Oil-Immersed Distribution Transformer | S11-S22, 30-2500kVA

S11 / S13 / S20 / S22 Series Three-Phase Oil-Immersed Fully Sealed Distribution Transformer

The GOHO S11 / S13 / S20 / S22 series is a complete family of three-phase oil-immersed, fully sealed distribution transformers offering four efficiency levels in one platform. All models share the same corrugated-wall fully sealed tank, off-circuit tap changer (±5% in two steps), and a capacity range of 30–2500kVA, available in two primary-voltage models — 10kV and 20kV — allowing customers to select the model that matches their local grid voltage.

The transformer features a fully sealed oil tank with corrugated wall construction for natural cooling, eliminating the need for an oil conservator and breather. This sealed design prevents moisture ingress and oil oxidation, significantly extending service life and reducing maintenance compared to conventional open-breathing transformers.

Built on the same core platform, the four models differ in no-load and load losses, covering the full efficiency spectrum: S11 is the economical entry model for budget-sensitive markets; S13 meets GB 20052-2020 Class 3 efficiency for mainstream grid projects; S20 delivers Class 2 efficiency for long-term operating savings; and S22 achieves the highest Class 1 efficiency with the lowest losses in the series.

Technical Specifications

Model	S11	S13	S20	S22
Efficiency Class	Legacy GB/T 6451	Class 3 — GB 20052-2020	Class 2 — GB 20052-2020	Class 1 — GB 20052-2020
No-Load Loss	Baseline (highest)	≈ 20% lower than S11	Lower than S13	Lowest in series
Load Loss	Baseline	≈ S11	Lower	Lowest
Best For	Budget-sensitive markets	Mainstream grid projects	Long operating hours	High-efficiency projects

* Exact loss values (W) for each capacity follow GB 20052-2020 Table 1; contact us for the type-test report of your required capacity.

Item	Specification
Rated Capacity	30 – 2500 kVA
Rated Voltage (HV)	10kV or 20kV (two models — specify when ordering)
Rated Voltage (LV)	400V (415V optional for export)
Rated Frequency	50Hz / 60Hz
Connection Group	Dyn11 / Yyn0 (selectable)
Voltage Regulation	±5% (off-circuit tap changer, 2 steps)
Cooling Method	ONAN (Oil Natural Air Natural) — corrugated wall tank
Insulation Level	LI 75 / AC 35 (HV) / LI 40 / AC 5 (LV)
Transformer Type	Oil-immersed, fully sealed, non-excitation voltage regulation
Tank Construction	Fully sealed corrugated wall — no oil conservator or breather
Oil Type	Mineral insulating oil (or ester fluid — optional)
Degree of Protection	IP44 / IP54 (tank and bushings)
Ambient Temperature Range	-25°C to +40°C
Altitude	Up to 1000m (derating required for higher altitudes)
Standards	GB/T 6451, GB 1094, GB 20052-2020, IEC 60076

Key Features

Dual-Voltage Design (10kV / 20kV)The transformer features a split-primary winding configuration that can be reconfigured between 10kV and 20kV operation by simple off-circuit tap changer adjustment — one transformer serves both 10kV and 20kV distribution networks, eliminating the need for separate transformer inventory for different grid voltage zones. This is particularly valuable during grid voltage upgrade programs where distribution networks are progressively converted from 10kV to 20kV operation.

Fully Sealed Oil Tank ConstructionThe corrugated wall tank is hermetically sealed with no oil conservator, breather, or silica gel air dryer — the sealed design prevents moisture absorption by the insulating oil, eliminates oil oxidation from atmospheric exposure, and prevents formation of sludge and acidic compounds that accelerate insulation degradation. Service life is extended by 30–50% compared to open-breathing designs.

Corrugated Wall CoolingThe tank walls are formed from thin steel plate pressed into corrugated panels, which expand and contract with oil volume changes while providing efficient natural convection cooling — the corrugated design eliminates the need for separate cooling radiators, reduces overall transformer dimensions, and provides built-in expansion compensation without requiring a separate oil conservator.

Low-Loss Grain-Oriented Silicon Steel CoreThe series achieves significantly lower no-load losses through optimized grain-oriented silicon steel core material, improved core joint design, and reduced flux density — no-load losses are typically 30–40% lower than legacy S9 series equivalents, delivering measurable energy savings over the transformer’s 20+ year service life.

Non-Excitation Voltage RegulationAn off-circuit (de-energized) tap changer provides ±5% voltage regulation in two steps, enabling field adjustment of the voltage ratio to match local distribution network voltage conditions — the tap changer operates only when the transformer is de-energized and provides reliable, maintenance-free voltage ratio adjustment capability.

Reduced Installation and Commissioning TimeThe sealed, oil-filled design eliminates the need for on-site oil filling, oil processing, oil sampling, and breather installation required by conventional transformers — the transformer arrives factory-filled, factory-tested, and ready for immediate installation and commissioning, significantly reducing site installation labor and time.

Four Efficiency Levels, One PlatformThe series is offered in four loss classes — S11, S13, S20 and S22 — sharing the identical tank, core and winding architecture. This lets customers choose the efficiency level that fits their budget and local energy standard without redesigning the installation, while keeping spare parts and footprint fully interchangeable across the whole series.

Applications

Urban and rural 10kV/20kV distribution networks — pole-mounted and ground-mounted installations
Industrial and commercial facility power supply — step-down transformation
Residential community and building complex power distribution
Infrastructure — schools, hospitals, public facility power supply
Grid upgrade projects — 10kV to 20kV conversion without transformer replacement
Oil and gas field distribution power supply
Agricultural and rural electrification

Which Model Should You Choose?

Choose This Model	When…
S11	Budget-sensitive markets, legacy grid retrofits, temporary or non-critical loads
S13	Mainstream urban & rural grid upgrades, industrial and commercial distribution
S20	High-duty-cycle industrial sites, government / utility tenders, long operating hours
S22	Green buildings, data centers, regions with mandatory high-efficiency standards

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