Transformer manufacturing workshop

Oil-immersed
Transformers

For medium-voltage distribution
and industrial substations.

Transformer manufacturing workshop

Oil-immersed
transformer series

Sealed distribution designs and a 35 kV substation family, with electrical configurations matched to the network.

6–10 kV Distribution Transformers

30–4000 kVA at 10 kV · 0.4 kV secondary

Fully sealed three-phase distribution transformers.

20 kV Distribution Transformers

30–4000 kVA · 20/0.4 kV

Fully sealed distribution transformers with ONAN cooling.

35 kV Oil-immersed Transformers

Substation and industrial duty

ONAN-cooled oil-immersed construction for distribution substations and industrial power transformation.

Electrical range

Electrical scope by voltage family
FamilyPrimary voltageSecondary voltageRated-capacity coverageRating detail
S series 6–10 kV6 / 6.3 / 10 / 10.5 kV options0.4 kV30–4000 kVA at 10 kV19 reference ratings up to 2500 kVA with S13-M, S20-M and S22-M loss data
S series 20 kV20 kV0.4 kV30–4000 kVA19 reference ratings up to 2500 kVA with loss, no-load current and impedance data
S series 35 kV35 kV classSpecified by projectSpecified by projectONAN cooling; substation and industrial applications

Capacity, impedance and loss values belong to the same rating entry. Primary-voltage options identify alternative winding designs; they do not describe switching between system voltage classes in service.

S-series model designation

The model designation separates the number of phases, design series, tank arrangement, rated capacity and high-voltage class. S identifies a three-phase transformer. For the sealed distribution designs, M identifies the fully sealed tank construction.

S11, S13, S20 and S22 appear in the distribution-family descriptions. The 6–10 kV rating table gives separate no-load and load-loss values for S13-M, S20-M and S22-M. Use the complete rating row and the purchase specification when selecting a loss level; the design code alone does not define the secondary voltage, vector group or every accessory.

Sealed S-series model fields
FieldMeaningHow it is used
SThree-phaseIdentifies the phase arrangement
11 / 13 / 20 / 22Design seriesIdentifies the series; use the corresponding electrical schedule
MFully sealedIdentifies the sealed distribution-tank arrangement
Capacity fieldRated capacity in kVADefines the rated apparent power
Voltage field after /High-voltage class in kVIdentifies the primary-voltage class

Core and winding
construction

Copper winding manufacture on a winding machine
Transformer winding manufacture

Core

The 6–10 kV and 20 kV designs use high-permeability, grain-oriented cold-rolled silicon-steel laminations. Fully oblique joints form the stacked core; stepped core limbs approach a circular cross-section, while the yoke and limbs use equal cross-sectional areas. The core limbs and yoke provide the magnetic path.

Windings & oil passages

Concentric high- and low-voltage windings incorporate oil passages and compression binding. The oil passages carry heat from the winding region into the surrounding insulating oil. Compression binding maintains winding position within the active assembly. These channels provide circulation paths for heat transfer.

Tap leads

High-voltage tapping leads connect the winding to the cover-mounted tap switch, keeping voltage adjustment within the specified winding design. The selected winding tap connects to the supply.

Tank, cooling & connections

Corrugated tank and cooling surfaces of the distribution family
Corrugated tank and cooling surfaces

Sealed corrugated tank

6–10 kV / 20 kV

The fully sealed designs use corrugated tank walls.

Oil volume
Flexible wall sections accommodate oil-volume changes as operating temperature changes.
Heat release
The external tank surface transfers heat to the surrounding air.
Conservator
This arrangement eliminates the separate conservator used on other tank designs.

Vacuum oil filling

6–10 kV manufacturing description
Before final sealing
Vacuum filling limits moisture and air within the insulation assembly.
After sealing
Sealed construction reduces direct exposure of the oil to ambient air.

Inspection still applies. Follow the operating instructions and installation conditions.

