A 66 kV power transformer is the main transformer of a substation on a 63, 66 or 69 kV network. It feeds a 6.3, 6.6 or 10.5 kV busbar in utility sub-transmission substations and in plants with a 66 kV incomer, such as mines, oil and gas sites and metallurgical or petrochemical works; in solar and wind plants it steps the collection voltage up to the HV network. Ratings of 3150 to 63000 kVA cover a single plant incomer up to a large grid substation.
66 kV Oil-Immersed Power Transformer
For substation contractors, utilities and plant owners: 63/66/69 kV main transformers to 63000 kVA, alongside ETENZ GIS and control E-Houses.
Renewable Energy Collector Station SupportRenewable Grid-Connection Power Distribution
Key Metrics
63 / 66 / 69kV
High voltage
6300 / 6600 / 10500V
Low voltage
3150–63000kVA
Rated power
6300–63000kVA
OLTC ratings
Product Features
Three HV classes
Specify the HV winding at 63, 66 or 69 kV to suit the network, with a 6.3, 6.6 or 10.5 kV LV side for the busbar it feeds.
Three HV classes
Specify the HV winding at 63, 66 or 69 kV to suit the network, with a 6.3, 6.6 or 10.5 kV LV side for the busbar it feeds.
3150 to 63000 kVA
Fourteen ratings from 3150 to 63000 kVA (3.15–63 MVA) cover everything from a single plant incomer to a large grid substation.
On-load ±10% control
Hold the MV busbar voltage as the grid or load moves: from 6300 kVA an on-load tap changer adjusts the ratio ±10% in 1.25% steps, with no outage.
Three loss levels
Each rating is offered at S22, S20 or S18. S22 carries about a third less no-load loss than S18, the loss a substation transformer incurs every hour it is energised.
Neutral brought out
YNd11 on every rating: the star HV winding brings its neutral out for earthing the HV system, and the delta LV winding feeds the MV switchgear.
Product Details
The designation is written S(F)(Z)□-□/66. S stands for three-phase. F, when present, marks forced-air cooling (ONAF); without it the transformer is naturally cooled (ONAN). Z, when present, marks an on-load tap changer; without it the tap changer is off-circuit. The digits that follow are the loss-level code: 18, 20 or 22. The rating in kVA and the voltage class in kV come last, written -rating/66. SZ20-31500/66 therefore reads: three-phase, on-load tap changing, loss level 20, 31500 kVA, 66 kV class.
The HV winding is rated 63, 66 or 69 kV and connected in star with the neutral brought out; the LV winding is rated 6.3, 6.6 or 10.5 kV and connected in delta. The vector group is YNd11 on every rating, with off-circuit and on-load tap changing alike.
Off-circuit ratings run from 3150 to 63000 kVA in fourteen steps; on-load ratings start at 6300 kVA and run to 63000 kVA in eleven. From 3150 to 5000 kVA the off-circuit tapping range is ±5% and the short-circuit impedance 8%. From 6300 kVA the off-circuit range is ±2×2.5% and the impedance 9%, the same 9% as the on-load units.
The off-circuit tap changer is set with the transformer de-energised: ±5% up to 5000 kVA and ±2×2.5% from 6300 kVA. It suits networks whose voltage is steady and where taps are reset rarely. The on-load tap changer switches under load across ±8×1.25%, in 1.25% steps, and is available from 6300 kVA. It suits plants and generation connections where the voltage moves during operation. At the same rating both versions have the same load loss and no-load current; the on-load version’s no-load loss is 7–11% higher, for example 17.5 kW against 16.0 kW at 31500 kVA, loss level S20.
Every rating is offered at three loss levels. S22 and S20 share the same load loss and differ in no-load loss; S18 is higher in both. At 31500 kVA with an off-circuit tap changer, the no-load loss is 13.5 kW for S22, 16.0 kW for S20 and 19.7 kW for S18, and the load loss is 108.0, 108.0 and 114.0 kW. At 63000 kVA the figures are 22.9, 27.0 and 33.3 kW no-load and 178.2, 178.2 and 188.1 kW load. The specification table gives all three levels for every rating.
