110kV Three-Phase Three-Winding Oil-Immersed Power Transformer

A 110kV Three-Phase Three-Winding Oil-Immersed Power Transformer integrates three voltage levels into one oil-filled tank, which reduces the number of high-voltage terminations and simplifies substation layout. Yulan Transformer supplies these units up to 110kV class with single-unit capacity reaching 120,000 kVA. The design follows IEC 60076 and GB 1094, and the voltage combination, capacity split, tap changer, and cooling method are configured for each project.

Voltage and Capacity Arrangement

Typical configurations use 110kV on the high-voltage side, 38.5kV or 35kV on the medium-voltage side, and 10.5kV or 6.6kV on the low-voltage side. Other medium voltages such as 22kV or 33kV can be designed within the same insulation class.

The capacity split between secondary windings is agreed at the specification stage. Common ratios include 100/100/100, 100/100/50, and 100/50/50. Load may be drawn from all three windings simultaneously, and the heating effect of the combined losses is considered in the thermal design.

Core and Winding Construction

The core uses grain-oriented silicon steel laminations with 45-degree step-lap joints. This joint pattern aligns the flux path with the rolling direction of the steel, reducing localized saturation and lowering magnetizing current.

Windings are copper, insulated with paper or enamel depending on voltage class and current rating. The high-voltage winding is normally placed outside the medium-voltage and low-voltage windings, which improves access for tap leads and helps control impedance. Radial and axial ampere-turn distributions are balanced to limit stray flux and eddy losses in structural parts. Short-circuit forces are calculated for all specified fault conditions, and winding supports, spacers, and clamping structures are dimensioned accordingly. A dynamic short-circuit test certificate can be provided when required.

Tap Changing and Voltage Regulation

Voltage adjustment is provided on the high-voltage winding. Two options are available.

Off-circuit tap changer

The A 110kV Three-Phase Three-Winding Oil-Immersed Power Transformer integrates three voltage levels into one oil-filled tank, which reduces the number of high-voltage terminations and simplifies substation layout. Yulan Transformer supplies these units up to 110kV class with single-unit capacity reaching 120,000 kVA. The design follows IEC 60076 and GB 1094, and the voltage combination, capacity split, tap changer, and cooling method are configured for each project.

 must be de-energized before changing taps. Typical tapping range is ±2×2.5% or ±5%. This option suits installations with stable grid voltage and infrequent adjustment.

On-load tap changer

Tap position can be changed while the transformer carries load. Ranges such as ±8×1.25% are common for 110kV units. The tap changer can be specified from a preferred manufacturer, and motor drive, remote indication, and automatic voltage control interfaces can be included.

Cooling, Tank, and Protection

The tank is designed to withstand full vacuum during factory oil filling. Lifting lugs, jacking pads, and towing eyes are provided. The cover is bolted and sealed with oil-resistant gaskets. Bushings are arranged according to the customer’s preferred layout.

Smaller ratings use natural oil natural air cooling. Larger units employ detachable radiators with cooling fans. The fan control panel starts and stops fans based on winding or oil temperature. For high ambient temperatures, the cooling class is selected with appropriate margin.

A conservator with silica gel breather is standard. The Buchholz relay is mounted between tank and conservator. A magnetic oil level gauge, winding temperature indicator, oil temperature indicator, and pressure relief device are included.

Reference Parameters

The table below gives typical values for a 110kV / 38.5kV / 10.5kV unit with on-load tap changer. Final parameters are confirmed in the technical agreement.

Rated Capacity (kVA)	HV (kV)	MV (kV)	LV (kV)	Vector Group	No-load Loss (kW)	Load Loss HV-MV (kW)	Impedance HV-MV (%)	Impedance HV-LV (%)	Impedance MV-LV (%)	Dimensions L×W×H (mm)	Total Weight (t)
6,300	110±8×1.25%	38.5	10.5	YNyn0d11	8.5	42	10.5	17.5	6.5	4600×3600×4300	18.5
8,000	110±8×1.25%	38.5	10.5	YNyn0d11	10.2	50	10.5	17.5	6.5	4800×3700×4400	21.0
10,000	110±8×1.25%	38.5	10.5	YNyn0d11	12.0	59	10.5	17.5	6.5	5000×3800×4500	24.5
12,500	110±8×1.25%	38.5	10.5	YNyn0d11	14.2	70	10.5	17.5	6.5	5200×3900×4600	28.0
16,000	110±8×1.25%	38.5	10.5	YNyn0d11	17.0	84	10.5	17.5	6.5	5400×4000×4700	32.5
20,000	110±8×1.25%	38.5	10.5	YNyn0d11	20.0	100	10.5	17.5	6.5	5600×4100×4800	37.0
25,000	110±8×1.25%	38.5	10.5	YNyn0d11	23.8	118	10.5	17.5	6.5	5800×4200×4900	42.0
31,500	110±8×1.25%	38.5	10.5	YNyn0d11	28.5	140	10.5	17.5	6.5	6100×4300×5000	49.0
40,000	110±8×1.25%	38.5	10.5	YNyn0d11	34.0	166	10.5	17.5	6.5	6400×4400×5100	57.0
50,000	110±8×1.25%	38.5	10.5	YNyn0d11	40.5	198	10.5	17.5	6.5	6700×4500×5200	66.0
63,000	110±8×1.25%	38.5	10.5	YNyn0d11	48.0	235	10.5	17.5	6.5	7000×4600×5300	78.0

Notes:

Loss values correspond to rated capacity at rated voltage.

Impedance values are given at rated capacity and can be adjusted within standard tolerances.

Dimensions and weights are for reference. Final values depend on tap changer type, radiator size, and site accessories.

Higher capacities up to 120,000 kVA are available on request.

Standards and Testing

Design, manufacture, and testing follow IEC 60076. Chinese standards GB 1094 and GB/T 6451 are applied where relevant. Customer-specific requirements from other standards can be accommodated.

Each unit undergoes routine tests: winding resistance, ratio and vector group, insulation resistance, dielectric loss, separate-source withstand, induced overvoltage, no-load loss and current, load loss, and short-circuit impedance. Type tests and special tests, including lightning impulse, temperature rise, noise level, and short-circuit withstand, can be arranged on request.

Project-Specific Questions

What if the station requires a different medium voltage, such as 22kV or 33kV?

The medium-voltage winding can be designed for any standard level within the insulation class. The specification should include the exact system voltage and the required capacity split.

Can the medium and low voltage windings operate at different power factors?

Yes. Each winding is rated independently, and the design considers the combined heating effect of the losses.

Does a three-winding transformer need a special protection scheme?

Protection usually includes differential protection covering all three windings, plus overcurrent and earth fault protection on each side. Standard devices such as Buchholz relay and pressure relief are also required.

What is the typical delivery lead time?

For standard ratings, production and testing normally take four to six months after technical agreement is signed. Custom voltage combinations or special accessories may extend the schedule.

Can Yulan Transformer provide installation and commissioning supervision?

Yes. Site supervision, oil processing guidance, and commissioning support are available as part of the supply contract or as a separate item.