Oil Immersed Transformer Manufacturer for Power Distribution Projects

Oil immersed transformers are used in power transmission and distribution systems where reliable voltage conversion is required. The transformer core and windings are submerged in insulating oil, which provides both electrical insulation and heat dissipation. These transformers are installed in utility substations, industrial plants, renewable energy projects, and infrastructure developments.

For EPC contractors and project owners, selecting a manufacturer involves more than comparing equipment specifications. It requires evaluating production capability, engineering support, quality control procedures, and export experience. Zisheng Electric provides oil immersed transformer manufacturing services for international projects, with customization based on project voltage levels, capacity requirements, installation conditions, and applicable standards.

Technical Specifications: Oil Immersed Distribution Transformers

The following table shows standard parameters for our commonly supplied oil immersed distribution transformers. These values serve as reference points; actual specifications are configured according to project requirements.

Parameter	Standard Range
Rated Power	50 kVA – 5,000 kVA
Primary Voltage	6 kV, 10 kV, 11 kV, 13.8 kV, 20 kV, 33 kV
Secondary Voltage	0.4 kV, 0.415 kV, 0.69 kV
Frequency	50 Hz / 60 Hz
Vector Group	Dyn11, Yyn0, YNd11
Cooling Method	ONAN (Oil Natural Air Natural)
Tapping Range	±2×2.5%, ±5% (Off-circuit or On-load)
Insulation Class	A Class (105°C oil temperature rise)
Winding Material	Copper or Aluminum (per specification)
Core Material	Grain-oriented silicon steel (high-permeability grades)
Tank Type	Corrugated fin wall or panel-type radiator
Applicable Standard	IEC 60076, customer-specific standards

No-Load Loss Reference Values (11 kV, Copper Winding, ONAN):

Rated Power (kVA)	Typical No-Load Loss (W)	Typical Load Loss at 75°C (W)
100	320	1,650
200	540	2,800
315	760	3,900
500	1,080	5,600
800	1,540	7,800
1,000	1,800	9,200
1,600	2,600	13,500
2,000	3,100	16,200

Above values are indicative. Actual losses depend on core material grade, winding design, and customer specifications. Efficiency levels can be configured to meet local regulations.

Product Range

We manufacture oil immersed transformers in multiple configurations to suit different applications:

• Three-Phase Oil Immersed Distribution Transformers (50 kVA – 5,000 kVA): For utility distribution networks, secondary substations, and industrial power supply.
• Single-Phase Oil Immersed Transformers (5 kVA – 167 kVA): For rural electrification, residential distribution, and light commercial loads.
• Step-Up Transformers for Solar PV Plants (200 kVA – 3,150 kVA): Designed for photovoltaic power stations, configured for inverter-side low voltage input and MV grid connection.
• Oil Immersed Power Transformers (up to 20 MVA, 33 kV class): For primary substations and larger industrial applications.
• Pad-Mounted Oil Filled Transformers: For underground distribution systems in residential or commercial zones.
• Hermetically Sealed Oil Transformers: Fully sealed tank design, no conservator, suitable for locations where regular oil maintenance is difficult.

Factory Production Process

The following images show key production stages at our manufacturing facility. These photographs were taken during routine production runs.

Figure 1: CNC silicon steel slitting line. Core laminations are cut with controlled burr height to minimize inter-laminar losses.

Figure 2: LV coil winding station. Winding tension is mechanically controlled to maintain consistent turn geometry.

Figure 3: Core and coil assembly. The active part is prepared for insertion into the tank prior to vacuum drying.

Figure 4: Vapor-phase vacuum drying chamber. Active parts are processed to remove moisture from cellulose insulation materials.

Figure 5: Routine test bay. Each transformer undergoes voltage ratio, winding resistance, insulation resistance, and applied voltage testing before release.

Project Information

Project Case: Distribution Network Upgrade, Southeast Asia

• Equipment Supplied: 28 units of 200 kVA and 500 kVA three-phase oil immersed transformers, 11/0.415 kV, Dyn11, ONAN, corrugated tank design
• Project Background: Replacement of end-of-life transformers in a regional distribution network serving mixed residential and commercial load
• Technical Requirements: Transformers required low no-load loss values aligned with local utility efficiency regulations. Tank design needed to accommodate existing plinth dimensions at multiple substation sites.
• Manufacturing & Delivery: All 28 units produced over a 15-week period. Factory acceptance testing (routine tests) completed and documented for each serial number prior to packing. Export packing with moisture-proof sealing applied for sea freight.
• Status: All transformers installed and energized. No warranty claims reported in the initial 18-month operational period.