The core is stacked from high-permeability, low-loss silicon steel, with multi-step mitred joints where the limbs meet the yokes to reduce no-load loss. The windings are disc-type, and the active part is assembled with formed insulation components. The tank is process-treated for humid and polluted sites and for metallurgical and petrochemical plants. Radiators, conservator, bushings and the cooling arrangement are set out on the outline drawing for the selected rating.
Delivery Scope Options
Scope 1
Single Unit or Complete Package Supply
Scope 1Single Unit or Complete Package Supply
Transformers are supplied as single units against the order schedule, or as a complete package together with the protective enclosure, the temperature controller and the cooling fans. The active part is wound, assembled and routine-tested at the works and shipped as a complete unit; the assembly interface for the accessories follows the transport conditions. Where the transformer is to arrive together with a prefabricated power module, the E-House line takes on the enclosure, the internal arrangement and the foundation fixing, and the transformer is delivered as equipment housed within it.
Scope Includes:
Single unit or complete package
Complete-unit shipment and assembly interface
Foundation and fixing interface
In-cabin delivery handled by the E-House line
Technical Specifications
Product form
Three-phase, two-winding oil-immersed power transformer, 66 kV class
Type designation
S(F)(Z)□-□/66 (F forced-air cooling, Z on-load tap changing, loss level, rated power, voltage class)
HV rated voltage
63, 66 or 69
kV
LV rated voltage
6.3, 6.6 or 10.5
kV
Vector group
YNd11
Rated frequency
To the grid frequency, confirmed for the project
Rated power, off-circuit tap changing
3150 / 4000 / 5000 / 6300 / 8000 / 10000 / 12500 / 16000 / 20000 / 25000 / 31500 / 40000 / 50000 / 63000
kVA
Rated power, on-load tap changing
6300 / 8000 / 10000 / 12500 / 16000 / 20000 / 25000 / 31500 / 40000 / 50000 / 63000
kVA
Tapping range, off-circuit
±5% (3150–5000 kVA); ±2×2.5% (6300–63000 kVA)
Tapping range, on-load
±8×1.25%
Short-circuit impedance
8% (off-circuit, 3150–5000 kVA); 9% (6300–63000 kVA)
No-load loss, off-circuit, S22 / S20 / S18
3150 kVA: 2.2 / 2.6 / 3.2; 4000 kVA: 2.6 / 3.1 / 3.8; 5000 kVA: 3.1 / 3.7 / 4.6; 6300 kVA: 4.0 / 4.7 / 5.8; 8000 kVA: 4.9 / 5.8 / 7.1; 10000 kVA: 5.8 / 6.8 / 8.4; 12500 kVA: 6.8 / 8.1 / 9.9; 16000 kVA: 8.3 / 9.8 / 12.0; 20000 kVA: 9.7 / 11.4 / 14.1; 25000 kVA: 11.4 / 13.5 / 16.6; 31500 kVA: 13.5 / 16.0 / 19.7; 40000 kVA: 16.2 / 19.1 / 23.5; 50000 kVA: 19.4 / 22.9 / 28.2; 63000 kVA: 22.9 / 27.0 / 33.3
kW
No-load loss, on-load, S22 / S20 / S18
6300 kVA: 4.4 / 5.2 / 6.4; 8000 kVA: 5.3 / 6.2 / 7.7; 10000 kVA: 6.2 / 7.3 / 9.0; 12500 kVA: 7.4 / 8.7 / 10.7; 16000 kVA: 8.9 / 10.5 / 12.9; 20000 kVA: 10.6 / 12.5 / 15.4; 25000 kVA: 12.5 / 14.8 / 18.2; 31500 kVA: 14.8 / 17.5 / 21.5; 40000 kVA: 17.7 / 20.9 / 25.8; 50000 kVA: 20.9 / 24.7 / 30.4; 63000 kVA: 24.7 / 29.2 / 35.9
