 6.6kV.
The final application should be evaluated according to load demand, fault level, environmental conditions, protection coordination, and applicable standards.
Before installation, inspect the transformer and supplied accessories for transportation damage, oil leakage, damaged bushings, loose components, or other visible abnormalities.
Confirm that the installation location, foundation, clearances, lifting arrangements, and grounding system correspond with the approved drawings.
Before energization, verify all high-voltage and low-voltage connections.
Check phase identification, terminal arrangement, grounding conductors, cable connections, and tap position against the approved technical documents.
Check the oil level and inspect the tank, radiators, conservator, valves, bushings, temperature indicators, pressure relief device, and Buchholz relay where installed.
Any abnormal oil level, leakage, damaged accessory, or loose connection should be corrected before commissioning.
Test the transformer protection, alarm, trip, temperature-monitoring, oil-level, and communication circuits according to the approved commissioning procedure.
Protection settings should be coordinated with the upstream and downstream electrical system before energization.
After completion of the installation and commissioning checks, energize the transformer according to the approved site procedure.
During initial operation, observe for abnormal noise, vibration, oil leakage, unusual temperature rise, or unexpected electrical conditions.
During normal service, monitor the relevant transformer operating parameters, including:
Primary and secondary voltage
Load current
Oil temperature
Winding temperature
Oil level
Cooling condition
Protection alarms
Abnormal sound or vibration
Oil leakage
Actual operating limits should follow the manufacturer's documentation and the approved project requirements.
Maintenance should be planned according to loading conditions, environmental exposure, operating hours, manufacturer's recommendations, and applicable maintenance standards.
Periodic inspection may include transformer oil condition, electrical connections, bushings, grounding, cooling components, protection equipment, and monitoring devices.
