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The SFZ-15000/20000kVA Three Phase On-Load Tap Changing Oil Immersed Power Transformer is designed for high-capacity substation and industrial power systems. It converts 33kV incoming power to 11.5kV/6.9kV secondary voltage and features an On-Load Tap Changer (OLTC) for voltage regulation during energized operation. With a Ynyn0d5 vector group and 9.89% impedance, the transformer can be engineered for utility substations, industrial plants, mining facilities, process industries, and other large-scale electrical installations. Custom configurations are available for tap range, cooling system, insulation level, protection, monitoring, and applicable project standards.
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SFZ-15000/20000
YAWEI
The SFZ-15000/20000kVA Three Phase On-Load Tap Changing Oil Immersed Power Transformer 33kV to 11.5/6.9kV Ynyn0d5 is designed for high-capacity power transformation in industrial substations, utility systems, and large electrical installations. With a rated capacity of 15MVA/20MVA, the transformer transfers electrical power from a 33kV medium-voltage network to 11.5kV/6.9kV secondary systems, providing a reliable interface between incoming grid power and downstream medium-voltage loads.
The transformer incorporates an on-load tap changer (OLTC), allowing the transformation ratio to be adjusted while the transformer remains energized and supplying the connected load. This feature provides a practical means of maintaining the required secondary voltage when the incoming system voltage or load conditions change.
An oil immersed construction is used for electrical insulation and thermal management of the active components. The magnetic core is manufactured from high-grade grain-oriented electrical steel, while the winding and insulation system are engineered to withstand the electrical, thermal, and mechanical stresses associated with high-capacity transformer operation.
The Ynyn0d5 vector group provides the specified winding connection and phase relationship for integration with the corresponding electrical system. With an impedance voltage of 9.89%, the transformer can be coordinated with the project's short-circuit level, protection scheme, and system voltage regulation requirements.
The SFZ series can be engineered according to project-specific requirements, including OLTC specifications, insulation level, cooling capacity, winding material, monitoring equipment, protection devices, terminal arrangement, and applicable IEC, IEEE, or utility standards.
With available ratings of 15MVA and 20MVA, the transformer is intended for substantial electrical loads and high-capacity substation applications.
Its 33kV primary side and 11.5kV/6.9kV secondary system provide a suitable voltage transformation stage for industrial power networks, utility substations, process facilities, and large electrical infrastructures.
The integrated On-Load Tap Changer (OLTC) allows the transformer ratio to be adjusted without interrupting the connected electrical load.
This enables operators to compensate for changes in incoming voltage and system loading, helping maintain the required secondary voltage during normal operating conditions.
The tap range and number of positions can be configured according to the project voltage-regulation requirements.
Transformer oil provides electrical insulation around the active components while also transferring heat away from the core and windings.
The tank, radiators, bushings, conservator system, and associated components can be engineered for reliable operation under the specified environmental and loading conditions.
The core uses grain-oriented electrical steel selected to provide controlled magnetic flux characteristics and reduced excitation losses.
The core assembly is mechanically secured to withstand transportation forces and the electromagnetic stresses that can occur during short-circuit conditions.
The Ynyn0d5 configuration provides the specified connection arrangement and phase relationship between the transformer windings.
The vector group should be coordinated with the upstream and downstream network configuration, grounding arrangement, protection system, and parallel-operation requirements before manufacturing.
The transformer is specified with an impedance voltage of 9.89%.
Transformer impedance is an important parameter for system voltage regulation and short-circuit calculations. The selected impedance should be coordinated with the expected fault level, protection settings, and system operating requirements.
Depending on the project specification, the transformer can be equipped with monitoring and protection components such as:
Oil temperature indicator
Winding temperature indicator
Oil level gauge
Pressure relief device
Buchholz relay
OLTC monitoring and control system
Conservator system
Oil flow or pressure monitoring where applicable
Cooling system monitoring
Grounding terminals
Online monitoring interfaces
Remote control and communication functions
The final configuration depends on the customer's technical specification.
The transformer can be customized according to the electrical characteristics and installation conditions of the project.
Engineering options may include:
15MVA or 20MVA rating
33kV primary voltage
11.5kV/6.9kV secondary voltage
OLTC tap range and position quantity
Impedance voltage
Insulation level and BIL
Copper or aluminum windings
Cooling arrangement
Temperature-rise requirements
Protection and monitoring equipment
Terminal configuration
Outdoor installation requirements
IEC/IEEE or utility-specific standards
>> Technical Parameters
| Type | Step downpower transformer |
| Model | SFZ-15000/20000-33/11.5(6.9) |
| Cooling Method | ONAN/ONAF |
| Primary Voltage | 33KV |
| Secondary Voltage | 11.5/6.kV |
| Rated Frequency | 50HZ |
| Rated Power | 20MVA |
| Winding Material | Copper |
| Voltage Regulation | OLTC (On-Load Tap Changer) |
| Tapping Range | ±9×1.67% |
| Connection Group | Ynyn0d5 |
| Transformer Dimension | 6800×4500×5300 mm (approx.) |
| Weight | 42000 kg (approx.) |
The transformer can serve as a main power transformer for large industrial facilities requiring high-capacity medium-voltage power distribution.
