Oil-Immersed Three-Phase Two-Winding Power Transformer

Yulan Transformer (Jiangshan Yulan Transformer Co., Ltd.) has been manufacturing power transformers, distribution transformers and reactors since 1999. The 110kv oil-immersed three-phase two-winding power transformer is fully sealed, conservator-free, and intended for outdoor installation on poles, in compact substations, or inside dedicated transformer rooms.

Why a Sealed Tank Design

Conventional oil-immersed transformers use a conservator and a silica gel breather, which means the insulating oil is in contact with ambient air. Over time the oil absorbs moisture and oxygen, requiring periodic replacement of the breather and oil top-up.

This transformer eliminates the conservator and breather. The internal oil volume is isolated from the atmosphere.

Key consequences of the sealed design:

● The insulating oil does not come into direct contact with air, so oxidation proceeds much more slowly and oil life is extended.

● Corrugated tank walls expand and contract as the oil volume changes with temperature. This automatically compensates for thermal expansion and contraction.

● A slight positive pressure is maintained inside the tank, which helps block ingress of moisture and oxygen.

● No routine replacement of breather silica gel is needed. Field inspection focuses mainly on oil level and leakage.

Core, Windings and Tank Construction

Core

The core is built from cold-rolled grain-oriented silicon steel laminations with a step-lap mitred joint structure. The magnetic flux path follows the grain orientation of the steel, reducing flux distortion at the joints. No-load loss and no-load current are lower than those of a conventional butt-lap core.

Windings

High-voltage and low-voltage windings are wound with high-strength enameled wire or paper-covered wire. The ampere-turn distribution is balanced, and the insulation structure is designed to withstand the mechanical stresses of an external short circuit. The winding arrangement is verified by calculation before production.

Tank and Sealing

The tank is of corrugated steel construction. The corrugated fins serve both as cooling surfaces and as volume compensation elements. The core and coil assembly is built as a non-lifting structure, meaning routine maintenance does not require removal of the active part. Gaskets and seals are made of acrylic rubber, which resists ultraviolet degradation and thermal ageing better than ordinary nitrile rubber.

Standards

The electromagnetic design is performed with dedicated transformer design software. Performance values comply with IEC 60076, GB 1094, GB/T 6451, and GB/T 25289-2010.

Technical Data

The table below lists standard ratings. For capacities up to 500kVA, the load loss value above the slash applies to Dyn11 connection, and the value below the slash applies to Yyn0 connection.

Note: The loss values in the table also apply to three-phase transformers with dual high voltage 20(10) kV.

Typical Applications

This sealed-type distribution transformer is suitable for several common installation environments:

● Terminal distribution in 20kV medium-voltage networks

● Power distribution in industrial parks, commercial buildings, and residential areas

● Integration inside compact transformer substations

● Projects that require reduced footprint and controlled noise levels

● Coastal or high-humidity locations where internal moisture ingress should be minimised

Frequently Asked Questions

How does the transformer handle oil expansion without a conservator?

The corrugated tank walls are designed to flex slightly as the oil temperature changes. When the oil expands, the fins move outward and the tank volume increases. When the oil cools, the fins return to their original position. The tank remains sealed and maintains a slight positive internal pressure.

Does this transformer need routine replacement of silica gel?

No. The transformer has no breather and no silica gel. Daily inspection only requires checking the oil level indicator and looking for any oil leakage on the tank surface.

Can it operate on a 10kV system?

Yes. A dual high voltage version with 20kV and 10kV taps is available. The high-voltage winding is designed with two voltage ratings, allowing the same unit to be connected to either a 20kV or 10kV network depending on site conditions.

How often should the transformer oil be tested?

After the first year of service, a standard oil sample test is recommended. Following that, testing every three to five years is normally sufficient. The sealed design greatly reduces contact between oil and air, so oil ageing is slower than in open-type transformers.

Can non-standard voltage ratios or special impedance values be supplied?

Yes. Yulan Transformer can adjust voltage ratio, vector group, impedance, and other design parameters according to specific project requirements.

Quality Assurance and Testing

Yulan Transformer holds ISO 9001:2015, ISO 14001, and ISO 45001:2018 certifications. Each transformer undergoes routine tests before delivery, including winding resistance measurement, voltage ratio test, insulation resistance, dielectric loss, separate-source voltage withstand, induced voltage withstand, no-load loss, load loss, and short-circuit impedance measurement. Type tests and special tests are also available.