Project Case: Mining Facility Power Supply, Africa

• Equipment Supplied: 3 units of 3,150 kVA, 33/6.6 kV oil immersed power transformers, ONAN, panel radiator type
• Project Background: New power supply system for a remote mining site requiring step-down transformation from the utility 33 kV feeder to site distribution voltage
• Technical Requirements: Transformers specified for high-altitude derating, with bushing creepage distance configured for moderately polluted environment. Off-circuit tapping range of ±5% in 2.5% steps provided on the HV side.
• Manufacturing & Delivery: Custom design with reinforced tank structure for road transport over unpaved access routes. Factory testing included separate-source voltage withstand and induced voltage withstand tests.
• Status: Units commissioned and operating under continuous load conditions.

Quality Control Process

Our internal quality management covers four primary stages:

Material Receiving Inspection

• Verification of silicon steel grade and thickness
• Copper conductor purity and dimension check
• Transformer oil dielectric strength and moisture content testing before filling
• Welding consumable certification for tank fabrication

In-Process Control

• Core loss measurement after lamination stacking
• Winding resistance check after coil completion
• Dimensional inspection of tank weld seams
• Leak testing of completed tank before painting

Final Routine Testing (Every Unit)

• Insulation resistance measurement
• Voltage ratio and vector group verification
• Winding resistance measurement
• No-load loss and no-load current
• Load loss and impedance voltage (at 75°C)
• Applied voltage test (power frequency withstand)
• Induced voltage test
• Oil leakage test under pressure

Pre-Shipment Inspection

• Visual inspection of paint finish and nameplate data
• Verification of supplied accessories against packing list
• Internal packing humidity indicator card insertion
• Wooden case or steel pallet packing per export requirements

Manufacturing Experience

Zisheng has been producing oil immersed transformers for over 20 years. During this period, the factory has supplied transformers for:

• Utility distribution networks across multiple countries
• Industrial power supply systems (mining, manufacturing, processing plants)
• Solar photovoltaic step-up applications
• Commercial building electrical infrastructure
• Rural electrification programs

Export markets served include countries in Southeast Asia, Africa, the Middle East, and South America. Our factory team understands the documentation, testing, and shipping requirements typical of international procurement.

Working With EPC Contractors

For EPC projects, transformer procurement typically involves several stages:

1. Initial Technical Review: Our engineering team reviews your project specifications, single-line diagrams, and technical data sheets to confirm feasibility and identify any clarification points.
2. Design Proposal: We provide outline drawings, loss guarantee values, and a compliance statement against your technical requirements.
3. Production Scheduling: Upon order confirmation, a production schedule is issued with planned milestones for material procurement, core and coil manufacturing, tank fabrication, assembly, testing, and packing.
4. Factory Acceptance Testing: Clients or third-party inspectors can witness routine tests at our facility. Test reports with serial number traceability are provided.
5. Export Logistics: We coordinate container loading, sea freight booking, and documentation including packing list, commercial invoice, bill of lading, and certificate of origin.

Frequently Asked Questions

What is the typical lead time for an order?

Lead time depends on order quantity and specification complexity. Standard distribution transformers (up to 1,000 kVA) are typically produced within 8–12 weeks from order confirmation. Larger units or highly customized designs may require 14–18 weeks. A firm schedule is provided at contract stage.

Can you supply transformers with copper or aluminum windings?

We manufacture both copper-wound and aluminum-wound transformers. The winding material affects cost, weight, and certain electrical characteristics. We produce according to the material specified in the project’s technical requirements.

What testing documentation do you provide?

Every transformer ships with a routine test report containing measured values for all standard tests: ratio, resistance, losses, impedance, and dielectric withstand. Type test certificates for the relevant design family can be provided upon request.

Do you manufacture transformers with on-load tap changers?

Yes. For transformers above 500 kVA where voltage regulation under load is required, we can integrate on-load tap changers (OLTC) according to project specifications. Off-circuit tap changers remain standard for smaller distribution units.

Can you provide transformers with natural ester fluid instead of mineral oil?

Yes. Natural ester-filled transformers are available for projects with environmental sensitivity or elevated fire safety requirements. The fluid type must be specified during the design stage, as it affects internal clearances and thermal calculations.

Contact our engineering team with your project specifications for a technical review and quotation.
Request Technical Consultation →

Explore other product lines:

• Dry Type Transformers — for indoor installations and fire-sensitive environments
• Substation Transformers — for primary substation applications
• Pad-Mounted Transformers — for underground residential distribution