kW
Load loss, S22 and S20 / S18 (off-circuit and on-load)
3150 kVA: 20.7 / 21.9; 4000 kVA: 24.6 / 25.9; 5000 kVA: 27.6 / 29.2; 6300 kVA: 30.8 / 32.5; 8000 kVA: 36.5 / 38.5; 10000 kVA: 43.0 / 45.4; 12500 kVA: 51.1 / 54.0; 16000 kVA: 62.8 / 66.3; 20000 kVA: 76.1 / 80.4; 25000 kVA: 90.0 / 95.0; 31500 kVA: 108.0 / 114.0; 40000 kVA: 126.9 / 134.0; 50000 kVA: 150.3 / 158.7; 63000 kVA: 178.2 / 188.1
kW
No-load current
3150 kVA: 0.84; 4000 kVA: 0.80; 5000 kVA: 0.68; 6300 and 8000 kVA: 0.60; 10000 and 12500 kVA: 0.56; 16000 and 20000 kVA: 0.52; 25000 kVA: 0.48; 31500 and 40000 kVA: 0.44; 50000 kVA: 0.40; 63000 kVA: 0.36
%
Cooling
ONAN; ONAF where the designation carries F
Core and windings
High-permeability, low-loss silicon steel core with multi-step mitred joints; disc-type windings; formed insulation components
Insulation levels, temperature rise, sound level, dimensions and mass
Confirmed with the project specification and drawings
| Parameter | Specification |
|---|---|
| Product form | Three-phase, two-winding oil-immersed power transformer, 66 kV class |
| Type designation | S(F)(Z)□-□/66 (F forced-air cooling, Z on-load tap changing, loss level, rated power, voltage class) |
| HV rated voltage | 63, 66 or 69 kV |
| LV rated voltage | 6.3, 6.6 or 10.5 kV |
| Vector group | YNd11 |
| Rated frequency | To the grid frequency, confirmed for the project |
| Rated power, off-circuit tap changing | 3150 / 4000 / 5000 / 6300 / 8000 / 10000 / 12500 / 16000 / 20000 / 25000 / 31500 / 40000 / 50000 / 63000 kVA |
| Rated power, on-load tap changing | 6300 / 8000 / 10000 / 12500 / 16000 / 20000 / 25000 / 31500 / 40000 / 50000 / 63000 kVA |
| Tapping range, off-circuit | ±5% (3150–5000 kVA); ±2×2.5% (6300–63000 kVA) |
| Tapping range, on-load | ±8×1.25% |
| Short-circuit impedance | 8% (off-circuit, 3150–5000 kVA); 9% (6300–63000 kVA) |
| No-load loss, off-circuit, S22 / S20 / S18 | 3150 kVA: 2.2 / 2.6 / 3.2; 4000 kVA: 2.6 / 3.1 / 3.8; 5000 kVA: 3.1 / 3.7 / 4.6; 6300 kVA: 4.0 / 4.7 / 5.8; 8000 kVA: 4.9 / 5.8 / 7.1; 10000 kVA: 5.8 / 6.8 / 8.4; 12500 kVA: 6.8 / 8.1 / 9.9; 16000 kVA: 8.3 / 9.8 / 12.0; 20000 kVA: 9.7 / 11.4 / 14.1; 25000 kVA: 11.4 / 13.5 / 16.6; 31500 kVA: 13.5 / 16.0 / 19.7; 40000 kVA: 16.2 / 19.1 / 23.5; 50000 kVA: 19.4 / 22.9 / 28.2; 63000 kVA: 22.9 / 27.0 / 33.3 kW |
| No-load loss, on-load, S22 / S20 / S18 | 6300 kVA: 4.4 / 5.2 / 6.4; 8000 kVA: 5.3 / 6.2 / 7.7; 10000 kVA: 6.2 / 7.3 / 9.0; 12500 kVA: 7.4 / 8.7 / 10.7; 16000 kVA: 8.9 / 10.5 / 12.9; 20000 kVA: 10.6 / 12.5 / 15.4; 25000 kVA: 12.5 / 14.8 / 18.2; 31500 kVA: 14.8 / 17.5 / 21.5; 40000 kVA: 17.7 / 20.9 / 25.8; 50000 kVA: 20.9 / 24.7 / 30.4; 63000 kVA: 24.7 / 29.2 / 35.9 kW |
