Transformers

Power transformers and reactors up to 550 kV.

Bespoke transmission-class transformers and reactors up to 550 kV. Power transformers, autotransformers, phase shifting, rectifier, furnace and traction transformers, and shunt / series / neutral-grounding / filter reactors, engineered with margin above the standards, for decades of low-loss, low-noise, low-partial-discharge operation.

Make an enquiry

Power transformer with conservator tank, radiator banks and bushings, shown standing on its foundation

Voltage class: Up to 550 kV
Ratings: 630 kVA to 1,170 MVA
Cooling classifications: ONAN to ODAF
Insulation: Oil-immersed

The range

Our transmission-class range covers seven product lines, all built to the same design principles, standards, materials specifications and testing regimes. Every unit is bespoke, specified to your project's rating, voltage class, cooling regime, insulation coordination, vector group and installation environment.

Power Transformers

Bulk power transformation between transmission voltage levels. We supply power transformers as bespoke, project-specific units for utility transmission, generation, and heavy industrial applications. Configurations include two-winding and three-winding designs and generator step-up (GSU) transformers for continuous full-load operation at generation facilities.

Technical dataPower transformers

Voltage class	Up to 550 kV
Ratings	630 kVA to 1,170 MVA
Configurations	Two-winding, three-winding, generator step-up
Cooling classifications	ONAN, ONAF, OFAF, ODAF; water-cooled OFWF / ODWF (typical for GSU at hydroelectric stations)
Insulation	Oil-immersed (sealed conservator or free-breathing); dry-type available for indoor installations
Tap changer	On-load (OLTC) and de-energised (DETC); customer-specified vector groups
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076, IEEE C57, AS/NZS 60076

Autotransformers

Cost- and space-efficient transformers where primary and secondary share a common winding. Where the voltage ratio between two systems is close (e.g., 220 / 110 kV, 275 / 132 kV, 500 / 275 kV), an autotransformer offers significantly lower losses, smaller footprint, and lower unit cost than a separate-winding transformer of the same rating.

We supply autotransformers as three-winding units with a tertiary common winding for delta-connected auxiliary loads, third harmonic filtering, and neutral grounding. Typical applications include HV / EHV network interconnection, transmission ties between voltage levels, and specific generator step-up configurations.

Technical dataAutotransformers

Common ratios	220 / 110 kV, 275 / 132 kV, 275 / 66 kV, 500 / 275 kV
Ratings	30 MVA to 500 MVA
Configurations	Three-winding with tertiary (common)
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076, IEEE C57, AS/NZS 60076

Phase Shifting Transformers

Transformers configured with fixed or adjustable phase shift between primary and secondary windings, for controlling active power flow across interconnected transmission networks. Adjustable PSTs use an on-load tap changer to vary the phase angle and redirect power between parallel circuits, resolve grid congestion, or interconnect networks with different phase relationships.

Fixed-phase zig-zag configurations provide artificial neutrals in delta-connected systems for grounding and earth-fault current management. We supply zig-zag, delta-hexagonal, symmetrical, and two-core PST designs.

Technical dataPhase shifting transformers

Voltage class	12 kV to 550 kV
PST ratings	100 MVA to 1,000 MVA
Grounding transformer ratings	Sized to application
Configurations	Zig-zag, delta-hexagonal, symmetrical, two-core
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076, IEEE C57, AS/NZS 60076

Rectifier Transformers

Transformers for rectifier systems feeding electrochemical plants, smelters and other large industrial DC loads. Units are supplied for 6 and 12 pulse operation per set, with 24, 36, 48 and 72 pulse arrangements designed to suit the application. Larger units are water cooled with forced oil circulation, and voltage regulation is by tap changing.

Technical dataRectifier transformers

Voltage class	6 kV to 220 kV
Ratings	2.72 MVA to 120 MVA
DC voltage	Designed to the process; 575 V to 3,550 V typical on 10 kV class units
Pulse number	6 and 12 pulse per set; 24, 36, 48 and 72 pulse arrangements on request
Connection	Delta, star-delta on 10 kV class units; other classes designed to the project
Cooling	Water cooled, forced oil circulation on larger units
Voltage regulation	Tap changing on larger units
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076

Furnace Transformers

Transformers for submerged arc furnaces producing ferroalloys, silicon compounds, calcium carbide and magnesium oxide, and for electric arc furnaces in steel production. Units carry on-load tap changers, with secondary voltage ranges selected to suit the furnace and the smelting process, and are cooled by forced oil water or forced oil air.

