S13 1600 kVA Three-Phase Oil-Immersed Transformer: Low-Loss Core and Service Conditions
Nov 06, 2025
Leave a message
The S13 1600 kVA three-phase oil-immersed transformer is a low-loss distribution unit intended for 10 kV and 35 kV networks where the annual energy cost of the transformer is a significant part of the total cost of ownership. It is a development of the earlier S9 generation, and the improvement comes from the core material, the joint design and the mechanical restraint of the core. This article describes the core construction, the loss performance, the sealed tank arrangement, the technical specification and the service conditions of the rating.
Low-Loss Core Construction
The core is stacked from high-quality, high-permeability silicon steel sheet using a full oblique multi-stage joint, also described as a step-lap joint. Instead of aligning all the joint gaps in one plane, the joints are staggered between successive laminations so that no two adjacent laminations have a gap at the same position. That arrangement reduces the reluctance of the joint, keeps the flux distribution uniform across the limb and yoke, and lowers both the no-load loss and the no-load current.
The core is positioned at several points on the clamping frame and all fasteners are fitted with anti-loosening nuts, so the assembly resists vibration, shock and inclined transport. The core is designed to be handled without a lifting yoke, which simplifies installation where headroom is limited. The high-voltage windings are wound in a multi-layer cylindrical structure, which improves the impulse voltage distribution across the winding and therefore the dielectric withstand of the insulation system.
Loss Performance
Compared with the S9 generation, the S13 design reduces no-load loss by about 30 percent or more at the same rating. The table lists catalogue values for the 10 kV class of the series so that the progression of losses with capacity can be seen.
| Rated capacity | No-load loss | Load loss | No-load current | Impedance |
|---|---|---|---|---|
| 630 kVA | 570 W | 6200 W | 1.1 % | 4.5 % |
| 800 kVA | 700 W | 7500 W | 1.0 % | 4.5 % |
| 1000 kVA | 830 W | 10300 W | 1.0 % | 4.5 % |
| 1250 kVA | 970 W | 12000 W | 0.9 % | 4.5 % |
| 1600 kVA | 1170 W | 14500 W | 0.8 % | 4.5 % |
| 2000 kVA | 1260 W | 17800 W | 0.6 % | 4.5 % |
| 2500 kVA | 1490 W | 20700 W | 0.5 % | 4.5 % |
The reference for the improvement is the older generation: relative to the S7 design, the S9 generation reduced no-load loss by an average of about 10 percent, no-load current by about 38 percent and operating cost by about 19 percent, and the S13 generation takes the same progression further. Efficiency limits for these ratings are verified against GB 20052-2020, and technical parameters against GB/T 6451-2015.
Sealed Tank and Cooling
The tank can be supplied with a plate radiator or as a corrugated-wave tank with an oil storage tank and an oil-sealed moisture absorber where that arrangement is preferred. In the corrugated version, the expansion and contraction of the corrugated wall compensates for changes in oil volume, so a separate expansion tank is not required. The corrugated wall has a small footprint and a large cooling surface, and the tank can be bolted or welded closed so that the oil never contacts the air. Keeping the oil sealed extends its service life because oxidation and moisture ingress, the two mechanisms that degrade insulating oil, are suppressed.
Sealing reliability is a design issue rather than a maintenance issue: the seal faces, the gaskets and the bushing glands are specified and assembled so that the joint does not relax over years of thermal cycling. Oil quality is verified against the requirements of IEC 60296 for mineral insulating oils, and temperature-rise limits are verified against IEC 60076-2.
Technical Specification and Service Conditions
| Item | Value |
|---|---|
| Rated power | 1600 kVA |
| Primary voltage | 2.4 kV to 34.5 kV |
| Secondary voltage | 480/277 V, 400/230 V, 380/220 V or customised |
| Frequency | 50 Hz or 60 Hz |
| Vector group | Dyn11, Yyn0 or Dyn5 |
| Winding material | Copper or aluminium |
| Impedance voltage | 4.5 percent for the 10 kV class |
| Altitude | Not exceeding 1000 m, or corrected to the site |
| Insulating oil weight | Approximately 800 kg |
| Total weight | Approximately 4500 kg |
| Outline dimensions | Approximately 2600 x 1600 x 2400 mm |
| Tank material | Mild steel or 304 stainless steel |
The service conditions assumed for the rating are an installation altitude not exceeding 1000 m, a maximum ambient temperature of plus 40 degrees Celsius, a maximum daily average ambient temperature of plus 30 degrees Celsius, a maximum annual average ambient temperature of plus 20 degrees Celsius, and a minimum outdoor temperature of minus 25 degrees Celsius. Where any of those figures is exceeded, the design is corrected so that the temperature rise and the dielectric withstand remain inside the standard limits.
Frequently Asked Questions
Q: How much lower is the no-load loss of an S13 transformer than an S9 transformer?
A: The S13 core design reduces no-load loss by about 30 percent or more at the same rating, mainly through the high-permeability core material and the full oblique multi-stage joint.
Q: What are the losses of an S13 1600 kVA 10 kV transformer?
A: Catalogue data for the 10 kV class gives 1170 W no-load loss and 14500 W load loss with a short-circuit impedance of 4.5 percent.
Q: Why is a corrugated tank used on this rating?
A: The corrugated wall absorbs the oil volume changes so no expansion tank is needed, provides the cooling surface, and allows the tank to be closed so that the oil stays out of contact with air.
Q: What ambient temperature range does the design cover?
A: The rating assumes a maximum ambient of plus 40 degrees Celsius, a maximum daily average of plus 30 degrees Celsius, a maximum annual average of plus 20 degrees Celsius and a minimum outdoor temperature of minus 25 degrees Celsius.
Q: Can the transformer be installed above 1000 m altitude?
A: It can, but the external insulation distances and the cooling design must be corrected for the lower air density at the site so that the dielectric withstand and the temperature rise still meet the standard limits.
Q: What testing is carried out before dispatch?
A: Winding resistance, ratio and vector group, no-load loss and current, load loss and impedance, applied and induced voltage tests and an oil dielectric strength test, with temperature rise and impulse tests available as type tests.