ONAN cooling

Oil natural · Air natural

20 kV / 35 kV
Circulating
oil
Tank / radiator
surfaces
Ambient
air

Heat moves through circulating oil and then from the tank or radiator surfaces to ambient air. Tank arrangement, surface treatment and available cooling space form part of the installation specification.

Installation & quotation inputs

Item & configurationInstallation or quotation requirement
6–10 kV and 20 kV tankFully sealed corrugated-wall constructionAllow space for cooling surfaces and access to fittings
20 kV coolingONANKeep the air path around the tank unobstructed
35 kV coolingONANCoordinate tank and radiator arrangement with the substation layout
Surface protectionCoating selected for the installation environmentIdentify humidity, coastal exposure and corrosive contamination at quotation stage

Voltage & frequency

20 kV distribution family
Rated voltage ratio
20 / 0.4 kV
Tapping options
±5%or±2 × 2.5%As specified
50 Hz

20 kV public configuration.

50/60 Hz

Versions discussed in the wider distribution-family descriptions.

Connection-group options

20 kV distribution family

Dyn11 Yzn11 Yyn0

The selected vector group must agree with the network neutral arrangement and the other equipment connected to the busbar.

Parallel operation

Coordinate these four items as a system:

  • Voltage ratio
  • Vector group
  • Impedance
  • Tap position

Tap-switch arrangement

6–10 kV / 20 kV
Operation
De-energized operation
Location
Mounted on the tank cover.
Winding connection
Tap changes select a different connection on the high-voltage winding.

Monitoring and protection

Local indications and signals for the station protection scheme.

Pressure-relief valve

Releases abnormal internal pressure

Specified range
30–2500 kVA

Described distribution design.

Gas relay

Provides alarm and trip contacts

Configuration
Optional

Coordinate with the transformer design.

Oil thermometer

Indicates oil temperature

Pocket location
Top of the distribution oil tank
Outdoor signal thermometers
Described for 1000–2000 kVA units

Oil-level gauge

Indicates oil level

Listed family
35 kV

Select to suit the tank arrangement.

Configuration scope

The 35 kV family lists oil-level indication, thermometers, pressure relief and gas-relay protection as configuration items.

The protection arrangement must match the tank construction and the project protection design.

Signal & wiring

Local gauges, alarm contacts and trip contacts perform different functions.

  • Indicator location
  • Contact functions
  • Wiring destination

The station control drawing should show how each specified device is used.

Oil thermometer: define the pocket location and any signal contacts in the accessory schedule.

Performance &
engineering configuration

6–10 kV

6–10 kV distribution transformer

No-load loss

No-load loss contributes whenever the transformer is energized.

Load loss

Load loss changes with operating current.

The project loading profile determines how each loss component affects energy consumption.

A loss figure therefore needs its voltage, frequency and test conditions before it can be used in a lifecycle-cost calculation.

Losses and impedance at the selected rating

Three separate loss schedules

The 6–10 kV reference table lists 19 ratings up to 2500 kVA, with separate loss schedules for S13-M, S20-M and S22-M.

Both no-load and load losses are expressed in watts.

Short-circuit impedance by capacity

30–630 kVA
4%
800–1250 kVA
4.5%
1600–2500 kVA
5%

For 10 kV ratings above 2500 kVA, request the no-load loss, load loss and short-circuit impedance for the proposed design.

20 kV

20 kV distribution transformer

No-load loss

No-load loss contributes whenever the transformer is energized.

Load loss

Load loss changes with operating current.

The project loading profile determines how each loss component affects energy consumption.

A loss figure therefore needs its voltage, frequency and test conditions before it can be used in a lifecycle-cost calculation.

Losses and impedance at the selected rating

20 kV rating schedule

The 20 kV reference table lists 19 ratings up to 2500 kVA.

Its loss values are expressed in kilowatts, while no-load current and short-circuit impedance are percentages.

Short-circuit impedance by capacity

30–500 kVA
5.5%
630–2500 kVA
6%

For the 30–500 kVA entries, this schedule does not state a single load-loss value. The required value and test condition must be agreed in the project electrical schedule.