Technical dataFurnace transformers

Submerged arc ratings	5 MVA to 50 MVA, primary 10 kV to 110 kV
Electric arc ratings	10 MVA to 100 MVA, primary 35 kV to 110 kV
Secondary voltage	70 V to 850 V (submerged arc); constant power and constant current ranges (electric arc)
Tap changer	On-load; 11 to 47 taps (submerged arc), 11 to 23 taps (electric arc)
Short-circuit impedance	4% to 9% (submerged arc); 6% to 8.5% (electric arc)
Vector groups	Dd0, Yd11, YNd11
Cooling	Forced oil water (OFWF) or forced oil air (OFAF)
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076

Railway Traction Transformers

Traction transformers for railway electrification, connected to 110 kV and 220 kV networks and supplying a 27.5 kV traction line. Available in V,v and V,x connections, with ratings stated for each of the two traction phases. Rating, voltage, vector group and performance can be designed to the project.

Technical dataRailway traction transformers

Primary voltage	110 kV and 220 kV, with ±4 × 2.5% tapping
Secondary voltage	27.5 kV (V,v); 2 × 27.5 kV (V,x)
Ratings, 110 kV	6.3 + 10 MVA to 31.5 + 31.5 MVA
Ratings, 220 kV	20 + 20 MVA to 60 + 60 MVA
Connections	V,v and V,x
Short-circuit impedance	8.4% to 12%
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60076

Reactors

Inductive equipment for specific electrical purposes, built to the same design principles as our power transformers.

Reactor types supplied include shunt reactors (reactive power compensation on long HV / EHV transmission lines), series reactors (fault-current limiting on feeders and busbars), neutral grounding reactors and Petersen-coil systems (resonant / compensated network grounding), and harmonic filter reactors (tuned inductance for harmonic filter systems, VFD applications, and heavy industrial installations). Design variants include air-core dry-type, iron-core oil-immersed, and gapped-core designs, in single-phase banks and three-phase units, for indoor and outdoor installation.

Technical dataReactors

Voltage class	Up to 550 kV
Types	Shunt, series, NGR, harmonic filter
Shunt reactor ratings	10 to 200 MVAr
Series reactors and NGRs	Sized to application
Corrosion protection	ISO 12944 C5, high durability (15 to 25 years), as standard
Standards	IEC 60289, IEC 60076-6 (reactors)

Designed for decades of service

At transmission scale, transformer and reactor performance is decided at the design stage. The range is built around three interlocking design disciplines (thermal, mechanical, and dielectric), each engineered with meaningful margin above the applicable standards, not just to comply with them. Every design carries declared margins between calculated stresses and both expected test values and in-service operating stresses.

Thermal Design

Thermal performance turns on loss profile, cooling system design, and winding hot-spot control. These transformers are engineered with margin above IEC 60076-2 temperature-rise limits, using low-loss grain-oriented electrical steel, current-density-optimised copper windings, and carefully sized oil ducts and cooler redundancy to hold operating temperatures well within insulation limits under normal and overload loading. Cooling classifications supplied include ONAN, ONAF, OFAF, ODAF, and water-cooled OFWF / ODWF (typical for GSU applications at hydroelectric power stations).

Mechanical Design

Windings and clamping structures face severe electromagnetic forces during through-faults and short-circuit events; poor mechanical design leads to winding deformation and eventual dielectric failure. These transformers are designed and verified to IEC 60076-5 with defined safety margins above the calculated axial and radial short-circuit stresses, using reinforced winding structures, rigid clamping systems, and structural analysis of tank, core supports, and internal supports. Short-circuit withstand can be demonstrated by calculation or by witness type-testing at accredited laboratories.

Dielectric Design

The insulation system determines impulse, switching, and induced-voltage withstand plus long-term dielectric stress capability. These transformers are designed with margin above specified BIL and test voltage levels, with insulation systems selected against the application's temperature class (Class A through Class H equivalents, including thermally-upgraded paper). Turn-to-turn, section-to-section, winding-to-winding, winding-to-ground, and phase-to-phase stresses are analysed with declared dielectric safety factors. Partial discharge is measured at factory acceptance testing to well below IEC 60076-3 thresholds, with values below 10 pC achievable for HV and EHV designs.

Operational performance

Our transformers and reactors are specified to deliver:

Low Partial Discharge

Partial discharge (PD) values verified at factory acceptance testing well below the IEC 60076-3 acceptance thresholds. Values below 10 pC are achievable for HV and EHV designs. Consistently low PD is one of the most reliable predictors of long-term dielectric health and freedom from in-service failure.

Low Noise

Core lamination quality, tank construction, and cooling system integration are optimised for low audible noise. Sound levels below 40 dB(A) are achievable depending on rating and configuration. Additional sound enclosures and low-noise cooler options are available for urban substations, hospitals, data centres, and other noise-sensitive receivers. Sound level guarantees, measurement standard, and applicable no-load / load conditions are agreed on a per-project basis.

Low Losses

Two-tier design optimisation targets both no-load (iron) and load (copper) losses, with additional attention to stray losses in the tank, clamping structures, and leads. Loss guarantees and test tolerances are declared per IEC 60076-1. Combined with modern cooling design, reduced losses cut both operating cost and heat rejection into the substation environment (a real advantage for indoor and enclosed installations).

