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Oil-Immersed Transformers
12 Series · 1274 Models
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Oil-Immersed Transformers Overview
Oil-immersed transformers are the workhorse of power distribution worldwide — in IEC markets the 10kV and 11kV classes carry the bulk of distribution capacity — and remain the default choice wherever capacity, overload capability, and cost per kVA matter most. QDTB supplies oil-filled transformers from 100 kVA to 10,000 kVA, up to 110 kV per IEC 60076 and GB 1094, with efficiency grades evolving from S11 through S13 to the latest S20. The insulating oil does double duty - cooling the windings and suppressing partial discharge - which is why oil units handle higher continuous and short-time overloads than dry-type of the same rating. Options include hermetic sealing, on-load tap changers, and amorphous alloy cores for the lowest no-load loss.
Available Series
S Series
The S series three-phase oil-immersed distribution transformers serve North American markets, operating at 60Hz with standard primary voltages of 480V and secondary 240V per IEEE C57 / ANSI C84.1 standards. Rated 10–5000 kVA, 0.48–34.5 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
SZ Series
The SZ series oil-immersed transformers integrate an on-load tap changer (OLTC) for automatic voltage regulation under load, available across 6kV, 10kV and 35kV primary voltages per IEC 60076. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
S11-M Series
The S11-M series features sealed construction with Level 11 energy efficiency, providing enhanced protection against moisture and environmental contaminants. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
S13-M Series
The S13-M series delivers enhanced energy efficiency with Level 13 rating, combining sealed construction with improved performance. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
S20-M Series
The S20-M series represents the highest energy efficiency class for oil-immersed transformers, achieving Level 20 rating with exceptional performance. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
S11 Series
The S11 series represents standard oil-immersed distribution transformers meeting Level 11 energy efficiency standards, widely used in power distribution networks. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
SL11 Series
The SL11 series features aluminum winding construction with Level 11 energy efficiency, offering cost-effective solutions for power distribution. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, mineral-oil insulation with 65 K temperature rise. Suitable for utility distribution networks, substations, solar farms, and industrial power systems.
Other Series
A comprehensive collection of specialty and custom oil-immersed transformers including amorphous alloy core models, high-efficiency variants, and non-standard voltage configurations. These transformers serve diverse power distribution needs beyond standard S-series models.
Pad-Mounted Transformers Series
Pad-mounted transformers are dead-front, tamper-resistant oil-immersed units for underground distribution, built to ANSI/IEEE C57.12 with loop-feed or radial-feed configurations. Rated 25–2500 kVA, 2.4–35 kV primary and 120/240–600 V secondary, mineral-oil insulation with 65 K temperature rise. Suitable for underground residential distribution, commercial complexes, and industrial sites.
Special Configuration Oil-Immersed Transformers Series
Special-configuration oil-immersed transformers cover biodegradable natural-ester and silicone liquid insulation, fully sealed corrugated-tank construction, on-load tap changing, double-split windings for photovoltaic duty, and Z-type grounding transformers. Rated 10–5000 kVA, 0.48–35 kV primary and 0.208–0.48 kV secondary, 65 K temperature rise. Suitable for green-energy projects, solar farms, utility grounding, and high-reliability networks.
Renewable Step-Up Transformers Series
Renewable step-up transformers raise the low-voltage output of photovoltaic and wind generation to the medium-voltage grid connection, with low no-load and load losses for high annual energy yield. Rated 100–5000 kVA, 0.4/0.69 kV low voltage to 10–35 kV high voltage, mineral-oil or sealed construction with 65 K temperature rise. Suitable for solar farms, wind farms, and energy-storage interconnection.
Wound Core Transformers Series
Three-dimensional wound core (triangular core) oil-immersed transformers use a continuously wound core forming a triangular (delta) magnetic circuit with no air gaps, giving lower no-load loss, lower noise and a more compact, lighter tank than conventional stacked-core designs. Rated 30–2500 kVA in S13/S20-M·RL grades, 6–35 kV primary, built to IEC 60076 for energy-saving distribution applications.
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| Base price (interpolation) | $2,332 |
| × Product factor | ×1.0000 |
| × Country factor | ×1.0000 |
| × Copper-linked factor | ×1.0000 |
| + Options / accessories | $0 |
Aluminum winding — no copper linkage
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Application Scenarios
Utility Power Grids
Primary and distribution transformers for substations up to 110 kV.
Industrial Power
Heavy-duty transformers for steel mills, chemical plants, and mining.
Commercial Distribution
Energy-efficient distribution for large commercial complexes.
Power Generation
Station transformers for thermal, hydro, and nuclear plants.
Agricultural Irrigation
Rural electrification with cost-effective solutions.
Infrastructure
Power for railways, airports, ports, and telecom.
Technical Advantages
S11 to S20 efficiency evolution
Each generation lowers no-load and load losses; S13 is the mainstream low-loss grade and S20 is the latest ultra-low-loss generation.
Superior overload capability
Insulating oil cools and quenches arcs, so oil units carry higher short-time overloads than dry-type of the same rating.
Hermetic sealing option
Fully sealed tanks keep oil from contact with air, extending oil life and cutting maintenance to periodic testing.
Amorphous core option
Combines oil cooling with an amorphous core for the lowest no-load loss in the range.
FAQ - Oil-Immersed Transformers
What are the advantages of oil-immersed over dry-type transformers?
How often does the oil need maintenance?
What cooling methods are available?
What efficiency class do they meet?
Is an on-load tap changer available?
What do the S11, S13 and S20 designations mean?
What is a 10kV oil-immersed transformer?
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