It can supply downstream 11.5kV or 6.9kV systems serving motors, production equipment, process loads, auxiliary systems, and plant substations.
Mining operations and mineral-processing facilities often require substantial electrical capacity for crushers, conveyors, mills, pumps, ventilation equipment, and other large motor loads.
The 15MVA/20MVA configuration provides a suitable platform for high-capacity power transformation where voltage regulation and continuous operation are important.
The transformer can be incorporated into suitable power-generation or energy infrastructure as an auxiliary or distribution transformer, depending on the plant electrical architecture.
The OLTC function can assist with voltage regulation where changing operating conditions require adjustment of the transformer ratio.
The transformer can be used in utility and private substations to transform 33kV incoming power to 11.5kV/6.9kV distribution levels.
Protection, grounding, insulation coordination, and system voltage requirements should be determined according to the applicable utility specifications.
Large water treatment plants, transportation systems, ports, industrial parks, and other infrastructure facilities may require medium-voltage substations with significant installed capacity.
The transformer can provide the required voltage conversion while allowing integration with switchgear, protection systems, and supervisory monitoring equipment.
Steel plants, chemical facilities, cement plants, paper mills, and other process industries may use high-capacity transformers to supply large and continuously operating electrical loads.
The OLTC arrangement provides additional flexibility where load variations can result in changes in the downstream voltage profile.
The following information provides general guidance for transportation, installation, commissioning, operation, and maintenance of the SFZ-15000/20000kVA 33kV to 11.5/6.9kV On-Load Tap Changing Oil Immersed Power Transformer.
All work involving high-voltage equipment, transformer oil, OLTC equipment, and protection systems must be performed by qualified personnel. The manufacturer's approved drawings and technical documentation take precedence over this general guide.
Transport the transformer using equipment rated for its actual shipping weight and dimensions.
Use the designated lifting and jacking points shown in the manufacturer's drawings. Avoid uncontrolled tilting, severe vibration, impact, and mechanical shock.
After delivery, inspect the transformer and its accessories for transportation damage.
Check the:
Main tank
Radiators
Bushings
Conservator
OLTC mechanism
Control cabinet
Temperature indicators
Pressure relief device
Valves and piping
Grounding terminals
Accessories
Verify the nameplate information and shipping documents before installation.
Install the transformer on the engineered foundation according to the approved general arrangement drawing.
Provide adequate space for cooling, inspection, OLTC maintenance, oil sampling, lifting operations, and electrical clearances.
Check the oil level and inspect all accessible flanges, valves, bushings, and joints for leakage.
Where applicable, verify the condition of the conservator and oil preservation system before commissioning.
Connect the transformer tank, neutral points where specified, OLTC equipment, and other designated grounding points to the site grounding system.
The grounding arrangement must comply with the approved project design.
Connect the 33kV high-voltage side and 11.5kV/6.9kV secondary side according to the approved single-line diagram and transformer drawings.
Verify phase identification, terminal connections, cable clearances, grounding, and protection wiring before energization.
Inspect the on-load tap changer, drive mechanism, control cabinet, position indicator, and associated wiring before commissioning.
Verify the tap position indication and remote/local control functions according to the manufacturer's commissioning procedure.
Depending on project requirements, commissioning tests may include:
Insulation resistance
Winding DC resistance
Transformer turns ratio
Vector group verification
OLTC functional testing
Insulation power-factor testing
Dielectric tests where required
Grounding continuity
Protection and alarm testing
Control circuit verification
Compare test results with factory test records and approved project requirements.
Before energization, confirm that all required mechanical, electrical, protection, and control checks have been completed.
Energize the transformer according to the approved commissioning sequence and monitor voltage, current, oil temperature, winding temperature, OLTC position, oil level, and protection signals.
Operate the OLTC only within its specified tap range and operating conditions.
Monitor the tap position, motor-drive mechanism, control system, and voltage response during operation.
Any abnormal noise, position mismatch, control failure, or alarm should be investigated before continued operation.
During service, monitor transformer loading, voltage, temperature, oil level, cooling performance, OLTC status, and protection indications.
Operating records should be maintained to assist with condition assessment and preventive maintenance.
Inspect radiators, cooling surfaces, valves, fans or pumps where fitted, and associated control circuits.
Remove accumulated dust and debris where necessary to maintain adequate heat dissipation.
Periodically evaluate transformer oil condition according to the manufacturer's maintenance recommendations and applicable standards.
Oil testing may include dielectric strength, moisture, acidity, dissolved gas analysis, and other condition-monitoring tests where required.
Periodic diagnostic testing may include winding resistance, insulation resistance, turns ratio, insulation condition, and other tests specified by the maintenance program.
Compare current measurements with previous results and factory baseline data.
The OLTC should be inspected and maintained according to its operating frequency, switching duty, manufacturer's recommendations, and applicable maintenance standards.
Inspect the diverter switch, selector mechanism, drive motor, control system, and associated oil where applicable.
Before maintenance, isolate the transformer from all energy sources and apply appropriate lockout/tagout procedures.
Verify the absence of voltage and establish protective grounding before beginning maintenance.
Important: This guide provides general information only. Actual installation, commissioning, operation, OLTC adjustment, maintenance, oil handling, and repair must follow the manufacturer's approved documentation, project specifications, applicable standards, and local electrical safety requirements.