Long Service Life

With controlled operating temperatures, low PD, defined mechanical margins, and appropriate insulation systems for the specified thermal class, our transformers and reactors are engineered for the multi-decade service lives that utility asset management programmes depend on. Sealed conservator systems and inert gas cushions extend oil life and insulation integrity across the full operating window.

Competitive Lead Times

We coordinate directly with manufacturing partners to schedule production, testing, and shipping in line with customer construction programmes. Lead time is treated as a project-critical commitment, not a soft target.

Applications

Our power transformer and reactor range is supplied across:

Utility Transmission and Sub-Transmission Substations

Step-up and step-down duty across transmission substations, bulk supply substations, and brownfield replacement projects.

HV / EHV Network Interconnection

Autotransformers for cost- and space-efficient transmission ties, phase shifting transformers for power flow control and congestion management in meshed grids.

Generator Step-Up (GSU) and Hydroelectric Power Stations

Utility, independent power producer, and hydroelectric generation with water-cooled OFWF / ODWF variants for hydro.

Renewable Energy and Battery Storage Interconnection

Wind farm, solar farm, and battery energy storage system (BESS) connection assets.

Data Centre and Hyperscale Power Infrastructure

Bulk power supply for hyperscale campuses, 24/7 duty, redundant supply architecture.

Railway Traction and Electrification

Traction power substations, 12-pulse rectifier duty, metro and light-rail systems.

Mining, Oil and Gas, and Heavy Industry

MV substation supply for processing plants, refineries, LNG facilities, and heavy industrial installations.

Reactive Power Compensation

Shunt reactors on long HV / EHV transmission lines to absorb capacitive reactive power and maintain voltage stability.

Short-Circuit Current Management

Series reactors on feeders and busbars to reduce short-circuit levels at downstream equipment.

Compensated Network Grounding

Neutral grounding reactors (NGRs), Petersen coil systems, and zig-zag grounding transformers for compensated MV networks.

Harmonic Filter Systems

Tuned filter reactors for harmonic filter systems, VSD applications, and heavy industrial harmonic mitigation.

Asset Renewal and Replacement

End-of-life planning, brownfield replacement, life-extension programmes, and utility asset renewal.

Sourcing and quality assurance

We source premium transformers and reactors from established, highest-quality international manufacturers whose units are operating in demanding networks worldwide. Where transformers and reactors fall short in service, the cause is typically traceable to active-part design, materials, or manufacturing quality. Every unit supplied is:

Constructed from the highest quality materials and components: grain-oriented low-loss electrical steel cores, high-purity copper windings, insulation systems selected against the specified thermal class (Class A through Class H, including thermally-upgraded paper and higher-temperature media), and specification-grade transformer oils, bushings, and tap changers
From a design that is type tested, including temperature rise to IEC 60076-2, lightning and switching impulse to IEC 60076-3, sound level to IEC 60076-10, and short-circuit withstand to IEC 60076-5, demonstrated by test or by calculation and design review
Factory acceptance tested before dispatch, to a test programme based on IEC 60076 (or AS/NZS 60076 where it applies) and your own specification, with any customer-specific requirements built in
Every unit receives the full IEC 60076-1 routine test suite, including the extended tests required above 72.5 kV:
- Winding resistance
- Voltage ratio and phase displacement
- Short-circuit impedance and load loss
- No-load loss and current, including at 90% and 110% of rated voltage
- Lightning impulse and, at the higher voltage classes, switching impulse
- Applied and induced voltage with partial discharge measurement
- Insulation resistance, capacitance and dissipation factor (tan delta)
- Dissolved gas analysis of the oil
- On-load tap-changer operation
- Core and frame insulation
- Current transformer ratio and polarity
Factory acceptance testing can be witnessed by you or your representative at the manufacturer's facility
Pressure and leak tested before oil filling and dispatch
Built with tanks welded to ISO 3834 quality requirements, 316 stainless steel fasteners and nameplates, and corrosion protection to ISO 12944 C5, high durability (15 to 25 years), as standard
Available with seismic qualification (IEEE 693 High Performance Level / AS 1170.4 / NZS 1170.5) for installations in seismic zones
Available with natural ester insulating fluid in place of mineral oil: biodegradable and less flammable (K-class)
Supplied with full routine test reports and material traceability

Lifecycle support

Our transformer and reactor supply is backed by the engineering services required to install, commission, and maintain each unit across its operational life:

Installation and commissioning: site delivery coordination, plant installation, vacuum oil filling, on-site testing, and energisation support
Testing services: diagnostic testing (DGA, SFRA, insulation, ratio), condition assessment, and periodic performance evaluation
Asset management: lifecycle planning, remedial works, refurbishment versus replacement analysis, and end-of-life planning

Explore our services

Talk to our team

Discuss your transformer or reactor requirements

Whether you are specifying a bespoke power transformer for a new substation, an autotransformer for network interconnection, a phase shifting transformer for load flow control, or reactors for reactive power compensation or fault current limiting, our engineering team is available to advise on specification and confirm lead times.

Make an enquiry