For 20 kV ratings above 2500 kVA, request the no-load loss, load loss and short-circuit impedance for the proposed design.

35 kV

35 kV oil-immersed transformer construction with conservator and cooling surfaces
35 kV family: conservator and main tank arrangement

Electrical design

Its role is voltage transformation within a medium-voltage supply system. The voltage ratio, insulation requirements, capacity and protection arrangement are defined together with the substation single-line diagram.

Core and mechanical assembly

The described construction combines a grain-oriented silicon-steel core with oblique stacked joints, a rigid clamping frame and axially compressed windings.

Core-clamping frame; axial winding compression and positioning.

ONAN cooling

ONAN cooling transfers heat through the oil circuit and the external cooling surfaces.

Substation configuration and interfaces

Applications

The 35 kV oil-immersed family serves distribution substations, industrial parks, mines and factories.

Protection coordination

Pressure relief, oil-level indication, temperature indication and gas-relay protection are coordinated with the chosen tank design.

Indication devices: oil-level gauge and thermometer.

Installation interfaces

The installation drawing establishes the bushing positions, terminal clearances, cooling layout, foundation interface and service access.

These interfaces are specific to the selected transformer configuration; they should be checked alongside the electrical schedule when planning the substation.

Applications

Oil-immersed transformers support utility networks and industrial facilities. Each installation combines a different load profile, operating environment and equipment layout.

Illustrative outdoor utility distribution site and its surrounding service area

Utility distribution

Supply utility distribution networks with configurations reviewed against continuous load, peak demand and expected growth.

Illustrative manufacturing campus with factory buildings and a dedicated power distribution area

Manufacturing facilities

Serve textile, light-industry and other manufacturing facilities. Load profiles and available installation space guide the electrical rating and equipment arrangement.

Illustrative heavy-industrial facility and its outdoor electrical infrastructure

Heavy industry

For metallurgy, petroleum and chemical facilities, review process loading alongside contamination exposure, protection interfaces and maintenance access.

Illustrative application environments.

Before you specify your transformer

Common questions about site conditions, installation and the information needed for a project quotation.

What should I include in a quotation request?

Provide the electrical duty and site requirements together, so the proposed rating can be reviewed against the intended installation.

Electrical duty
Product type, capacity, voltage ratio, frequency and quantity. Include continuous load, peak demand and expected growth for capacity and loss evaluation.
Project brief
Installation environment, applicable standard and required delivery date. Attach the single-line diagram or technical specification where available.
What changes for a hot, high-altitude or coastal site?

These conditions need a project-specific design review. Confirm the selected transformer’s suitability before finalizing its rating and installation arrangement.

Temperature & altitude
State the minimum and maximum ambient temperature, site altitude and ventilation conditions for thermal and insulation review.
Exposure
Identify dust, humidity, coastal salt and chemical or corrosive contaminants. Review tank coating, external insulation, terminals and available cooling space together.
Which installation interfaces should be agreed first?

Use the installation drawing for the selected transformer configuration to coordinate the equipment with the site layout.

Position & access
Foundation, equipment clearances, delivery access and service space.
Connections & cooling
Tank and bushing arrangement, terminals, cable approach and the unobstructed air path around cooling surfaces.
Are all monitoring and protection devices included?

Confirm the accessory schedule for the selected family and tank design. The devices described on this page do not form one universal standard package; gas-relay configuration is optional.

Functions
Distinguish local indication, station alarm contacts and trip contacts.
Interfaces
Agree indicator locations, contact functions and wiring destinations with the station protection scheme and control drawing.
Which technical documents should be agreed before an order?

Agree the project document scope alongside the equipment configuration.

Design basis
The selected electrical rating and schedule, connection diagram and general-arrangement drawing should describe the same transformer configuration.
Inspection
Define the inspection requirements and the technical records to be reviewed against the order. Use the series-specific rating tables above when preparing the electrical schedule.