Power Transformers
Oil-immersed units from 6.3 to 120 MVA, built to your duty
A power transformer fixes your substation for the next thirty years: the loss budget, the fault level, the footprint and the outage plan all follow from it. Atlas Energy supplies oil-immersed units from 6,300 to 120,000 kVA, up to 750 kV class, with published designs at 110 kV / 121 kV HV, 35 / 38.5 kV MV and 6.3 / 6.6 / 10.5 / 11 kV LV. Two-winding and three-winding configurations are both standard.
Two-winding units are supplied as YNd11 at 10.5% impedance. Three-winding units are YNyn0d11 at 17.5–18.5% / 10.5% / 6.5%. Tapping is off-circuit ±2 × 2.5% or on-load ±8 × 1.25% across 17 positions. The core is cold-rolled grain-oriented (CRGO) silicon steel with 45° six-step mitred joints, machine-cut and stacked. Core clamping, short-circuit withstand and noise are verified by 3D finite-element analysis, and leakage flux, short-circuit forces and load loss are optimized in design software before the first lamination is cut. Cooling is ONAN, ONAF or OFAF to specification.
Why it matters
Losses are published, not estimated. No-load loss runs from 9.3 kW at 6.3 MVA to 84.8 kW at 120 MVA and load loss from 36 kW to 397 kW, so you can drop real figures into your capitalized loss evaluation instead of a placeholder.
One three-winding YNyn0d11 unit serves three voltage levels at a tie substation. That removes a transformer bay, its protection and its civil works from the layout.
On-load tap changing over 17 positions at ±1.25% per step holds secondary voltage through load swing and reverse power flow without taking the unit out of service.
Short-circuit forces and clamping strength are modelled in 3D before manufacture, so the mechanical withstand on the drawing is the mechanical withstand that shows up on the test floor.
The transformer, the instrument transformers around it and the equipment that commissions it come from one supplier on one purchase order, with one set of qualification documents.
Ratings
Voltage class: Up to 750 kV class; published data 110 kV / 121 kV HV, 35 / 38.5 kV MV, 6.3 / 6.6 / 10.5 / 11 kV LV
Power: 6,300 – 120,000 kVA (6.3 – 120 MVA)
Windings: Two-winding and three-winding
Vector groups: YNd11 (two-winding), YNyn0d11 (three-winding)
Tapping: Off-circuit ±2 × 2.5% (NVTC) or on-load ±8 × 1.25%, 17 positions (OLTC)
Impedance: 10.5% two-winding; 17.5–18.5% / 10.5% / 6.5% three-winding
No-load loss: 9.3 kW (6.3 MVA) to 84.8 kW (120 MVA)
Load loss: 36 kW (6.3 MVA) to 397 kW (120 MVA)
No-load current: 0.77% down to 0.34%
Cooling: ONAN / ONAF / OFAF to specification
Core: CRGO silicon steel, 45° six-step mitred joints, machine-cut and stacked
Standards
ANSI/IEEE C57
IEC 60076 series
ISO 9001 · ISO 14001 · ISO 45001 · ISO 10012 manufacturing systems
Applications
Utility substations and sub-transmission step-down
Generation step-up (GSU)
Industrial main intake substations
Tie substations with three voltage levels
Questions engineers ask
What power and voltage range do you supply? Published designs cover 6,300 to 120,000 kVA, which is 6.3 to 120 MVA, in two-winding and three-winding arrangements. The voltage range extends to 750 kV class, with published windings at 110 kV / 121 kV HV, 35 / 38.5 kV MV and 6.3 / 6.6 / 10.5 / 11 kV LV. Anything outside that envelope is quoted as a custom design.
Should I specify an off-circuit tap changer or an OLTC? Off-circuit tapping at ±2 × 2.5% suits a stable source where you set the ratio once at commissioning. Specify the on-load tap changer, ±8 × 1.25% over 17 positions, where feeder load swings hard, where distributed generation pushes voltage up during light load, or where you cannot de-energize to correct a ratio.