| Load loss, S22 and S20 / S18 (off-circuit and on-load) | 3150 kVA: 20.7 / 21.9; 4000 kVA: 24.6 / 25.9; 5000 kVA: 27.6 / 29.2; 6300 kVA: 30.8 / 32.5; 8000 kVA: 36.5 / 38.5; 10000 kVA: 43.0 / 45.4; 12500 kVA: 51.1 / 54.0; 16000 kVA: 62.8 / 66.3; 20000 kVA: 76.1 / 80.4; 25000 kVA: 90.0 / 95.0; 31500 kVA: 108.0 / 114.0; 40000 kVA: 126.9 / 134.0; 50000 kVA: 150.3 / 158.7; 63000 kVA: 178.2 / 188.1 kW |
| No-load current | 3150 kVA: 0.84; 4000 kVA: 0.80; 5000 kVA: 0.68; 6300 and 8000 kVA: 0.60; 10000 and 12500 kVA: 0.56; 16000 and 20000 kVA: 0.52; 25000 kVA: 0.48; 31500 and 40000 kVA: 0.44; 50000 kVA: 0.40; 63000 kVA: 0.36 % |
| Cooling | ONAN; ONAF where the designation carries F |
| Core and windings | High-permeability, low-loss silicon steel core with multi-step mitred joints; disc-type windings; formed insulation components |
| Insulation levels, temperature rise, sound level, dimensions and mass | Confirmed with the project specification and drawings |
Product FAQs
Choose on-load tap changing where the network or load voltage moves during operation, as at large industrial plants and solar or wind connections: it switches ±8×1.25% under load and is offered from 6300 kVA. Choose off-circuit tap changing where the voltage is steady and taps are reset rarely: it is set de-energised, ±5% up to 5000 kVA and ±2×2.5% from 6300 kVA, and it has the lower no-load loss at every rating.
They are three loss levels of the same rating. S22 and S20 have the same load loss, and S22 has about 15% less no-load loss; S18 is the highest of the three in both no-load and load loss. Where a tender capitalises losses, its evaluation figures decide the level; otherwise weigh the no-load difference against the hours the transformer will stay energised.
Price follows the rating, the tap changer type, the loss level, the cooling and the accessories. For a quotation, send the HV and LV rated voltages, the rating, the tap changer type and range, the impedance, the loss level or the tender’s loss evaluation, the cooling, the grid frequency, the site altitude and ambient temperature range, the HV and LV terminations (bushings or cable boxes), the tests to be witnessed and the document language.
Mass and dimensions follow the rating, loss level and cooling, and are fixed on the outline drawing for the selected design together with the oil volume, transport mass and lifting points. They set the foundation, crane and transport plan, so they are confirmed before the substation layout is frozen.
Yes. The transformer stands outdoors on its own foundation, and the rooms around it can be prefabricated as E-Houses: a GIS E-House for the 66 kV switchgear bays, a control E-House for the protection, control and DC panels, and an MV switchgear E-House for the 6.3–10.5 kV switchgear the transformer feeds. ETENZ builds these enclosures with their HVAC, fire protection and auxiliary power, and the cable, earthing and protection interfaces with the transformer are agreed on one set of drawings.
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